Гринхаус эффект на английском и русском сочинение

A greenhouse is a glass house in which plants grow. The glass lets light in and at the same time keeps heat from getting out. This heat keeps the plants warm, even when it is cold outside. The same happens to the Earth’s atmosphere. It lets sunlight in and keeps carbon dioxide and other gases from getting out. We need these gases but too much of them trap more heat.

Causes of global warming

For a long time people on our Earth didn’t think a lot about greenhouse gases. The situation changed when people started using more and more energy in the form of fossil fuels, like oil, gas and coal. We burn fossil fuels to power factories, run cars, produce electricity and heat houses. As fossil fuels burn they let carbon dioxide into the atmosphere.

During the last few decades people have also cut down many forests. Trees use carbon dioxide when they make their own food. Fewer trees mean that less carbon dioxide is taken out of the atmosphere.

Possible effects of global warming

Scientists have different opinions on how warm the Earth’s surface will really get. The increase may be between 1.5° C and 6° C by the year 2100. Warmer weather will make ice caps and glaciers melt. Sea levels could rise dramatically. Plants, animals and people living in coastal areas all could be in danger. The weather may change in many areas of the world. Floods, droughts and damaging storms could be the result.

People in colder regions might welcome warmer weather but those who live in regions that are already hot may suffer from new diseases. At the same time some animals may not survive because they cannot adapt to the new environment. They could move to other places in order to live there.

Reducing global warming

Finding a solution to solve the world’s biggest environmental problem is not an easy task. Although we need energy to make our economy grow there are things that could be done to fight off this problem. Carpools or travelling by public transport could take many cars off the roads. You could turn off lights, TV sets, computers and other electrical items if you don’t need them. Companies have been spending a lot of money to produce items that use little energy.

We also need to use more alternative

energy, like sunlight, wind power or wave power. Car companies have started to produce a new type of cars known as hybrids. It works like an electric car but also has a small petrol engine.

The Kyoto Protocol

In 1997 over 150 countries signed the Kyoto Protocol at the United Nations Climate Conference. Industrialized countries should reduce their emissions of greenhouse gases. The United States which produces about 25% of all greenhouse gases has often made public that it will not support the agreement.

Greenhouse effect

• 13.11.2018

Тема по английскому языку: Изменение климата

Топик по английскому языку: Изменение климата (Climate changes). Данный текст может быть использован в качестве презентации, проекта, рассказа, эссе, сочинения или сообщения на тему.

Парниковый эффект

В настоящее время происходят значительные изменения климата. Они тесно связаны с парниковым эффектом и глобальным потеплением. Парниковый эффект представляет собой поглощение энергии, отраженной от поверхности Земли углекислым газом и другими газами в атмосфере, что вызывает повышение температуры. По этой причине температура повышается, что создает множество проблем, которые скажутся на нашей планете в ближайшие десятилетия.

Факты изменения климата

Сегодня люди проводят своего рода незапланированный глобальный эксперимент по изменению облика целой планеты. Мы разрушаем озоновый слой, благодаря которому возможна жизнь на поверхности Земли. Все наши действия негативно сказываются на составе биосферы и температурном равновесии. За последние столетие средние температуры выросли на один градус, а к середине следующего века могут вырасти на 5 – 10 градусов. В некоторых областях, особенно в Северном полушарии, ожидается страшная засуха, что приведет к многочисленным лесным пожарам. Если вырубка тропических лесов продолжится с нынешней скоростью, то они также вскоре исчезнут. Уровень испарения воды также возрастет, что приведет к изменению характеру оборота воды. Уменьшение количества осадков в некоторых областях приведет к избыточному выпадению осадков в других областях. А некоторых регионах реки станут более мелководными или вовсе пересохнут, тогда как в других внезапные продолжительные ливневые дожди приведут к наводнениям.

Таяние арктических льдов

Если продолжится начавшееся таяние арктических льдов, уровень моря сожжет подняться на два метра к середине следующего столетия. Исчезнут многие участки суши. Потепление вызовет изменение в составе биологических сообществ, в результате чего вымрут некоторые виды. В конце концов, перегрев воздуха приведет к глобальному потеплению.

Заключение

В заключение хотелось бы сказать, что чрезвычайно важно начать действовать, чтобы предотвратить эти изменения и спасти нашу планету и наше будущее.

Скачать Топик по английскому языку: Изменение климата

Climate changes

The greenhouse effect

Nowadays major changes in climate are taking place. They are closely connected with the greenhouse effect and global warming. The greenhouse effect is the absorption of energy radiated from the Earth’s surface by carbon dioxide and other gases in the atmosphere, causing it to become warmer. So due to the greenhouse effect the temperature on the Earth is rising and this creates lots of problems that will begin to take place in the coming decades.

Early indicators of climate change

Today people are conducting an unplanned global experiment by changing the face of the entire planet. We are destroying the ozone layer which allows life to exist on the Earth’s surface. All of these activities are unfavourably changing the composition of the biosphere and the Earth’s heat balance. Average global temperatures have risen by 1 degree over the last century and they could rise by 5 to 10 degrees by the middle of the next century. Some areas, particularly in the Northern Hemisphere, will dry out and there will be more forest fires. At the present rate of destruction most of the rain forests will be gone. Evaporation rates will also increase and water circulation patterns will change. Decreased rainfall in some areas will result in increased rainfall in others. In some regions river flow will be reduced or stopped completely while others will experience sudden downpours that create massive floods.

Arctic ice melting

If the present arctic ice melting continues, the sea could rise by as much as 2 meters by the middle of the next century. Large areas of coastal land would disappear. The warming will rearrange entire biological communities and cause a number of species to become died out. In the end, the overheat of the air will result in the global warming effect.

Conclusion

In conclusion, I’d like to say that it’s very important to start doing something now, so that our future and our planet will be safe.

Greenhouse
effect is the term for the role the atmosphere in warming the earth’s
surface. The atmosphere is largely transparent to incoming short-wave
solar radiation, which heats the earth’s surface. Much of this
radiation is reflected back by gases such as carbon dioxide, methane,
nitrous oxide and ozone in the atmosphere. This heating effect is at
the root of the theories concerning global warming.

The
amount of carbon dioxide in the atmosphere has been increasing by 0.4
per cent a year because of the use of fossil fuels such as oil, gas,
and coal. The cutting of tropical forests has also been a
contributing factor in the carbon cycle. Other gases that contribute
to the greenhouse effect, such as methane and halocarbons, are
increasing even faster. The net effect of these increases could be a
worldwide rise in temperature, estimated at 2˚ to 6˚ C (4˚ to 11˚
F) over the next 100 years. Warming of this magnitude would alter
climates throughout the world, affect crop production, and cause sea
levels to rise significantly. If this happened, millions of people
would be badly affected by flooding.

Слова к тексту:

absorb
(v)
[əb´sכ:b] –
поглощать

alter
(v)
[´כ:ltə] –
изменять

affect
(v)
– влиять

be
affected
by
– подвергаться воздействию

чего-либо

carbon
dioxide
[´kα:bən
daı´oksaıd] –
двуокись углерода, углекислый

газ

cause
(v)
– послужить причиной/поводом

для
чего-либо

contribute
(v)
– содействовать, способствовать

estimate
(v)
– оценивать

flood
(n)
[fld]
– наводнение

fossil
(n)
[fכsl] –
ископаемое

greenhouse
effect – парниковый
эффект

halocarbons
(n) [´hælokα:bənz] –
хлороуглероды

heating
effect – эффект
нагревания

magnitude
(n) – величина

methane
(n)[´mi:θeın] –
метан

net
effect –
суммарный эффект

nitrous
oxide
[´naıtrəs´
oksaıd] –
окись азота

root
(n) –
корень

surface
(n)
[´sə:fıs]
– поверхность

transparent
[træns´pεərənt] –
прозрачный

Ответьте на вопросы:

1. How
   is the surface of the Earth heated?

2. What gases reflect heat back
   in the atmosphere?

3. Why
   is the amount of carbon dioxide in the atmosphere increasing?

4. What
   can you say about possible worldwide rise in temperature in the next
   100 years?

Техт № з Global Warming

Global
warming is an increase in the earth’s temperature due to the use of
fossil fuels and other industrial processes leading to a build-up of
«greenhouse gases» (carbon dioxide, methane, nitrous oxide)
in the at­mosphere. It has been known since 1896 that carbon
dioxide helps stop the sun’s infrared radiation from escaping into
space and thus functions to maintain the Earth’s relatively warm
temperature (this is called the green­house effect). The question
is whether the increasing levels of carbon di­oxide in the
atmosphere will lead to elevated global temperatures, which could
result major climatic changes, and have serious problems for
agri­cultural productivity.

Since
1850 there has been a mean rise in global temperature of
approximately 1˚ C (1.8˚ F), but this rise could just be part of a
natural fluctuation. Such fluctuations have been recorded for tens of
thousands of years.

The
potencial concequences of global warming are so great that many of
the world’s top scientists have insisted on immediate action and
have called for international cooperation on the problem.

Greenhouse effect is the trapping of radiation in the lower atmosphere warming the temperature of the Earth. The natural greenhouse effect is essential for sustaining life on Earth. The effect of greenhouse gases in the atmosphere is intensified due to the emission of these harmful gases in the atmosphere by mankind. This warms the temperature of the earth leading to Global warming.

Here are essays on Greenhouse Effect of varying lengths to help you with the topic in your exam. You can select any Greenhouse Effect essay as per your need and interest:

Essay on Greenhouse Effect – Essay 1 (200 words)

The greenhouse effect refers to the warming of the surface of Earth caused by the presence of greenhouse gases in the atmosphere. The presence of radiatively active gases in the atmosphere spreads its energy in all directions and a part of these gases is also directed towards planet’s surface making it warmer. The intensity of the radiation depends on the amount of greenhouse gases in the atmosphere and the temperature of the Earth’s atmosphere. The primary greenhouse gases are carbon dioxide, water vapor, ozone, nitrous oxide and methane.

Greenhouse effect occurs naturally but has increased mainly due to human activities such as clearing forests, burning fossil fuels and so on which has resulted in global warming. Since the beginning of industrial revolution, the amount of methane in the atmosphere has doubled and the amount of carbon dioxide has also increased by approx 30 percent.

The increase in emission of greenhouse gases in the atmosphere has altered the climate of our planet and can alter it further. This will result in extreme drought and rainfall that will disrupt the production of food in various regions. Biodiversity, ecosystem and life of people is adversely affected due to global warming caused because of greenhouses gases. Global warming is a major issue worldwide that needs to be prevented by taking serious measures.

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Essay on Greenhouse Effect and Global Warming – Essay 2 (300 words)

Introduction

Global warming is the increase in temperature of Earth and its oceans. Greenhouse gases absorb and emit infrared radiation and trap the radiation in the atmosphere in the form of heat causing greenhouse effect by warming the temperature of Earth.

Greenhouse Effect and Global Warming

The primary greenhouse gases in the atmosphere are namely carbon dioxide (CO₂), water vapor (H₂O), methane (CH₄), Ozone (O₃), nitrous oxide (N₂O) that retain much of the heat. The average temperature of the Earth’s atmosphere is 15⁰c (59⁰F), whereas the temperature without greenhouse effect would have been – 18 degree F.

The increased emission of greenhouse gases released by burning fossil fuels, agriculture, deforestation and other human activities are the primary reasons for global warming over the past few decades. It is resulting in the melting of ice sheets and glaciers which causes rise in sea levels. Warmer climate may probably lead to precipitation and evaporation. Global warming also results in changing the weather patterns making some places dryer and other places wetter.

It may result in frequent natural disasters like drought, floods and hurricanes. The climate change adversely affects nature and human life and we might see worse effects of it in future if the emission of greenhouse gases continues to grow. The consequences of global warming will be disastrous for the coastal regions. The poles will start melting due to rise in temperature causing rise in sea levels due to which coastal cities might get submerged.

Conclusion

There is no country in the world that is not affected by the adverse effects of global warming. Reduction in the emission of greenhouse gases can prevent the adverse effects of global warming. Measures need to be taken by government and non-governmental organizations to control the emission of toxic gases in the atmosphere. Greater use of renewable energy and forestation instead of deforestation should be promoted.

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Essay on Causes of Greenhouse Effect – Essay 3 (400 words)

Introduction

The warming of the temperature of Earth by the gases trapped in the atmosphere is known as greenhouse effect. It is natural and is important to sustain life on Earth. Unfortunately since industrial revolution there has been an excessive increase in the emission of greenhouse gases in the atmosphere. It has increased manifolds due to human activities. This has contributed to climate change and global warming.

Major Causes of Greenhouse Effect

Here are some of the major causes of Greenhouse effect:

Natural Causes:

• Some naturally present elements on Earth produce greenhouse gases such as carbon dioxide that can be found in oceans, methane that is produced by decaying of plants due to natural forest fires and nitrogen oxide that is present in soil and water in small amounts. Only fluorinated gases are produced by humans and are not present in nature.
• Water Vapour is also crucial in greenhouse effect. Water vapour absorbs thermal energy, mostly when the humidity rises in the air. This raises the temperature in the atmosphere.
• Animals breathe oxygen from the atmosphere and release carbon dioxide and methane gases. It is also one of the natural causes of greenhouse effect.

Manmade Causes:

• Burning of fossil fuels such as oil and coal is one of the greatest contributors of the greenhouse effect. Burning fossil fuels emits carbon dioxide in the atmosphere which is the cause of greenhouse effect. Further, the atmosphere is polluted by the release of methane gas from Earth when the gas, coal mines or oil wells are dug.
• Deforestation is another major cause of greenhouse effect. Trees help in reducing the carbon dioxide and producing oxygen. By clearing away forests and trees the carbon dioxide in the atmosphere continues to rise.
• Artificial nitrogen is used for the fertilization of crops, which is released as nitrogen oxide in the atmosphere. Nitrogen oxide in the atmosphere increases greenhouse effect.
• Industrial gas is released in to the atmosphere at very high rate across the world. Industrial gases include gases such as methane, carbon dioxide and fluorine gas.
• Farm animals such as goats, pigs, cows also contribute to greenhouse gases. Methane is produced in their stomach when they digest their food and is released through their manure into the atmosphere. Clearing away forest to expand farmland for raising farm animals further elevates the emission of greenhouse gases.

Conclusion

So, the human activities are the major reason for the rise in emission of greenhouse gases. Greenhouse gas emission causes global warming which has several adverse effects on human life and our nature.

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Essay on Greenhouse Effect on Climate – Essay 4 (500 words)

Introduction

Greenhouse gases prevent radiation from escaping in to the outer space which results in gradual warming of the temperature of the Earth surface that causes global warming. The equilibrium of the radiation earth receives and the radiation that is reflected back to the space makes the Earth habitable for humans, with average temperature of 15⁰C (59 degrees), as per NASA.

Without this balance our planet would be either too cold or too hot. The exchange of the radiation of the sun that warms up the temperature of our planet is called greenhouse effect as a greenhouse also works in a similar way.

Greenhouse Effects on the Climate

Climate is dramatically affected by greenhouse gas emission in the atmosphere. Emission of various greenhouse gases in the atmosphere has increased significantly since Industrialization. Greenhouse gases are majorly produced by burning fossil fuels. The gases that add to the greenhouse effect are Carbon dioxide (CO₂), Water vapor (H₂O), Methane (CH₄), Ozone (O₃) and Nitrous Oxide (N₂O).

CO₂ contributes majorly to the greenhouse gases and has increased by 40 percent since industrialization. Natural processes can absorb the gases in the atmosphere. For instance, the process of photosynthesis can absorb carbon dioxide, but the emission of the gases gradually began exceeding the capacity to absorb greenhouse gases through natural process. This imbalance between the ability of natural processes to absorb gases and emission of greenhouse gases has increased the intensity of greenhouse gases in the atmosphere.

We have burnt large amount of fossil fuels, cut down vast areas of forests, farmed livestock producing large amount of methane and contaminated our atmosphere with toxic gases. Greenhouse gases that absorb the radiation are in excessive quantity in the atmosphere and can force climate changes. Global warming is the biggest challenge we are witnessing presently.

Effects of Climate Change

• Forests play a vital role in absorbing carbon dioxide in the atmosphere majorly responsible for global warming. Destroying trees further emit carbon dioxide adding to the greenhouse gas in atmosphere and causing global warming.
• Climate change affects the water systems and may result in floods and droughts more frequently. Water bodies are also contaminated around the world and the quality of water has degraded due to excessive pollution and presence of greenhouse gases in the atmosphere. Glaciers are melting that impacts the freshwater ecosystems. Increasing acidification of oceans is a threat for the oceanic wildlife.
• Climate change is a threat for several species. It is the cause of extinction of various species. Species that live in the areas that are highly affected by climate change are unable to adapt to rapid change in the climate.
• Increase in the temperature of Earth may result in extremely dangerous climate change.

Conclusion

The damage already caused to the Earth’s atmosphere and climate is severe and cannot be reversed. We can either adapt to the climate change and live with the adverse consequences like floods and rising sea levels or mitigate the impact of global warming by implementing policies that reduce the concentration of greenhouse gases in the atmosphere.

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Essay on Greenhouse Effect and Greenhouse Gases – Essay 5 (600 words)

Introduction

Greenhouse is made of glass and is designed to trap heat inside. Even on cold winter days there is warmth inside greenhouse. Like greenhouse the atmosphere on Earth also traps some energy that enters from sun and blocks it from escaping back from the Earth. In the atmosphere of the Earth there are molecules called greenhouse gases that trap the heat.

The greenhouse effect is important as absorbing the energy keeps the temperature of Earth warm and appropriate for living. The problem is that the greenhouse effect is warming up rapidly as excessive greenhouse gases are released in our atmosphere leading to climate change. Greenhouse gases occur naturally in the atmosphere and also occur due to human activities.

Greenhouse Gases and their Effects

The most dominant gases present in our atmosphere are as follows:

1. Carbon dioxide (CO₂): Of all the greenhouse gases the most prominent is Carbon dioxide. The chief sources of carbon dioxide in the atmosphere include manmade activities such as clearing of land, burning of fossil fuels and production of cement and natural sources such as volcanoes, respiration by oxygen-using organisms, combustion and decay of organic matter. The natural sinks that absorb carbon dioxide from the atmosphere involve the process of photosynthesis which is very important. The marine life also absorbs the carbon dioxide dissolved in the oceans. But the deforestation and cutting of plants at huge level without new tree plantation is harming the environment very badly.
2. Water vapor (H₂O):Water vapor is one of the most powerful greenhouse gases in the atmosphere of our planet. The warmer the climate on Earth, the greater the evaporation of water from the Earth’s surface. The greater the evaporation, the greater the concentration of this powerful greenhouse gas.
3. Methane (CH₄):Methane is present in lesser concentration in the Earth’s atmosphere. Methane also resides in atmosphere for shorter duration compared to carbon dioxide. The sources of methane include volcanoes, wetlands, seepage vents, methane oxidizing bacteria, livestock farming, burning of natural gases and coal, decomposition in landfills, biomass combustion and so on. The natural sink for this gas is soil and atmosphere.
4. Nitrous oxides (N₂O) and fluorinated gases:Greenhouse gases produced due to industrial activities include fluorinated gases and nitrous oxide. The three main fluorinated gases are hydrofluorocarbons (HFCꜱ), sulfur hex fluorocarbons (SF₆) and perfluorocarbons (PFCꜱ). Fluorinated gases are manmade and not natural. These are created by human activities mostly due to Industrial processes. The sources of Nitrous oxides include bacteria in soil, livestock waste management and use of fertilizers in agriculture.
5. Surface Level Ozone (O₃):Surface Ozone is the most significant greenhouse gas in the atmosphere. It is caused due to air pollution and it has a very different role in balancing radiation on Earth. Ozone occurs in both, Earth’s upper and ground level atmosphere. Ozone is a harmful air pollutant produced in the atmosphere when contaminants are released by vehicles, power plants, chemical plants, industrial boilers, refiners and other such sources chemically react in the presence of sun radiation.

Conclusion

Greater the emission of greenhouse gases, greater the concentrations in the atmosphere. Each gas remains in the atmosphere of the planet for different time period i.e. from few years to thousands of years. Each gas impacts differently, some are more effective than others making Earth warmer. Several aspects of environment are changing due to climate change i.e. warmer climate, rising sea levels, droughts and so on. It will impact Earth for centuries and we must be ready for the adverse effects of climate change in future if we still overlook the extent of damage it has caused. Efforts should be made to prevent the emission of greenhouse gases and more use of renewable sources of energy should be encouraged.

Related Information:

Green House Effect and Global Warming Essay

Global Warming and Greenhouse Gas Emissions Essay

Другие языки

Questions:

Global warming is the increase in the average temperature of the Earth’s near-surface air and the oceans since the mid-twentieth century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 years ending in 2005. The Intergovernmental Panel on Climate Change (IPCC) concludes that anthropogenic greenhouse gases are responsible for most of the observed temperature increase since the middle of the twentieth century, and that natural phenomena such as solar variation and volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect afterward. These basic conclusions have been endorsed by more than 40 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries.

Climate model projections summarized in the latest IPCC report indicate that global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century. The uncertainty in this estimate arises from the use of models with differing climate sensitivity, and the use of differing estimates of future greenhouse gas emissions. Some other uncertainties include how warming and related changes will vary from region to region around the globe. Most studies focus on the period up to 2100. However, warming is expected to continue beyond 2100, even if emissions stop, because of the large heat capacity of the oceans and the long lifetime of carbon dioxide in the atmosphere.

Increasing global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, likely including expansion of subtropical deserts.[8] The continuing retreat of glaciers, permafrost and sea ice is expected, with the Arctic region being particularly affected. Other likely effects include shrinkage of the Amazon rainforest and Boreal forests, increases in the intensity of extreme weather events, species extinctions and changes in agricultural yields.

Political and public debate continues regarding the appropriate response to global warming. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions. A successor to the first commitment period of the Kyoto protocol is expected to be agreed at the COP15 talks in December 2009.

Forcing

See also: Global cooling, Global dimming, and Ozone depletion

The Earth’s climate changes in response to external forcings, including changes in greenhouse gas concentrations, variations in Earth’s orbit around the Sun,[9][10][11] changes in solar luminosity, and volcanic eruptions.[12] The thermal inertia of the oceans and slow responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. Climate commitment studies indicate that even if greenhouse gases were stabilized at 2000 levels a further warming of about 0.5 °C (0.9 °F) would still occur.[13]

Global dimming, a gradual reduction in the amount of global direct irradiance at the Earth’s surface, may have partially counteracted global warming during the period 1960-1990. Human-caused aerosols likely precipitated this effect. Scientists have stated with 66–90% confidence that the effects of human-caused aerosols, along with volcanic activity, have offset some of the warming effect of increasing greenhouse gases.[1]

Ozone depletion, the steady decline in the total amount of ozone in Earth’s stratosphere, is sometimes cited in relation to global warming. Although there are a few areas of linkage the relationship between the two is not strong.

Greenhouse effect

Main articles: Greenhouse gas and Greenhouse effect

The scientific consensus[14][15] is that the increase in atmospheric greenhouse gases due to human activity has caused most of the warming observed since the start of the industrial era and that the observed warming cannot be satisfactorily explained by natural causes alone.[16] This attribution is clearest for the most recent 50 years, which is the period when most of the increase in greenhouse gas concentrations took place and for which the most complete measurements exist.

The greenhouse effect was discovered by Joseph Fourier in 1824 and first investigated quantitatively by Svante Arrhenius in 1896.[17] It is the process by which absorption and emission of infrared radiation by atmospheric gases warm a planet’s lower atmosphere and surface. Existence of the greenhouse effect as such is not disputed even by those who do not agree that the recent temperature increase is attributable to human activity. The question is instead how the strength of the greenhouse effect changes when human activity increases the atmospheric concentrations of greenhouse gases.

Naturally occurring greenhouse gases have a mean warming effect of about 33 °C (59 °F), without which Earth would be uninhabitable.[18][C] The major greenhouse gases are water vapor, which causes about 36–70 percent of the greenhouse effect (not including clouds); carbon dioxide (CO2), which causes 9–26 percent; methane (CH4), which causes 4–9 percent; and ozone, which causes 3–7 percent.[19][20]

Human activity since the industrial revolution has increased the amount of greenhouse gases in the atmosphere, leading to increased radiative forcing from CO2, methane, tropospheric ozone, CFCs and nitrous oxide. The concentrations of CO2 and methane have increased by 36% and 148% respectively since the mid-1700s.[21] These levels are considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores.[22] Less direct geological evidence indicates that CO2 values this high were last seen approximately 20 million years ago.[23] Fossil fuel burning has produced approximately three-quarters of the increase in CO2 from human activity over the past 20 years. Most of the rest is due to land-use change, in particular deforestation.[24]

CO2 concentrations are continuing to rise due to burning of fossil fuels and land-use change. The future rate of rise will depend on uncertain economic, sociological, technological, and natural developments. The IPCC Special Report on Emissions Scenarios gives a wide range of future CO2 scenarios, ranging from 541 to 970 ppm by the year 2100.[25] Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100 if coal, tar sands or methane clathrates are extensively exploited.[26]

Solar variation

Main article: Solar variation

An alternative hypothesis is that recent warming may be the result of variations in solar activity.[27][28] Stott and colleagues have suggested that climate models overestimate the relative effect of greenhouse gases compared to solar forcing; they also suggest that the cooling effects of volcanic dust and sulfate aerosols have been underestimated.[29] They nevertheless conclude that even with an enhanced climate sensitivity to solar forcing, most of the warming since the mid-20th century is likely attributable to the increases in greenhouse gases. Another paper suggests that the Sun may have contributed about 45–50 percent of the increase in the average global surface temperature over the period 1900–2000, and about 25–35 percent between 1980 and 2000.[30] In 2006, Peter Foukal and colleagues found no net increase of solar brightness over the last 1,000 years. Solar cycles led to a small increase of 0.07 percent in brightness over the last 30 years. This effect is too small to contribute significantly to global warming.[31][32] The general view is that the combined effect of the two main sources of natural climate forcing, solar variation and changes in volcanic activity, probably had a warming effect from pre-industrial times to 1950 but a cooling effect since.[1]

An increase in solar activity should warm the stratosphere, whereas an increase in greenhouse gases should produce cooling there.[33] The observed trend since at least 1960 has been a cooling of the lower stratosphere.[34] Reduction of stratospheric ozone also has a cooling influence, but substantial ozone depletion did not occur until the late 1970s.[35]

Svensmark and colleagues have proposed another hypothesis related to solar activity, which is that magnetic activity of the sun deflects cosmic rays that may influence the generation of cloud condensation nuclei and thereby affect the climate.[36][37][38] Another paper found no relation between global warming and solar radiation since 1985, whether through variations in solar output or variations in cosmic rays.[39] Henrik Svensmark and Eigil Friis-Christensen, the main proponents of cloud seeding by galactic cosmic rays, disputed this criticism of their hypothesis.[40] A 2007 paper found that in the last 20 years there has been no significant link between changes in cosmic rays coming to Earth and cloudiness and temperature.[41][42]

Feedback

When a warming trend results in effects that induce further warming, the process is referred to as a positive feedback; when the warming results in effects that act to reduce the original warming, the process is referred to as a negative feedback. The main positive feedback involves the tendency of warming to increase the amount of water vapor in the atmosphere. The main negative feedback is the effect of temperature on emission of infrared radiation: as the temperature of a body increases, the emitted radiation increases with the fourth power of its absolute temperature.

Water vapor feedback

If the atmosphere is warmed the saturation vapour pressure increases, and the amount of water vapor in the atmosphere will tend to increase. Since water vapor is a greenhouse gas the increase in water vapor content makes the atmosphere warm further; this warming causes the atmosphere to hold still more water vapor (a positive feedback), and so on until other processes stop the feedback loop. The result is a much larger greenhouse effect than that due to CO2 alone. Although this feedback process causes an increase in the absolute moisture content of the air, the relative humidity stays nearly constant or even decreases slightly because the air is warmer.[43]

Clouds

Feedback effects due to clouds are an area of ongoing research. Seen from below, clouds emit infrared radiation back to the surface, and so exert a warming effect; seen from above, clouds reflect sunlight and emit infrared radiation to space, and so exert a cooling effect. Whether the net effect is warming or cooling depends on details such as the type and altitude of the cloud, details that have been difficult to represent in climate models.[43]

Lapse rate

A subtler feedback process relates to changes in the lapse rate as the atmosphere warms. The atmosphere’s temperature decreases with height in the troposphere. Since emission of infrared radiation varies with the fourth power of temperature, longwave radiation emitted from the upper atmosphere is less than that emitted from the lower atmosphere. Most of the radiation emitted from the upper atmosphere escapes to space, while most of the radiation emitted from the lower atmosphere is re-absorbed by the surface or the atmosphere. Thus, the strength of the greenhouse effect depends on the atmosphere’s rate of temperature decrease with height: if the rate of temperature decrease is greater the greenhouse effect will be stronger, and if the rate of temperature decrease is smaller then the greenhouse effect will be weaker. Both theory and climate models indicate that with increased greenhouse gas content the rate of temperature decrease with height will be reduced, producing a negative lapse rate feedback that weakens the greenhouse effect. Measurements of the rate of temperature change with height are very sensitive to small errors in observations, making it difficult to establish whether the models agree with observations.[44]

Ice-albedo feedback

When global temperatures increase, ice near the poles melts at an increasing rate. As the ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice, and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and this cycle continues.[45] Rapid Arctic shrinkage is already occurring, with 2007 being the lowest ever recorded sea ice area. Some models suggest that tipping points exist, leading to a potentially rapid collapse of sea ice cover in the Arctic.[46]

Arctic methane release

Warming is also the triggering variable for the release of methane from sources both on land and on the deep ocean floor, making both of these possible feedback effects. Thawing permafrost, such as the frozen peat bogs in Siberia, creates a positive feedback due to the potentially rapid release of CO2 and CH4.[47][unreliable source?] Methane discharge from permafrost is presently under intensive study.[citation needed]

Clathrate gun hypothesis

Warmer deep ocean temperatures could also release the greenhouse gas methane from the ‘frozen’ state of the vast deep ocean deposits of methane clathrate, according to the Clathrate Gun Hypothesis, albeit over millenial time-scales. A further release of methane from shallow cold water clathrates is also expected, and is predicted to be faster.[48] Buffett and Archer predict a large release of methane in response to warming, and a large increase in methane stores if oxygen levels in the ocean fall.[49] They offer a «global estimate of 3×1018 g of carbon (3000 Gton C) in clathrate and 2×1018 g (2000 Gton C) in methane bubbles. The predicted methane inventory decreases by 85% in response to 3 °C of warming. Conversely, the methane inventory increases by a factor of 2 if the O2 concentration of the deep ocean decreases by 40 μM or carbon rain increases by 50%

Reduced absorption of CO2 by the oceans

Ocean ecosystems’ ability to sequester carbon are expected to decline as the oceans warm. This is because warming reduces the nutrient levels of the mesopelagic zone (about 200 to 1000 m depth), which limits the growth of diatoms in favor of smaller phytoplankton that are poorer biological pumps of carbon.[50]

Temperature changes

Main article: Temperature record

Recent

Global temperatures have increased by 0.75 °C (1.35 °F) relative to the period 1860–1900, according to the instrumental temperature record. This measured temperature increase is not significantly affected by the urban heat island effect.[51] Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).[52] Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Temperature is believed to have been relatively stable over the one or two thousand years before 1850, with possibly regional fluctuations such as the Medieval Warm Period or the Little Ice Age.[citation needed]

Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean can lose heat by evaporation more readily than the land.[53] The Northern Hemisphere has more land than the Southern Hemisphere, so it warms faster. The Northern Hemisphere also has extensive areas of seasonal snow and sea-ice cover subject to the ice-albedo feedback. More greenhouse gases are emitted in the Northern than Southern Hemisphere, but this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres.[54]

Based on estimates by NASA’s Goddard Institute for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree.[55] Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[56][57] Temperatures in 1998 were unusually warm because the strongest El Niño-Southern Oscillation in the past century occurred during that year.[58]

Anthropogenic emissions of other pollutants—notably sulfate aerosols—can exert a cooling effect by increasing the reflection of incoming sunlight. This partially accounts for the cooling seen in the temperature record in the middle of the twentieth century,[59] though the cooling may also be due in part to natural variability. James Hansen and colleagues have proposed that the effects of the products of fossil fuel combustion—CO2 and aerosols—have, for the short term, largely offset one another, so that net warming in recent decades has been driven mainly by non-CO2 greenhouse gases.[60]

Paleoclimatologist William Ruddiman has argued that human influence on the global climate began around 8,000 years ago with the start of forest clearing to provide land for agriculture and 5,000 years ago with the start of Asian rice irrigation.[61][62] Ruddiman’s interpretation of the historical record, with respect to the methane data, has been disputed.[63]

Pre-human climate variations

Further information: Paleoclimatology

See also: Snowball Earth and Paleocene-Eocene thermal maximum

Earth has experienced warming and cooling many times in the past. The recent Antarctic EPICA ice core spans 800,000 years, including eight glacial cycles timed by orbital variations with interglacial warm periods comparable to present temperatures.[64]

A rapid buildup of greenhouse gases amplified warming in the early Jurassic period (about 180 million years ago), with average temperatures rising by 5 °C (9 °F). Research by the Open University indicates that the warming caused the rate of rock weathering to increase by 400%. As such weathering locks away carbon in calcite and dolomite, CO2 levels dropped back to normal over roughly the next 150,000 years.[65]

Sudden releases of methane from clathrate compounds (the clathrate gun hypothesis) have been hypothesized as both a cause for and an effect of other warming events in the distant past, including the Permian–Triassic extinction event (about 251 million years ago) and the Paleocene–Eocene Thermal Maximum (about 55 million years ago).

Climate models

Main article: Global climate model

The main tool for projecting future climate changes are computer models of the climate. These models are based on physical principles including fluid dynamics and radiative transfer. Although they attempt to include as many processes as possible, simplifications of the actual climate system are inevitable because of the constraints of available computer power and limitations in knowledge of the climate system. All modern climate models include an atmospheric model that is coupled to an ocean model and models for ice cover on land and sea. Some models also include treatments of chemical and biological processes.[66] These models project a warmer climate due to increasing levels of greenhouse gases.[67] Although much of the variation in model outcomes depends on the greenhouse gas emissions used as inputs, the temperature effect of a specific greenhouse gas concentration (climate sensitivity) varies depending on the model used. The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem.[68]

Global climate model projections of future climate depend on estimates of greenhouse gas emissions, most often those from the IPCC Special Report on Emissions Scenarios (SRES). In addition to human-caused emissions, some models also include a simulation of the carbon cycle; this generally shows a positive feedback, though this response is uncertain. Some observational studies also show a positive feedback.[69][70][71]

Including uncertainties in future greenhouse gas concentrations and climate sensitivity, the IPCC anticipates a warming of 1.1 °C to 6.4 °C (2.0 °F to 11.5 °F) by the end of the 21st century, relative to 1980–1999.[1] A 2008 paper predicts that the global temperature will not increase during the next decade because of short-term natural climate cycles.[72]

Models are also used to help investigate the causes of recent climate change by comparing the observed changes to those that the models project from various natural and human-derived causes. Although these models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects, they do indicate that the warming since 1975 is dominated by man-made greenhouse gas emissions.

Current climate models produce a good match to observations of global temperature changes over the last century, but do not simulate all aspects of climate.[73] The physical realism of models is tested by examining their ability to simulate current or past climates.[74] While a 2007 study by David Douglass and colleagues found that the models did not accurately predict observed changes in the tropical troposphere,[75] a 2008 paper published by a 17-member team led by Ben Santer noted errors in the Douglass study, and found instead that the models and observations were not statistically different.[76] Not all effects of global warming are accurately predicted by the climate models used by the IPCC. For example, observed Arctic shrinkage has been faster than that predicted.[77]

Attributed and expected effects

Environmental

Main article: Effects of global warming

See also: Regional effects of global warming and Ocean acidification

Although it is difficult to connect specific weather events to global warming, an increase in global temperatures may in turn cause broader changes, including glacial retreat, Arctic shrinkage, and worldwide sea level rise. Changes in the amount and pattern of precipitation may result in flooding and drought. There may also be changes in the frequency and intensity of extreme weather events. These changes are not likely to be reversible on timescales shorter than a thousand years.[7] Other effects may include changes in agricultural yields, addition of new trade routes,[78] reduced summer streamflows, species extinctions,[79] and increases in the range of disease vectors.

Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming. A 2001 report by the IPCC suggests that glacier retreat, ice shelf disruption such as that of the Larsen Ice Shelf, sea level rise, changes in rainfall patterns, and increased intensity and frequency of extreme weather events are attributable in part to global warming.[80] Other expected effects include water scarcity in some regions and increased precipitation in others, changes in mountain snowpack, and adverse health effects from warmer temperatures.[81]

Social and economic effects of global warming may be exacerbated by growing population densities in affected areas. Temperate regions are projected to experience some benefits, such as fewer deaths due to cold exposure.[82] A summary of probable effects and recent understanding can be found in the report made for the IPCC Third Assessment Report by Working Group II.[80] The newer IPCC Fourth Assessment Report summary reports that there is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic Ocean since about 1970, in correlation with the increase in sea surface temperature (see Atlantic Multidecadal Oscillation), but that the detection of long-term trends is complicated by the quality of records prior to routine satellite observations. The summary also states that there is no clear trend in the annual worldwide number of tropical cyclones.[1]

Additional anticipated effects include sea level rise of 0.18 to 0.59 meters (0.59 to 1.9 ft) in 2090-2100 relative to 1980-1999, [1] repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increasingly intense (but less frequent)[83] hurricanes and extreme weather events, lowering of ocean pH, oxygen depletion in the oceans,[84] and the spread of diseases such as malaria and dengue fever,[85][86] as well as Lyme disease, hantavirus infections, bubonic plague, and cholera.[87] One study predicts 18% to 35% of a sample of 1,103 animal and plant species would be extinct by 2050, based on future climate projections.[88] However, few mechanistic studies have documented extinctions due to recent climate change[89] and one study suggests that projected rates of extinction are uncertain.[90]

Increased atmospheric CO2 increases the amount of CO2 dissolved in the oceans.[91] CO2 dissolved in the ocean reacts with water to form carbonic acid, resulting in ocean acidification. Ocean surface pH is estimated to have decreased from 8.25 near the beginning of the industrial era to 8.14 by 2004,[92] and is projected to decrease by a further 0.14 to 0.5 units by 2100 as the ocean absorbs more CO2.[1][93] Since organisms and ecosystems are adapted to a narrow range of pH, this raises extinction concerns, directly driven by increased atmospheric CO2, that could disrupt food webs and impact human societies that depend on marine ecosystem services.[94]

Economic

Main articles: Economics of global warming and Low-carbon economy

Some economists have tried to estimate the aggregate net economic costs of damages from climate change across the globe. Such estimates have so far yielded no conclusive findings; in a survey of 100 estimates, the values ran from US$-10 per tonne of carbon (tC) (US$-3 per tonne of carbon dioxide) up to US$350/tC (US$95 per tonne of carbon dioxide), with a mean of US$43 per tonne of carbon (US$12 per tonne of carbon dioxide).[82]

One widely publicized report on potential economic impact is the Stern Review. It suggests that extreme weather might reduce global gross domestic product by up to one percent, and that in a worst-case scenario global per capita consumption could fall 20 percent.[95] The report’s methodology, advocacy and conclusions have been criticized by many economists, primarily around the Review’s assumptions of discounting and its choices of scenarios.[96] Others have supported the general attempt to quantify economic risk, even if not the specific numbers.[97][98]

Preliminary studies suggest that costs and benefits of mitigating global warming are broadly comparable in magnitude.[99]

According to United Nations Environment Programme (UNEP), economic sectors likely to face difficulties related to climate change include banks, agriculture, transport and others.[100] Developing countries dependent upon agriculture will be particularly harmed by global warming.[101]

Responses to global warming

Main articles: Mitigation of global warming, Kyoto Protocol, Geoengineering, and Adaptation to global warming

The broad agreement among climate scientists that global temperatures will continue to increase has led some nations, states, corporations and individuals to implement responses. These responses to global warming can be divided into mitigation of the causes and effects of global warming, and adaptation to the changing global environment.

Mitigation

Emissions reduction

The world’s primary international agreement on reducing greenhouse gas emissions is the Kyoto Protocol, an amendment to the UNFCCC negotiated in 1997. The Protocol now covers more than 160 countries and over 55 percent of global greenhouse gas emissions.[102] Only the United States and Kazakhstan have not ratified the treaty, with the United States historically being the world’s largest emitter of greenhouse gases. This treaty expires in 2012, and international talks began in May 2007 on a future treaty to succeed the current one.[103]

Many environmental groups encourage individual action against global warming, often by the consumer, but also by community and regional organizations. Others have suggested a quota on worldwide fossil fuel production, citing a direct link between fossil fuel production and CO2 emissions.[104][105]

There has also been business action on climate change, including efforts at increased energy efficiency and limited moves towards use of alternative fuels. In January 2005 the European Union introduced its European Union Emission Trading Scheme, a greenhouse gas emissions trading scheme through which companies, in conjunction with government, agree to cap their emissions or to purchase credits from those below their allowances. Australia announced its Carbon Pollution Reduction Scheme in 2008. United States President Barack Obama has announced he will introduce an economy wide cap and trade scheme.[106]

The IPCC’s Working Group III is responsible for crafting reports that deal with the mitigation of global warming and analyzing the costs and benefits of different approaches. In the 2007 IPCC Fourth Assessment Report, they conclude that no one technology or sector can be completely responsible for mitigating future warming. They find there are key practices and technologies in various sectors, such as energy supply, transportation, industry, and agriculture, that should be implemented to reduced global emissions. They estimate that stabilization of carbon dioxide equivalent between 445 and 710 ppm by 2030 will result in between a 0.6 percent increase and three percent decrease in global gross domestic product.[107]

Geoengineering

Geoengineering would involve the deliberate modification of Earth’s environment on a large scale «to suit human needs and promote habitability».[108] It can be divided two major approaches. The first is remediation, in which greenhouse gases would be removed from the atmosphere, principally by carbon sequestration methods such as air capture.[109] The second is solar radiation management, in which incoming solar radiation would be reduced, such as by the insertion of stratospheric sulfur aerosols.[110] The slow pace of action to reduce greenhouse gas emissions have led some scientists to suggest that these techniques may be necessary.[111] Whilst some cool roof and tree planting projects are underway, no planetary-scale geoengineering has yet been attempted.

Adaptation

The effects of global warming are wide in their scope, and a similarly wide variety of measures have been suggested for adaptation to global warming. These range from the trivial, such as the installation of air-conditioning equipment, up to major infrastructure projects, such as abandonment of settlements threatened by rising sea levels. Measures including water conservation,[112] changes to agricultural practices,[113] construction of flood defences,[114] changes to medical care,[115] and interventions to protect threatened species[116] have all been suggested. A wide ranging study of the possible opportunities for adaptation of infrastructure has been published by the Institute of Mechanical Engineers[117]

Economic and political debate

Main articles: Global warming controversy, Politics of global warming, and Economics of global warming

See also: Scientific opinion on climate change, Climate change denial, List of countries by greenhouse gas emissions per capita, List of countries by carbon dioxide emissions per capita, List of countries by carbon dioxide emissions, and List of countries by ratio of GDP to carbon dioxide emissions

Increased publicity of the scientific findings surrounding global warming has resulted in political and economic debate.[118] Poor regions, particularly Africa, appear at greatest risk from the projected effects of global warming, while their emissions have been small compared to the developed world.[119] At the same time, developing country exemptions from provisions of the Kyoto Protocol have been criticized by the United States and Australia, and used as part of a rationale for continued non-ratification by the U.S.[120] In the Western world, the idea of human influence on climate has gained wider public acceptance in Europe than in the United States.

The issue of climate change has sparked debate weighing the benefits of limiting industrial emissions of greenhouse gases against the costs that such changes would entail. There has been discussion in several countries about the cost and benefits of adopting alternative energy sources in order to reduce carbon emissions.[123] Business-centered organizations, conservative commentators, and companies such as the Competitive Enterprise Institute and ExxonMobil have downplayed IPCC climate change scenarios, funded scientists who disagree with the scientific consensus, and provided their own projections of the economic cost of stricter controls.[124][125][126][127] Likewise, environmental organizations and a number of public figures have emphasized the potential risks of climate change and promote the implementation of GHG emissions reduction measures. Some fossil fuel companies have scaled back their efforts in recent years,[128] or called for policies to reduce global warming.[129]

Another point of contention is the degree to which emerging economies such as India and China should be expected to constrain their emissions. According to recent reports, China’s gross national CO2 emissions may now exceed those of the U.S. China has contended that it has less of an obligation to reduce emissions since its per capita emissions are roughly one-fifth that of the United States. India, also exempt from Kyoto restrictions and another of the biggest sources of industrial emissions, has made similar assertions. The U.S. contends that if it must bear the cost of reducing emissions, then China should do the same.

The greenhouse effect is a process that occurs when energy from a planet’s host star goes through the planet’s atmosphere and heats the planet’s surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly to space, resulting in a warmer planet. Earth’s natural greenhouse effect makes life as we know it possible and carbon dioxide plays a significant role in providing for the relatively high temperature on Earth. The greenhouse effect is a process by which thermal radiation from a planetary atmosphere warms the planet’s surface beyond the temperature it would have in the absence of its atmosphere.^[1][2][3] Without the greenhouse effect, the Earth’s average surface temperature would be about −18 °C (−0.4 °F)^[4][5] compared to Earth’s actual average surface temperature of approximately 14 °C (57.2 °F).^[6] In addition to the naturally present greenhouse gases, human-caused increases in greenhouse gases trap greater amounts of heat, causing the Earth to become warmer over time.^[7][8]

Anything radiates energy related to its temperature: the Sun—at about 5,500 °C (9,930 °F)—sends most of its energy as visible and near infrared light, while Earth’s average surface temperature—at about 15 °C (59 °F)—emits longer-wavelength infrared, radiant heat.^[8] The atmosphere is transparent to most incoming sunlight, and allows its energy through to heat the surface. Most gases in the atmosphere are transparent to infrared, but the small proportion of the atmosphere that constitutes greenhouse gases absorbs some of the heat emitted by the surface rather than letting it escape into space. These greenhouse gas molecules then emit radiant heat in all directions, passing heat to the surrounding air and warming other greenhouse gas molecules. Radiant heat going downwards further increases the temperature of the surface, which then returns heat to the atmosphere in a positive feedback cycle. Without Earth’s natural greenhouse effect the Earth would be more than 30 °C (54 °F) colder.^[9][8]

A runaway greenhouse effect occurs when greenhouse gases accumulate in the atmosphere through a positive feedback cycle to such an extent that they substantially block thermal radiation (heat) from escaping into space, thus preventing the planet from cooling.^[10] The runaway greenhouse effect occurred with carbon dioxide and water vapor on Venus. It is unlikely that human-caused greenhouse gas emissions alone could trigger a runaway effect on Earth.

The term greenhouse effect comes from a flawed analogy to greenhouses, which have transparent glass that passes sunlight but retains heat by physically restricting air movement; radiative effects are not involved.^[11]

History

The existence of the greenhouse effect, while not named as such, was proposed by Joseph Fourier in 1824.^[12] The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide. She concluded that «An atmosphere of that gas would give to our earth a high temperature…»^[13][14] John Tyndall was the first to measure the infrared absorption and emission of various gases and vapors. From 1859 onwards, he showed that the effect was due to a very small proportion of the atmosphere, with the main gases having no effect, and was largely due to water vapor, though small percentages of hydrocarbons and carbon dioxide had a significant effect.^[15] The effect was more fully quantified by Svante Arrhenius in 1896, who made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric carbon dioxide.^[16] However, the term «greenhouse» was not used to refer to this effect by any of these scientists; the term was first used in this way by Nils Gustaf Ekholm in 1901.^[17][18]

Definition

The greenhouse effect is defined as follows:

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. These substances emit infrared radiation in all directions, but, everything else being equal, the net amount emitted to space is normally less than would have been emitted in the absence of these absorbers because of the decline of temperature with altitude in the troposphere and the consequent weakening of emission. An increase in the concentration of GHGs increases the magnitude of this effect; the difference is sometimes called the enhanced greenhouse effect. The change in a GHG concentration because of anthropogenic emissions contributes to an instantaneous radiative forcing. Earth’s surface temperature and troposphere warm in response to this forcing, gradually restoring the radiative balance at the top of the atmosphere.^{[19]: AVII-28}

Earth receives energy from the Sun in the form of ultraviolet, visible, and near-infrared radiation. About 26% of the incoming solar energy is reflected back to space by the atmosphere and clouds, and 19% is absorbed by the atmosphere and clouds. Most of the remaining energy is absorbed at the surface of Earth. Because the Earth’s surface is colder than the Sun, it radiates at wavelengths that are much longer than the wavelengths that were absorbed. Most of this thermal radiation is absorbed by the atmosphere and warms it. The atmosphere also gains heat by sensible and latent heat fluxes from the surface. The atmosphere radiates energy both upwards and downwards; the part radiated downwards is absorbed by the surface of Earth. This leads to a higher equilibrium temperature than if the atmosphere did not radiate.

An ideal thermally conductive blackbody at the same distance from the Sun as Earth would have a temperature of about 5.3 °C (41.5 °F). However, because Earth reflects about 30%^[20][21] of the incoming sunlight, this idealized planet’s effective temperature (the temperature of a blackbody that would emit the same amount of radiation) would be about −18 °C (0 °F).^[22][23] The surface temperature of this hypothetical planet is 33 °C (59 °F) below Earth’s actual surface temperature of approximately 14 °C (57 °F).^[24] The greenhouse effect is the contribution of greenhouse gases and aerosols to this difference, with imperfect modelling of clouds being the main uncertainty.^{[25]: 7–61}

Details

The idealized greenhouse model is a simplification. In reality, the atmosphere near the Earth’s surface is largely opaque to thermal radiation and most heat loss from the surface is by convection. However radiative energy losses become increasingly important higher in the atmosphere, largely because of the decreasing concentration of water vapor, an important greenhouse gas. Rather than the surface itself, it is more realistic to think of the greenhouse effect as applying to a layer in the mid-troposphere, which is effectively coupled to the surface by a lapse rate.^[26] A simple picture also assumes a steady state, but in the real world, the diurnal cycle, as well as the seasonal cycle and weather disturbances, complicate matters. Solar heating applies only during daytime. At night the atmosphere cools somewhat, but not greatly because the thermal inertia of the climate system resists changes both day and night, as well as for longer periods.^[27] Diurnal temperature changes decrease with height in the atmosphere.

Within the region where radiative effects are important, the description given by the idealized greenhouse model becomes realistic. Earth’s surface, warmed to an «effective temperature» around −18 °C (0 °F), radiates long-wavelength, infrared heat in the range of 4–100 μm.^[28] At these wavelengths, greenhouse gases that were largely transparent to incoming solar radiation are more absorbent.^[28] Each layer of the atmosphere with greenhouse gases absorbs some of the heat being radiated upwards from lower layers. It reradiates in all directions, both upwards and downwards; in equilibrium (by definition) the same amount as it has absorbed. This results in more warmth below. Increasing the concentration of the gases increases the amount of absorption and re-radiation, and thereby further warms the layers and ultimately the surface below.^[23]

Greenhouse gases—including most diatomic gases with two different atoms (such as carbon monoxide, CO) and all gases with three or more atoms—are able to absorb and emit infrared radiation. Though more than 99% of the dry atmosphere is IR transparent (because the main constituents—N
₂, O
₂, and Ar—are not able to directly absorb or emit infrared radiation), intermolecular collisions cause the energy absorbed and emitted by the greenhouse gases to be shared with the other, non-IR-active, gases.

Examples in the atmosphere

Greenhouse gases

A greenhouse gas (GHG) is a gas capable of trapping solar radiation energy within a planet’s atmosphere. Greenhouse gases contribute most of the greenhouse effect in Earth’s energy budget.

Greenhouse gases can be divided into two types, direct and indirect. Gases that can directly absorb solar energy are direct greenhouse gases, e.g., water vapor, carbon dioxide and ozone. The molecules of these gases can directly absorb solar radiation at certain ranges of wavelength. Some gases are indirect greenhouse gases, as they do not absorb solar energy directly or significantly, but have capability of producing other greenhouse gases. For example, methane plays an important role in producing tropospheric ozone and formation of more carbon dioxide.^[29] NO_x^[30] and CO^[31] can also produce tropospheric ozone and carbon dioxide through photochemical processes.

By their percentage contribution to the overall greenhouse effect on Earth, the four major greenhouse gases are:^[33][34]

• Water vapor (H₂O), 36~72% (~75% including clouds);^[35]
• Carbon dioxide (CO₂), 9~26%;
• Methane (CH₄), 4~9%;
• Tropospheric ozone (O₃), 3~7%.

It is not practical to assign a specific percentage to each gas because the absorption and emission bands of the gases overlap (hence the ranges given above). A water molecule only stays in the atmosphere for an average 8 to 10 days, which corresponds with high variability in the contribution from clouds and humidity at any particular time and location.^{[25]: 1–41}

There are other influential gases that contribute to the greenhouse effect, including nitrous oxide (N₂O), perfluorocarbons (PFCs), chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), and sulfur hexafluoride (SF₆).^{[25]: AVII-60} These gases are mostly produced through human activities, thus they have played important parts in climate change.

Concentration change of greenhouse gases from 1750 to 2019^[36] (ppm: parts per million; ppb: parts per billion):

• Carbon dioxide (CO₂), 278.3 to 409.9 ppm, up 47%;
• Methane (CH₄), 729.2 to 1866.3 ppb, up 156%;
• Nitrous oxide (N₂O), 270.1 to 332.1 ppb, up 23%.

The global warming potential (GWP) of a greenhouse gas is calculated by quantifying the lifetime and the efficiency of greenhouse effect of the gas. Typically, nitrous oxide has a lifetime of about 121 years, and over 270 times higher GWP than carbon dioxide for 20-year time span. Sulfur hexafluoride has a lifetime of over 3000 years and 25000 times higher GWP than carbon dioxide.^[36]

Clouds

This section needs expansion. You can help by adding to it. (January 2022)

Clouds play an important part in global radiative balance and thin cirrus clouds have some greenhouse effects. They can absorb and emit infrared radiation and thus affect the radiative properties of the atmosphere.^[37] Clouds include liquid clouds, mixed-phase clouds and ice clouds. Liquid clouds are low clouds and have negative radiative forcing. Mixed-phase clouds are clouds coexisted with both liquid water and solid ice at subfreezing temperatures and their radiative properties (optical depth or optical thickness) are substantially influenced by the liquid content. Ice clouds are high clouds and their radiative forcing depends on the ice crystal number concentration, cloud thickness and ice water content.

The radiative properties of liquid clouds depend strongly on cloud microphysical properties, such as cloud liquid water content and cloud drop size distribution. The liquid clouds with higher liquid water content and smaller water droplets will have a stronger negative radiative forcing. The cloud liquid contents are usually related to the surface and atmospheric circulations. Over the warm ocean, the atmosphere is usually rich with water vapor and thus the liquid clouds contain higher liquid water content. When the moist air flows converge in the clouds and generate strong updrafts, the water content can be much higher. Aerosols will influence the cloud drop size distribution. For example, in the polluted industrial regions with lots of aerosols, the water droplets in liquid clouds are often small.

The mixed phase clouds have negative radiative forcing. The radiative forcing of mix-phase clouds has a larger uncertainty than liquid clouds. One reason is that the microphysics are much more complicated because the coexistence of both liquid and solid water. For example, Wegener–Bergeron–Findeisen process can deplete large amounts of water droplets and enlarge small ice crystals to large ones in a short period of time. Hallett-Mossop process^[38] will shatter the liquid droplets in the collision with large ice crystals and freeze into a lot of small ice splinters. The cloud radiative properties can change dramatically during these processes because small ice crystals can reflect much more sun lights and generate larger negative radiative forcing, compared with large water droplets.

Cirrus clouds can either enhance or reduce the greenhouse effects, depending on the cloud thickness.^[39] Thin cirrus is usually considered to have positive radiative forcing and thick cirrus has negative radiative forcing.^[40] Ice water content and ice size distribution also determines cirrus radiative properties. The larger ice water content is, the more cooling effects cirrus have. When cloud ice water contents are the same, cirrus with more smaller ice crystals have larger cooling effects, compared with cirrus with fewer larger ice crystals. Some scientists suggest doing some cirrus seeding into thin cirrus clouds in order to decrease the size of ice crystals and thus reduce their greenhouse effects, but some other studies doubt its efficiency and think it would be useless to fight with global warming.^[41]

Aerosols

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Atmospheric aerosols are typically defined as suspensions of liquid, solid, or mixed particles with various chemical and physical properties,^[42] which play a really important role in modulating earth energy budget that will further cause climate change. There are two major sources of the atmospheric aerosols, one is natural sources, and the other is anthropogenic sources. For example, desert dust, sea salt, volcanic ash, volatile organic compounds (VOC) from vegetation and smoke from forest fire are some of the important natural sources of aerosols. For the aerosols that are generated from human activities, such as fossil fuel burning, deforestation fires, and burning of agricultural waste, are considered as anthropogenic aerosols. The amount of anthropogenic aerosols has been dramatically increases since preindustrial times, which is considered as a major contribution to the global air pollution. Since these aerosols have different chemical composition and physical properties, they can produce different Radiative forcing effect to warm or cool the global climate.

Impact of atmospheric aerosols on climate can be classified as direct or indirect with respect to radiative forcing of the climate system. Aerosols can directly scatter and absorb solar and infrared radiance in the atmosphere, hence it has a direct radiative forcing to the global climate system. Aerosols can also act as cloud condensation nuclei (CCN) to form clouds, resulting in changing the formation and precipitation efficiency of liquid water, ice and mixed phase clouds, thereby causing an indirect radiative forcing associated with these changes in cloud properties.^[43][44]

Aerosols that mainly scatter solar radiation can reflect solar radiation back to space, which will cause cooling effect to the global climate. All of the atmospheric aerosols have such capability to scatter incoming solar radiation. But only a few types of aerosols can absorb solar radiation, such as Black carbon (BC), organic carbon (OC) and mineral dust, which can induce non negligible warming effect to the Earth atmosphere.^[45] The emission of black carbon is really large in the developing countries, such as China and India, and this increase trend is still expected to continue. Black carbon can be transported over long distances, and mixed with other aerosols along the way.The solar-absorption efficiency has positive correlation with the ratio of black carbon to sulphate, thus people should focus both on the black carbon emissions and the atmospheric ratio of carbon to sulphate.^[46] Particle size and mixing ratio can not only determine the absorption efficiency of BC, but also affect the lifetime of BC. The surface albedo of the surfaces covered by snow or ice could be reduced due to the deposition of these kinds of absorbing aerosol, which will also cause heating effect.^[47] The heating effect from black carbon at high elevations is just important as carbon dioxide in the melting of snowpacks and glaciers.^[48] In addition to these absorbing aerosols, it is found that the stratospheric aerosol can also induce strong local warming effect by increasing long wave radiation to the surface and reducing the outgoing longwave radiation.^[49]

Role in climate change

Strengthening of the greenhouse effect through human activities is known as the enhanced (or anthropogenic) greenhouse effect.^[51] As well as being inferred from measurements by the CERES satellite throughout the 21st century,^{[25]: 7–17} this increase in radiative forcing from human activity has been observed directly,^[52][53] and is attributable mainly to increased atmospheric carbon dioxide levels.^[54] According to the 2014 Assessment Report from the Intergovernmental Panel on Climate Change, «atmospheric concentrations of carbon dioxide, methane and nitrous oxide are unprecedented in at least the last 800,000 years. Their effects, together with those of other anthropogenic drivers, have been detected throughout the climate system and are extremely likely to have been the dominant cause of the observed warming since the mid-20th century'».^[55]

CO₂ is produced by fossil fuel burning and other activities such as cement production and tropical deforestation.^[56] Measurements of CO₂ from the Mauna Loa Observatory show that concentrations have increased from about 313 parts per million (ppm)^[57] in 1960, passing the 400 ppm milestone in 2013.^[58] The current observed amount of CO₂ exceeds the geological record maxima (≈300 ppm) from ice core data.^[59] The effect of combustion-produced carbon dioxide on the global climate, a special case of the greenhouse effect first described in 1896 by Svante Arrhenius, has also been called the Callendar effect.

Over the past 800,000 years,^[60] ice core data shows that carbon dioxide has varied from values as low as 180 ppm to the pre-industrial level of 270 ppm.^[61] Paleoclimatologists consider variations in carbon dioxide concentration to be a fundamental factor influencing climate variations over this time scale.^[62][63]

Real greenhouses

The «greenhouse effect» of the atmosphere is named by analogy to greenhouses which become warmer in sunlight. However, a greenhouse is not primarily warmed by the «greenhouse effect».^[64]
«Greenhouse effect» is actually a misnomer since heating in the usual greenhouse is due to the reduction of convection,^[65][66] while the «greenhouse effect» works by preventing absorbed heat from leaving the structure through radiative transfer.^[7]

A greenhouse is built of any material that passes sunlight: usually glass or plastic. The sun warms the ground and contents inside just like the outside, and these then warm the air. Outside, the warm air near the surface rises and mixes with cooler air aloft, keeping the temperature lower than inside, where the air continues to heat up because it is confined within the greenhouse. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature will drop considerably. It was demonstrated experimentally (R. W. Wood, 1909) that a (not heated) «greenhouse» with a cover of rock salt (which is transparent to infrared) heats up an enclosure similarly to one with a glass cover.^[67] Thus greenhouses work primarily by preventing convective cooling.^[66]

Heated greenhouses are yet another matter: as they have an internal source of heating, it is desirable to minimize the amount of heat leaking out by radiative cooling. This can be done through the use of adequate glazing.^[68]

It is possible in theory to build a greenhouse that lowers its thermal emissivity during dark hours;^[69] such a greenhouse would trap heat by two different physical mechanisms, combining multiple greenhouse effects, one of which more closely resembles the atmospheric mechanism, rendering the misnomer debate moot.

Anti-greenhouse effect

The anti-greenhouse effect is a mechanism similar and symmetrical to the greenhouse effect: in the greenhouse effect, the atmosphere lets radiation in while not letting thermal radiation out, thus warming the body surface; in the anti-greenhouse effect, the atmosphere keeps radiation out while letting thermal radiation out, which lowers the equilibrium surface temperature. Such an effect has been proposed for Saturn’s moon Titan.^[70]

Runaway greenhouse effect

A runaway greenhouse effect occurs if positive feedbacks lead to the evaporation of all greenhouse gases into the atmosphere.^[10] A runaway greenhouse effect involving carbon dioxide and water vapor has long ago been hypothesized to have occurred on Venus,^[71] this idea is still largely accepted.^[72] The planet Venus experienced a runaway greenhouse effect, resulting in an atmosphere which is 96% carbon dioxide, and a surface atmospheric pressure roughly the same as found 900 m (3,000 ft) underwater on Earth. Venus may have had water oceans, but they would have boiled off as the mean surface temperature rose to the current 735 K (462 °C; 863 °F).^[73][74][75]

A 2012 journal article stated that almost all lines of evidence indicate that is unlikely to be possible to trigger a full runaway greenhouse on Earth, merely by adding greenhouse gases to the atmosphere.^[76] However, the authors cautioned that «our understanding of the dynamics, thermodynamics, radiative transfer and cloud physics of hot and steamy atmospheres is weak», and that we «cannot therefore completely rule out the possibility that human actions might cause a transition, if not to full runaway, then at least to a much warmer climate state than the present one».^[76] A 2013 article concluded that runaway greenhouse «could in theory be triggered by increased greenhouse forcing», but that «anthropogenic emissions are probably insufficient».^[77]

Bodies other than Earth

Apart from the Earth, there are other planets in the solar system that also have greenhouse effect. The greenhouse effect on Venus is particularly large, which brings its surface temperature to as high as 462 °C (864 °F). This is due to several reasons:

1. It is nearer to the Sun than Earth by about 30%.
2. Its very dense atmosphere consists mainly of carbon dioxide, approximately 97%.^[78]

«Venus experienced a runaway greenhouse effect in the past, and we expect that Earth will in about 2 billion years as solar luminosity increases».^[76]

Titan is a body with both a greenhouse effect and an anti-greenhouse effect. The presence of N₂, CH₄, and H₂ in the atmosphere contribute to a greenhouse effect, increasing the surface temperature by 21K over the expected temperature of the body with no atmosphere. The existence of a high-altitude haze, which absorbs wavelengths of solar radiation but is transparent to infrared, contribute to an anti-greenhouse effect of approximately 9K. The net effect of these two phenomena result is a net warming of 21K — 9K = 12K, so Titan is 12 K warmer than it would be if there were no atmosphere.^[79][80]

See also

• Top contributors to greenhouse gas emissions
• Lapse rate
• Climate change feedback
• Climate tipping point
• Radiative forcing
• Global dimming
• Intergovernmental Panel on Climate Change
• United Nations Framework Convention on Climate Change

References

Further reading

• Henderson-Sellers, Ann; McGuffie, Kendal (2005). A climate modelling primer (3rd ed.). Wiley. ISBN 978-0-470-85750-2.

External links

• Rutgers University: Earth Radiation Budget Archived 1 September 2006 at the Wayback Machine