green house effect essay points

Essay on Greenhouse Effect for Students and Children

500 words essay on greenhouse effect.

The past month, July of 2019, has been the hottest month in the records of human history. This means on a global scale, the average climate and temperatures are now seen a steady rise year-on-year. The culprits of this climate change phenomenon are mainly pollution , overpopulation and general disregard for the environment by the human race. However, we can specifically point to two phenomenons that contribute to the rising temperatures – global warming and the greenhouse effect. Let us see more about them in this essay on the greenhouse effect.

The earth’s surface is surrounded by an envelope of the air we call the atmosphere. Gasses in this atmosphere trap the infrared radiation of the sun which generates heat on the surface of the earth. In an ideal scenario, this effect causes the temperature on the earth to be around 15c. And without such a phenomenon life could not sustain on earth.

However, due to rapid industrialization and rising pollution, the emission of greenhouse gases has increased multifold over the last few centuries. This, in turn, causes more radiation to be trapped in the earth’s atmosphere. And as a consequence, the temperature on the surface of the planet steadily rises. This is what we refer to when we talk about the man-made greenhouse effect.

Causes of Greenhouse Effect

As we saw earlier in this essay on the greenhouse effect, the phenomenon itself is naturally occurring and an important one to sustain life on our planet. However, there is an anthropogenic part of this effect. This is caused due to the activities of man.

The most prominent among this is the burning of fossil fuels . Our industries, vehicles, factories, etc are overly reliant on fossil fuels for their energy and power. This has caused an immense increase in emissions of harmful greenhouse gasses such as carbon dioxide, carbon monoxide, sulfides, etc. This has multiplied the greenhouse effect and we have seen a steady rise in surface temperatures.

Other harmful activities such as deforestation, excessive urbanization, harmful agricultural practices, etc. have also led to the release of excess carbon dioxide and made the greenhouse effect more prominent. Another harmful element that causes harm to the environment is CFC (chlorofluorocarbon).

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Some Effects of Greenhouse Effect

Even after overwhelming proof, there are still people who deny the existence of climate change and its devastating pitfalls. However, there are so many effects and pieces of evidence of climate change it is now undeniable. The surface temperature of the planet has risen by 1c since the 19th century. This change is largely due to the increased emissions of carbon dioxide. The most harm has been seen in the past 35 years in particular.

The oceans and the seas have absorbed a lot of this increased heat. The surfaces of these oceans have seen a rise in temperatures of 0.4c. The ice sheets and glaciers are also rapidly shrinking. The rate at which the ice caps melt in Antartica has tripled in the last decade itself. These alarming statistics and facts are proof of the major disaster we face in the form of climate change.

600 Words Essay on Greenhouse Effect

A Greenhouse , as the term suggests, is a structure made of glass which is designed to trap heat inside. Thus, even on cold chilling winter days, there is warmth inside it. Similarly, Earth also traps energy from the Sun and prevents it from escaping back. The greenhouse gases or the molecules present in the atmosphere of the Earth trap the heat of the Sun. This is what we know as the Greenhouse effect.

Greenhouse Gases

These gases or molecules are naturally present in the atmosphere of the Earth. However, they are also released due to human activities. These gases play a vital role in trapping the heat of the Sun and thereby gradually warming the temperature of Earth. The Earth is habitable for humans due to the equilibrium of the energy it receives and the energy that it reflects back to space.

Global Warming and the Greenhouse Effect

The trapping and emission of radiation by the greenhouse gases present in the atmosphere is known as the Greenhouse effect. Without this process, Earth will either be very cold or very hot, which will make life impossible on Earth.

The greenhouse effect is a natural phenomenon. Due to wrong human activities such as clearing forests, burning fossil fuels, releasing industrial gas in the atmosphere, etc., the emission of greenhouse gases is increasing.

Thus, this has, in turn, resulted in global warming . We can see the effects due to these like extreme droughts, floods, hurricanes, landslides, rise in sea levels, etc. Global warming is adversely affecting our biodiversity, ecosystem and the life of the people. Also, the Himalayan glaciers are melting due to this.

There are broadly two causes of the greenhouse effect:

I. Natural Causes

• Some components that are present on the Earth naturally produce greenhouse gases. For example, carbon dioxide is present in the oceans, decaying of plants due to forest fires and the manure of some animals produces methane , and nitrogen oxide is present in water and soil.
• Water Vapour raises the temperature by absorbing energy when there is a rise in the humidity.
• Humans and animals breathe oxygen and release carbon dioxide in the atmosphere.

II. Man-made Causes

• Burning of fossil fuels such as oil and coal emits carbon dioxide in the atmosphere which causes an excessive greenhouse effect. Also, while digging a coal mine or an oil well, methane is released from the Earth, which pollutes it.
• Trees with the help of the process of photosynthesis absorb the carbon dioxide and release oxygen. Due to deforestation the carbon dioxide level is continuously increasing. This is also a major cause of the increase in the greenhouse effect.
• In order to get maximum yield, the farmers use artificial nitrogen in their fields. This releases nitrogen oxide in the atmosphere.
• Industries release harmful gases in the atmosphere like methane, carbon dioxide , and fluorine gas. These also enhance global warming.

All the countries of the world are facing the ill effects of global warming. The Government and non-governmental organizations need to take appropriate and concrete measures to control the emission of toxic greenhouse gases. They need to promote the greater use of renewable energy and forestation. Also, it is the duty of every individual to protect the environment and not use such means that harm the atmosphere. It is the need of the hour to protect our environment else that day is not far away when life on Earth will also become difficult.

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Understanding Global Change

Discover why the climate and environment changes, your place in the Earth system, and paths to a resilient future.

Greenhouse effect

Life as we know it would be impossible if not for the greenhouse effect, the process through which heat is absorbed and re-radiated in that atmosphere. The intensity of a planet’s greenhouse effect is determined by the relative abundance of greenhouse gases in its atmosphere. Without greenhouse gases, most of Earth’s heat would be lost to outer space, and our planet would quickly turn into a giant ball of ice. Increase the amount of greenhouse gases to the levels found on the planet Venus, and the Earth would be as hot as a pizza oven! Fortunately, the strength of Earth’s greenhouse effect keeps our planet within a temperature range that supports life

On this page

What is the greenhouse effect, earth system models about the greenhouse effect, how human activities influence the greenhouse effect, explore the earth system, investigate, links to learn more.

For the classroom:

• Teaching Resources

Global Change Infographic

The greenhouse effect occurs in the atmosphere, and is an essential part of How the Earth System Works. Click the image on the left to open the Understanding Global Change Infographic . Locate the greenhouse effect icon and identify other topics that cause changes to, or are affected by, the greenhouse effect.

Adapted from the Environmental Protection Agency greenhouse effect file

Greenhouse gases such as methane, carbon dioxide, nitrous oxide, and water vapor  significantly affect the amount of energy in the Earth system, even though they make up a tiny percentage of Earth’s atmosphere.  Solar radiation that passes through the atmosphere and reaches Earth’s surface is either reflected or absorbed . Reflected sunlight doesn’t add any heat to the Earth system because this energy bounces back into space.

However, absorbed sunlight increases the temperature of Earth’s surface, and the warmed surface re-radiates as long-wave radiation (also known as infrared radiation). Infrared radiation is invisible to the eye, but we feel it as heat.

If there were not any greenhouse gases in the atmosphere, all that heat would pass directly back into space. With greenhouse gases present, however, most of the long-wave radiation coming from Earth’s surface is absorbed and then re-radiated in all directions many times before passing back into space. Heat that is re-radiated downward, toward the Earth, is absorbed by the surface and re-radiated again.

Clouds also influence the greenhouse effect. A thick, low cloud cover can enhance the reflectivity of the atmosphere, reducing the amount of solar radiation reaching Earth’s surface, but clouds high in the atmosphere can intensify the greenhouse effect by re-radiating heat from the Earth’s surface.

Altogether, this cycle of absorption and re-radiation by greenhouse gases impedes the loss of heat from our atmosphere to space, creating the greenhouse effect. Increases in the amount of greenhouses gases will mean that more heat is trapped, increasing the amount of energy in the Earth system (Earth’s energy budget), and raising Earth’s temperature. This increase in Earth’s average temperature is also known as global warming.

This Earth system model is one way to represent the essential processes and interactions related to the greenhouse effect. Hover over the icons for brief explanations; click on the icons to learn more about each topic. Download the Earth system models on this page. There are a few ways that the relationships among these topics can be represented and explained using the Understanding Global Change icons ( download examples ).  

The greenhouse effect, which influences Earth’s average temperature, affects many of the processes that shape global climate and ecosystems.  This model shows some of the other parts of the Earth system that the greenhouse effect influences, including the water cycle and water temperature .

Humans directly affect the greenhouse effect through activities that result in greenhouse gas emissions. The Earth system model below includes some of the ways that human activities increase the amount of greenhouse gases in the atmosphere. Releasing greenhouse gases intensifies the greenhouse effect, and increases Earth’s average air temperatures (also known as global warming). Hover over or click on the icons to learn more about these human causes of change and how they influence the greenhouse effect.

Click the scene icons and bolded terms on this page to learn more about these process and phenomena.

Learn more in these real-world examples, and challenge yourself to  construct a model  that explains the Earth system relationships.

• Ancient fossils and modern climate change
• How Global Warming Works
• NASA:  Global Climate Change:  A Blanket Around the Earth
• UCAR Center for Science Education: The Greenhouse Effect
• IPCC:  What is the Greenhouse Effect?
• Indicators of Change (NCA.2014)
• Human influence on the greenhouse effect
• The Carbon Cycle and Earth’s Climate

• ENVIRONMENT

What is global warming, explained

The planet is heating up—and fast.

Glaciers are melting , sea levels are rising, cloud forests are dying , and wildlife is scrambling to keep pace. It has become clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than at any time in the last 800,000 years .

We often call the result global warming, but it is causing a set of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. While many people think of global warming and climate change as synonyms , scientists use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems—in part because some areas actually get cooler in the short term.

Climate change encompasses not only rising average temperatures but also extreme weather events , shifting wildlife populations and habitats, rising seas , and a range of other impacts. All of those changes are emerging as humans continue to add heat-trapping greenhouse gases to the atmosphere, changing the rhythms of climate that all living things have come to rely on.

What will we do—what can we do—to slow this human-caused warming? How will we cope with the changes we've already set into motion? While we struggle to figure it all out, the fate of the Earth as we know it—coasts, forests, farms, and snow-capped mountains—hangs in the balance.

Understanding the greenhouse effect

The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat . These gases let in light but keep heat from escaping, like the glass walls of a greenhouse, hence the name.

Sunlight shines onto the Earth's surface, where the energy is absorbed and then radiate back into the atmosphere as heat. In the atmosphere, greenhouse gas molecules trap some of the heat, and the rest escapes into space. The more greenhouse gases concentrate in the atmosphere, the more heat gets locked up in the molecules.

Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This natural greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit (33 degrees Celsius) cooler.

A polar bear stands sentinel on Rudolf Island in Russia’s Franz Josef Land archipelago, where the perennial ice is melting.

In 1895, the Swedish chemist Svante Arrhenius discovered that humans could enhance the greenhouse effect by making carbon dioxide , a greenhouse gas. He kicked off 100 years of climate research that has given us a sophisticated understanding of global warming.

Levels of greenhouse gases have gone up and down over the Earth's history, but they had been fairly constant for the past few thousand years. Global average temperatures had also stayed fairly constant over that time— until the past 150 years . Through the burning of fossil fuels and other activities that have emitted large amounts of greenhouse gases, particularly over the past few decades, humans are now enhancing the greenhouse effect and warming Earth significantly, and in ways that promise many effects , scientists warn.

Aren't temperature changes natural?

Human activity isn't the only factor that affects Earth's climate. Volcanic eruptions and variations in solar radiation from sunspots, solar wind, and the Earth's position relative to the sun also play a role. So do large-scale weather patterns such as El Niño .

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But climate models that scientists use to monitor Earth’s temperatures take those factors into account. Changes in solar radiation levels as well as minute particles suspended in the atmosphere from volcanic eruptions , for example, have contributed only about two percent to the recent warming effect. The balance comes from greenhouse gases and other human-caused factors, such as land use change .

The short timescale of this recent warming is singular as well. Volcanic eruptions , for example, emit particles that temporarily cool the Earth's surface. But their effect lasts just a few years. Events like El Niño also work on fairly short and predictable cycles. On the other hand, the types of global temperature fluctuations that have contributed to ice ages occur on a cycle of hundreds of thousands of years.

For thousands of years now, emissions of greenhouse gases to the atmosphere have been balanced out by greenhouse gases that are naturally absorbed. As a result, greenhouse gas concentrations and temperatures have been fairly stable, which has allowed human civilization to flourish within a consistent climate.

Greenland is covered with a vast amount of ice—but the ice is melting four times faster than thought, suggesting that Greenland may be approaching a dangerous tipping point, with implications for global sea-level rise.

Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the Industrial Revolution. Changes that have historically taken thousands of years are now happening over the course of decades .

Why does this matter?

The rapid rise in greenhouse gases is a problem because it’s changing the climate faster than some living things can adapt to. Also, a new and more unpredictable climate poses unique challenges to all life.

Historically, Earth's climate has regularly shifted between temperatures like those we see today and temperatures cold enough to cover much of North America and Europe with ice. The difference between average global temperatures today and during those ice ages is only about 9 degrees Fahrenheit (5 degrees Celsius), and the swings have tended to happen slowly, over hundreds of thousands of years.

But with concentrations of greenhouse gases rising, Earth's remaining ice sheets such as Greenland and Antarctica are starting to melt too . That extra water could raise sea levels significantly, and quickly. By 2050, sea levels are predicted to rise between one and 2.3 feet as glaciers melt.

As the mercury rises, the climate can change in unexpected ways. In addition to sea levels rising, weather can become more extreme . This means more intense major storms, more rain followed by longer and drier droughts—a challenge for growing crops—changes in the ranges in which plants and animals can live, and loss of water supplies that have historically come from glaciers.

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The Effects of Climate Change

The effects of human-caused global warming are happening now, are irreversible for people alive today, and will worsen as long as humans add greenhouse gases to the atmosphere.

• We already see effects scientists predicted, such as the loss of sea ice, melting glaciers and ice sheets, sea level rise, and more intense heat waves.
• Scientists predict global temperature increases from human-made greenhouse gases will continue. Severe weather damage will also increase and intensify.

Earth Will Continue to Warm and the Effects Will Be Profound

Global climate change is not a future problem. Changes to Earth’s climate driven by increased human emissions of heat-trapping greenhouse gases are already having widespread effects on the environment: glaciers and ice sheets are shrinking, river and lake ice is breaking up earlier, plant and animal geographic ranges are shifting, and plants and trees are blooming sooner.

Effects that scientists had long predicted would result from global climate change are now occurring, such as sea ice loss, accelerated sea level rise, and longer, more intense heat waves.

The magnitude and rate of climate change and associated risks depend strongly on near-term mitigation and adaptation actions, and projected adverse impacts and related losses and damages escalate with every increment of global warming.

Intergovernmental Panel on Climate Change

Some changes (such as droughts, wildfires, and extreme rainfall) are happening faster than scientists previously assessed. In fact, according to the Intergovernmental Panel on Climate Change (IPCC) — the United Nations body established to assess the science related to climate change — modern humans have never before seen the observed changes in our global climate, and some of these changes are irreversible over the next hundreds to thousands of years.

Scientists have high confidence that global temperatures will continue to rise for many decades, mainly due to greenhouse gases produced by human activities.

The IPCC’s Sixth Assessment report, published in 2021, found that human emissions of heat-trapping gases have already warmed the climate by nearly 2 degrees Fahrenheit (1.1 degrees Celsius) since 1850-1900. 1 The global average temperature is expected to reach or exceed 1.5 degrees C (about 3 degrees F) within the next few decades. These changes will affect all regions of Earth.

The severity of effects caused by climate change will depend on the path of future human activities. More greenhouse gas emissions will lead to more climate extremes and widespread damaging effects across our planet. However, those future effects depend on the total amount of carbon dioxide we emit. So, if we can reduce emissions, we may avoid some of the worst effects.

The scientific evidence is unequivocal: climate change is a threat to human wellbeing and the health of the planet. Any further delay in concerted global action will miss the brief, rapidly closing window to secure a liveable future.

Here are some of the expected effects of global climate change on the United States, according to the Third and Fourth National Climate Assessment Reports:

Future effects of global climate change in the United States:

U.S. Sea Level Likely to Rise 1 to 6.6 Feet by 2100

Global sea level has risen about 8 inches (0.2 meters) since reliable record-keeping began in 1880. By 2100, scientists project that it will rise at least another foot (0.3 meters), but possibly as high as 6.6 feet (2 meters) in a high-emissions scenario. Sea level is rising because of added water from melting land ice and the expansion of seawater as it warms. Image credit: Creative Commons Attribution-Share Alike 4.0

Climate Changes Will Continue Through This Century and Beyond

Global climate is projected to continue warming over this century and beyond. Image credit: Khagani Hasanov, Creative Commons Attribution-Share Alike 3.0

Hurricanes Will Become Stronger and More Intense

Scientists project that hurricane-associated storm intensity and rainfall rates will increase as the climate continues to warm. Image credit: NASA

More Droughts and Heat Waves

Droughts in the Southwest and heat waves (periods of abnormally hot weather lasting days to weeks) are projected to become more intense, and cold waves less intense and less frequent. Image credit: NOAA

Longer Wildfire Season

Warming temperatures have extended and intensified wildfire season in the West, where long-term drought in the region has heightened the risk of fires. Scientists estimate that human-caused climate change has already doubled the area of forest burned in recent decades. By around 2050, the amount of land consumed by wildfires in Western states is projected to further increase by two to six times. Even in traditionally rainy regions like the Southeast, wildfires are projected to increase by about 30%.

Changes in Precipitation Patterns

Climate change is having an uneven effect on precipitation (rain and snow) in the United States, with some locations experiencing increased precipitation and flooding, while others suffer from drought. On average, more winter and spring precipitation is projected for the northern United States, and less for the Southwest, over this century. Image credit: Marvin Nauman/FEMA

Frost-Free Season (and Growing Season) will Lengthen

The length of the frost-free season, and the corresponding growing season, has been increasing since the 1980s, with the largest increases occurring in the western United States. Across the United States, the growing season is projected to continue to lengthen, which will affect ecosystems and agriculture.

Global Temperatures Will Continue to Rise

Summer of 2023 was Earth's hottest summer on record, 0.41 degrees Fahrenheit (F) (0.23 degrees Celsius (C)) warmer than any other summer in NASA’s record and 2.1 degrees F (1.2 C) warmer than the average summer between 1951 and 1980. Image credit: NASA

Arctic Is Very Likely to Become Ice-Free

Sea ice cover in the Arctic Ocean is expected to continue decreasing, and the Arctic Ocean will very likely become essentially ice-free in late summer if current projections hold. This change is expected to occur before mid-century.

U.S. Regional Effects

Climate change is bringing different types of challenges to each region of the country. Some of the current and future impacts are summarized below. These findings are from the Third 3 and Fourth 4 National Climate Assessment Reports, released by the U.S. Global Change Research Program .

• Northeast. Heat waves, heavy downpours, and sea level rise pose increasing challenges to many aspects of life in the Northeast. Infrastructure, agriculture, fisheries, and ecosystems will be increasingly compromised. Farmers can explore new crop options, but these adaptations are not cost- or risk-free. Moreover, adaptive capacity , which varies throughout the region, could be overwhelmed by a changing climate. Many states and cities are beginning to incorporate climate change into their planning.
• Northwest. Changes in the timing of peak flows in rivers and streams are reducing water supplies and worsening competing demands for water. Sea level rise, erosion, flooding, risks to infrastructure, and increasing ocean acidity pose major threats. Increasing wildfire incidence and severity, heat waves, insect outbreaks, and tree diseases are causing widespread forest die-off.
• Southeast. Sea level rise poses widespread and continuing threats to the region’s economy and environment. Extreme heat will affect health, energy, agriculture, and more. Decreased water availability will have economic and environmental impacts.
• Midwest. Extreme heat, heavy downpours, and flooding will affect infrastructure, health, agriculture, forestry, transportation, air and water quality, and more. Climate change will also worsen a range of risks to the Great Lakes.
• Southwest. Climate change has caused increased heat, drought, and insect outbreaks. In turn, these changes have made wildfires more numerous and severe. The warming climate has also caused a decline in water supplies, reduced agricultural yields, and triggered heat-related health impacts in cities. In coastal areas, flooding and erosion are additional concerns.

1. IPCC 2021, Climate Change 2021: The Physical Science Basis , the Working Group I contribution to the Sixth Assessment Report, Cambridge University Press, Cambridge, UK.

2. IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

3. USGCRP 2014, Third Climate Assessment .

4. USGCRP 2017, Fourth Climate Assessment .

Related Resources

A Degree of Difference

So, the Earth's average temperature has increased about 2 degrees Fahrenheit during the 20th century. What's the big deal?

What’s the difference between climate change and global warming?

“Global warming” refers to the long-term warming of the planet. “Climate change” encompasses global warming, but refers to the broader range of changes that are happening to our planet, including rising sea levels; shrinking mountain glaciers; accelerating ice melt in Greenland, Antarctica and the Arctic; and shifts in flower/plant blooming times.

Is it too late to prevent climate change?

Humans have caused major climate changes to happen already, and we have set in motion more changes still. However, if we stopped emitting greenhouse gases today, the rise in global temperatures would begin to flatten within a few years. Temperatures would then plateau but remain well-elevated for many, many centuries.

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What Is the Greenhouse Effect?

Watch this video to learn about the greenhouse effect! Click here to download this video (1920x1080, 105 MB, video/mp4). Click here to download this video about the greenhouse effect in Spanish (1920x1080, 154 MB, video/mp4).

How does the greenhouse effect work?

As you might expect from the name, the greenhouse effect works … like a greenhouse! A greenhouse is a building with glass walls and a glass roof. Greenhouses are used to grow plants, such as tomatoes and tropical flowers.

A greenhouse stays warm inside, even during the winter. In the daytime, sunlight shines into the greenhouse and warms the plants and air inside. At nighttime, it's colder outside, but the greenhouse stays pretty warm inside. That's because the glass walls of the greenhouse trap the Sun's heat.

A greenhouse captures heat from the Sun during the day. Its glass walls trap the Sun's heat, which keeps plants inside the greenhouse warm — even on cold nights. Credit: NASA/JPL-Caltech

The greenhouse effect works much the same way on Earth. Gases in the atmosphere, such as carbon dioxide , trap heat similar to the glass roof of a greenhouse. These heat-trapping gases are called greenhouse gases .

During the day, the Sun shines through the atmosphere. Earth's surface warms up in the sunlight. At night, Earth's surface cools, releasing heat back into the air. But some of the heat is trapped by the greenhouse gases in the atmosphere. That's what keeps our Earth a warm and cozy 58 degrees Fahrenheit (14 degrees Celsius), on average.

Earth's atmosphere traps some of the Sun's heat, preventing it from escaping back into space at night. Credit: NASA/JPL-Caltech

How are humans impacting the greenhouse effect?

Human activities are changing Earth's natural greenhouse effect. Burning fossil fuels like coal and oil puts more carbon dioxide into our atmosphere.

NASA has observed increases in the amount of carbon dioxide and some other greenhouse gases in our atmosphere. Too much of these greenhouse gases can cause Earth's atmosphere to trap more and more heat. This causes Earth to warm up.

What reduces the greenhouse effect on Earth?

Just like a glass greenhouse, Earth's greenhouse is also full of plants! Plants can help to balance the greenhouse effect on Earth. All plants — from giant trees to tiny phytoplankton in the ocean — take in carbon dioxide and give off oxygen.

The ocean also absorbs a lot of excess carbon dioxide in the air. Unfortunately, the increased carbon dioxide in the ocean changes the water, making it more acidic. This is called ocean acidification .

More acidic water can be harmful to many ocean creatures, such as certain shellfish and coral. Warming oceans — from too many greenhouse gases in the atmosphere — can also be harmful to these organisms. Warmer waters are a main cause of coral bleaching .

This photograph shows a bleached brain coral. A main cause of coral bleaching is warming oceans. Ocean acidification also stresses coral reef communities. Credit: NOAA

5 things you should know about the greenhouse gases warming the planet

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News stories about the climate crisis often contain mentions of greenhouse gases, and the greenhouse effect. Whilst most will find the analogy easy to understand, what exactly are these gases, and why are they contributing to the warming of the Earth?

1. What is the greenhouse effect?

In a greenhouse, sunlight enters, and heat is retained. The greenhouse effect describes a similar phenomenon on a planetary scale but, instead of the glass of a greenhouse,  certain gases are increasingly raising global temperatures.

The surface of the Earth absorbs just under half of the sun’s energy, while the atmosphere absorbs 23 per cent, and the rest is reflected back into space. Natural processes ensure that the amount of incoming and outgoing energy is equal, keeping the planet’s temperature stable.

However, human activity is resulting in the increased emission of so-called greenhouse gases (GHGs) which, unlike other atmospheric gases such as oxygen and nitrogen, becomes trapped in the atmosphere, unable to escape the planet. This energy returns to the surface, where it is reabsorbed.

Because more energy enters than exits the planet, surface temperatures increase until a new balance is achieved. 

2. Why does the warming matter?

This temperature increase has long-term, adverse effects on the climate, and affects a myriad of natural systems. Effects include increases in the frequency and intensity of extreme weather events – including flooding, droughts, wildfires and hurricanes – that affect millions of people and cause trillions in economic losses.

“Human-caused greenhouse gas emissions endanger human and environmental health,” says Mark Radka, Chief of the UN Environment Programme’s ( UNEP ) Energy and Climate Branch. “And the impacts will become more widespread and severe without strong climate action.”

GHG emissions are critical to understanding and addressing the climate crisis: despite an initial dip due to COVID-19 , the latest UNEP Emissions Gap Report shows a rebound, and forecasts a disastrous global temperature rise of at least 2.7 degrees this century, unless countries make much greater efforts to reduce emissions.

The report found that GHG emissions need to be halved by 2030, if we are to limit global warming to 1.5°C compared to pre-industrial levels by the end of the century.

3. What are the major greenhouse gases?

Water vapour is the biggest overall contributor to the greenhouse effect. However, almost all the water vapour in the atmosphere comes from natural processes.

Carbon dioxide (CO2), methane and nitrous oxide are the major GHGs to worry about. CO2 stays in the atmosphere for up to 1,000 years, methane for around a decade, and nitrous oxide for approximately 120 years.

Measured over a 20-year period, methane is 80 times more potent than CO2 in causing global warming, while nitrous oxide is 280 times more potent.

4. How is human activity producing these greenhouse gases?

Coal, oil, and natural gas continue to power many parts of the world. Carbon is the main element in these fuels and, when they’re burned to generate electricity, power transportation, or provide heat, they produce CO2.

Oil and gas extraction, coal mining, and waste landfills account for 55 per cent of human-caused methane emissions. Approximately 32 per cent of human-caused methane emissions are attributable to cows, sheep and other ruminants that ferment food in their stomachs. Manure decomposition is another agricultural source of the gas, as is rice cultivation. 

Human-caused nitrous oxide emissions largely arise from agriculture practices. Bacteria in soil and water naturally convert nitrogen into nitrous oxide, but fertilizer use and run-off add to this process by putting more nitrogen into the environment.

Fluorinated gases – such as hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride – are GHGs that do not occur naturally. Hydrofluorocarbons are refrigerants used as alternatives to chlorofluorocarbons (CFCs), which, having depleted the ozone layer,were phased out thanks to the Montreal Protocol. The others have industrial and commercial uses.

While fluorinated gases are far less prevalent than other GHGs and do not deplete the ozone layer like CFCs, they are still very powerful. Over a 20-year period, the global warming potential of some fluorinated gases is up to 16,300 times greater than that of CO2.

5. What can we do to reduce GHG emissions?

Shifting to renewable energy, putting a price on carbon, and phasing out coal are all important elements in reducing GHG emissions. Ultimately, stronger emission-reduction targets are necessary for the preservation of long-term human and environmental health.

“We need to implement strong policies that back the raised ambitions,” says Mr. Radka. “We cannot continue down the same path and expect better results. Action is needed now.”

During COP26, the European Union and the United States launched the Global Methane Pledge, which will see over 100 countries aim to reduce 30 per cent of methane emissions in the fuel, agriculture and waste sectors by 2030.

Despite the challenges, there is reason to be positive. From 2010 to 2021, policies were put in place  to lower annual emissions by 11 gigatons by 2030 compared to what would have otherwise happened. Individuals can also join the UN’s #ActNow campaign for ideas to take climate-positive actions.

By making choices that have less harmful effects on the environment, everyone can be a part of the solution and influence change. Speaking up is one way to multiply impact and create change on a much bigger scale.  

UNEP’s role in reducing GHGs

• UNEP has outlined its six-sector solution, which can reduce 29–32 gigatons of carbon dioxide by 2030 to meet the 1.5°C warming limit. The six sectors identified are: energy; industry; agricultureand food; forests andland use; transport; and buildings and cities.
• UNEP also maintains an online “Climate Note,” a tool that visualizes the changing state of the climate with a baseline of 1990.
• Through its other multilateral environmental agreements and reports, UNEP raises awareness and advocates for effective environmental action. UNEP will continue to work closely with its 193 Member States and other stakeholders to set the environmental agenda and advocate for a drastic reduction in GHG emissions.
• greenhouse gas emissions

How Do We Reduce Greenhouse Gases?

To stop climate change , we need to stop the amount of greenhouse gases, like carbon dioxide, from increasing. For the past 150 years, burning fossil fuels and cutting down forests, which naturally pull carbon dioxide out of the air, has caused greenhouse gas levels to increase. There are two main ways to stop the amount of greenhouse gases from increasing: we can stop adding them to the air, and we can increase the Earth’s ability to pull them out of the air.

This is called climate mitigation . There is not one single way to mitigate climate change. Instead, we will have to piece together many different solutions to stop the climate from warming. Below are descriptions of the main methods that we can use.

Many of these solutions are already being implemented in places around the world. Some can be tackled by individuals, such as using less energy, riding a bike instead of driving, driving an electric car, and switching to renewable energy. Other actions to mitigate climate change involve communities, regions, or nations working together to make changes, such as switching power plants from burning coal or gas to renewable energy and growing public transit.

Use less electricity.

Taking steps to use less electricity, especially when it comes from burning coal or gas, can take a big bite out of greenhouse gas emissions. Worldwide, electricity use is responsible for a quarter of all emissions. 

Some steps that you can take to use less electricity are simple and save money, like replacing incandescent light bulbs with LED bulbs that use less electricity, adding insulation to your home, and setting the thermostat lower in the winter and higher in the summer, especially when no one is home. There are also new technologies that help keep buildings energy efficient, such as glass that reflects heat, low-flow water fixtures, smart thermostats, and new air conditioning technology with refrigerants that don’t cause warming. In urban and suburban environments, green or cool roofs can limit the amount of heat that gets into buildings during hot days and help decrease the urban heat island effect .

Green roof on the Walter Reed Community Center in Arlington, VA, US Credit: Arlington County on Flickr/CC BY-SA 2.0

Generate electricity without emissions.

Renewable energy sources include solar energy, geothermal energy, wind turbines, ocean wave and tidal energy, waste and biomass energy, and hydropower. Because they do not burn fossil fuels, these renewable energy sources do not release greenhouse gases into the atmosphere as they generate electricity. Nuclear energy also creates no greenhouse gas emissions, so it can be thought of as a solution to climate change. However, it does generate radioactive waste that needs long-term, secure storage.

Today, the amount of electricity that comes from renewable energy is growing. A few countries, such as Iceland and Costa Rica, now get nearly all of their electricity from renewable energy. In many other countries, the percentage of electricity from renewable sources is currently small (5 - 10%) but growing.

Wind turbines can be on land or in the ocean, where high winds are common. Credit: Nicholas Doherty on Unsplash

Shrink the footprint of food.

Today, about a fifth of global carbon emissions come from raising farm animals for meat. For example, as cattle digest food they burp, releasing methane, a powerful greenhouse gas, and their manure releases the greenhouse gases carbon dioxide and nitrous oxide. And forests, which take carbon dioxide out of the air, are often cut down so that cattle have space to graze.

Eating a diet that is mostly or entirely plant-based (such as vegetables, bread, rice, and beans) lowers emissions. According to the Drawdown Project , if half the population worldwide adopts a plant-rich diet by 2050, 65 gigatons of carbon dioxide would be kept out of the atmosphere over about 30 years. (For a sense of scale, 65 gigatons of carbon dioxide is nearly two-years-worth of recent emissions from fossil fuels and industry.) Reducing food waste can make an even larger impact, saving about 90 gigatons of carbon dioxide from the atmosphere over 30 years.

Eating a plant-rich diet lowers greenhouse gas emissions. Credit: Victoria Shes on Unsplash

Travel without making greenhouse gases.

Most of the ways we have to get from place to place currently rely on fossil fuels: gasoline for vehicles and jet fuel for planes. Burning fossil fuels for transportation adds up to 14% of global greenhouse gas emissions worldwide. We can reduce emissions by shifting to alternative technologies that either don’t need gasoline (like bicycles and electric cars) or don’t need as much (like hybrid cars). Using public transportation, carpooling, biking, and walking leads to fewer vehicles on the road and less greenhouse gases in the atmosphere. Cities and towns can make it easier for people to lower greenhouse gas emissions by adding bus routes, bike paths, and sidewalks.

Electric bicycles can be a way to get around without burning gasoline. Credit: Karlis Dambrans/CC BY 2.0

Reduce household waste.

Waste we put in landfills releases greenhouse gases. Almost half the gas released by landfill waste is methane, which is an especially potent greenhouse gas. Landfills are, in fact, the third largest source of methane emissions in the U.S., behind natural gas/petroleum use and animals raised for food production (and their manure). In the U.S., each member of a household produces an average of 2 kg (4.4 lbs) of trash per day. That's 726 kg (1660 lbs) of trash per person per year! Conscious choices, including avoiding unnecessary purchases, buying secondhand, eliminating reliance on single-use containers, switching to reusable bags, bottles, and beverage cups, reducing paper subscriptions and mail in favor of digital options, recycling, and composting, can all help reduce household waste.     

Reduce emissions from industry.

Manufacturing, mining for raw materials, and dealing with the waste all take energy. Most of the products that we buy — everything from phones and TVs to clothing and shoes — are created in factories, which produce up to about 20% of the greenhouse gases emitted worldwide.

There are ways to decrease emissions from manufacturing. Using materials that aren’t made from fossil fuels and don’t release greenhouse gases is a good start. For example, cement releases carbon dioxide as it hardens, but there are alternative products that don’t create greenhouse gases. Similarly, bioplastics made from plants are an alternative to plastics that come from fossil fuels. Companies can also use renewable energy sources to power factories and ship the products that they create in fuel-saving cargo ships.

Take carbon dioxide out of the air.

Along with reducing the amount of carbon dioxide that we add to the air, we can also take action to increase the amount of carbon dioxide we take out of the air. The places where carbon dioxide is pulled out of the air are called carbon sinks. For example, planting trees, bamboo, and other plants increases the number of carbon sinks. Conserving forests, grasslands, peatlands, and wetlands, where carbon is held in plants and soils, protects existing carbon sinks. Farming methods such as planting cover crops and crop rotation keep soils healthy so that they are effective carbon sinks. There are also carbon dioxide removal technologies, which may be able to pull large amounts of greenhouse gases out of the atmosphere.

As the trees and other plants in a forest use sunlight to create the food they need, they are also pulling carbon dioxide out of the air. Credit: B NW on Unsplash

© 2020 UCAR

• Solving Climate Change
• Why Earth Is Warming
• The Greenhouse Effect
• What's Your Carbon Footprint?
• Classroom Activity: Mitigation or Adaptation?
• Classroom Activity: Solving the Carbon Dioxide Problem
• Stabilization Wedges (Activity and Resources)

The Basics of Climate Change

Greenhouse gases affect Earth’s energy balance and climate

The Sun serves as the primary energy source for Earth’s climate. Some of the incoming sunlight is reflected directly back into space, especially by bright surfaces such as ice and clouds, and the rest is absorbed by the surface and the atmosphere. Much of this absorbed solar energy is re-emitted as heat (longwave or infrared radiation). The atmosphere in turn absorbs and re-radiates heat, some of which escapes to space. Any disturbance to this balance of incoming and outgoing energy will affect the climate. For example, small changes in the output of energy from the Sun will affect this balance directly.

If all heat energy emitted from the surface passed through the atmosphere directly into space, Earth’s average surface temperature would be tens of degrees colder than today. Greenhouse gases in the atmosphere, including water vapour, carbon dioxide, methane, and nitrous oxide, act to make the surface much warmer than this because they absorb and emit heat energy in all directions (including downwards), keeping Earth’s surface and lower atmosphere warm [Figure B1]. Without this greenhouse effect, life as we know it could not have evolved on our planet. Adding more greenhouse gases to the atmosphere makes it even more effective at preventing heat from escaping into space. When the energy leaving is less than the energy entering, Earth warms until a new balance is established.

Greenhouse gases emitted by human activities alter Earth’s energy balance and thus its climate. Humans also affect climate by changing the nature of the land surfaces (for example by clearing forests for farming) and through the emission of pollutants that affect the amount and type of particles in the atmosphere.

Scientists have determined that, when all human and natural factors are considered, Earth’s climate balance has been altered towards warming, with the biggest contributor being increases in CO 2 .

Figure b1. Greenhouse gases in the atmosphere, including water vapour, carbon dioxide, methane, and nitrous oxide, absorb heat energy and emit it in all directions (including downwards), keeping Earth’s surface and lower atmosphere warm. Adding more greenhouse gases to the atmosphere enhances the effect, making Earth’s surface and lower atmosphere even warmer. Image based on a figure from US EPA.

Human activities have added greenhouse gases to the atmosphere

The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased significantly since the Industrial Revolution began. In the case of carbon dioxide, the average concentration measured at the Mauna Loa Observatory in Hawaii has risen from 316 parts per million (ppm) in 1959 (the first full year of data available) to more than 411 ppm in 2019 [Figure B2]. The same rates of increase have since been recorded at numerous other stations worldwide. Since preindustrial times, the atmospheric concentration of CO 2  has increased by over 40%, methane has increased by more than 150%, and nitrous oxide has increased by roughly 20%. More than half of the increase in CO 2  has occurred since 1970. Increases in all three gases contribute to warming of Earth, with the increase in CO 2  playing the largest role. See page B3 to learn about the sources of human emitted greenhouse gases.  Learn about the sources of human emitted greenhouse gases.

Scientists have examined greenhouse gases in the context of the past. Analysis of air trapped inside ice that has been accumulating over time in Antarctica shows that the CO 2  concentration began to increase significantly in the 19th century [Figure B3], after staying in the range of 260 to 280 ppm for the previous 10,000 years. Ice core records extending back 800,000 years show that during that time, CO 2  concentrations remained within the range of 170 to 300 ppm throughout many “ice age” cycles -  learn about the ice ages  -  and no concentration above 300 ppm is seen in ice core records until the past 200 years.

Measurements of the forms (isotopes) of carbon in the modern atmosphere show a clear fingerprint of the addition of “old” carbon (depleted in natural radioactive  14 C) coming from the combustion of fossil fuels (as opposed to “newer” carbon coming from living systems). In addition, it is known that human activities (excluding land use changes) currently emit an estimated 10 billion tonnes of carbon each year, mostly by burning fossil fuels, which is more than enough to explain the observed increase in concentration. These and other lines of evidence point conclusively to the fact that the elevated CO 2  concentration in our atmosphere is the result of human activities. 

Fig b2. Measurements of atmospheric CO 2  since 1958 from the Mauna Loa Observatory in Hawaii (black) and from the South Pole (red) show a steady annual increase in atmospheric CO 2  concentration. The measurements are made at remote places like these because they are not greatly influenced by local processes, so therefore they are representative of the background atmosphere. The small up-and-down saw-tooth pattern reflects seasonal changes in the release and uptake of CO 2  by plants. Source: Scripps CO2 Program

Figure b3. CO 2  variations during the past 1,000 years, obtained from analysis of air trapped in an ice core extracted from Antarctica (red squares), show a sharp rise in atmospheric CO 2  starting in the late 19th century. Modern atmospheric measurements from Mauna Loa are superimposed in gray. Source: figure by Eric Wolff, data from Etheridge et al., 1996; MacFarling Meure et al., 2006; Scripps CO 2  Program. 

Climate records show a warming trend

Estimating global average surface air temperature increase requires careful analysis of millions of measurements from around the world, including from land stations, ships, and satellites. Despite the many complications of synthesising such data, multiple independent teams have concluded separately and unanimously that global average surface air temperature has risen by about 1 °C (1.8 °F) since 1900 [Figure B4]. Although the record shows several pauses and accelerations in the increasing trend, each of the last four decades has been warmer than any other decade in the instrumental record since 1850.

Going further back in time before accurate thermometers were widely available, temperatures can be reconstructed using climate-sensitive indicators “proxies” in materials such as tree rings, ice cores, and marine sediments. Comparisons of the thermometer record with these proxy measurements suggest that the time since the early 1980s has been the warmest 40-year period in at least eight centuries, and that global temperature is rising towards peak temperatures last seen 5,000 to 10,000 years ago in the warmest part of our current interglacial period.

Many other impacts associated with the warming trend have become evident in recent years. Arctic summer sea ice cover has shrunk dramatically. The heat content of the ocean has increased. Global average sea level has risen by approximately 16 cm (6 inches) since 1901, due both to the expansion of warmer ocean water and to the addition of melt waters from glaciers and ice sheets on land. Warming and precipitation changes are altering the geographical ranges of many plant and animal species and the timing of their life cycles. In addition to the effects on climate, some of the excess CO 2  in the atmosphere is being taken up by the ocean, changing its chemical composition (causing ocean acidification).

Figure b4. Earth’s global average surface temperature has risen, as shown in this plot of combined land and ocean measurements from 1850 to 2019 derived from three independent analyses of the available data sets. The top panel shows annual average values from the three analyses, and the bottom panel shows decadal average values, including the uncertainty range (grey bars) for the maroon (HadCRUT4) dataset. The temperature changes are relative to the global average surface temperature, averaged from 1961−1990. Source: Based on IPCC AR5, data from the HadCRUT4 dataset (black), NOAA Climate.gov; data from UK Met Office Hadley Centre (maroon), US National Aeronautics and Space Administration Goddard Institute for Space Studies (red), and US National Oceanic and Atmospheric Administration National Centers for Environmental Information (orange). 

Many complex processes shape our climate

Based just on the physics of the amount of energy that CO 2 absorbs and emits, a doubling of atmospheric CO 2 concentration from pre-industrial levels (up to about 560 ppm) would by itself cause a global average temperature increase of about 1 °C (1.8 °F). In the overall climate system, however, things are more complex; warming leads to further effects (feedbacks) that either amplify or diminish the initial warming.

The most important feedbacks involve various forms of water. A warmer atmosphere generally contains more water vapour. Water vapour is a potent greenhouse gas, thus causing more warming; its short lifetime in the atmosphere keeps its increase largely in step with warming. Thus, water vapour is treated as an amplifier, and not a driver, of climate change. Higher temperatures in the polar regions melt sea ice and reduce seasonal snow cover, exposing a darker ocean and land surface that can absorb more heat, causing further warming. Another important but uncertain feedback concerns changes in clouds. Warming and increases in water vapour together may cause cloud cover to increase or decrease which can either amplify or dampen temperature change depending on the changes in the horizontal extent, altitude, and properties of clouds. The latest assessment of the science indicates that the overall net global effect of cloud changes is likely to be to amplify warming.

The ocean moderates climate change. The ocean is a huge heat reservoir, but it is difficult to heat its full depth because warm water tends to stay near the surface. The rate at which heat is transferred to the deep ocean is therefore slow; it varies from year to year and from decade to decade, and it helps to determine the pace of warming at the surface. Observations of the sub-surface ocean are limited prior to about 1970, but since then, warming of the upper 700 m (2,300 feet) is readily apparent, and deeper warming is also clearly observed since about 1990.

Surface temperatures and rainfall in most regions vary greatly from the global average because of geographical location, in particular latitude and continental position. Both the average values of temperature, rainfall, and their extremes (which generally have the largest impacts on natural systems and human infrastructure), are also strongly affected by local patterns of winds.

Estimating the effects of feedback processes, the pace of the warming, and regional climate change requires the use of mathematical models of the atmosphere, ocean, land, and ice (the cryosphere) built upon established laws of physics and the latest understanding of the physical, chemical and biological processes affecting climate, and run on powerful computers. Models vary in their projections of how much additional warming to expect (depending on the type of model and on assumptions used in simulating certain climate processes, particularly cloud formation and ocean mixing), but all such models agree that the overall net effect of feedbacks is to amplify warming.

Human activities are changing the climate

Rigorous analysis of all data and lines of evidence shows that most of the observed global warming over the past 50 years or so cannot be explained by natural causes and instead requires a significant role for the influence of human activities.

In order to discern the human influence on climate, scientists must consider many natural variations that affect temperature, precipitation, and other aspects of climate from local to global scale, on timescales from days to decades and longer. One natural variation is the El Niño Southern Oscillation (ENSO), an irregular alternation between warming and cooling (lasting about two to seven years) in the equatorial Pacific Ocean that causes significant year-to-year regional and global shifts in temperature and rainfall patterns. Volcanic eruptions also alter climate, in part increasing the amount of small (aerosol) particles in the stratosphere that reflect or absorb sunlight, leading to a short-term surface cooling lasting typically about two to three years. Over hundreds of thousands of years, slow, recurring variations in Earth’s orbit around the Sun, which alter the distribution of solar energy received by Earth, have been enough to trigger the ice age cycles of the past 800,000 years.

Fingerprinting is a powerful way of studying the causes of climate change. Different influences on climate lead to different patterns seen in climate records. This becomes obvious when scientists probe beyond changes in the average temperature of the planet and look more closely at geographical and temporal patterns of climate change. For example, an increase in the Sun’s energy output will lead to a very different pattern of temperature change (across Earth’s surface and vertically in the atmosphere) compared to that induced by an increase in CO 2 concentration. Observed atmospheric temperature changes show a fingerprint much closer to that of a long-term CO 2 increase than to that of a fluctuating Sun alone. Scientists routinely test whether purely natural changes in the Sun, volcanic activity, or internal climate variability could plausibly explain the patterns of change they have observed in many different aspects of the climate system. These analyses have shown that the observed climate changes of the past several decades cannot be explained just by natural factors.

How will climate change in the future?

Scientists have made major advances in the observations, theory, and modelling of Earth’s climate system, and these advances have enabled them to project future climate change with increasing confidence. Nevertheless, several major issues make it impossible to give precise estimates of how global or regional temperature trends will evolve decade by decade into the future. Firstly, we cannot predict how much CO 2  human activities will emit, as this depends on factors such as how the global economy develops and how society’s production and consumption of energy changes in the coming decades. Secondly, with current understanding of the complexities of how climate feedbacks operate, there is a range of possible outcomes, even for a particular scenario of CO 2  emissions. Finally, over timescales of a decade or so, natural variability can modulate the effects of an underlying trend in temperature. Taken together, all model projections indicate that Earth will continue to warm considerably more over the next few decades to centuries. If there were no technological or policy changes to reduce emission trends from their current trajectory, then further globally-averaged warming of 2.6 to 4.8 °C (4.7 to 8.6 °F) in addition to that which has already occurred would be expected during the 21st century [Figure B5]. Projecting what those ranges will mean for the climate experienced at any particular location is a challenging scientific problem, but estimates are continuing to improve as regional and local-scale models advance.

Figure b5. The amount and rate of warming expected for the 21st century depends on the total amount of greenhouse gases that humankind emits. Models project the temperature increase for a business-as-usual emissions scenario (in red) and aggressive emission reductions, falling close to zero 50 years from now (in blue). Black is the modelled estimate of past warming. Each solid line represents the average of different model runs using the same emissions scenario, and the shaded areas provide a measure of the spread (one standard deviation) between the temperature changes projected by the different models. All data are relative to a reference period (set to zero) of 1986-2005. Source: Based on IPCC AR5

Climate change and biodiversity

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The Greenhouse Effect and our Planet

The greenhouse effect happens when certain gases, which are known as greenhouse gases, accumulate in Earth’s atmosphere. Greenhouse gases include carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), ozone (O 3 ), and fluorinated gases.

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Greenhouse gases include gases such as carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), ozone (O 3 ), and fluorinated gases. These greenhouse gases allow the sun's light to shine onto Earth's surface. Then the gases, such as ozone, trap the heat that reflects back from the surface inside Earth's atmosphere . The gases act like the glass walls of a greenhouse. In other words, they are warming.

The greenhouse effect happens when these gases gather in Earth's atmosphere. According to scientists, without the greenhouse effect, the average temperature of Earth would drop from 57 degrees Fahrenheit (14 degrees Celsius) to as low as negative 0.4 degrees F (minus 18 degrees C).

Do We Blame the Industrial Revolution ? Some greenhouse gases come from natural sources. For example, evaporation adds water vapor to the atmosphere. Animals and plants release carbon dioxide when they breathe. Methane is released naturally from decomposition, when soils and living things break down. Volcanoes —both on land and under the ocean —release greenhouse gases.

The Industrial Revolution happened in the late 1700s and early 1800s, when factories began producing more. Since then, people have been releasing larger quantities of greenhouse gases into the atmosphere. Greenhouse gas emissions increased 70 percent between 1970 and 2004. Emissions of carbon dioxide (CO 2 ), rose about 80 percent during that time.

The amount of CO 2 in the atmosphere far exceeds Earth's natural amount seen over the last 650,000 years.

Most of the CO 2 that people put into the atmosphere comes from burning fossil fuels . Cars, trucks, t rains and planes all burn fossil fuels. Many electric power plants do, as well. Another way humans release CO 2 into the atmosphere is by cutting down forests , because trees contain large amounts of carbon.

Human Activity + Greenhouse Gases = A Warming Earth People add methane to the atmosphere through livestock farming, landfills and fossil fuel production such as coal mining and natural gas processing. Nitrous oxide comes from agriculture and fossil fuel burning.

Fluorinated gases include chlorofluoro carbons (CFCs), hydro chlorofluoro carbons (HCFCs), and hydrofluorocarbons (HFCs). They are produced during the manufacturing of refrigeration and cooling products. Some come through aerosol cans , such as some hairsprays or spray paint.

As greenhouse gases increase, so does the temperature of Earth. The rise in Earth's average temperature contributed to by human activity is known as global warming .

The Greenhouse Effect and Climate Change Even slight increases in average global temperatures can have huge effects.

Perhaps the biggest effect is that glaciers and ice caps melt faster than usual. The meltwater d rains into the oceans , causing sea levels to rise.

Glaciers and ice caps cover about 10 percent of the world's land. They hold between 70 and 75 percent of the world's freshwater . If all of this ice melted, sea levels would rise about 70 meters (230 feet).

The Intergovernmental Panel on Climate Change says that the global sea level rose about 1.8 millimeters (0.07 inch) per year from 1961 to 1993. It rose about 3.1 millimeters (1/8 inch) per year since 1993.

This seems like only a tiny bit, but rising sea levels can cause flooding in cities along the coasts . This could force millions of people in low-lying areas out of their homes, such as in Bangladesh, the U.S. state of Florida, and the Netherlands.

Millions more people in countries such as Peru and India depend on water from melted glaciers . They use it for drinking, watering crops and hydroelectric power . Rapid loss of these glaciers would greatly hurt those countries.

Predictable Rain is Important to Many Greenhouse gas emissions also affect changes in precipitation , such as rain and snow .

In the 20th century, precipitation increased in eastern parts of North and South America, Northern Europe, and northern and Central Asia. However, it has decreased in parts of Africa, the Mediterranean, and southern Asia.

As climates change, so do the habitats for living things. Animals that are adapted to a certain climates might become threatened. Many humans depend on predictable rain patterns to grow specific crops . If the climate of an area changes, the people who live there may no longer be able to grow the crops they depend on for survival.

Scientists aren't the only Ones Who Can Help

• Drive less. Use  public transportation , carpool, walk, or ride a bike.
• Fly less. Airplanes produce huge amounts of greenhouse gas emissions.
• Reduce, reuse, and  recycle .
• Plant a tree. Trees absorb carbon dioxide, keeping it out of the atmosphere.
• Use less  electricity .
• Eat less meat. Cows are one of the biggest methane producers.
• Support alternative energy sources that don’t burn fossil fuels.

Artificial Gas

Chlorofluorocarbons (CFCs) are the only greenhouse gases not created by nature. They are created through refrigeration and aerosol cans.

CFCs, used mostly as refrigerants, are chemicals that were developed in the late 19th century and came into wide use in the mid-20th century.

Other greenhouse gases, such as carbon dioxide, are emitted by human activity, at an unnatural and unsustainable level, but the molecules do occur naturally in Earth's atmosphere.

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Human activity affects global surface temperatures by changing Earth ’s radiative balance—the “give and take” between what comes in during the day and what Earth emits at night. Increases in greenhouse gases —i.e., trace gases such as carbon dioxide and methane that absorb heat energy emitted from Earth’s surface and reradiate it back—generated by industry and transportation cause the atmosphere to retain more heat, which increases temperatures and alters precipitation patterns.

Global warming, the phenomenon of increasing average air temperatures near Earth’s surface over the past one to two centuries, happens mostly in the troposphere , the lowest level of the atmosphere, which extends from Earth’s surface up to a height of 6–11 miles. This layer contains most of Earth’s clouds and is where living things and their habitats and weather primarily occur.

Continued global warming is expected to impact everything from energy use to water availability to crop productivity throughout the world. Poor countries and communities with limited abilities to adapt to these changes are expected to suffer disproportionately. Global warming is already being associated with increases in the incidence of severe and extreme weather, heavy flooding , and wildfires —phenomena that threaten homes, dams, transportation networks, and other facets of human infrastructure. Learn more about how the IPCC’s Sixth Assessment Report, released in 2021, describes the social impacts of global warming.

Polar bears live in the Arctic , where they use the region’s ice floes as they hunt seals and other marine mammals . Temperature increases related to global warming have been the most pronounced at the poles, where they often make the difference between frozen and melted ice. Polar bears rely on small gaps in the ice to hunt their prey. As these gaps widen because of continued melting, prey capture has become more challenging for these animals.

Recent News

global warming , the phenomenon of increasing average air temperatures near the surface of Earth over the past one to two centuries. Climate scientists have since the mid-20th century gathered detailed observations of various weather phenomena (such as temperatures, precipitation , and storms) and of related influences on climate (such as ocean currents and the atmosphere’s chemical composition). These data indicate that Earth’s climate has changed over almost every conceivable timescale since the beginning of geologic time and that human activities since at least the beginning of the Industrial Revolution have a growing influence over the pace and extent of present-day climate change .

Giving voice to a growing conviction of most of the scientific community , the Intergovernmental Panel on Climate Change (IPCC) was formed in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP). The IPCC’s Sixth Assessment Report (AR6), published in 2021, noted that the best estimate of the increase in global average surface temperature between 1850 and 2019 was 1.07 °C (1.9 °F). An IPCC special report produced in 2018 noted that human beings and their activities have been responsible for a worldwide average temperature increase between 0.8 and 1.2 °C (1.4 and 2.2 °F) since preindustrial times, and most of the warming over the second half of the 20th century could be attributed to human activities.

AR6 produced a series of global climate predictions based on modeling five greenhouse gas emission scenarios that accounted for future emissions, mitigation (severity reduction) measures, and uncertainties in the model projections. Some of the main uncertainties include the precise role of feedback processes and the impacts of industrial pollutants known as aerosols , which may offset some warming. The lowest-emissions scenario, which assumed steep cuts in greenhouse gas emissions beginning in 2015, predicted that the global mean surface temperature would increase between 1.0 and 1.8 °C (1.8 and 3.2 °F) by 2100 relative to the 1850–1900 average. This range stood in stark contrast to the highest-emissions scenario, which predicted that the mean surface temperature would rise between 3.3 and 5.7 °C (5.9 and 10.2 °F) by 2100 based on the assumption that greenhouse gas emissions would continue to increase throughout the 21st century. The intermediate-emissions scenario, which assumed that emissions would stabilize by 2050 before declining gradually, projected an increase of between 2.1 and 3.5 °C (3.8 and 6.3 °F) by 2100.

Many climate scientists agree that significant societal, economic, and ecological damage would result if the global average temperature rose by more than 2 °C (3.6 °F) in such a short time. Such damage would include increased extinction of many plant and animal species, shifts in patterns of agriculture , and rising sea levels. By 2015 all but a few national governments had begun the process of instituting carbon reduction plans as part of the Paris Agreement , a treaty designed to help countries keep global warming to 1.5 °C (2.7 °F) above preindustrial levels in order to avoid the worst of the predicted effects. Whereas authors of the 2018 special report noted that should carbon emissions continue at their present rate, the increase in average near-surface air temperature would reach 1.5 °C sometime between 2030 and 2052, authors of the AR6 report suggested that this threshold would be reached by 2041 at the latest.

The AR6 report also noted that the global average sea level had risen by some 20 cm (7.9 inches) between 1901 and 2018 and that sea level rose faster in the second half of the 20th century than in the first half. It also predicted, again depending on a wide range of scenarios, that the global average sea level would rise by different amounts by 2100 relative to the 1995–2014 average. Under the report’s lowest-emission scenario, sea level would rise by 28–55 cm (11–21.7 inches), whereas, under the intermediate emissions scenario, sea level would rise by 44–76 cm (17.3–29.9 inches). The highest-emissions scenario suggested that sea level would rise by 63–101 cm (24.8–39.8 inches) by 2100.

The scenarios referred to above depend mainly on future concentrations of certain trace gases, called greenhouse gases , that have been injected into the lower atmosphere in increasing amounts through the burning of fossil fuels for industry, transportation , and residential uses. Modern global warming is the result of an increase in magnitude of the so-called greenhouse effect , a warming of Earth’s surface and lower atmosphere caused by the presence of water vapour , carbon dioxide , methane , nitrous oxides , and other greenhouse gases. In 2014 the IPCC first reported that concentrations of carbon dioxide, methane, and nitrous oxides in the atmosphere surpassed those found in ice cores dating back 800,000 years.

Of all these gases, carbon dioxide is the most important, both for its role in the greenhouse effect and for its role in the human economy. It has been estimated that, at the beginning of the industrial age in the mid-18th century, carbon dioxide concentrations in the atmosphere were roughly 280 parts per million (ppm). By the end of 2022 they had risen to 419 ppm, and, if fossil fuels continue to be burned at current rates, they are projected to reach 550 ppm by the mid-21st century—essentially, a doubling of carbon dioxide concentrations in 300 years.

A vigorous debate is in progress over the extent and seriousness of rising surface temperatures, the effects of past and future warming on human life, and the need for action to reduce future warming and deal with its consequences. This article provides an overview of the scientific background related to the subject of global warming. It considers the causes of rising near-surface air temperatures, the influencing factors, the process of climate research and forecasting, and the possible ecological and social impacts of rising temperatures. For an overview of the public policy developments related to global warming occurring since the mid-20th century, see global warming policy . For a detailed description of Earth’s climate, its processes, and the responses of living things to its changing nature, see climate . For additional background on how Earth’s climate has changed throughout geologic time , see climatic variation and change . For a full description of Earth’s gaseous envelope, within which climate change and global warming occur, see atmosphere .

• Biology Article
• Greenhouse Effect Gases

Greenhouse Effect

Table of Contents

What is the Greenhouse Effect?

Greenhouse gases, causes of greenhouse effect, effects of greenhouse effect, runaway greenhouse effect, greenhouse effect definition.

“Greenhouse effect is the process by which radiations from the sun are absorbed by the greenhouse gases and not reflected back into space. This insulates the surface of the earth and prevents it from freezing.”

A greenhouse is a house made of glass that can be used to grow plants. The sun’s radiations warm the plants and the air inside the greenhouse. The heat trapped inside can’t escape out and warms the greenhouse which is essential for the growth of the plants. Same is the case in the earth’s atmosphere.

During the day the sun heats up the earth’s atmosphere. At night, when the earth cools down the heat is radiated back into the atmosphere. During this process, the heat is absorbed by the greenhouse gases in the earth’s atmosphere. This is what makes the surface of the earth warmer, that makes the survival of living beings on earth possible.

However, due to the increased levels of greenhouse gases, the temperature of the earth has increased considerably. This has led to several drastic effects.

Let us have a look at the greenhouse gases and understand the causes and consequences of greenhouse effects with the help of a diagram.

Also Read:  Global Warming

“Greenhouse gases are the gases that absorb the infrared radiations and create a greenhouse effect. For eg., carbondioxide and chlorofluorocarbons.” Greenhouse Effect Diagram

The Diagram shows Greenhouse Gases such as carbon dioxide are the primary cause for the Greenhouse Effect

The major contributors to the greenhouse gases are factories, automobiles, deforestation , etc. The increased number of factories and automobiles increases the amount of these gases in the atmosphere. The greenhouse gases never let the radiations escape from the earth and increase the surface temperature of the earth. This then leads to global warming.

Also Read:  Our Environment

The major causes of the greenhouse effect are:

Burning of Fossil Fuels

Fossil fuels are an important part of our lives. They are widely used in transportation and to produce electricity. Burning of fossil fuels releases carbon dioxide. With the increase in population, the utilization of fossil fuels has increased. This has led to an increase in the release of greenhouse gases in the atmosphere.

Deforestation

Plants and trees take in carbon dioxide and release oxygen. Due to the cutting of trees, there is a considerable increase in the greenhouse gases which increases the earth’s temperature.

Nitrous oxide used in fertilizers is one of the contributors to the greenhouse effect in the atmosphere.

Industrial Waste and Landfills

The industries and factories produce harmful gases which are released in the atmosphere.

Landfills also release carbon dioxide and methane that adds to the greenhouse gases.

The main effects of increased greenhouse gases are:

Global Warming

It is the phenomenon of a gradual increase in the average temperature of the Earth’s atmosphere. The main cause for this environmental issue is the increased volumes of greenhouse gases such as carbon dioxide and methane released by the burning of fossil fuels, emissions from the vehicles, industries and other human activities.

Depletion of  Ozone Layer

Ozone Layer protects the earth from harmful ultraviolet rays from the sun. It is found in the upper regions of the stratosphere. The depletion of the ozone layer results in the entry of the harmful UV rays to the earth’s surface that might lead to skin cancer and can also change the climate drastically.

The major cause of this phenomenon is the accumulation of natural greenhouse gases including chlorofluorocarbons, carbon dioxide, methane, etc.

Smog and Air Pollution

Smog is formed by the combination of smoke and fog. It can be caused both by natural means and man-made activities.

In general, smog is generally formed by the accumulation of more greenhouse gases including nitrogen and sulfur oxides. The major contributors to the formation of smog are automobile and industrial emissions, agricultural fires, natural forest fires and the reaction of these chemicals among themselves.

Acidification of Water Bodies

Increase in the total amount of greenhouse gases in the air has turned most of the world’s water bodies acidic. The greenhouse gases mix with the rainwater and fall as acid rain. This leads to the acidification of water bodies.

Also, the rainwater carries the contaminants along with it and falls into the river, streams and lakes thereby causing their acidification.

This phenomenon occurs when the planet absorbs more radiation than it can radiate back. Thus, the heat lost from the earth’s surface is less and the temperature of the planet keeps rising. Scientists believe that this phenomenon took place on the surface of Venus billions of years ago.

This phenomenon is believed to have occurred in the following manner:

• A runaway greenhouse effect arises when the temperature of a planet rises to a level of the boiling point of water. As a result, all the water from the oceans converts into water vapour, which traps more heat coming from the sun and further increases the planet’s temperature. This eventually accelerates the greenhouse effect. This is also called the “positive feedback loop”.
• There is another scenario giving way to the runaway greenhouse effect. Suppose the temperature rise due to the above causes reaches such a high level that the chemical reactions begin to occur. These chemical reactions drive carbon dioxide from the rocks into the atmosphere. This would heat the surface of the planet which would further accelerate the transfer of carbon dioxide from the rocks to the atmosphere, giving rise to the runaway greenhouse effect.

In simple words, increasing the greenhouse effect gives rise to a runaway greenhouse effect which would increase the temperature of the earth to such an extent that no life will exist in the near future.

Also Read:  Environmental Issues

To learn more about what is the greenhouse effect, its definition, causes and effects, keep visiting BYJU’S website or download the BYJU’S app for further reference.

Frequently Asked Questions

What is global warming.

The gradual increase in temperature due to the greenhouse effect caused by pollutants, CFCs and carbon dioxide is called global warming. This phenomenon has disturbed the climatic pattern of the earth.

List gases which are responsible for the greenhouse effect.

The major greenhouse gases are: 1) Carbon dioxide 2) Methane 3) Water 4) Nitrous oxide 5) Ozone 6) Chlorofluorocarbons (CFCs)

What is the greenhouse effect?

What are the major causes of the greenhouse effect.

Burning of fossil fuels, deforestation, farming and livestock production all contribute to the greenhouse effect. Industries and factories also play a major role in the release of greenhouse gases.

What would have happened if the greenhouse gases were totally missing in the earth’s atmosphere?

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base (1992)

Chapter: a questions and answers about greenhouse warming, appendix a questions and answers about greenhouse warming, the greenhouse effect: what is known, what can be predicted.

1. What is the "greenhouse effect"?

In simplest terms, "greenhouse gases" let sunlight through to the earth's surface while trapping "outbound" radiation. This alters the radiative balance of the earth (see Figure A.1) and results in a warming of the earth's surface. The major greenhouse gases are water vapor, carbon dioxide (CO 2 ), methane (CH 4 ), chlorofluorocarbons (CFCs) and hydrogenated chlorofluorocarbons (HCFCs), tropospheric ozone (O 3 ), and nitrous oxide (N 2 O). Without the naturally occurring greenhouse gases (principally water vapor and CO 2 ), the earth's average temperature would be nearly 35°C (63°F) colder, and the planet would be much less suitable for human life.

2. Why is it called the "greenhouse" effect?

The greenhouse gases in the atmosphere act in much the same way as the glass panels of a greenhouse, which allow sunlight through and trap heat inside.

3. Why have experts become worried about the greenhouse effect now?

Rising atmospheric concentrations of CO 2 , CH 4 , and CFCs suggest the possibility of additional warming of the global climate. The panel refers to warming due to increased atmospheric concentrations of greenhouse gases as "greenhouse warming." Measurements of atmospheric CO 2 show that the 1990 concentration of 353 parts per million by volume (ppmv) is about one-quarter larger than the concentration before the Industrial Revolution (prior

FIGURE A.1 Earth's radiation balance. The solar radiation is set at 100 percent; all other values are in relation to it. About 25 percent of incident solar radiation is reflected back into space by the atmosphere, about 25 percent is absorbed by gases in the atmosphere, and about 5 percent is reflected into space from the earth's surface, leaving 45 percent to be absorbed by the oceans, land, and biotic material (white arrows).

Evaporation and mechanical heat transfer inject energy into the atmosphere equal to about 29 percent of incident radiation (grey arrow). Radiative energy emissions from the earth's surface and from the atmosphere (straight black arrows) are determined by the temperatures of the earth's surface and the atmosphere, respectively. Upward energy radiation from the earth's surface is about 104 percent of incident solar radiation. Atmospheric gases absorb part (25 percent) of the solar radiation penetrating the top of the atmosphere and all of the mechanical heat transferred from the earth's surface and the outbound radiation from the earth's surface. The downward radiation from the atmosphere is about 88 percent and outgoing radiation about 70 percent of incident solar radiation.

Note that the amounts of outgoing and incoming radiation balance at the top of the atmosphere, at 100 percent of incoming solar radiation (which is balanced by 5 percent reflected from the surface, 25 percent reflected from the top of the atmosphere, and 70 percent outgoing radiation), and at the earth's surface, at 133 percent (45 percent absorbed solar radiation plus 88 percent downward radiation from the atmosphere balanced by 29 percent evaporation and mechanical heat transfer and 104 percent upward radiation). Energy transfers into and away from the atmosphere also balance, at the atmosphere line, at 208 percent of incident solar radiation (75 percent transmitted solar radiation plus 29 percent mechanical transfer from the surface plus 104 percent upward radiation balanced by 50 percent of incoming solar continuing to the earth's surface, 70 percent outgoing radiation, and 88 percent downward radiation). These different energy transfers are due to the heat-trapping effects of the greenhouse gases in the atmosphere, the reemission of energy absorbed by these gases, and the cycling of energy through the various components in the diagram. The accuracy of the numbers in the diagram is typically ±5.

This diagram pertains to a period during which the climate is steady (or unchanging); that is, there is no net change in heat transfers into earth's surface, no net change in heat transfers into the atmosphere, and no net radiation change into the atmosphere-earth system from beyond the atmosphere.

to 1750). Atmospheric CO 2 is increasing at about 0.5 percent per year. The concentration of CH 4 is about 1.72 ppmv, or slightly more than twice that before 1750. It is rising at a rate of 0.9 percent per year. CFCs do not occur naturally, and so they were not found in the atmosphere until production began a few decades ago. Continued increases in atmospheric concentrations of greenhouse gases would affect the earth's radiative balance and could cause a large amount of additional greenhouse warming. Increasing the capture of energy in this fashion is also called "radiative forcing." Other factors, such as variation in incoming solar radiation, could be involved.

4. Has there been greenhouse warming in the recent past?

Best estimates are that the average global temperature rose between 0.3° and 0.6°C over about the last 100 years. However, it is not possible to say with a high degree of confidence whether this is due to increased atmospheric concentrations of greenhouse gases or to other natural or human causes. The temperature record much before 1900 is not reliable for estimates of changes smaller than 1°C–1.8°F).

5. What about CO 2 and temperature in the prehistoric past?

According to best estimates based on analysis of air bubbles trapped in ice sheets, ocean and lake sediments, and other records from the geologic past, there have been three especially "warm" periods in the last 4 million years. The Holocene optimum occurred from 6,000 to 5,000 years ago. During that period, atmospheric concentrations of CO 2 were about 270 to 280 ppmv, and average air temperatures about 1°C (1.8°F) warmer than modern times. The Eemian interglacial period happened with its midpoint about 125,000 years ago. Atmospheric concentrations of CO 2 were 280 to 300 ppmv, and temperatures up to 2°C (3.6°F) warmer than now. The Pliocene climate optimum occurred between 4.3 and 3.3 million years ago. Atmospheric concentrations of CO 2 have been estimated for that period to be about 450 ppmv, with temperatures 3° to 4°C (5.4° to 7.2°F) warmer than modern times. The prehistoric temperature estimates are from evidence dependent

on conditions during growing seasons and probably are better proxies for summer than winter temperatures. The estimate for the Pliocene period is especially controversial.

6. What natural things affect climate in the long run?

On the geologic time scale, many things affect climate:

• Changes in solar output

• Changes in the earth's orbital path

• Changes in land and ocean distribution (tectonic plate movements and the associated changes in mountain geography, ocean circulation, and sea level)

• Changes in the reflectivity of the earth's surface

• Changes in atmospheric concentrations of trace gases (especially CO 2 and CH 4 )

• Changes of a catastrophic nature (such as meteor impacts or extended volcanic eruptions)

7. What is meant by ''atmospheric lifetime" and "sinks"?

These concepts can be illustrated by referring to what is called the "carbon cycle." When CO 2 is emitted into the atmosphere, it moves among four main sinks, or pools, of stored carbon: the atmosphere, the oceans, the soil, and the earth's biomass (plants and animals). The movement of CO 2 among these sinks is not well understood. About 45 percent of the total emissions of CO 2 from human activity since preindustrial times is missing in the current accounting of CO 2 in the atmosphere, oceans, soil, and biomass. Three possible sinks for this missing CO 2 have been suggested. First, more CO 2 may have been absorbed into the oceans than was thought. Second, the storage of CO 2 in terrestrial plant life may be greater than estimated. Third, more CO 2 may have been absorbed directly into soil than is thought. However, there is no direct evidence for any of these explanations accounting for all the missing CO 2 . CO 2 in the atmosphere is relatively "long-lived" in that it does not easily break down into its constituent parts. CH 4 , by contrast, decomposes in the atmosphere in about 10 years. The greenhouse gas with the longest atmospheric lifetime (except for CO 2 ), CFC-115, has an average atmospheric lifetime of about 400 years. The overall contribution of greenhouse gases to global warming depends on their atmospheric lifetime as well as their ability to trap radiation. Table A.1 shows the relevant characteristics of the principal greenhouse gases.

8. Do all greenhouse gases have the same effect?

Each gas has different radiative properties, atmospheric chemistry, typical atmospheric lifetime, and atmospheric concentration. For example, CFC-12 is roughly 15,800 times more efficient molecule for molecule at trapping heat than CO 2 . Because CFC-12 is a large, heavy molecule with many atoms and a

TABLE A.1 Key Greenhouse Gases Influenced by Human Activity

CO2 CH4 CPC-11 CFC-12 N2O Preindustrial atmospheric concentration 280 ppmv 0.8 ppmv 0 0 288 ppbv Current atmospheric concentration (1990) 353 ppmv 1.72 ppmv 280 pptv 484pptv 310 ppbv Current rate of annual atmospheric accumulation 1.8 ppmv (0.5%) 0.015 ppmv (0.9%) 9.5 pptv (4%) 17 pptv (4%) 0.8 ppbv (0.25%) Atmospheric lifetime (years) (50–200) 10 65 130 150 NOTES: Ozone has not been included in the table because of lack of precise data. Here ppmv = parts per million by volume, ppbv = parts per billion by volume, and pptv = parts per trillion by volume. The 1990 concentrations have been estimated on the basis of an extrapolation of measurements reported for earlier years, assuming that the recent trends remained approximately constant. Net annual emissions of CO2 from the biosphere not affected by human activity, such as volcanic emissions, are assumed to be small. Estimates of human-induced emissions from the biosphere are controversial. For each gas in the table, except CO2, the "lifetime" is defined as the ratio of the atmospheric concentration to the total rate of removal. This time scale also characterizes the rate of adjustment of the atmospheric concentrations if the emission rates are changed abruptly. CO2 is a special case because it is merely circulated among various reservoirs (atmosphere, ocean, biota). The "lifetime" of CO2 given in the table is a rough indication of the time it would take for the CO2 concentration to adjust to changes in the emissions. SOURCE: Intergovernment Panel on Climate Change. 1990. J. T. Houghton, G. J. Jenkins, and J. J. Ephraums, eds. New York: Cambridge University Press. Reprinted by permission of Cambridge University Press. CO 2 molecule is small and light in comparison, there are fewer molecules of CFC-12 in each ton of CFC-12 emissions than CO 2 molecules in each ton of CO 2 emissions. Each ton of CFC-12 emissions is about 5,750 times more efficient at trapping heat than each ton of CO 2 . The comparatively greater amount of CO 2 in the atmosphere, however, means that it accounts for roughly half of the radiative forcing associated with the greenhouse effect. 9. Do greenhouse gases have different effects over time? Yes. Figure A.2 shows projected changes in radiative forcing for different greenhouse gases between now and 2030. The potential increase for each FIGURE A.2 Additional radiative forcing of principal greenhouse gases from 1990 to 2030 for different emission rates. The horizontal axis shows changes in greenhouse gas emissions ranging from completely eliminating emissions (-100 percent) to doubling current emissions (+100 percent). Emission changes are assumed to be linear from 1990 levels to the 2030 level selected. The vertical axis shows the change in radiative forcing in watts per square meter at the earth's surface in 2030. Each asterisk indicates the projected emissions of that gas assuming no additional regulatory policies, based on the Intergovernmental Panel on Climate Change estimates and the original restrictions agreed to under the Montreal Protocol, which limits emissions of CFCs. Chemical interactions among greenhouse gas species are not included. For CO 2 emissions remaining at 1990 levels through 2030, the resulting change in radiative forcing can be determined in two steps: (1) Find the point on thecurvelabeled "CO 2 " that is vertically above 0 percent change on the bottom scale. (2) The radiative forcing on the surface-troposphere system can be read in watts per square meter by moving horizontally to the left-hand scale, or about 1 W/m 2 . These steps must be repeated for each gas. For example, the radiative forcing for continued 1990-level emissions of CH 4 through 2030 would be about 0.2W/m 2 . SOURCE : Courtesy of Michael C. MacCracken. gas is plotted for different emissions of each gas compared to 1990 emission levels. The figure shows the impact of different percentage changes in emissions (compared to 1990 emission rates) on the radiative forcing. Figure A.3 extends this to show the impact on equilibrium temperature for different sensitivities of the climatic system (in degrees Celsius). 10. What is meant by a "feedback" mechanism? One example of a greenhouse warming feedback mechanism involves water vapor. As air warms, each cubic meter of air can hold more water vapor. Since water vapor is a greenhouse gas, this increased concentration of water vapor further enhances greenhouse warming. In turn, the warmer air can hold more water, and so on. This is an example of a positive feedback, providing a physical mechanism for "multiplying" the original impetus for change beyond its initial force. Some mechanisms provide a negative feedback, which decreases the initial impetus. For example, increasing the amount of water vapor in the air may lead to forming more clouds. Low-level, white clouds reflect sunlight, thereby preventing sunlight from reaching the earth and warming the surface. Increasing the geographical coverage of low-level clouds would reduce greenhouse warming, whereas increasing the amount of high, convective clouds could enhance greenhouse warming. This is because high, convective clouds absorb energy from below at higher temperatures than they radiate energy into space from their tops, thereby effectively trapping energy. Satellite measurements indicate that clouds currently have a slightly negative effect on current planetary temperature. It is not known whether increased temperatures would lead to more low-level clouds or more high, convective clouds. 11. Can the temperature record be used to show whether or not greenhouse warming is occurring? The estimated warming of between 0.3° and 0.6°C (0.5° and 1.1°F) over the last 100 years is roughly consistent with increased concentrations of greenhouse gases, but it is also within the bounds of "natural" variability for weather and climate. It cannot be proven to a high degree of confidence that this warming is the result of the increased atmospheric concentrations of greenhouse gases. There may be an underlying increase or decrease in average temperature from other, as yet undetected, causes. 12. What is the basis for predictions of global warming? General circulation models (GCMs) are the principal tools for projecting climatic changes. GCMs project equilibrium temperature increases between 1.9° and 5.2°C (3.4° and 9.4°F) for greenhouse gas concentrations equivalent to a doubling of the preindustrial level of atmospheric CO 2 . The midpoint of this range corresponds to an average global climate warmer than FIGURE A.3 Commitment to future warming. An incremental change in radiative forcing between 1990 and 2030 due to emissions of greenhouse gases implies a change in global average equilibrium temperature (see text). The scales on the right-hand side show two ranges of global average temperature responses. The first corresponds to a climate whose temperature response to an equivalent of doubling of the preindustrial level of CO 2 is 1°C; the second corresponds to a rise of 5°C for an equivalent doubling of CO 2 . These scales indicate the equilibrium commitment to future warming caused by emissions from 1990 through 2030. Assumptions are as in Figure A.2. To determine equilibrium warming in 2030 due to continued emissions of CO 2 at the 1990 level, find the point on the curve labeled "CO 2 " that is vertically above 0 percent change on the bottom scale. The equilibrium warming on the right-hand scales is about 0.23°C (0.4°F) for a climate system with 1° sensitivity and about 1.2°C (2.2°F) for a system with 5° sensitivity. For CH 4 emissions continuing at 1990 levels through 2030, the equilibrium warming would be about 0.04°C (0.07°F) at 1°sensitivity and about 0.25°C (0.5°F) at 5° sensitivity. These steps must be repeated for each gas. Total warming associated with 1990-level emissions of the gases shown until 2030 would be about 0.41°C (0.7°F) at 1°sensitivity and about 2.2°C (4°F) at 5° sensitivity. Scenarios of changes in committed future warming accompanying different greenhouse gas emission rates can be constructed by repeating this process for given emission rates and adding up the results. any in the last 1 million years. The consequences of this amount of warming are unknown and may include extremely unpleasant surprises. 13. What is "equilibrium temperature"? The oceans, covering roughly 70 percent of the earth's surface, absorb heat from the sun and redistribute it to the deep oceans slowly. It will be decades, perhaps centuries, before the oceans and the atmosphere fully redistribute the absorbed energy and the currently "committed" temperature rise is actually "realized." The temperature at which the system would ultimately come to rest given a particular level of greenhouse gas concentrations is called the "equilibrium temperature.'' Since atmospheric concentrations of greenhouse gases are constantly changing, the temperature measured at any time is the "transient" temperature, which lags behind the committed equilibrium warming. The lag depends in part on the sensitivity of the climate system and is believed to be between 10 and 100 years. This phenomenon makes it difficult to use temperature alone to "prove" that greenhouse warming is occurring. 14. How can we know when greenhouse warming is occurring? The only tools we have for trying to produce credible scientific results are observations combined with theoretical calculation. Detecting additional greenhouse warming will require careful monitoring of temperature and other variables over years or even decades. Further development of numerical models will help characterize the climatic system, including the atmosphere, oceans, and land-based elements like forests and ice fields. However, only careful interpretation of actual measurements can reveal what has occurred and when. 15. How can credible estimates of future global warming be made? Several approaches can be used. Scientific "first principles" can be used to estimate physical bounds on future trends. GCMs can be used to conduct "what if" experiments under differing conditions. Comparisons can be made with paleoclimatic data of previous interglacial periods. None of these methods is absolutely conclusive, but it is generally agreed that GCMs are the best available tools for predicting climatic changes. Substantial improvements in GCM capabilities are needed, however, for GCM forecasts to increase their credibility. 16. What influences future warming? The amount of climatic warming depends on several things: • The amount of sunlight reaching the earth • Emission rates of greenhouse gases • Chemical interactions of greenhouse gases in the atmosphere • Atmospheric lifetimes of greenhouse gases until they decompose or transfer into sinks • Effectiveness of positive or negative feedback mechanisms that enhance or reduce warming • Human actions, which effect radiative forcing in both positive and negative directions 17. What are the major "unknowns" in predictions? Major uncertainties include: • Future emissions of greenhouse gases • Role of the oceans and biosphere in uptake of heat and CO 2 • Amount of CO 2 and carbon in the atmosphere, oceans, biota, and soils • Effectiveness of sinks for CO 2 and other greenhouse gases, especially CH 4 • Interactions between temperature change and cloud formation and the resulting feedbacks • Effects of global warming on biological sources of greenhouse gases • Interactions between changing climate and ice cover and the resulting feedbacks • Amount and regional distribution of precipitation • Other factors, like variation in solar radiation 18. How can the uncertainties best be handled? Data can be arrayed to validate components of the models. Increasing the number of data sets can also help. In addition, the variation in GCM results can be compared to provide a sense of their "robustness." A major "intercomparison" of GCMs is being conducted, and has shown large differences in regional precipitation and reduction of snow and ice fields at high latitudes. 19. Are these changes associated with an equivalent doubling of the preindustrial level of atmospheric CO 2 that can be stated with confidence? Because of the uncertainty in our understanding of various factors, projections reflect different levels of confidence. Highly plausible: Global average surface warming   Global average precipitation increase   Reduction in sea ice   High-latitude surface winter warming Plausible: Global sea level rise   Intensification of summer mid-latitude, mid-continental drying   High-latitude precipitation increase Highly uncertain: Local details of climate change   Regional distribution of precipitation   Regional vegetation changes   Increase in tropical storm intensity or frequency 20. What about storms and other extreme weather events? The factors governing tropical storms are different from those governing mid-latitude storms and need to be considered separately. One of the conditions for formation of typhoons or hurricanes today is a sea surface temperature of 26°C (79°F) or greater. With higher global average surface temperature, the area of sea with this temperature should be larger. Thus the number of hurricanes could increase. However, air pressure, humidity, and a number of other conditions also govern the creation and propagation of tropical cyclones. The critical temperature for their creation may increase as climate changes these other factors. There is no consistent indication whether tropical storms will increase in number or intensity as climate changes. Nor is there any evidence of change over the past several decades. Mid-latitude storms are driven by equator-to-pole temperature contrast. In a warmer world, this contrast will probably weaken since surface temperatures in high latitudes are projected to increase more than at the equator (at least in the northern hemisphere). Higher in the atmosphere, however, the temperature contrast strengthens. Increased atmospheric water vapor could also supply extra energy to storm development. We do not currently know which of these factors would be more important and how mid-latitude storms would change in frequency, intensity, or location. 21. Can projections be improved? Better computers alone will not solve the problems associated with positive and negative feedbacks. Better understanding of atmospheric physics and chemistry and better mathematical descriptions of relevant mechanisms in the models are also needed, as are data to validate models and their subcomponents. Significant improvements may require decades. 22. Is it possible to avoid the projected warming? It is possible only at great expense or by incurring risks not now understood, unless the earth is itself self-correcting. Continued increases in atmospheric concentrations of greenhouse gases would probably result in additional global warming. Avoiding all future warming either would be very costly (if we significantly reduce atmospheric concentrations of greenhouse gases) or potentially very risk (if we use climate engineering). However, a comprehensive action program could slow or reduce the onset of greenhouse warming. A Framework for Responding to Additional Greenhouse Warming 23. What kinds of responses to potential greenhouse warming are possible? Human interventions in natural and economic activities can affect the net rate of change in the radiative forcing of the earth. It is useful to categorize the possible types of intervention into three types: • Actions to eliminate or reduce emissions of greenhouse gases • Actions to "offset" such emissions by removing such gases from the atmosphere, blocking solar radiation, or altering the earth's reflectivity or absorption of energy • Actions to help human and ecologic systems adjust to new climatic conditions and events In this study the panel analyzes the first two types of action together under the label of "mitigation," since they are aimed at avoiding or reducing greenhouse warming. The third type of action is here called "adaptation." 24. How can response options be evaluated? The choice of response options to potential greenhouse warming can be guided by a standard cost-benefit approach, augmented to handle some important aspects of the issues involved. The anticipated impacts (both adverse and beneficial) can be arrayed to produce a "damage function" showing the anticipated costs (or benefits) associated with projected climatic changes. The mitigation and adaptation options can be arrayed similarly according to their respective costs and effectiveness to produce an "abatement cost function." Optimal policies involve balancing incremental costs and benefits, which is called cost-benefit balancing. A necessary condition for an optimal policy is that the level of policy chosen should be cost-effective (any step undertaken minimizes costs). Employing such guidelines requires estimating both the anticipated damages and the cost-effectiveness of alternative response options, and choosing a discount rate to use for assessing the current value of future expenditures or returns. In practice, a full cost-benefit approach can only be approximated. It is impossible to determine in detail the impacts of climatic changes that will not occur for 40 or 100 years. Thus the damage function can be only roughly approximated. Estimation of the abatement cost function is considerably easier. Responses to greenhouse warming should be regarded as investments in the future. Cost-effectiveness and cost-benefit balancing should guide the selection of options. In general, a mixed strategy employing some investment in many different alternatives will be most effective. Impacts of Additional Greenhouse Warming 25. Can impacts of expected climatic changes be projected? It currently is not possible to predict regional temperature, precipitation, and other effects of climate change with much confidence. And without quantitative projections of regional and local climatic changes, it is not possible to produce quantitative projections of the consequences of greenhouse warming. Instead, the degree of "sensitivity" of affected human and natural systems to the projected changes can be estimated. The sensitivity of a particular system to the climate changes expected to accompany different amounts of additional greenhouse warming can be used to estimate the impacts of those changes. A crucial aspect of the sensitivity of a system is the speed at which it can react. For example, investment decisions in many industries typically have a "life-cycle" of 10 years or less. Climatic changes associated with additional greenhouse warming are expected to emerge slowly enough that these industries may be expected to adjust as climate changes. Some industries, such as electric power production, have longer investment cycles, and might have more difficulty responding as quickly. Natural ecological systems would not be expected to anticipate climate change and probably would not be able to adapt as quickly as climatic conditions change. The impacts of climate change are thus hard to assess because the response of human and natural systems to climate change must be included. 26. How can the impacts on affected systems be classified? Likely impacts of climate change can be divided into four categories: • Low sensitivity. The projected changes would likely have little effect on the system. An example is most industrial production not requiring large quantities of water. Temperature changes of the magnitude projected would not matter much for most industrial processes. These impacts do not give rise to much concern. • High sensitivity, but adaptation possible at some cost. The system would likely adapt or otherwise cope with the projected changes without completely restructuring the system. An example is American agriculture. Although some crops would likely move into new locations, agricultural scientists and plant breeders would almost certainly develop new crops suitable for changed growing conditions. There would be costs, but food supply would not be interrupted. As a class, these impacts give rise to concern because the affected systems may have difficulty adapting. • High sensitivity, and adaptation problematic. The system would be seriously affected, and adaptation would probably not be easy or effective. Natural communities of plants and animals would probably lose their current structure, and reformulate with different mixes of species. Some individual species, especially animals, would move to new locations. The natural landscape as we know it today would almost certainly be altered by a climate change at or above the midpoint of the range used in this study. These impacts are of considerable concern because the affected systems may not be able to adapt without assistance. • Uncertain sensitivity, but cataclysmic consequences. The sensitivity of the system cannot be assessed with certainty, but the consequences would be extremely severe. An example is the possible shifting, slowing, or even stopping of major ocean currents like the Gulf Stream or the Japanese Current. These ocean currents strongly affect weather patterns, and changes in them could drastically alter weather in Europe or the West Coast of the United States. We have no credible way, however, of assessing the conditions that could lead to such shifts. 27. What are the likely impacts of climate change? Human societies exhibit a wide range of adaptive mechanisms in the face of changing climatic events and conditions. Projected climatic changes, especially at the upper end of the range, may overwhelm human adaptive mechanisms in areas of marginal productivity and in countries where traditional coping mechanisms have been disrupted. In general, natural ecosystems would be much more sorely stressed, probably beyond their capacities for adjustment. For example, even temperature changes at the lower end of the range would result in shifts of local climates at rates faster than the movement of long-lived trees with large seeds. A comprehensive catalog of beneficial and harmful impacts is not available. Nor is an estimation of the magnitude of the likely impacts of projected climatic changes. Table A.2 summarizes impacts to human and natural systems in the United States according to the sensitivity categories. 28. Can costs be calculated for the various impacts of projected climate changes? Not directly. The climatic changes likely to occur in the future cannot be directly measured. The costs and benefits associated with some aspects of certain changes can be estimated, however. These can be used to produce very rough estimates of the costs of climatic impacts. However, these must be recognized as very imprecise indicators. In general, the costs in the United States associated with the first category of sensitivity are low in relation to overall economic activity. The TABLE A.2 The Sensitivity and Adaptability of Human Activities and Nature   Low Sensitivity Sensitive, but Adaptation at Some Cost Sensitive, Adaptation Problematic Industry and energy X     Health X     Farming   X   Managed forests and grasslands   X   Water resources   X   Tourism and recreation   X   Settlements and coastal structures   X   Human migration   X   Political tranquility   X   Natural landscapes     X Marine ecosystems     X NOTE: Sensitivity can be defined as the degree of change in the subject for each "unit" of change in climate. The impact (sensitivity times climate change) will thus be positive or negative depending on the direction of climate change. Many things can change sensitivity, including intentional adaptations and natural and social surprises, and so classifications might shift over time. For the gradual changes assumed in this study, the Adaptation Panel believes these classifications are justified for the United States and similar nations. costs associated with the second category are higher but still should not result in major disruption of the economy. Appropriate adjustments could probably be accomplished without replacing current systems. Costs associated with the third category are much larger, and the adjustments could involve disruption. Some type of anticipation for meeting them may be justified. The category of extremely adverse impacts would be associated with high potential costs and would disrupt most aspects of the system in question. These outcomes, however, are extremely difficult to assess. Table A.3 summarizes some "benchmark" costs illustrative of impacts similar to those that might be associated with climate change. TABLE A.3 Illustrative Costs of Impacts and Adaptations Class Description Dollars (1990) Per GNP 1985 total U.S. 4015 billion       1985 average U.S. 17 thousand capita     1985 global average 3 thousand capita     2100 global average projected 7–36 thousand capita     2100 average U.S. 150 thousand capita Climate hazards 1980 U.S. heatwave 20 billion       1988 U.S. drought 39 billion       1983 Utah heavy snow, floods, and landslide 300 million       1985 Ohio and Pennsylvania tornados 500 million       1985 West Virginia floods 700 million       1989 Hurricane Hugo 5 billion   Recent annual average U.S. losses Hurricanes 800–1800 million       Floods 3 billion       Tornados and thunderstorms 300–2000 million       Winter storms and snows 3 billion       Drought 800–1000 million       1988 budget U.S. Weather Service 323 million   Farming Create successful wheat variety 1 million       Kansas Agricultural Research Experiment Station 33 million       U.S. and state agricultural research 2.3 billion       1974–1977 drought, federal expenditures 7 billion       1986 U.S. farm GNP 76 billion   Forestry Prepare and plant 130 acre     Treat with herbicide 41 acre     Fertilize 36 acre     Thin 55 acre     Protect from fire for 1 year 1.36 acre     1983 fire protection on state and private forests 245 million       1986 U.S. forestry and fishery GNP 17 billion   Natural landscape Preserve a large mammal in zoo 1500–3000 year     Preserve a large bird in zoo 100–1000 year     Preserve a plant in botanical garden 500 year     Recover peregrine falcon 3 million 1970–1990     Recover all endangered birds of prey 5 million year     Preserve an acre in a large reserve 50–5000 acre     1985 expenditure on wildlife-related recreation, including hunting and fishing 55.4 billion       Budget National Park Service 1 billion year Water Delaware River above Philadelphia 51 acrefoot     Sacramento delta 137 acrefoot     High flow skimming, Hudson River 555 acrefoot     Desalting 2200–5400 acrefoot     Present national average 533 acrefoot     Present irrigation water in California 15 acrefoot     Annual water bill for domestic use 60 capita     Annual cost of water for irrigation 45 acre     Value of an acre of tomatoes 4000 acre Industry Raise offshore drilling platform 1 meter 16 million       1986 U.S. manufacturing GNP 824 billion   Settlement Raise a Dutch dike 1 meter 3 thousand m length     Build seawall, Charleston, South Carolina 6 thousand m length     Nourish beach for 1 year, Florida 35–200 m length     Nourish beach for 1 year, Charleston, South Carolina 300 m length     Hurricane evacuation 35–50 person     Strengthen coastal property for 100-mph wind 30–90 billion U.S. coast     Floodproof by raising house 3 feet 10–40 thousand house     Move house from floodplain 20–70 thousand house     Levees, berms, and pumps 17 thousand 1/4 acre     1986 U.S. state and local services 331 billion   Migration Resettle a refugee in 1989, federal contribution 7 thousand person National Income in 1985 was $3222 billion. Assumes 1.9 percent growth per year, which is the annual average growth rate for U.S. GNP from 1800 to 1985. In an extremely adverse year, climate hazards may cost $40 billion or 1 percent of the $4000 billion U.S. GNP, which is about $160 per capita. During the drought of the 1970s, annual federal expenditures on drought relief averaged about 3 to 4 percent of GNP. In 1983, expenditures on about a half billion acres of state and private forest land were $0.50 per acre. Increasing expenditures on all forest land to $1.36 per acre would cost about $500 million or 3 percent of forest and fishery GNP. The cost of recovering all endangered birds of prey is 1 ten-thousandth and the cost of the National Park Service is 2 percent of the annual expenditures on wildlife-associated recreation. Doubling the cost of domestic water would cost a person a third of a percent of per capita GNP in the United States. Raising the cost of irrigation water from the present $15 per acre-foot to the $137 per acre-foot for the prospective water from the Sacramento delta would cost 2 percent of the value of the tomatoes on an acre. The cost of raising an offshore drilling platform 1 m is less than 1 percent of its total cost. Strengthening coastal properties for 100-mph wind would cost between a tenth and a third of current state and local service budgets for the entire United States. The cost of moving a house would be 1 to 4 times the present U.S. per capita GNP and a tenth to a half of that of 2100. 29. Are there possible consequences of greenhouse warming with highly adverse impacts? Two have been identified. • Deep ocean currents could be interrupted. Increased freshwater runoff in the Arctic might alter the salinity of northern oceans, thereby reducing or stopping the vertical flow of water into the deep ocean along Greenland and Iceland. This might interrupt a major deep ocean current running from the North Atlantic around the Cape of Good Hope and through the Indian Ocean to the Pacific. This could affect temperature and precipitation, with repercussions that might be catastrophic. Very little is currently known about the potential of this phenomenon. • The West Antarctic Ice Sheet could surge. The Antarctic and Greenland ice sheets combined make up the world's largest reservoir of fresh water. The West Antarctic Ice Sheet alone contains enough water to raise global average sea level about 7 meters (23 feet). Warming could affect the speed at which the ice sheet flows to the sea and breaks off into icebergs. A large subsequent influx of fresh water could alter the salinity of the world's oceans, affecting currents and plant and animal populations alike. The ramifications are extreme, and it might lead to disruption of deep ocean currents and all that that entails. The timing of such a possibility is controversial. Current thinking is that it would take centuries, but there is little empirical evidence on which to base estimates. 30. What are appropriate responses to very uncertain, but highly adverse impacts? Both individuals and societies must decide how to handle events that are very unlikely but which have severe consequences. Homeowners purchase insurance against the very unlikely event of fire. In essence, insurance is a cost today (the insurance premium) to avoid undesirable consequences later (losing one's possessions to fire). If we want to avoid unsure adverse impacts of possible climate change, we might want to spend money now that would reduce the likelihood that those things can happen. In principle, there are two different kinds of "climate insurance." We could do things that reduce the likelihood that the climate will change (mitigation options), or we could do things that reduce the sensitivity of affected human and natural systems to future climate change (adaptation options). 31. Does looking at potential impacts tell us where to set priorities for responding to greenhouse warming? Partly. The examination of potential impacts can help provide rough estimates of the cost at which adaptation could be accomplished should climate change. This is an approximation of the "damage function" and can be used to assess how much to spend on emission reductions or offsets. However, all estimates are approximations with very little precision. The amount to allocate to prevent additional greenhouse warming depends significantly on the preferred degree of risk aversion. Preventing or Reducing Additional Greenhouse Warming 32. What are the sources of greenhouse gas emissions? All of the major greenhouse gases except CFCs are produced by both natural processes and human activity. Table A.4 summarizes the principal sources of greenhouse gases associated with human activity. 33. What interventions could reduce greenhouse warming? It is useful to examine two different aspects of reducing emissions or offsetting emissions: • ''Direct" reduction or offsetting of emissions through altering equipment, products, physical processes, or behaviors • "Indirect" reduction or offsetting of emissions through altering the behavior of people in their economic or private lives and thus affecting the overall level of activity leading to emissions It is much easier to estimate potential effectiveness and costs of direct reductions than of indirect incentives on human behavior. This is mostly because of the many factors that affect behavior in addition to the incentives in any particular program. 34. How can specific mitigation options be compared? Mitigation options can be compared quantitatively in terms of their cost-effectiveness and qualitatively in terms of the obstacles to their implementation and in terms of other benefits and costs. The standard quantitative unit used to compare mitigation options is the cost per metric ton of carbon emissions reduced or per metric ton of carbon removed from the atmosphere. The amount of carbon can be converted to the amount of CO 2 in the atmosphere by multiplying by 3.67, which is the ratio of the molecular weights of carbon and CO 2 . Other greenhouse gases can be "translated" to CO 2 equivalency by using two calculations. First, the amount of radiative forcing caused by a specific concentration of the gas is estimated in terms of the change in energy reaching the surface (in watts per square meter). This estimate accounts for atmospheric chemistry, atmospheric lifetime of the gas, and other relevant factors affecting the total contribution of that gas to greenhouse warming. Second, the amount of TABLE A.4 Estimated 1985 Global Greenhouse Gas Emissions from Human Activities       Greenhouse Gas Emissions (Mt/yr) CO2-equivalent Emissions (Mt/yr) CO2 Emissions           Commercial energy 18,800 18,800 (57)     Tropical deforestation 2,600 2,600 (8)     Other 400 400 (1)     TOTAL 21,800 21,800 (66) CH4 Emissions           Fuel production 60 1,300 (4)     Enteric fermentation 70 1,500 (5)     Rice cultivation 110 2,300 (7)     Landfills 30 600 (2)     Tropical deforestation 20 400 (1)     Other 30 600 (2)     TOTAL 320 6,700 (20) CFC-11 and CFC-12 Emissions           TOTAL 0.6 3,200 (10) N2O Emissions           Coal combustion 1 290 (>1>     Fertilizer use 1.5 440 (1)     Gain of cultivated land 0.5 150 (>1)     Tropical deforestation 0.5 150 (>1)     Fuel wood and industrial biomass 0.2 60 (>1)     Agricultural wastes 0.4 120 (>1)     TOTAL 4 1,180 (4)   TOTAL   32,880 (100) NOTE: Mt/yr = million (106) metric tons (t) per year. All entries are rounded because the exact values are controversial. CO2-equivalent emissions are calculated from the Greenhouse Gas Emissions column by using the following multipliers:     CO2 1         CH4 21         CFC-11 and -12 5,400         N2 290     Numbers in parentheses are percentages of total. Total does not sum due to rounding errors. SOURCE: Adapted from U.S. Department of Energy. 1990. . Springfield, Va.: National Technical Information Service. CO 2 that would produce the same amount of forcing at the surface is calculated. This is the CO 2 equivalent for that specific concentration of the other greenhouse gas. The respective costs per ton for different options can then be compared directly. It is important to recognize, however, that these calculations allow comparison only of initial contributions. They do not account for changes in energy-trapping effectiveness over the various lifetimes of these gases in the atmosphere. 35. What mitigation options are most cost-effective? The panel ranks options for reducing greenhouse gas emissions or removing greenhouse gases from the atmosphere according to their cost-effectiveness. Some of these options have net savings or very low net implementation costs compared to other investments. The options range from net savings to more than $100 per metric ton of CO 2 -equivalent emissions avoided or removed from the atmosphere. The most cost-effective mitigation options are presented in Table A.5. 36. What are examples of options with large potential to reduce or offset emissions? The so-called geoengineering options have the potential of substantially affecting atmospheric concentrations of greenhouse gases. They have the ability to screen incoming sunlight, stimulate uptake of CO 2 by plants and animals in the oceans, or remove CO 2 from the atmosphere. Although they appear feasible, they require additional investigation because of their potential environmental impacts. 37. How much would it cost to significantly reduce current U.S. greenhouse gas emissions? It depends on the level of emission reduction desired and how it is done. The most cost-effective options are those that enhance efficient use of energy: efficiency improvements in lighting and appliances, white roofs and paving to enhance reflectivity, and improvement in building and construction practices. Figure A.4 compares mitigation options, and Table A.5 gives the panel's estimates of net cost and emission reductions for several options. It must be emphasized that the table presents the panel's estimates of the maximum technical potential for each option. The calculation of cost-effectiveness of lighting efficiency, for example, does not consider whether the supply of light bulbs could meet the demand with current production capacities. Nor does it consider the trade-off between expenditures on light bulbs and on health care, education, or basic shelter for low-income families. In addition, there is a danger of some "double counting." For example, in the area of energy supply both nuclear and natural gas energy options assume replacement TABLE A.5 Comparison of Selected Mitigation Options in the United States Mitigation Option Net Implementation Cost Potential Emission Reduction (t CO2 equivalent per year) Building energy efficiency Net benefit 900 million Vehicle efficiency (no fleet change) Net benefit 300 million Industrial energy management Net benefit to low cost 500 million Transportation system management Net benefit to low cost 50 million Power plant heat rate improvements Net benefit to low cost 50 million Landfill gas collection Low cost 200 million Halocarbon-CFC usage reduction Low cost 1400 million Agriculture Low cost 200 million Reforestation Low to moderate cost 200 million Electricity supply Low to moderate cost 1000 million NOTE: Here and throughout this report, tons are metric. Net benefit = cost less than or equal to zero Low cost = cost between $1 and $9 per ton of CO2 equivalent Moderate cost = cost between $10 and $99 per ton of CO2 equivalent High cost = cost of $100 or more per ton of CO2 equivalent This "maximum feasible" potential emission reduction assumes 100 percent implementation of each option in reasonable applications and is an optimistic "upper bound" on emission reductions. This depends on the actual implementation level and is controversial. This represents a middle value of possible rates. Some portions do fall in low cost, but it is not possible to determine the amount of reductions obtainable at that cost. The potential emission reduction for electricity supply options is actually 1700 Mt CO2 equivalent per year, but 1000 Mt is shown here to remove the double-counting effect. of the same coal-fired power plants. Table A.5, however, presents only options that avoid double counting. Finally, although there is evidence that efficiency programs can pay, there is no field evidence showing success with programs on the massive scale suggested here. Thus there may be very good reasons why "negative cost options" on the figure are not implemented today. The United States could reduce its greenhouse gas emissions by between 10 and 40 percent of the 1990 levels at low cost, or perhaps some net savings, if proper policies are implemented. FIGURE A.4 Comparison of mitigation options. Total potential reduction of CO 2 equivalent emissions is compared to the cost in dollars per ton of CO 2 reduction. Options are ranked from left to right in CO 2 emissions according to cost. Some options show the possibility of reductions of CO 2 emissions at a net savings. Adapting to Additional Greenhouse Warming 38. Will human and natural systems adapt without assistance? Farmers adjust their crops and cultivation practices in response to weather patterns over time. Natural ecosystems also adapt to changing conditions. The real issue is the rate at which human and natural systems will be able to adjust. 39. At what rates can human and natural systems adapt? Many human systems have decision and investment cycles that are shorter than the time in which impacts of climate change would become manifest. These systems in the United States should be able to adjust to climate change without governmental intervention, as long as it is gradual and information about the rates of change is widely available. This applies to agriculture, commercial forestry, and most of industry. Industrial sectors with extremely long investment cycles (e.g., transport systems, urban infrastructure, and major structures and facilities) or requiring high volumes of water may require special attention. Coastal urban settlements would be able to react quickly (within 3 to 5 years) if sea level rises. Response would be much more difficult, however, where financial and other resources are limited, such as in many developing countries. Some natural systems adjust at rates an order of magnitude or more slower than those anticipated for global-scale temperature changes. For example, the observed and theoretical migration of large trees with heavy seeds is an order of magnitude slower than the anticipated change in climate zones. Furthermore, natural ecosystems cannot anticipate climate change but must wait until after conditions have changed to respond. 40. What is the value of the vulnerable natural ecosystems? Natural ecosystems contribute commercial products, but their value is generally considered to exceed this contribution to the economy. For example, genetic resources are generally undervalued because people cannot capture the benefits of investments they might make in preserving biodiversity. Many species are unlikely to ever have commercial value, and it is virtually impossible to predict which ones will become marketable. In addition, some people value natural systems regardless of their economic value. Loss of species, in their view, is undesirable whether or not those species have any commercial value. They generally hold that preservation of the potential for evolutionary change is a desirable goal in and of itself. Humanity, they claim, should not do things that alter the course of natural evolution. This view is sometimes also applied to humanity's cultural heritage—to buildings, music, art, and other cultural artifacts. 41. How much would it cost to adapt to the anticipated climatic changes? The panel's analysis suggests that some human and natural systems are not very sensitive to the anticipated climatic changes. These include most sectors of industry. Other systems are sensitive to climatic changes but can be adapted at a cost whose present value is small in comparison to the overall level of economic activity. These include agriculture, commercial forestry, urban coastal infrastructure, and tourism. Some systems are sensitive, and their adaptation is questionable. The unmanaged systems of plants and animals that occupy much of our lands and oceans adapt at a pace slower than the anticipated rate of climatic change. Their future under climate change would be problematic. Poor nations may also adapt painfully. Finally, some possible climatic changes like shifts in ocean currents have consequences that could be extremely severe, and thus the costs of adaptation might be very large. However, it is not currently possible to assess the likelihood of such cataclysmic changes. No attempt has been made to comprehensively assess the costs of anticipated climatic changes on a global basis. 42. How much should be spent in response to greenhouse warming? The answer depends on the estimated costs of prevention and the estimated damages from greenhouse warming. In addition, the likelihood and severity of extreme events, the discount rate, and the degree of risk aversion will modify this first-order approximation. The appropriate level of expenditure depends on the value attached to the adverse outcomes compared to other allocations of available funds, human resources, and so on. In essence, the answer depends on the degree of risk aversion attached to adverse outcomes of climate change. The fact that less is known about the more adverse outcomes makes this a classic example of dealing with high-consequence, low-probability events. Programs that truly increase our knowledge and monitor relevant changes are especially needed. Implementing Response Programs 43. What policy instruments could be used to implement response options? A wide array of policy instruments of two different types are available: regulation and incentives. Regulatory instruments mandate action, and include controls on consumption (bans, quotas, required product attributes), production (quotas on products or substances), factors in design or production (efficiency, durability, processes), and provision of services (mass transit, land use). Incentive instruments are designed to influence decisions by individuals and organizations and include taxes and subsidies on production factors (carbon tax, fuel tax), on products and other outputs (emission taxes, product taxes), financial inducements (tax credits, subsidies), and transferable emission rights (tradable emission reductions, tradable credits). The choice of policy instrument depends on the objective to be served. 44. At what level of society should actions be taken? Interventions at all levels of human aggregation could effectively reduce greenhouse warming. For example, individuals could reduce energy consumption, recycle goods, and reduce consumption of deleterious materials. Local governments could control emissions from buildings, transport fleets, waste processing plants, and landfill dumps. State governments could restructure electric utility pricing structures and stimulate a variety of efficiency incentives. National governments could pursue action in most of the policy areas of relevance. International organizations could coordinate programs in various parts of the world, manage transfers of resources and technologies, and facilitate exchange of monitoring and other relevant data. 45. Is international action necessary? The greenhouse phenomenon is global. Unilateral actions can contribute significantly, but national efforts alone would not be sufficient to eliminate the problem. The United States is the largest contributor of CO 2 emissions (with estimates ranging from 17 to 21 percent of the global total). But even if this country were to totally eliminate or offset its emissions, the effect on overall greenhouse warming might be lost if no other countries acted in concert with that aim. 46. What about differences between rich and poor countries? Poor and developing countries are likely to be the most vulnerable to climate change. In addition, many developing countries today are sorely pressed in a variety of other ways. They may conclude that other issues have more immediate consequences for their citizens. Incentives in all parts of the world for intervention in the area of greenhouse warming may thus draw heavily on the industrialized nations. They may be called upon to help poor countries stimulate economic development and thus become better able to cope with climate change. They may also be asked to provide expertise and technologies to help poor countries adapt to the conditions they face. Actions to be Taken 47. Do scientific assessments of greenhouse warming tell us what to do? Current scientific understanding of greenhouse warming is both incomplete and uncertain. Response depends in part on the degree of risk aversion attached to poorly understood, low-probability events with extremely adverse outcomes. Lack of scientific understanding should not be used as a justification for avoiding reasoned decisions about responses to possible additional greenhouse warming. 48. Is it better to prevent greenhouse warming now or wait and adapt to the consequences ? This complicated question has several parts. • First, will it be possible to live with the consequences if nothing is done now? The panel's analysis suggests that advanced, industrialized countries will be able to adapt to most of the anticipated consequences of additional greenhouse warming without great economic hardship. In some regions, climate and related conditions may be noticeably worse, but in other regions better. Countries that currently face difficulty coping with extreme climatic events, or whose traditional coping mechanisms are breaking down, may be sorely pressed by the climatic changes accompanying an equivalent doubling of atmospheric CO 2 concentrations. It is important to recognize that there may be dramatic improvement or disastrous deterioration in specific locales. In addition, this analysis applies to the next 30 to 50 years. The situation may be different beyond that time horizon. Natural communities of plants and animals, however, face much greater difficulties. Greenhouse warming would likely stress such ecosystems sufficiently to break them apart, resulting in a restructuring of the community in any given locale. New species would be likely to gain dominance, with a different overall mix of species. Some individual species would migrate to new, more livable locations. Greenhouse warming would most likely change the face of the natural landscape. Similar changes would occur in lakes and oceans. In addition, there are possible extremely adverse consequences, such as changing ocean currents, that are poorly understood today. The response to such possibilities depends on the degree of risk aversion concerning those outcomes. The greater the degree of risk aversion, the greater the impetus for preventive action. • Second, does it matter when interventions are made? Yes, for three different kinds of reasons. Because greenhouse gases have relatively long lifetimes in the atmosphere, and because of lags in the response of the system, their effect builds up over time. These time-dependent phenomena lead to the long-term "equilibrium" warming being greater than the "realized" warming at any given point in time. These dynamic aspects of the climate system show the importance of acting now to change traditional patterns of behavior that we have recently recognized to be detrimental, such as heavy reliance on fossil fuels. In addition, the implications of intervention programs for the overall economy vary with time. Gradual imposition of restraints is much less disruptive to the overall economy than their sudden application. Finally, the length of investment cycles can be crucial in determining the costs of intervention. In addition, some investments can be thought of as insurance, or payments now to avoid undesirable outcomes in the future. The choice is made more complicated by the fact that the outcomes are highly uncertain. • Third, what discount rate should be used? The selection of a discount rate is very controversial. Macroeconomic calculations for the United States show a return on capital investment of 12 percent. The choice of discount rate reflects time preference. The panel has used discount rates of 3, 6, and 10 percent in its analysis. Finally, consumers often behave as if they have used a discount rate closer to 30 percent. The panel has also included this rate for comparison when options involve individual action. 49. Are there special attributes of programs appropriate for response to greenhouse warming? Yes. The uncertainties present in all aspects of climate change and our understanding of response to potential greenhouse warming place a high premium on information. Small-scale interventions that are both reversible and yield information about key aspects of the relevant phenomena are especially attractive for both mitigation and adaptation options. Monitoring of emission rates, climatic changes, and human and ecologic responses should yield considerable payoffs. Perhaps the most important attribute of preferred policies is that they be able to accommodate surprises. They should be constructed so that they are flexible and can change if the nature or speed of stress is different than anticipated. 50. What should be done now? The panel developed a set of recommended options in five areas: reducing or offsetting emissions, enhancing adaptation to greenhouse warming, improving knowledge for future decisions, evaluating geoengineering options, and exercising international leadership. The panel recommends moving decisively to undertake all of the actions described under questions 51 through 55 below. 51. What can be done to reduce or offset emissions of greenhouse gases? Three areas dominate the panel's analysis of reducing or offsetting current emissions: eliminating CFC emissions and developing substitutes that minimize or eliminate greenhouse gas emissions, changing energy policy, and utilizing forest offsets. Eliminating CFC emissions has the biggest single contribution. Recommendations concerning energy policy are to examine how to make the price of energy reflect all health, environmental, and other social costs with a goal of gradual introduction of such a system; to make conservation and efficiency the chief element in energy policy; and to consider the full range of supply, conversion, end use, and external effects in planning future energy supply. Global deforestation should be reduced, and a moderate domestic reforestation program should be explored. 52. What can be done now to help people and natural systems of plants and animals adapt to future greenhouse warming? Most of the actions that can be taken today improve the capability of the affected systems to deal with current climatic variability. Options include maintaining agricultural basic, applied, and experimental research; making water supplies more robust by coping with present variability; taking into consideration possible climate change in the margins of safety for long-lived structures; and reducing present rates of loss in biodiversity. 53. What can be done to improve knowledge for future decisions? Action is needed in several areas. Collection and dissemination of data that provide an uninterrupted record of the evolving climate and of data that are needed for the improvement and testing of climate models should be expanded. Weather forecasts should be improved, especially of extremes, for weeks and seasons to ease adaptation to climate change. The mechanisms that play a significant role in the responses of the climate to changing concentrations of greenhouse gases need further identification, and quantification at scales appropriate for climate models. Field research should be conducted on entire systems of species over many years to learn how CO 2 enrichment and other facets of greenhouse warming alter the mix of species and changes in total production or quality of biomass. Research on social and economic aspects of global change and greenhouse warming should be strengthened. 54. Do geoengineering options really have potential? Preliminary assessments of these options suggest that they have large potential to mitigate greenhouse warming and are relatively cost-effective in comparison to other mitigation options. However, their feasibility and especially the side-effects associated with them need to be carefully examined. Because the geoengineering options have the potential to affect greenhouse warming on a substantial scale, because there is convincing evidence that some of these cause or alter a variety of chemical reactions in the atmosphere, and because the climate system is poorly understood, such options must be considered extremely carefully. If greenhouse warming occurs, and the climate system turns out to be highly sensitive to radiative forcing, they may be needed. 55. What should the United States do at the international level? The United States should resume full participation in international programs to slow population growth and contribute its share to their financial and other support. In addition, the United States should participate fully in international agreements and programs to address greenhouse warming, including representation by officials at an appropriate level. Global warming continues to gain importance on the international agenda and calls for action are heightening. Yet, there is still controversy over what must be done and what is needed to proceed. Policy Implications of Greenhouse Warming describes the information necessary to make decisions about global warming resulting from atmospheric releases of radiatively active trace gases. The conclusions and recommendations include some unexpected results. The distinguished authoring committee provides specific advice for U.S. policy and addresses the need for an international response to potential greenhouse warming. It offers a realistic view of gaps in the scientific understanding of greenhouse warming and how much effort and expense might be required to produce definitive answers. The book presents methods for assessing options to reduce emissions of greenhouse gases into the atmosphere, offset emissions, and assist humans and unmanaged systems of plants and animals to adjust to the consequences of global warming. READ FREE ONLINE Welcome to OpenBook! 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By Daniel Fienberg Daniel Fienberg Chief Television Critic Share on Facebook Share to Flipboard Send an Email Show additional share options Share on LinkedIn Share on Pinterest Share on Reddit Share on Tumblr Share on Whats App Print the Article Post a Comment The White House Effect , Bonni Cohen, Pedro Kos and Jon Shenk’s new documentary, doesn’t make viewers wait long for its most shocking moment. The White House Effect “It can be done and we must do it and these issues know no ideology,” Bush says.  Related Stories Leni riefenstahl documentary sells wide after venice, telluride premiere, the awards pundits: feinberg and keegan on telluride's rocky mountain highs and lows. In this moment, if you didn’t live through that period, you might be flummoxed enough to believe that, as he claimed himself, Bush would be the “environmental candidate” for the presidency. Spoiler alert: He was not. Spoiler alert: Those issues did not, in fact, turn out to know no ideology. Spoiler alert: The White House Effect, presented in that Bush quip as a positive, turned out to be quite negative. And in many ways, the Bush presidency represented a pivot point from which we’ve never returned. How did we get from Bush’s 1988 pronouncement — which came at a moment when man-on-the-street interviews, many of which are seen here, strongly indicated that our national consensus was pro-“saving the planet” — to the 2024 election season, during which climate change has barely been a point of conversation? The White House Effect traces at least the beginning of that journey. Over 96 minutes, you’ll be horrified and saddened. You’ll probably also want more information on a lot of the broadly sketched details, because this project is an overview and not an in-depth thesis. It’s limited, but it’s convincing. The movie is composed entirely of archival footage, a nonfiction subgenre that I tend to associate with Brett Morgen’s 30 for 30 entry June 17, 1994 (even if it doesn’t deserve a “created by” credit). That means no new talking head interviews from those involved, no outside expert commentary, no distance. The meat of The White House Effect focuses on the clash between William Reilly, the actual environmentalist Bush tapped to run the EPA, and John Sununu, Bush’s chief of staff and an ardent opponent of everything Reilly attempted to stand for. How did two people in unelected positions manage to have such an outsized effect on the future of the planet? Well, that’s the documentary. Most of the crucial conversations and debates that turned the tide happened behind closed doors. There isn’t a second of footage that exists of Reilly and Sununu in a room swearing at each other while Bush nods submissively. What we get instead are ripples: Bush’s shifting rhetoric, news coverage of the environmental conferences the United States waffled on participating in, snippets from previously unseen memos. The directors have embarked on a hugely difficult task and they’ve executed it well, understanding those obstacles. The White House Effect gives us heroes, like environmental scientist Stephen Schneider and a crusading young Al Gore, and villains, like Sununu making one of history’s largest power grabs. Reilly exists somewhere in the middle, as a man who believed he could change things from within and, instead, seemingly failed horribly. That we have to read his body language at press conferences and in snippets of sanitized interviews is a challenge for the documentarians and for history. I was also left with questions about a few details that the film evades. This was the same period during which the hole in the ozone was another major priority in the environmental debate. How and why were policy solutions able to produce tangible results on one front of this battle — nobody talks much about acid rain anymore — while the objectives outlined in the documentary mobilized the likes of Rush Limbaugh and turned environmentalism into another piece of the culture wars? I guess I understand why a 90-minute movie would avoid the complication, but that doesn’t stop me from wishing for the 10-part series that embraced it. The White House Effect is illuminating as a “How did we get here?” starting point, without eliminating the desire and need to see more light cast on a subject that feels like it’s too often being upstaged today. Full credits Thr newsletters. Sign up for THR news straight to your inbox every day More from The Hollywood Reporter Where to stream oscar-winning japanimation film ‘the boy and the heron’ online, ben stiller says making movies in canada is an “amazing experience” as toronto fest kicks off, protestors disrupt tiff opening night screening, vicky krieps sings ‘went up the hill’ closing song live at tiff premiere, ‘went up the hill’ review: vicky krieps and dacre montgomery are dazzling in a poetic ghost story, ‘nickel boys’ trailer stars daveed diggs, aunjanue ellis-taylor in adaptation of pulitzer-winning novel. Numbers, Facts and Trends Shaping Your World Read our research on: Full Topic List Regions & Countries Publications Our Methods Short Reads Tools & Resources Read Our Research On: Key things to know about U.S. election polling in 2024 Confidence in U.S. public opinion polling was shaken by errors in 2016 and 2020. In both years’ general elections, many polls underestimated the strength of Republican candidates, including Donald Trump. These errors laid bare some real limitations of polling. In the midterms that followed those elections, polling performed better . But many Americans remain skeptical that it can paint an accurate portrait of the public’s political preferences. Restoring people’s confidence in polling is an important goal, because robust and independent public polling has a critical role to play in a democratic society. It gathers and publishes information about the well-being of the public and about citizens’ views on major issues. And it provides an important counterweight to people in power, or those seeking power, when they make claims about “what the people want.” The challenges facing polling are undeniable. In addition to the longstanding issues of rising nonresponse and cost, summer 2024 brought extraordinary events that transformed the presidential race . The good news is that people with deep knowledge of polling are working hard to fix the problems exposed in 2016 and 2020, experimenting with more data sources and interview approaches than ever before. Still, polls are more useful to the public if people have realistic expectations about what surveys can do well – and what they cannot. With that in mind, here are some key points to know about polling heading into this year’s presidential election. Probability sampling (or “random sampling”). This refers to a polling method in which survey participants are recruited using random sampling from a database or list that includes nearly everyone in the population. The pollster selects the sample. The survey is not open for anyone who wants to sign up. Online opt-in polling (or “nonprobability sampling”). These polls are recruited using a variety of methods that are sometimes referred to as “convenience sampling.” Respondents come from a variety of online sources such as ads on social media or search engines, websites offering rewards in exchange for survey participation, or self-enrollment. Unlike surveys with probability samples, people can volunteer to participate in opt-in surveys. Nonresponse and nonresponse bias. Nonresponse is when someone sampled for a survey does not participate. Nonresponse bias occurs when the pattern of nonresponse leads to error in a poll estimate. For example, college graduates are more likely than those without a degree to participate in surveys, leading to the potential that the share of college graduates in the resulting sample will be too high. Mode of interview. This refers to the format in which respondents are presented with and respond to survey questions. The most common modes are online, live telephone, text message and paper. Some polls use more than one mode. Weighting. This is a statistical procedure pollsters perform to make their survey align with the broader population on key characteristics like age, race, etc. For example, if a survey has too many college graduates compared with their share in the population, people without a college degree are “weighted up” to match the proper share. How are election polls being conducted? Pollsters are making changes in response to the problems in previous elections. As a result, polling is different today than in 2016. Most U.S. polling organizations that conducted and publicly released national surveys in both 2016 and 2022 (61%) used methods in 2022 that differed from what they used in 2016 . And change has continued since 2022. One change is that the number of active polling organizations has grown significantly, indicating that there are fewer barriers to entry into the polling field. The number of organizations that conduct national election polls more than doubled between 2000 and 2022. This growth has been driven largely by pollsters using inexpensive opt-in sampling methods. But previous Pew Research Center analyses have demonstrated how surveys that use nonprobability sampling may have errors twice as large , on average, as those that use probability sampling. The second change is that many of the more prominent polling organizations that use probability sampling – including Pew Research Center – have shifted from conducting polls primarily by telephone to using online methods, or some combination of online, mail and telephone. The result is that polling methodologies are far more diverse now than in the past. (For more about how public opinion polling works, including a chapter on election polls, read our short online course on public opinion polling basics .) All good polling relies on statistical adjustment called “weighting,” which makes sure that the survey sample aligns with the broader population on key characteristics. Historically, public opinion researchers have adjusted their data using a core set of demographic variables to correct imbalances between the survey sample and the population. But there is a growing realization among survey researchers that weighting a poll on just a few variables like age, race and gender is insufficient for getting accurate results. Some groups of people – such as older adults and college graduates – are more likely to take surveys, which can lead to errors that are too sizable for a simple three- or four-variable adjustment to work well. Adjusting on more variables produces more accurate results, according to Center studies in 2016 and 2018 . A number of pollsters have taken this lesson to heart. For example, recent high-quality polls by Gallup and The New York Times/Siena College adjusted on eight and 12 variables, respectively. Our own polls typically adjust on 12 variables . In a perfect world, it wouldn’t be necessary to have that much intervention by the pollster. But the real world of survey research is not perfect. Predicting who will vote is critical – and difficult. Preelection polls face one crucial challenge that routine opinion polls do not: determining who of the people surveyed will actually cast a ballot. Roughly a third of eligible Americans do not vote in presidential elections , despite the enormous attention paid to these contests. Determining who will abstain is difficult because people can’t perfectly predict their future behavior – and because many people feel social pressure to say they’ll vote even if it’s unlikely. No one knows the profile of voters ahead of Election Day. We can’t know for sure whether young people will turn out in greater numbers than usual, or whether key racial or ethnic groups will do so. This means pollsters are left to make educated guesses about turnout, often using a mix of historical data and current measures of voting enthusiasm. This is very different from routine opinion polls, which mostly do not ask about people’s future intentions. When major news breaks, a poll’s timing can matter. Public opinion on most issues is remarkably stable, so you don’t necessarily need a recent poll about an issue to get a sense of what people think about it. But dramatic events can and do change public opinion , especially when people are first learning about a new topic. For example, polls this summer saw notable changes in voter attitudes following Joe Biden’s withdrawal from the presidential race. Polls taken immediately after a major event may pick up a shift in public opinion, but those shifts are sometimes short-lived. Polls fielded weeks or months later are what allow us to see whether an event has had a long-term impact on the public’s psyche. How accurate are polls? The answer to this question depends on what you want polls to do. Polls are used for all kinds of purposes in addition to showing who’s ahead and who’s behind in a campaign. Fair or not, however, the accuracy of election polling is usually judged by how closely the polls matched the outcome of the election. By this standard, polling in 2016 and 2020 performed poorly. In both years, state polling was characterized by serious errors. National polling did reasonably well in 2016 but faltered in 2020. In 2020, a post-election review of polling by the American Association for Public Opinion Research (AAPOR) found that “the 2020 polls featured polling error of an unusual magnitude: It was the highest in 40 years for the national popular vote and the highest in at least 20 years for state-level estimates of the vote in presidential, senatorial, and gubernatorial contests.” How big were the errors? Polls conducted in the last two weeks before the election suggested that Biden’s margin over Trump was nearly twice as large as it ended up being in the final national vote tally. Errors of this size make it difficult to be confident about who is leading if the election is closely contested, as many U.S. elections are . Pollsters are rightly working to improve the accuracy of their polls. But even an error of 4 or 5 percentage points isn’t too concerning if the purpose of the poll is to describe whether the public has favorable or unfavorable opinions about candidates , or to show which issues matter to which voters. And on questions that gauge where people stand on issues, we usually want to know broadly where the public stands. We don’t necessarily need to know the precise share of Americans who say, for example, that climate change is mostly caused by human activity. Even judged by its performance in recent elections, polling can still provide a faithful picture of public sentiment on the important issues of the day. The 2022 midterms saw generally accurate polling, despite a wave of partisan polls predicting a broad Republican victory. In fact, FiveThirtyEight found that “polls were more accurate in 2022 than in any cycle since at least 1998, with almost no bias toward either party.” Moreover, a handful of contrarian polls that predicted a 2022 “red wave” largely washed out when the votes were tallied. In sum, if we focus on polling in the most recent national election, there’s plenty of reason to be encouraged. Compared with other elections in the past 20 years, polls have been less accurate when Donald Trump is on the ballot. Preelection surveys suffered from large errors – especially at the state level – in 2016 and 2020, when Trump was standing for election. But they performed reasonably well in the 2018 and 2022 midterms, when he was not. During the 2016 campaign, observers speculated about the possibility that Trump supporters might be less willing to express their support to a pollster – a phenomenon sometimes described as the “shy Trump effect.” But a committee of polling experts evaluated five different tests of the “shy Trump” theory and turned up little to no evidence for each one . Later, Pew Research Center and, in a separate test, a researcher from Yale also found little to no evidence in support of the claim. Instead, two other explanations are more likely. One is about the difficulty of estimating who will turn out to vote. Research has found that Trump is popular among people who tend to sit out midterms but turn out for him in presidential election years. Since pollsters often use past turnout to predict who will vote, it can be difficult to anticipate when irregular voters will actually show up. The other explanation is that Republicans in the Trump era have become a little less likely than Democrats to participate in polls . Pollsters call this “partisan nonresponse bias.” Surprisingly, polls historically have not shown any particular pattern of favoring one side or the other. The errors that favored Democratic candidates in the past eight years may be a result of the growth of political polarization, along with declining trust among conservatives in news organizations and other institutions that conduct polls. Whatever the cause, the fact that Trump is again the nominee of the Republican Party means that pollsters must be especially careful to make sure all segments of the population are properly represented in surveys. The real margin of error is often about double the one reported. A typical election poll sample of about 1,000 people has a margin of sampling error that’s about plus or minus 3 percentage points. That number expresses the uncertainty that results from taking a sample of the population rather than interviewing everyone . Random samples are likely to differ a little from the population just by chance, in the same way that the quality of your hand in a card game varies from one deal to the next. The problem is that sampling error is not the only kind of error that affects a poll. Those other kinds of error, in fact, can be as large or larger than sampling error. Consequently, the reported margin of error can lead people to think that polls are more accurate than they really are. There are three other, equally important sources of error in polling: noncoverage error , where not all the target population has a chance of being sampled; nonresponse error, where certain groups of people may be less likely to participate; and measurement error, where people may not properly understand the questions or misreport their opinions. Not only does the margin of error fail to account for those other sources of potential error, putting a number only on sampling error implies to the public that other kinds of error do not exist. Several recent studies show that the average total error in a poll estimate may be closer to twice as large as that implied by a typical margin of sampling error. This hidden error underscores the fact that polls may not be precise enough to call the winner in a close election. Other important things to remember Transparency in how a poll was conducted is associated with better accuracy . The polling industry has several platforms and initiatives aimed at promoting transparency in survey methodology. These include AAPOR’s transparency initiative and the Roper Center archive . Polling organizations that participate in these organizations have less error, on average, than those that don’t participate, an analysis by FiveThirtyEight found . Participation in these transparency efforts does not guarantee that a poll is rigorous, but it is undoubtedly a positive signal. Transparency in polling means disclosing essential information, including the poll’s sponsor, the data collection firm, where and how participants were selected, modes of interview, field dates, sample size, question wording, and weighting procedures. There is evidence that when the public is told that a candidate is extremely likely to win, some people may be less likely to vote . Following the 2016 election, many people wondered whether the pervasive forecasts that seemed to all but guarantee a Hillary Clinton victory – two modelers put her chances at 99% – led some would-be voters to conclude that the race was effectively over and that their vote would not make a difference. There is scientific research to back up that claim: A team of researchers found experimental evidence that when people have high confidence that one candidate will win, they are less likely to vote. This helps explain why some polling analysts say elections should be covered using traditional polling estimates and margins of error rather than speculative win probabilities (also known as “probabilistic forecasts”). National polls tell us what the entire public thinks about the presidential candidates, but the outcome of the election is determined state by state in the Electoral College . The 2000 and 2016 presidential elections demonstrated a difficult truth: The candidate with the largest share of support among all voters in the United States sometimes loses the election. In those two elections, the national popular vote winners (Al Gore and Hillary Clinton) lost the election in the Electoral College (to George W. Bush and Donald Trump). In recent years, analysts have shown that Republican candidates do somewhat better in the Electoral College than in the popular vote because every state gets three electoral votes regardless of population – and many less-populated states are rural and more Republican. For some, this raises the question: What is the use of national polls if they don’t tell us who is likely to win the presidency? In fact, national polls try to gauge the opinions of all Americans, regardless of whether they live in a battleground state like Pennsylvania, a reliably red state like Idaho or a reliably blue state like Rhode Island. In short, national polls tell us what the entire citizenry is thinking. Polls that focus only on the competitive states run the risk of giving too little attention to the needs and views of the vast majority of Americans who live in uncompetitive states – about 80%. Fortunately, this is not how most pollsters view the world . As the noted political scientist Sidney Verba explained, “Surveys produce just what democracy is supposed to produce – equal representation of all citizens.” Survey Methods Trust, Facts & Democracy Voter Files Scott Keeter is a senior survey advisor at Pew Research Center . Courtney Kennedy is Vice President of Methods and Innovation at Pew Research Center . How do people in the U.S. take Pew Research Center surveys, anyway? How public polling has changed in the 21st century, what 2020’s election poll errors tell us about the accuracy of issue polling, a field guide to polling: election 2020 edition, methods 101: how is polling done around the world, most popular. 901 E St. NW, Suite 300 Washington, DC 20004 USA (+1) 202-419-4300 | Main (+1) 202-857-8562 | Fax (+1) 202-419-4372 |  Media Inquiries Research Topics Email Newsletters ABOUT PEW RESEARCH CENTER  Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research. Pew Research Center does not take policy positions. It is a subsidiary of  The Pew Charitable Trusts . © 2024 Pew Research Center 348 IMAGES Causes Greenhouse Effect Paragraph Greenhouse Gasses: How You Can Reduce Your Emissions The Greenhouse Effect, Simplified greenhouse effect How does a Greenhouse Work? Explanation & Diagram VIDEO Global Warming Green House Effects Essay In English Green House Effect Urdu Hindi green house effect project file/green house project file/green house effect project file What is Green House Effect ? || Green House Effect అంటే ఏమిటి? || La Excellence Green House Effect Urdu/Hindi medium @prof.masoodfuzail#greenhouse #greenhousegases COMMENTS Essay on Greenhouse Effect for Students 600 Words Essay on Greenhouse Effect. A Greenhouse, as the term suggests, is a structure made of glass which is designed to trap heat inside. Thus, even on cold chilling winter days, there is warmth inside it. Similarly, Earth also traps energy from the Sun and prevents it from escaping back. The greenhouse gases or the molecules present in the ... Greenhouse effect science. greenhouse effect, a warming of Earth 's surface and troposphere (the lowest layer of the atmosphere) caused by the presence of water vapour, carbon dioxide, methane, and certain other gases in the air. Of those gases, known as greenhouse gases, water vapour has the largest effect. The origins of the term greenhouse effect are unclear. Greenhouse Effect greenhouse effect. phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape. greenhouse gas. gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere. The Greenhouse Effect and our Planet The greenhouse effect happens when certain gases, which are known as greenhouse gases, accumulate in Earth's atmosphere. Greenhouse gases include carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2 O), ozone (O 3), and fluorinated gases.. Greenhouse gases allow the sun's light to shine onto Earth's surface, and then the gases, such as ozone, trap the heat that reflects back from ... What is the greenhouse effect? The greenhouse effect is the process through which heat is trapped near Earth's surface by substances known as 'greenhouse gases.' Imagine these gases as a cozy blanket enveloping our planet, helping to maintain a warmer temperature than it would have otherwise. Greenhouse gases consist of carbon dioxide, methane, ozone, nitrous oxide, chlorofluorocarbons, and water vapor. Greenhouse effect Life as we know it would be impossible if not for the greenhouse effect, the process through which heat is absorbed and re-radiated in that atmosphere. The intensity of a planet's greenhouse effect is determined by the relative abundance of greenhouse gases in its atmosphere. Without greenhouse gases, most of Earth's heat would be lost to outer space, and our planet would quickly turn into ... Greenhouse effect The greenhouse effect on Earth is defined as: "The infrared radiative effect of all infrared absorbing constituents in the atmosphere.Greenhouse gases (GHGs), clouds, and some aerosols absorb terrestrial radiation emitted by the Earth's surface and elsewhere in the atmosphere." [15]: 2232 The enhanced greenhouse effect describes the fact that by increasing the concentration of GHGs in the ... The Causes of Climate Change Takeaways Increasing Greenhouses Gases Are Warming the Planet Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect"1 — warming that results when the atmosphere traps heat radiating from Earth toward space. Life on Earth depends on energy coming from the Sun. What is global warming, facts and information The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse ... The Effects of Climate Change Takeaways Earth Will Continue to Warm and the Effects Will Be Profound Global climate change is not a future problem. Changes to Earth's climate driven by increased human emissions of heat-trapping greenhouse gases are already having widespread effects on the environment: glaciers and ice sheets are shrinking, river and lake ice is breaking up earlier, […] What Is the Greenhouse Effect? The Short Answer: The greenhouse effect is a process that occurs when gases in Earth's atmosphere trap the Sun's heat. This process makes Earth much warmer than it would be without an atmosphere. The greenhouse effect is one of the things that makes Earth a comfortable place to live. Watch this video to learn about the greenhouse effect! 5 things you should know about the greenhouse gases warming the planet The greenhouse effect describes a similar phenomenon on a planetary scale but, instead of the glass of a greenhouse, certain gases are increasingly raising global temperatures. The surface of the Earth absorbs just under half of the sun's energy, while the atmosphere absorbs 23 per cent, and the rest is reflected back into space. Natural ... How Do We Reduce Greenhouse Gases? To stop climate change, we need to stop the amount of greenhouse gases, like carbon dioxide, from increasing.For the past 150 years, burning fossil fuels and cutting down forests, which naturally pull carbon dioxide out of the air, has caused greenhouse gas levels to increase. There are two main ways to stop the amount of greenhouse gases from increasing: we can stop adding them to the air ... PDF TEACHER BACKGROUND: THE GREENHOUSE EFFECT ( 21%), exert almost no greenhouse effect. Instead, the greenhouse effect comes from molecules that are more complex and much less common. Water vapor is the most important greenhouse gas, and carbon dioxide (CO 2) is the second-most important one. Methane, nitrous oxide, ozone and several other gases present in the atmosphere in small amounts ... Climate change: evidence and causes Greenhouse gases affect Earth's energy balance and climate. ... Adding more greenhouse gases to the atmosphere enhances the effect, making Earth's surface and lower atmosphere even warmer. Image based on a figure from US EPA. ... These and other lines of evidence point conclusively to the fact that the elevated CO 2 concentration in our ... The Greenhouse Effect and our Planet greenhouse effect. noun. phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape. greenhouse gas. noun. gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere. Global warming Modern global warming is the result of an increase in magnitude of the so-called greenhouse effect, a warming of Earth's surface and lower atmosphere caused by the presence of water vapour, carbon dioxide, methane, nitrous oxides, and other greenhouse gases. In 2014 the IPCC first reported that concentrations of carbon dioxide, methane, and ... What Is Greenhouse Effect? What is the Greenhouse Effect? A greenhouse is a house made of glass that can be used to grow plants. The sun's radiations warm the plants and the air inside the greenhouse. The heat trapped inside can't escape out and warms the greenhouse which is essential for the growth of the plants. Same is the case in the earth's atmosphere. The Greenhouse Effect How do greenhouse gases affect the climate? Explore the atmosphere during the ice age and today. What happens when you add clouds? Change the greenhouse gas concentration and see how the temperature changes. Then compare to the effect of glass panes. Zoom in and see how light interacts with molecules. Do all atmospheric gases contribute to the greenhouse effect? Climate Change: Evidence and Causes: Update 2020 C ONCLUSION. This document explains that there are well-understood physical mechanisms by which changes in the amounts of greenhouse gases cause climate changes. It discusses the evidence that the concentrations of these gases in the atmosphere have increased and are still increasing rapidly, that climate change is occurring, and that most of ... Questions and Answers About Greenhouse Warming What is the "greenhouse effect"? In simplest terms, "greenhouse gases" let sunlight through to the earth's surface while trapping "outbound" radiation. ... To determine equilibrium warming in 2030 due to continued emissions of CO 2 at the 1990 level, find the point on the curve labeled "CO 2" that is vertically above 0 percent change on the ... 'The White House Effect' Review: Climate Change Doc at Telluride 'The White House Effect' Review: Limited but Convincing Doc Captures a Key Moment in the Climate Change Debate. Using only archival footage, directors Bonni Cohen, Pedro Kos and Jon Shenk lay ... Key things to know about U.S. election polling in 2024 Confidence in U.S. public opinion polling was shaken by errors in 2016 and 2020. In both years' general elections, many polls underestimated the strength of Republican candidates, including Donald Trump. These errors laid bare some real limitations of polling. In the midterms that followed those ... essay homework paper phd project resume review speech study