Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th 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.Global surface temperature is defined in the IPCC Fourth Assessment Report as the average of near-surface air temperature over land and sea surface temperature. The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the temperature increase since the mid-twentieth century is "very likely" due to the increase in anthropogenic greenhouse gas concentrations. 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 from 1950 onward. These basic conclusions have been endorsed by at least 30 scientific societies and academies of science,The 2001 joint statement was signed by the scientific academies of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, and the UK. The 2005 statement added Japan, Russia, and the U.S. The 2007 statement added Mexico and South Africa. Professional societies include American Meteorological Society, American Geophysical Union, American Institute of Physics, American Astronomical Society, American Association for the Advancement of Science, Stratigraphy Commission of the Geological Society of London, Geological Society of America, American Chemical Society, and Engineers Australia. including all of the national academies of science of the major industrialized countries. While individual scientists have voiced disagreement with these findings, the overwhelming majority of scientists working on climate change agree with the IPCC's main conclusions. Climate model projections indicate that global surface temperature will likely rise a further during the twenty-first century. The uncertainty in this estimate arises from use of differing estimates of future greenhouse gas emissions and from use of models with differing climate sensitivity. Another uncertainty is how warming and related changes will vary from region to region around the globe. Although most studies focus on the period up to 2100, warming is expected to continue for more than a thousand years even if greenhouse gas levels are stabilized. This results from the large heat capacity of the oceans. Increasing global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, likely including an expanse of the subtropical desert regions. Other likely effects include increases in the intensity of extreme weather events, changes in agricultural yields, modifications of trade routes, glacier retreat, species extinctions and increases in the ranges of disease vectors. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions. Political and public debate continues regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to its expected consequences. Greenhouse effect
The causes of the recent warming are an active field of research. The scientific consensus
is that the increase in atmospheric greenhouse gases due to human activity caused most of the warming observed since the start of the industrial era, and the observed warming cannot be satisfactorily explained by natural causes alone. 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. 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. The question is instead how the strength of the greenhouse effect changes when human activity increases the atmospheric concentrations of particular greenhouse gases. thumb|280px|right|Recent increases in atmospheric carbon dioxide (CO2). The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the Northern Hemisphere's late spring, and declines during the Northern Hemisphere growing season as plants remove some CO2 from the atmosphere. Naturally occurring greenhouse gases have a mean warming effect of about 33 °C (59 °F), without which Earth would be uninhabitable.Note that the Greenhouse Effect produces a temperature increase of about
33 °C (59 °F) with respect to black body predictions and not a surface temperature of 33 °C (91 °F) which is higher. The average surface temperature is about 14 °C (57 °F). Also note that both the
Celsius and Fahrenheit temperatures are expressed to 2 significant figures even though the conversion formula produces 3. On Earth 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. Human activity since the industrial revolution has increased the atmospheric concentration of various greenhouse gases, leading to increased radiative forcing from CO2, methane, tropospheric ozone, CFCs and nitrous oxide. The atmospheric concentrations of CO2 and methane have increased by 36% and 148% respectively since the beginning of the industrial revolution in the mid-1700s. 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.Neftel, A., E. Moor, H. Oeschger, and B. Stauffer. (1985). "Evidence from polar ice cores for the increase in atmospheric CO2 in the past two centuries". Nature 315:45-47. From less direct geological evidence it is believed that CO2 values this high were last seen approximately 20 million years ago. 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. CO2 concentrations are expected to continue to rise due to ongoing burning of fossil fuels and land-use change. The 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. Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100 if coal, tar sands or methane clathrates are extensively exploited. Solar variation
thumb|280px|right|Solar variation over the last thirty years. Some other hypotheses departing from the consensus view have been suggested to explain most of the temperature increase. One such hypothesis proposes that warming may be the result of variations in solar activity. A paper by Peter Stott and colleagues suggests 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. 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. A different hypothesis is that variations in solar output, possibly amplified by cloud seeding via galactic cosmic rays, may have contributed to recent warming. It suggests magnetic activity of the sun is a crucial factor which deflects cosmic rays that may influence the generation of cloud condensation nuclei and thereby affect the climate. One predicted effect of an increase in solar activity would be a warming of most of the stratosphere, whereas an increase in greenhouse gases should produce cooling there. The observed trend since at least 1960 has been a cooling of the lower stratosphere. Reduction of stratospheric ozone also has a cooling influence, but substantial ozone depletion did not occur until the late 1970s.Ozone History Solar variation combined with changes in volcanic activity probably did have a warming effect from pre-industrial times to 1950, but a cooling effect since. 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. One paper by Mike Lockwood and Claus Fröhlich found no relation between global warming and solar radiation since 1985, whether through variations in solar output or variations in cosmic rays. Henrik Svensmark and Eigil Friis-Christensen, the main proponents of cloud seeding by galactic cosmic rays, disputed this criticism of their hypothesis.Reply to Lockwood and Fröhlich - The persistent role of the Sun in climate forcing — Spacecenter 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.preprint of this paper can be found here
Forcing and feedback
thumb|280px|right| Components of the current radiative forcing as estimated by the IPCC Fourth Assessment Report. None of the effects of forcing are instantaneous. The thermal inertia of the Earth's oceans and slow responses of other indirect effects mean that the Earth's current climate is not in equilibrium with the forcing imposed. Climate commitment studies indicate that even if greenhouse gases were stabilized at 2000 levels, a further warming of about would still occur. Climate variability
The Earth's climate changes in response to external forcing, including greenhouse gases, variations in its orbit around the Sun (orbital forcing), changes in solar luminosity, and volcanic eruptions;Robock, Alan, and Clive Oppenheimer, Eds., 2003: Volcanism and the Earth’s Atmosphere, Geophysical Monograph 139, American Geophysical Union, Washington, DC, 360 pp. all examples of the earth's own variation in temperatures, for which the UNFCCC uses the term climate variability. Feedback
When a warming trend results in effects that induce further warming, the process is referred to as a positive feedback; when the effects induce cooling, the process is referred to as a negative feedback. The primary positive feedback involves water vapor. The primary 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."Stefan-Boltzmann Law", Britannica Online This provides a powerful negative feedback which stabilizes the climate system over time. One of the most pronounced positive feedback effects relates to the evaporation of water. If the atmosphere is warmed, the saturation vapour pressure increases, and the quantity 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. This feedback effect can only be reversed slowly as CO2 has a long average atmospheric lifetime. 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. These details are difficult to represent in climate models, in part because clouds are much smaller than the spacing between points on the computational grids of climate models. 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.Panel on Climate Change Feedbacks, Climate Research Committee, National Research Council, 2004: Understanding Climate Change Feedbacks. Another important feedback process is 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. 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 release of CO2 and CH4. Methane discharge from permafrost is presently under intensive study. Warmer deep ocean temperatures, likewise, could release the greenhouse gas methane from the 'frozen' state of the vast deep ocean deposits of methane clathrate/methane hydrate, according to the Clathrate Gun Hypothesis,
Ocean ecosystems' ability to sequester carbon are expected to decline as it warms. This is because the resulting low nutrient levels of the mesopelagic zone (about 200 to 1000 m depth) limits the growth of diatoms in favor of smaller phytoplankton that are poorer biological pumps of carbon. Temperature changes
Recent
thumb|280px|right|Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference. Global temperatures have increased by 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.Working group I, section 3.2.2.2 of the 2007 IPPC page 243 Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade). 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. Sea temperatures increase more slowly than those on land both because of the larger effective heat capacity of the oceans and because the ocean can lose heat by evaporation more readily than the land. 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. 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. Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998. Temperatures in 1998 were unusually warm because the strongest El Niño-Southern Oscillation in the past century occurred during that year. 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, 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 largely offset one another, so that warming in recent decades has been driven mainly by non-CO2 greenhouse gases. 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. Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed. Pre-human climate variations
thumb|250px|right|Curves of reconstructed temperature at two locations in Antarctica and a global record of variations in glacial ice volume. Today's date is on the left side of the graph. 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. 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. 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
Scientists have studied global warming with computer models of the climate. These models are based on physical principles of fluid dynamics, radiative transfer, and other processes, with simplifications being necessary because of limitations in computer power and the complexity 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. These models project a warmer climate due to increasing levels of greenhouse gases. However, even when the same assumptions of future greenhouse gas levels are used, there still remains a considerable range of climate sensitivity. Including uncertainties in future greenhouse gas concentrations and climate modeling, the IPCC anticipates a warming of by the end of the 21st century, relative to 1980–1999. Models have also been 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. 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. These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made greenhouse gas emissions. Global climate model projections of future climate are forced by imposed greenhouse gas emission scenarios, most often from the IPCC Special Report on Emissions Scenarios (SRES). Less commonly, models may 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. A recent paper has suggested that "global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming", based on the inclusion of ocean temperature observations. The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem. A minor issue in climate modeling is the perceived mismatch between actual conditions and those projected by the models. A 2007 study by David Douglass and colleagues compared the composite output of 22 leading global climate models with actual climate data and found that the models did not accurately project observed changes to the temperature profile in the tropical troposphere. The authors note that their conclusions contrast strongly with those of recent publications based on essentially the same data. A 2008 paper published by a 17-member team led by Ben Santer of Lawrence Livermore National Laboratory noted serious mathematical flaws in the Douglass study, and found instead that deviations between the models and observations were statistically insignificant. Attributed and expected effects
Environmental
right|thumb|280px|Sparse records indicate that glaciers have been retreating since the early 1800s. In the 1950s measurements began that allow the monitoring of glacial mass balance, reported to the WGMS and the NSIDC. 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. Other effects may include changes in agricultural yields, addition of new trade routes, reduced summer streamflows, species extinctions, 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. 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. 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. 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. 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. Additional anticipated effects include sea level rise of in 2090-2100 relative to 1980-1999, repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increasingly intense (but less frequent) hurricanes and extreme weather events, lowering of ocean pH, and the spread of diseases such as malaria and dengue fever. 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. However, few mechanistic studies have documented extinctions due to recent climate change and one study suggests that projected rates of extinction are uncertain. Economic
thumb|right|280px|The projected temperature increase for a range of stabilization scenarios (the colored bands). The black line in middle of the shaded area indicates 'best estimates'; the red and the blue lines the likely limits. From the work of IPCC AR4. 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). 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. 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.Tol and Yohe (2006) "A Review of the Stern Review" World Economics 7(4): 233-50. See also other critiques in World Economics 7(4). Others have supported the general attempt to quantify economic risk, even if not the specific numbers. Preliminary studies suggest that costs and benefits of mitigating global warming are broadly comparable in magnitude. According to United Nations Environment Programme (UNEP), economic sectors likely to face difficulties related to climate change include banks, agriculture, transport and others. Developing countries dependent upon agriculture will be particularly harmed by global warming. Adaptation and mitigation
The broad agreement among climate scientists that global temperatures will continue to increase has led some nations, states, corporations and individuals to implement actions to try to curtail global warming or adjust to it. 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. 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. The President elect of the United States Barack Obama has announced he will introduce an economy wide cap and trade scheme. The world's primary international agreement on combating global warming is the Kyoto Protocol, an amendment to the UNFCCC negotiated in 1997. The Protocol now covers more than 160 countries globally and over 55 percent of global greenhouse gas emissions. Only the United States and Kazakhstan have not ratified the treaty, with the United States historically being the world's largest emitter of greenhouse gas. This treaty expires in 2012, and international talks began in May 2007 on a future treaty to succeed the current one.Climate talks face international hurdles, by Arthur Max, Associated press, 5/14/07. China and India, though exempt from its provisions as developing countries, have ratified the Kyoto Protocol. China may have passed the U.S. in total annual greenhouse gas emissions according to some recent studies. Chinese Premier Wen Jiabao has called on the nation to redouble its efforts to tackle pollution and global warming. U.S. President George W. Bush contends that the Kyoto Protocol is an unfair and ineffective means of addressing global climate change concerns, claiming it that it "exempts 80 percent of the world, including major population centers such as China and India, from compliance, and would cause serious harm to the U.S. economy." Bush has instead promoted improved energy technology as a means to combat climate change,State of the Union Address, retrieved 2008-01-28. "The United States is committed to strengthening our energy security and confronting global climate change. And the best way to meet these goals is for America to continue leading the way toward the development of cleaner and more energy-efficient technology." while various state and city governments within the United States have begun their own initiatives to indicate support and compliance with the Kyoto Protocol on a local basis, such as the Regional Greenhouse Gas Initiative. Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades. Warming of the climate system is unequivocal, and most scientists are more than 90% certain most of it is caused by increasing concentrations of greenhouse gases produced by human activities such as deforestation and burning fossil fuels."Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level." IPCC, Synthesis Report, Section 1.1: Observations of climate change, in ."Three different approaches are used to describe uncertainties each with a distinct form of language. * * * Where uncertainty in specific outcomes is assessed using expert judgment and statistical analysis of a body of evidence (e.g. observations or model results), then the following likelihood ranges are used to express the assessed probability of occurrence: virtually certain >99%; extremely likely >95%; very likely >90%......" IPCC, Synthesis Report, Treatment of Uncertainty, in .IPCC, Synthesis Report, Section 2.4: Attribution of climate change, in . These findings are recognized by the national science academies of all the major industrialized countries. Climate model projections are summarized in the 2007 Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change (IPCC). They indicate that during the 21st century the global surface temperature is likely to rise a further for their lowest emissions scenario and for their highest.Meehl et al., Chap. 10: Global Climate Projections, Sec. 10.ES: Mean Temperature, in . The ranges of these estimates arise from the use of models with differing sensitivity to greenhouse gas concentrations.Meehl et al., Chap. 10: Global Climate Projections, Section 10.5: Quantifying the Range of Climate Change, in . An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, and a probable expansion of subtropical deserts. Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent occurrence of extreme weather events including heatwaves, droughts and heavy rainfall events, species extinctions due to shifting temperature regimes, and changes in crop yields. Warming and related changes will vary from region to region around the globe, with projections being more robust in some areas than others.Solomon et al., Technical Summary,
Section TS.5.3: Regional-Scale Projections, in . In a world, the limits for human adaptation are likely to be exceeded in many parts of the world, while the limits for adaptation for natural systems would largely be exceeded throughout the world. Hence, the ecosystem services upon which human livelihoods depend would not be preserved. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC),. Most countries in the world are Parties to the United Nations Framework Convention on Climate Change (UNFCCC), which has adopted the target. There are currently (as of November 25, 2011) 195 Parties (194 states and 1 regional economic integration organization (the European Union)) to the UNFCCC. whose ultimate objective is to prevent "dangerous" anthropogenic (i.e., human-induced) climate change., excerpt from the founding international treaty which entered into force on 21 March 1994. Parties to the UNFCCC have adopted a range of policies designed to reduce greenhouse gas emissionsGupta, S. et al. 13.2 Climate change and other related policies, in . and to assist in adaptation to global warming.Adger, W.N., et al., Chapter 17: Assessment of adaptation practices, options, constraints and capacity, Executive summary, in . 6. Generating the funding needed for mitigation and adaptation (PDF), in Parties to the UNFCCC have agreed that deep cuts in emissions are required, "(...) deep cuts in global greenhouse gas emissions are required according to science, and as documented in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, with a view to reducing global greenhouse gas emissions so as to hold the increase in global average temperature below above preindustrial levels" and that future global warming should be limited to below relative to the pre-industrial level. Analyses by the United Nations Environment Programme (published in 2011) UNEP Stock Number: DEW/1470/NA and International Energy Agency (2011) suggest that current efforts to reduce emissions may be inadequately stringent to meet the UNFCCC's target. Observed temperature changes
thumb|Two millennia of mean surface temperatures according to different reconstructions from climate proxies, each smoothed on a decadal scale, with the instrumental temperature record overlaid in black. Evidence for warming of the climate system includes observed increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.IPCC, Summary for Policymakers, Chapter 1: Observed changes in climate and their effects, in . The Earth's average surface temperature, expressed as a linear trend, rose by over the period 1906–2005. The rate of warming over the last half of that period was almost double that for the period as a whole ( per decade, versus per decade). The urban heat island effect is very small, estimated to account for less than of warming per decade since 1900.Trenberth et al., Ch. 3, Observations: Atmospheric Surface and Climate Change, Section 3.2.2.2: Urban Heat Islands and Land Use Effects, p. 244, in . Temperatures in the lower troposphere have increased between 0.13 and (0.22 and ) per decade since 1979, according to satellite temperature measurements. Climate proxies show the temperature to have been relatively stable over the one or two thousand years before 1850, with regionally varying fluctuations such as the Medieval Warm Period and the Little Ice Age.Jansen et al., Ch. 6, Palaeoclimate, Section 6.6.1.1: What Do Reconstructions Based on Palaeoclimatic Proxies Show?, pp. 466–478, in . Recent estimates by NASA's Goddard Institute for Space Studies (GISS) and the National Climatic Data Center show that 2005 and 2010 tied for the planet's warmest year since reliable, widespread instrumental measurements became available in the late 19th century, exceeding 1998 by a few hundredths of a degree. Current estimates by the Climatic Research Unit (CRU) show 2005 as the second warmest year, behind 1998 with 2003 and 2010 tied for third warmest year, however, “the error estimate for individual years ... is at least ten times larger than the differences between these three years.” The World Meteorological Organization (WMO) statement on the status of the global climate in 2010 explains that, “The 2010 nominal value of ranks just ahead of those of 2005 () and 1998 (), although the differences between the three years are not statistically significant...”
Temperatures in 1998 were unusually warm because the strongest El Niño in the past century occurred during that year. Global temperature is subject to short-term fluctuations that overlay long term trends and can temporarily mask them. The relative stability in temperature from 2002 to 2009 is consistent with such an episode. Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures ( per decade against per decade).Trenberth et al., Chap 3, Observations: Atmospheric Surface and Climate Change, Executive Summary, p. 237, in . Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. The Northern Hemisphere warms faster than the Southern Hemisphere because it has more land and because it has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo feedback. Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres.Ehhalt et al., Chapter 4: Atmospheric Chemistry and Greenhouse Gases, Section 4.2.3.1: Carbon monoxide (CO) and hydrogen (H2), p. 256, in . 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 () would still occur. Initial causes of temperature changes (external forcings)
External forcing refers to processes external to the climate system (though not necessarily external to Earth) that influence climate. Climate responds to several types of external forcing, such as radiative forcing due to changes in atmospheric composition (mainly greenhouse gas concentrations), changes in solar luminosity, volcanic eruptions, and variations in Earth's orbit around the Sun.* Attribution of recent climate change focuses on the first three types of forcing. Orbital cycles vary slowly over tens of thousands of years and at present are in an overall cooling trend which would be expected to lead towards an ice age, but the 20th century instrumental temperature record shows a sudden rise in global temperatures. Greenhouse gases
The greenhouse effect is the process by which absorption and emission of infrared radiation by gases in the atmosphere warm a planet's lower atmosphere and surface. It was proposed by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896. Naturally occurring amounts of greenhouse gases have a mean warming effect of about . The major greenhouse gases are water vapor, which causes about 36–70% of the greenhouse effect; carbon dioxide (CO2), which causes 9–26%; methane (CH4), which causes 4–9%; and ozone (O3), which causes 3–7%. Clouds also affect the radiation balance through cloud forcings similar to greenhouse gases. 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 1750. These levels are much higher than at any time during the last 800,000 years, the period for which reliable data has been extracted from ice cores. Less direct geological evidence indicates that CO2 values higher than this were last seen about 20 million years ago. Fossil fuel burning has produced about three-quarters of the increase in CO2 from human activity over the past 20 years. The rest of this increase is caused mostly by changes in land-use, particularly deforestation.IPCC, Summary for Policymakers, Concentrations of atmospheric greenhouse gases ..., p. 7, in . Over the last three decades of the 20th century, gross domestic product per capita and population growth were the main drivers of increases in greenhouse gas emissions.Le Treut et al., Chap. 1, Historical Overview of Climate Change Science, Section 1.3.1.2: Intensities, in . CO2 emissions are continuing to rise due to the burning of fossil fuels and land-use change. Emissions can be attributed to different regions. The two figures opposite show annual greenhouse gas emissions for the year 2005, including land-use change. Attribution of emissions due to land-use change is a controversial issue.Banuri et al., Chapter 3: Equity and Social Considerations, Section 3.3.3: Patterns of greenhouse gas emissions, and Box 3.1, pp. 92–93 in . Emissions scenarios, estimates of changes in future emission levels of greenhouse gases, have been projected that depend upon uncertain economic, sociological, technological, and natural developments.Fisher et al., Chapter 3: Issues related to mitigation in the long-term context, Section 3.1: Emissions scenarios: Issues related to mitigation in the long term context??, in . In most scenarios, emissions continue to rise over the century, while in a few, emissions are reduced. Morita, Chapter 2: Greenhouse Gas Emission Mitigation Scenarios and Implications, Section 2.5.1.4: Emissions and Other Results of the SRES Scenarios, in .Rogner et al., Introduction, Figure 1.7, in . Fossil fuel reserves are abundant, and will not limit carbon emissions in the 21st century.IPCC, Summary for Policymakers, Introduction, paragraph 6, in . Emission scenarios, combined with modelling of the carbon cycle, have been used to produce estimates of how atmospheric concentrations of greenhouse gases might change in the future. Using the six IPCC SRES "marker" scenarios, models suggest that by the year 2100, the atmospheric concentration of CO2 could range between 541 and 970 ppm. Prentence et al., Chapter 3: The Carbon Cycle and Atmospheric Carbon DioxideExecutive Summary, in . This is an increase of 90–250% above the concentration in the year 1750. The popular media and the public often confuse global warming with ozone depletion, i.e., the destruction of stratospheric ozone by chlorofluorocarbons.Newell, P.J., 2000: Climate for change: non-state actors and the global politics of greenhouse. Cambridge University Press, ISBN 0521632501. Although there are a few areas of linkage, the relationship between the two is not strong. Reduced stratospheric ozone has had a slight cooling influence on surface temperatures, while increased tropospheric ozone has had a somewhat larger warming effect. Particulates and soot
left|thumb|Ship tracks over the Atlantic Ocean on the east coast of the United States. The climatic impacts from particulate forcing could have a large effect on climate through the indirect effect. Global dimming, a gradual reduction in the amount of global direct irradiance at the Earth's surface, has partially counteracted global warming from 1960 to the present. Mitchell et al., Chapter 12: Detection of Climate Change and Attribution of Causes
Detection of Climate Change and Attribution of Causes: Space-time studies, in . The main cause of this dimming is particulates produced by volcanoes and human made pollutants, which exerts a cooling effect by increasing the reflection of incoming sunlight. The effects of the products of fossil fuel combustion—CO2 and aerosols—have largely offset one another in recent decades, so that net warming has been due to the increase in non-CO2 greenhouse gases such as methane. Radiative forcing due to particulates is temporally limited due to wet deposition which causes them to have an atmospheric lifetime of one week. Carbon dioxide has a lifetime of a century or more, and as such, changes in particulate concentrations will only delay climate changes due to carbon dioxide. In addition to their direct effect by scattering and absorbing solar radiation, particulates have indirect effects on the radiation budget. Sulfates act as cloud condensation nuclei and thus lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets, known as the Twomey effect. This effect also causes droplets to be of more uniform size, which reduces growth of raindrops and makes the cloud more reflective to incoming sunlight, known as the Albrecht effect. Indirect effects are most noticeable in marine stratiform clouds, and have very little radiative effect on convective clouds. Indirect effects of particulates represent the largest uncertainty in radiative forcing.IPCC, Summary for Policymakers, in . Soot may cool or warm the surface, depending on whether it is airborne or deposited. Atmospheric soot directly absorb solar radiation, which heats the atmosphere and cools the surface. In isolated areas with high soot production, such as rural India, as much as 50% of surface warming due to greenhouse gases may be masked by atmospheric brown clouds. When deposited, especially on glaciers or on ice in arctic regions, the lower surface albedo can also directly heat the surface. The influences of particulates, including black carbon, are most pronounced in the tropics and sub-tropics, particularly in Asia, while the effects of greenhouse gases are dominant in the extratropics and southern hemisphere. thumb|Satellite observations of Total Solar Irradiance from 1979–2006. Solar variation
Variations in solar output have been the cause of past climate changes. The effect of changes in solar forcing in recent decades is uncertain, but small, with some studies showing a slight cooling effect, while others studies suggest a slight warming effect.*Duffy, Santer and Wigley, "Solar variability does not explain late-20th-century warming" Physics Today, January, 2009, pp 48–49. The authors respond to recent assertions by Nicola Scafetta and Bruce West that solar forcing "might account" for up to about half of 20th-century warming. Greenhouse gases and solar forcing affect temperatures in different ways. While both increased solar activity and increased greenhouse gases are expected to warm the troposphere, an increase in solar activity should warm the stratosphere while an increase in greenhouse gases should cool the stratosphere.* Radiosonde (weather balloon) data show the stratosphere has cooled over the period since observations began (1958), though there is greater uncertainty in the early radiosonde record. Satellite observations, which have been available since 1979, also show cooling. A related hypothesis, proposed by Henrik Svensmark, is that magnetic activity of the sun deflects cosmic rays that may influence the generation of cloud condensation nuclei and thereby affect the climate. Other research has found no relation between warming in recent decades and cosmic rays. The influence of cosmic rays on cloud cover is about a factor of 100 lower than needed to explain the observed changes in clouds or to be a significant contributor to present-day climate change. Studies in 2011 have indicated that solar activity may be slowing, and that the next solar cycle could be delayed. To what extent is not yet clear; Solar Cycle 25 is due to start in 2020, but may be delayed to 2022 or even longer. It is even possible that Sol could be heading towards another Maunder Minimum. While there is not yet a definitive link between solar sunspot activity and global temperatures, the scientists conducting the solar activity study believe that global greenhouse gas emissions would prevent any possible cold snap.Jaggard, Victoria. "Sun Headed Into Hibernation, Solar Studies Predict." National Geographic News, 14 June 2011. Feedback
Feedback is a process in which changing one quantity changes a second quantity, and the change in the second quantity in turn changes the first. Positive feedback increases the change in the first quantity while negative feedback reduces it. Feedback is important in the study of global warming because it may amplify or diminish the effect of a particular process. The main positive feedback in the climate system is the water vapor feedback. The main negative feedback is radiative cooling through the Stefan–Boltzmann law, which increases as the fourth power of temperature. Positive and negative feedbacks are not imposed as assumptions in the models, but are instead emergent properties that result from the interactions of basic dynamical and thermodynamic processes. A wide range of potential feedback processes exist, such as Arctic methane release and ice-albedo feedback. Consequentially, potential tipping points may exist, which may have the potential to cause abrupt climate change. For example, the "emission scenarios" used by IPCC in its 2007 report primarily examined greenhouse gas emissions from human sources. In 2011, a joint study by the US National Snow and Ice Data Center and National Oceanic and Atmospheric Administration calculated the additional greenhouse gas emissions that would emanate from melted and decomposing permafrost, even if policymakers attempt to reduce human emissions from the currently-unfolding A1FI scenario to the A1B scenario. The team found that even at the much lower level of human emissions, permafrost thawing and decomposition would still result in C of permafrost carbon being added to the atmosphere on top of the human sources. Importantly, the team made three extremely conservative assumptions: (1) that policymakers will embrace the A1B scenario instead of the currently-unfolding A1FI scenario, (2) that all of the carbon would be released as carbon dioxide instead of methane, which is more likely and over a 20 year lifetime has 72x the greenhouse warming power of CO2, and (3) their model did not project additional temperature rise caused by the release of these additional gases. These very conservative permafrost carbon dioxide emissions are equivalent to about 1/2 of all carbon released from fossil fuel burning since the dawn of the Industrial Age, and is enough to raise atmospheric concentrations by an additional , beyond human emissions. Once initiated, permafrost carbon forcing (PCF) is irreversible, is strong compared to other global sources and sinks of atmospheric CO2, and due to thermal inertia will continue for many years even if atmospheric warming stops. A great deal of this permafrost carbon is actually being released as highly flammable methane instead of carbon dioxide. IPCC 2007's temperature projections did not take any of the permafrost carbon emissions into account and therefore underestimate the degree of expected climate change. Other research published in 2011 found that increased emissions of methane could instigate significant feedbacks that amplify the warming attributable to the methane alone. The researchers found that a 2.5-fold increase in methane emissions would cause indirect effects that increase the warming 250% above that of the methane alone. For a 5.2-fold increase, the indirect effects would be 400% of the warming from the methane alone. Climate models
A climate model is a computerized representation of the five components of the climate system: Atmosphere, hydrosphere, cryosphere, land surface, and biosphere.IPCC, Glossary A-D: "Climate Model", in . Such models are based on physical principles including fluid dynamics, thermodynamics and radiative transfer. There can be components which represent air movement, temperature, clouds, and other atmospheric properties; ocean temperature, salt content, and circulation; ice cover on land and sea; the transfer of heat and moisture from soil and vegetation to the atmosphere; chemical and biological processes; and others.Denman et al., Chapter 7: Couplings Between Changes in the Climate System and Biogeochemistry, Sec. ??, in . Although researchers 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. Results from models can also vary due to different greenhouse gas inputs and the model's climate sensitivity. For example, the uncertainty in IPCC's 2007 projections is caused by (1) the use of multiple models with differing sensitivity to greenhouse gas concentrations, (2) the use of differing estimates of humanities' future greenhouse gas emissions, (3) any additional emissions from climate feedbacks that were not included in the models IPCC used to prepare its report, i.e., greenhouse gas releases from permafrost. The models do not assume the climate will warm due to increasing levels of greenhouse gases. Instead the models predict how greenhouse gases will interact with radiative transfer and other physical processes. One of the mathematical results of these complex equations is a prediction whether warming or cooling will occur. Recent research has called special attention to the need to refine models with respect to the effect of cloudsStocker et al., Chapter 7: Physical Climate Processes and Feedbacks, Section 7.2.2: Cloud Processes and Feedbacks, in . and the carbon cycle. 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 1970 is dominated by man-made greenhouse gas emissions.*
The physical realism of models is tested by examining their ability to simulate current or past climates.Randall et al., Chapter 8, Climate Models and Their Evaluation, Sec. ?? in . 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.IPCC, Summary for Policymakers, in . Not all effects of global warming are accurately predicted by the climate models used by the IPCC. Observed Arctic shrinkage has been faster than that predicted. Precipitation increased proportional to atmospheric humidity, and hence significantly faster than current global climate models predict. Expected effects
"Detection" is the process of demonstrating that climate has changed in some defined statistical sense, without providing a reason for that change. Detection does not imply attribution of the detected change to a particular cause. "Attribution" of causes of climate change is the process of establishing the most likely causes for the detected change with some defined level of confidence.IPCC, Glossary A-D: "Detection and attribution", in . See also Hegerl et al., Section 9.1.2: What are Climate Change Detection and Attribution?, in . Detection and attribution may also be applied to observed changes in physical, ecological and social systems.Rosenzweig et al., Chapter 1: Assessment of Observed Changes and Responses in Natural and Managed Systems Section 1.2 Methods of detection and attribution of observed changes, in . thumb|left|Sparse records indicate that glaciers have been retreating since the early 1800s. In the 1950s measurements began that allow the monitoring of glacial mass balance, reported to the World Glacier Monitoring Service (WGMS) and the National Snow and Ice Data Center (NSIDC)
Natural systems
Global warming has been detected in a number of systems. Some of these changes, e.g., based on the instrumental temperature record, have been described in the section on temperature changes. Rising sea levels and observed decreases in snow and ice extent are consistent with warming.IPCC, Synthesis Report Summary for Policymakers, Section 1: Observed changes in climate and their effects, in . Most of the increase in global average temperature since the mid-20th century is, with high probability, attributable to human-induced changes in greenhouse gas concentrations.IPCC, Synthesis Report Summary for Policymakers, Section 2: Causes of change, in . Even with current policies to reduce emissions, global emissions are still expected to continue to grow over the coming decades.IPCC, Synthesis Report Summary for Policymakers, Section 3: Projected climate change and its impacts, in . Over the course of the 21st century, increases in emissions at or above their current rate would very likely induce changes in the climate system larger than those observed in the 20th century. In the IPCC Fourth Assessment Report, across a range of future emission scenarios, model-based estimates of sea level rise for the end of the 21st century (the year 2090–2099, relative to 1980–1999) range from 0.18 to 0.59 m. These estimates, however, were not given a likelihood due to a lack of scientific understanding, nor was an upper bound given for sea level rise. On the timescale of centuries to millennia, the melting of ice sheets could result in even higher sea level rise. Partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic Ice Sheet, could contribute 4–6 metres (13 to 20 ft) or more to sea level rise.IPCC, WG2 Summary for Policymakers, Magnitudes of impact, in . Changes in regional climate are expected to include greater warming over land, with most warming at high northern latitudes, and least warming over the Southern Ocean and parts of the North Atlantic Ocean. Snow cover area and sea ice extent are expected to decrease, with the Arctic expected to be largely ice-free in September by 2037. The frequency of hot extremes, heat waves, and heavy precipitation will very likely increase. Ecological systems
In terrestrial ecosystems, the earlier timing of spring events, and poleward and upward shifts in plant and animal ranges, have been linked with high confidence to recent warming. Future climate change is expected to particularly affect certain ecosystems, including tundra, mangroves, and coral reefs. It is expected that most ecosystems will be affected by higher atmospheric CO2 levels, combined with higher global temperatures.Fischlin, et al., Chapter 4: Ecosystems, their Properties, Goods and Services,
Executive Summary, p. 213, in . Executive summary not present in on-line text; see pdf. Overall, it is expected that climate change will result in the extinction of many species and reduced diversity of ecosystems.Schneider et al., Chapter 19: Assessing Key Vulnerabilities and the Risk from Climate Change, Section 19.3.4: Ecosystems and biodiversity, in . Social systems
Vulnerability of human societies to climate change mainly lies in the effects of extreme weather events rather than gradual climate change.Wilbanks et al., Chapter 7: Industry, Settlement and Society, Executive Summary, in . Impacts of climate change so far include adverse effects on small islands,x Schneider et al., Chapter 19: Assessing Key Vulnerabilities and the Risk from Climate Change, Section 19.3.3: Regional vulnerabilities, in . adverse effects on indigenous populations in high-latitude areas,Schneider et al., Chapter 19: Assessing Key Vulnerabilities and the Risk from Climate Change, Section 19.3.7: Update on ‘Reasons for Concern’, in . and small but discernable effects on human health.x Schneider et al., Chapter 19: Assessing Key Vulnerabilities and the Risk from Climate Change, Table 19.1, in . Over the 21st century, climate change is likely to adversely affect hundreds of millions of people through increased coastal flooding, reductions in water supplies, increased malnutrition and increased health impacts.IPCC, Synthesis Report Summary for Policymakers, Section 5.2: Key vulnerabilities, impacts and risks – long-term perspectives, in . Future warming of around (by 2100, relative to 1990–2000) could result in increased crop yields in mid- and high-latitude areas, but in low-latitude areas, yields could decline, increasing the risk of malnutrition. A similar regional pattern of net benefits and costs could occur for economic (market-sector) effects. Warming above could result in crop yields falling in temperate regions, leading to a reduction in global food production.Schneider et al., Chapter 19: Assessing Key Vulnerabilities and the Risk from Climate Change, Section 19.3.2.1: Agriculture, in . Most economic studies suggest losses of world gross domestic product (GDP) for this magnitude of warming.Yohe, et al., Chapter 20: Perspectives on Climate Change and Sustainability, Figure 20.3, in . Responses to global warming
Mitigation
Reducing the amount of future climate change is called mitigation of climate change. The IPCC defines mitigation as activities that reduce greenhouse gas (GHG) emissions, or enhance the capacity of carbon sinks to absorb GHGs from the atmosphere.IPCC, Glossary J-P: "Mitigation", in . Many countries, both developing and developed, are aiming to use cleaner, less polluting, technologies. Use of these technologies aids mitigation and could result in substantial reductions in CO2 emissions. Policies include targets for emissions reductions, increased use of renewable energy, and increased energy efficiency. Studies indicate substantial potential for future reductions in emissions.IPCC, Synthesis Report Summary for Policymakers, Section 4: Adaptation and mitigation options, in . To limit warming to the lower range in the overall IPCC's "Summary Report for Policymakers"IPCC,
Summary for Policymakers, in . means adopting policies that will limit emissions to one of the significantly different scenarios described in the full report.National Academy calls on nation to “substantially reduce greenhouse gas emissions” starting ASAP | ThinkProgress This will become more and more difficult, since each year of high emissions will require even more drastic measures in later years to stabilize at a desired atmospheric concentration of greenhouse gases, and energy-related carbon-dioxide (CO2) emissions in 2010 were the highest in history, breaking the prior record set in 2008.http://www.iea.org/index_info.asp?id=1959
Since even in the most optimistic scenario, fossil fuels are going to be used for years to come, mitigation may also involve carbon capture and storage, a process that traps CO2 produced by factories and gas or coal power stations and then stores it, usually underground. Adaptation
Other policy responses include adaptation to climate change. Adaptation to climate change may be planned, e.g., by local or national government, or spontaneous, i.e., done privately without government intervention. Smit et al., Chapter 18: Adaptation to Climate Change in the Context of Sustainable Development and Equity, Section 18.2.3: Adaptation Types and Forms, in . The ability to adapt is closely linked to social and economic development. Even societies with high capacities to adapt are still vulnerable to climate change. Planned adaptation is already occurring on a limited basis. The barriers, limits, and costs of future adaptation are not fully understood. Geoengineering
A body of the scientific literature has developed which considers alternative geoengineering techniques for climate change mitigation.Barker et al., Chapter 11: Mitigation from a cross-sectoral perspective Section 11.2.2: Ocean fertilization and other geo-engineering options, in . In the IPCC's Fourth Assessment Report (published in 2007) Working Group III (WG3) assessed some "apparently promising" geoengineering techniques, including ocean fertilization, capturing and sequestering , and techniques for reducing the amount of sunlight absorbed by the Earth's atmospheric system. The IPCC's overall conclusion was that geoengineering options remained "largely speculative and unproven, (...) with the risk of unknown side-effects."IPCC, Summary for Policymakers,C. Mitigation in the short and medium term (until 2030) - paragraph 17, in . In the IPCC's judgement, reliable cost estimates for geoengineering options had not yet been published. As most geoengineering techniques would affect the entire globe, deployment would likely require global public acceptance and an adequate global legal and regulatory framework, as well as significant further scientific research. Views on global warming
There are different views over what the appropriate policy response to climate change should be.Banuri, et al., Chapter 3: Equity and Social Considerations, Section 3.1.2: Concepts of equity,
p. 85 et seq. in . These competing views weigh the benefits of limiting emissions of greenhouse gases against the costs. In general, it seems likely that climate change will impose greater damages and risks in poorer regions.Banuri, et al., Chapter 3: Equity and Social Considerations, Section ??, p. 83, in . Global warming controversy
The global warming controversy refers to a variety of disputes, significantly more pronounced in the popular media than in the scientific literature, regarding the nature, causes, and consequences of global warming. The disputed issues include the causes of increased global average air temperature, especially since the mid-20th century, whether this warming trend is unprecedented or within normal climatic variations, whether humankind has contributed significantly to it, and whether the increase is wholly or partially an artifact of poor measurements. Additional disputes concern estimates of climate sensitivity, predictions of additional warming, and what the consequences of global warming will be. In the scientific literature, there is a strong consensus that global surface temperatures have increased in recent decades and that the trend is caused mainly by human-induced emissions of greenhouse gases. No scientific body of national or international standing disagrees with this view, though a few organisations hold non-committal positions. From 1990-1997 in the United States, conservative think tanks mobilized to undermine the legitimacy of global warming as a social problem. They challenged the scientific evidence; argued that global warming will have benefits; and asserted that proposed solutions would do more harm than good.Aaron M. McCright and Riley E. Dunlap, "Challenging Global Warming as a Social Problem: An Analysis of the Conservative Movement's Counter-Claims," Social Problems, Nov 2000, Vol. 47 Issue 4, pp 499-522 in JSTOR
Politics
thumb|right|Article 2 of the UN Framework Convention refers explicitly to "stabilization of greenhouse gas concentrations."IPCC, Synthesis of Scientific-Technical Information, paragraph 4.1, pdf p. 8, in . In order to stabilize the atmospheric concentration of , emissions worldwide would need to be dramatically reduced from their present level. Most countries are Parties to the United Nations Framework Convention on Climate Change (UNFCCC). The ultimate objective of the Convention is to prevent "dangerous" human interference of the climate system. As is stated in the Convention, this requires that GHG concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can proceed in a sustainable fashion.Rogner et al., Chapter 1: Introduction, Executive summary, in . The Framework Convention was agreed in 1992, but since then, global emissions have risen. During negotiations, the G77 (a lobbying group in the United Nations representing 133 developing nations) pushed for a mandate requiring developed countries to "[take] the lead" in reducing their emissions. This was justified on the basis that: the developed world's emissions had contributed most to the stock of GHGs in the atmosphere; per-capita emissions (i.e., emissions per head of population) were still relatively low in developing countries; and the emissions of developing countries would grow to meet their development needs. This mandate was sustained in the Kyoto Protocol to the Framework Convention, which entered into legal effect in 2005. In ratifying the Kyoto Protocol, most developed countries accepted legally binding commitments to limit their emissions. These first-round commitments expire in 2012. US President George W. Bush rejected the treaty on the basis that "it exempts 80% of the world, including major population centers such as China and India, from compliance, and would cause serious harm to the US economy."
At the 15th UNFCCC Conference of the Parties, held in 2009 at Copenhagen, several UNFCCC Parties produced the Copenhagen Accord. Parties associated with the Accord (140 countries, as of November 2010) This publication is also available in e-book format
aim to limit the future increase in global mean temperature to below . A preliminary assessment published in November 2010 by the United Nations Environment Programme (UNEP) suggests a possible "emissions gap" between the voluntary pledges made in the Accord and the emissions cuts necessary to have a "likely" (greater than 66% probability) chance of meeting the objective. The UNEP assessment takes the objective as being measured against the pre-industrial global mean temperature level. To having a likely chance of meeting the objective, assessed studies generally indicated the need for global emissions to peak before 2020, with substantial declines in emissions thereafter. The 16th Conference of the Parties (COP16) was held at Cancún in 2010. It produced an agreement, not a binding treaty, that the Parties should take urgent action to reduce greenhouse gas emissions to meet a goal of limiting global warming to above pre-industrial temperatures. It also recognized the need to consider strengthening the goal to a global average rise of . Public opinion
thumb|Based on Rasmussen polling of 1,000 adults in the USA conducted 29–30 July 2011. In 2007–2008 Gallup Polls surveyed 127 countries. Over a third of the world's population was unaware of global warming, with people in developing countries less aware than those in developed, and those in Africa the least aware. Of those aware, Latin America leads in belief that temperature changes are a result of human activities while Africa, parts of Asia and the Middle East, and a few countries from the Former Soviet Union lead in the opposite belief. In the Western world, opinions over the concept and the appropriate responses are divided. Nick Pidgeon of Cardiff University said that "results show the different stages of engagement about global warming on each side of the Atlantic", adding, "The debate in Europe is about what action needs to be taken, while many in the U.S. still debate whether climate change is happening." A 2010 poll by the Office of National Statistics found that 75% of UK respondents were at least "fairly convinced" that the world's climate is changing, compared to 87% in a similar survey in 2006. A January 2011 ICM poll in the UK found 83% of respondents viewed climate change as a current or imminent threat, while 14% said it was no threat. Opinion was unchanged from an August 2009 poll asking the same question, though there had been a slight polarisation of opposing views. A survey in October, 2009 by the Pew Research Center for the People & the Press showed decreasing public perception in the United States that global warming was a serious problem. All political persuasions showed reduced concern with lowest concern among Republicans, only 35% of whom considered there to be solid evidence of global warming. The cause of this marked difference in public opinion between the United States and the global public is uncertain but the hypothesis has been advanced that clearer communication by scientists both directly and through the media would be helpful in adequately informing the American public of the scientific consensus and the basis for it. The U.S. Climate Change Science Program is a joint program of over 20 U.S. federal agencies working together to investigate climate change. 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. According to Working Group III, to limit temperature rise to 2 degrees Celsius, "developed countries as a group would need to reduce their emissions to below 1990 levels in 2020 (on the order of –10 percent to 40 percent below 1990 levels for most of the considered regimes) and to still lower levels by 2050 (40 percent (Sic. 80 percent in Box 13.7, p776) to 95 percent below 1990 levels), even if developing countries make substantial reductions."
Geoengineering
The slow pace of action to reduce greenhouse gas emmissions have led some scientists, such as the Ken Caldeira and the Nobel Prize winning Paul Crutzenhttp://www.sciam.com/article.cfm?id=geoengineering-how-to-cool-earth to suggest geoengineering techniques, which can be employed to change the climate deliberately and thus control some of the effects of global warming. These include:
Albedo modification - changing the amount of sunlight that's reflected back into space. Techniques such as space sunshade, creating stratospheric sulfur aerosols and painting roofing and paving materials white all fall into this category. Greenhouse gas removal - techniques such as biomass energy with carbon capture and storagehttp://www.ingentaconnect.com/content/klu/clim/2006/00000074/F0030001/00003484, using lasers to break up CFCs in the atmospherehttp://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=593398 and iron fertilisation of oceans to stimulate phytoplankton growth. Hydrological geoengineering - typically seeking to preserve sea ice or adjust thermohaline circulation by using methods such as diverting rivers to keep warm water away from sea ice, or tethering icebergs to prevent them drifting into warmer waters and melting. Economic and political debate
Increased publicity of the scientific findings surrounding global warming has resulted in political and economic debate. 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. 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.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. Organizations and companies such as the Competitive Enterprise Institute and ExxonMobil have emphasized more conservative climate change scenarios while highlighting the potential economic cost of stricter controls. Likewise, various environmental lobbies and a number of public figures have launched campaigns to emphasize the potential risks of climate change and promote the implementation of stricter controls. Some fossil fuel companies have scaled back their efforts in recent years, or called for policies to reduce global warming. 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.China: US should take lead on climate, by Michael Casey, Associated Press, via newsvine.com 12/7/07. India, also exempt from Kyoto restrictions and another of the biggest sources of industrial emissions, has made similar assertions.Glaciers in Retreat, by Somini Sengupta, 7/17/07, New York Times. The U.S. contends that if it must bear the cost of reducing emissions, then China should do the same. Chinese object to climate draft, BBC, 5/1/07; In Battle for U.S. Carbon Caps, Eyes and Efforts Focus on China,by Steven Mufson, Washington Post, 6/6/07. Related climatic issues
A variety of issues are often raised in relation to global warming. One is ocean acidification. Increased atmospheric CO2 increases the amount of CO2 dissolved in the oceans.CO2 dissolved in the ocean reacts with water to form carbonic acid, resulting in acidification. Ocean surface pH is estimated to have decreased from 8.25 near the beginning of the industrial era to 8.14 by 2004,and is projected to decrease by a further 0.14 to 0.5 units by 2100 as the ocean absorbs more CO2. 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. Global dimming, the gradual reduction in the amount of global direct irradiance at the Earth's surface, may have partially mitigated global warming in the late 20th century. From 1960 to 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 global warming, and that greenhouse gases would have resulted in more warming than observed if not for these dimming agents. Ozone depletion, the steady decline in the total amount of ozone in Earth's stratosphere, is frequently cited in relation to global warming. Although there are areas of linkage, the relationship between the two is not strong. See also
Glossary of climate change
List of climate change topics
Paleoclimatology
Notes and references
Further reading
(online version requires registration)
(online version requires registration)
External links
Scientific
Intergovernmental Panel on Climate Change and UN Climate Panel Report's Key Findings. Nature Reports Climate Change
The UK Met Office Hadley Centre site
NOAA's Global Warming FAQ
Discovery of Global Warming – An extensive introduction to the topic and the history of its discovery, written by Spencer R. Weart
Caution urged on climate 'risks'
Impact of Livestock on Global Warming (UN Report)
Educational
Global Climate Change: NASA's Eyes on the Earth - Climate change overviews, key indicators, multimedia and current news. What Is Global Warming? – Shockwave presentation from National Geographic
The EdGCM (Educational Global Climate Modelling) Project – A free research-quality simulation for students, educators, and scientists alike, with a user-friendly interface that runs on desktop computers
DISCOVER Satellite-based ocean and climate data since 1979 from NASA
The Pew Center on global climate change
Global Warming Art
Video of a talk by Warren Washington titled "The Evolution of Global Warming Science: From Ideas to Scientific Facts"
Best Effort Global Warming Trajectories by Harvey Lam (Princeton University), The Wolfram Demonstrations Project. Other
Science and Technology Sources on the Internet – Extensive commented list of Internet resources
Union of Concerned Scientists Global Warming page
Watch and read 'Tipping Point', Australian science documentary about effects of global warming on rare, common, and endangered wildlife
Gateway to the UN System's Work on Climate Change
Category:Carbon finance
Category:Climate change feedbacks and causes
Category:Economic problems
Category:History of climate
Category:Climate change
Category:Anthropocene
Category:Crises
af:Aardverwarming
ang:Ƿoruldlicu ƿearmung
ar:احترار عالمي
zh-min-nan:Choân-kiû sio-lo̍h-hoà
bs:Globalno zatopljenje
bg:Глобално затопляне
ca:Escalfament global
ceb:Kalibotanong pagpanginit
cs:Globální oteplování
cy:Newid hinsawdd
da:Global opvarmning
de:Globale Erwärmung
et:Globaalne soojenemine
el:Παγκόσμια θέρμανση
es:Calentamiento global
eo:Tutmonda varmiĝo
eu:Berotze globala
fa:گرم شدن زمین
fr:Réchauffement climatique
fur:Riscjaldament globâl
gd:Blàthachadh na cruinne
gl:Quentamento global
zh-classical:全球暖化
ko:지구 온난화
hy:Գլոբալ տաքացում
hi:भूमंडलीय ऊष्मीकरण
hr:Globalno zatopljenje
id:Pemanasan global
is:Heimshlýnun
it:Riscaldamento globale
he:התחממות עולמית
jv:Pamanasan global
ka:გლობალური დათბობა
sw:Kupanda kwa halijoto duniani
la:Calefactio cuncta aeris
lv:Globālā sasilšana
lt:Visuotinis atšilimas
hu:Globális felmelegedés
mk:Глобално затоплување
ml:ആഗോളതാപനം
mr:जागतिक तापमानवाढ
mn:Дэлхийн дулаарал
nl:Opwarming van de Aarde
ja:地球温暖化
no:Global oppvarming
nn:Global oppvarming
oc:Escalfament global
pl:Globalne ocieplenie
pt:Aquecimento global
ro:Încălzirea globală
rm:Stgaudament global
ru:Глобальное потепление
si:පෘථිවිය උණුසුම් වීම
simple:Global warming
sk:Globálne otepľovanie
sl:Globalno segrevanje
sr:Глобално загревање
sh:Globalno zatopljenje
su:Jagat nyongkab
fi:Ilmaston lämpeneminen
sv:Global uppvärmning
tl:Pag-init ng daigdig
ta:புவி சூடாதல்
th:ปรากฏการณ์โลกร้อน
vi:Sự nóng lên của khí hậu toàn cầu
tg:Гармшавии глобалӣ
tr:Küresel ısınma
uk:Глобальне потепління
wuu:全球暖化
yi:גלאבאלע אנווארימונג
zh-yue:全球變暖
bat-smg:Gluobalėnis atšėlėms
zh:全球变暖 public appears to be unaware of the extent of scientific consensus regarding the issue, with 59% believing that scientists disagree "significantly" on global warming. By 2010, with 111 countries surveyed, Gallup determined that there was a substantial decrease in the number of Americans and Europeans who viewed Global Warming as a serious threat. In the United States, a little over half the population (53%) now viewed it as a serious concern for either themselves or their families; a number 10 percentage points below the 2008 poll (63%). Latin America had the biggest rise in concern, with 73% saying global warming was a serious threat to their families. That global poll also found that people are more likely to attribute global warming to human activities than to natural causes, except in the USA where nearly half (47%) of the population attributed global warming to natural causes. On the other hand, in May 2011 a joint poll by Yale and George Mason Universities found that nearly half the people in the USA (47%) attribute global warming to human activities, compared to 36% blaming it on natural causes. Only 5% of the 35% who were "disengaged", "doubtful", or "dismissive" of global warming were aware that 97% of publishing US climate scientists agree global warming is happening and is primarily caused by humans. Researchers at the University of Michigan have found that the public's belief as to the causes of global warming depends on the wording choice used in the polls. In the United States, according to the Public Policy Institute of California's (PPIC) eleventh annual survey on environmental policy issues, 75% said they believe global warming is a very serious or somewhat serious threat to the economy and quality of life in California.IVN. "PPIC survey puts spotlight on environmental issues." 1 August 2011
A July 2011 Rasmussen Reports poll found that 69% of adults in the USA believe it is at least somewhat likely that some scientists have falsified global warming research. A September 2011 Angus Reid Public Opinion poll found that Britons (43%) are less likely than Americans (49%) or Canadians (52%) to say that "global warming is a fact and is mostly caused by emissions from vehicles and industrial facilities." The same poll found that 20% of Americans, 20% of Britons and 14% of Canadians think "global warming is a theory that has not yet been proven."
Other views
Most scientists agree that humans are contributing to observed climate change. This document is also available in PDF format National science academies have called on world leaders for policies to cut global emissions. However, some scientists and non-scientists question aspects of climate-change science. Organizations such as the libertarian Competitive Enterprise Institute, conservative commentators, and some companies such as ExxonMobil have challenged IPCC climate change scenarios, funded scientists who disagree with the scientific consensus, and provided their own projections of the economic cost of stricter controls. In the finance industry, Deutsche Bank has set up an institutional climate change investment division (DBCCA),
which has commissioned and published research
on the issues and debate surrounding global warming. Environmental organizations and public figures have emphasized changes in the current climate and the risks they entail, while promoting adaptation to changes in infrastructural needs and emissions reductions. Some fossil fuel companies have scaled back their efforts in recent years, or called for policies to reduce global warming. Etymology
The term global warming was probably first used in its modern sense on 8 August 1975 in a science paper by Wally Broecker in the journal Science called "Are we on the brink of a pronounced global warming?".Wallace Broecker, "Climatic Change: Are We on the Brink of a Pronounced Global Warming?" Science, vol. 189 (8 August 1975), 460–463. Broecker's choice of words was new and represented a significant recognition that the climate was warming; previously the phrasing used by scientists was "inadvertent climate modification," because while it was recognized humans could change the climate, no one was sure which direction it was going.Erik Conway. "What's in a Name? Global Warming vs. Climate Change", NASA, 5 December 2008 The National Academy of Sciences first used global warming in a 1979 paper called the Charney Report, it said: "if carbon dioxide continues to increase, [we find] no reason to doubt that climate changes will result and no reason to believe that these changes will be negligible."National Academy of Science, Carbon Dioxide and Climate, Washington, D.C., 1979, p. vii. The report made a distinction between referring to surface temperature changes as global warming, while referring to other changes caused by increased CO2 as climate change. Global warming became more widely popular after 1988 when NASA climate scientist James Hansen used the term in a testimony to Congress. He said: "global warming has reached a level such that we can ascribe with a high degree of confidence a cause and effect relationship between the greenhouse effect and the observed warming."U.S. Senate, Committee on Energy and Natural Resources, "Greenhouse Effect and Global Climate Change, part 2" 100th Cong., 1st sess., 23 June 1988, p. 44. His testimony was widely reported and afterward global warming was commonly used by the press and in public discourse. See also
Glossary of climate change
History of climate change science
Index of climate change articles
Notes
Citations
References
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pdf. The "Full Report", consisting of "The IPCC Second Assessment Synthesis of Scientific-Technical Information Relevant to Interpreting Article 2 of the UN Framework Convention on Climate Change" and the Summaries for Policymakers of the three Working Groups. (pb: ) pdf. (pb: )
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Further reading
(online version requires registration)
External links
Research
NASA Goddard Institute for Space Studies – Global change research
NOAA State of the Climate Report – U.S. and global monthly state of the climate reports
Climate Change at the National Academies — repository for reports
Nature Reports Climate Change — free-access web resource
Met Office: Climate change — UK National Weather Service
Global Science and Technology Sources on the Internet — commented list of internet resources
Educational Global Climate Modelling (EdGCM) — research-quality climate change simulator
DISCOVER — satellite-based ocean and climate data since 1979 from NASA
Global Warming Art — collection of figures and images
Educational
What Is Global Warming? — by National Geographic
Global Climate Change Indicators – from NOAA
NOAA Climate Services – from NOAA
Global Warming Frequently Asked Questions — from NOAA
Understanding Climate Change – Frequently Asked Questions — from UCAR
Global Warming: Center for Global Studies at the University of Illinois
Global Climate Change: NASA's Eyes on the Earth — from NASA's JPL and Caltech
OurWorld 2.0 — from the United Nations University
Pew Center on Global Climate Change — business and politics
Best Effort Global Warming Trajectories – Wolfram Demonstrations Project — by Harvey Lam
Koshland Science Museum – Global Warming Facts and Our Future — graphical introduction from National Academy of Sciences
Climate Change: Coral Reefs on the Edge — A video presentation by Prof. Ove Hoegh-Guldberg, University of Auckland
Climate Change Indicators in the United States Report by United States Environmental Protection Agency, 80 pp. Global Warming
Video on the effects of global warming on St. Lawrence Island in the Bering Sea
Related information
Category:Climate change
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af:Aardverwarming
als:Globale Erwärmung
ang:Ƿoruldlicu ƿearmung
ar:احترار عالمي
an:Escalfamiento global
bn:ভূমণ্ডলীয় উষ্ণতা বৃদ্ধি
zh-min-nan:Choân-kiû sio-lo̍h-hoà
be:Глабальнае пацяпленне
be-x-old:Глябальнае пацяпленьне
bs:Globalno zatopljenje
br:Tommadur ar blanedenn
bg:Глобално затопляне
ca:Escalfament global
ceb:Kalibotanong pagpanginit
cs:Globální oteplování
cy:Cynhesu byd eang
da:Global opvarmning
de:Globale Erwärmung
et:Globaalne soojenemine
el:Παγκόσμια θέρμανση
es:Calentamiento global
eo:Tutmonda varmiĝo
eu:Berotze globala
fa:گرمشدن زمین
fr:Réchauffement climatique
fur:Riscjaldament globâl
ga:Téamh domhanda
gd:Blàthachadh na cruinne
gl:Quecemento global
ko:지구 온난화
hy:Գլոբալ տաքացում
hi:भूमंडलीय ऊष्मीकरण
hr:Globalno zatopljenje
io:Globala varmesko
id:Pemanasan global
ia:Calefaction global
is:Heimshlýnun
it:Riscaldamento globale
he:התחממות עולמית
jv:Pamanasan global
kn:ಜಾಗತಿಕ ತಾಪಮಾನ ಏರಿಕೆ
ka:გლობალური დათბობა
sw:Kupanda kwa halijoto duniani
ht:Rechofman atmosferik
la:Calefactio globalis
lv:Globālā sasilšana
lt:Visuotinis atšilimas
hu:Globális felmelegedés
mk:Глобално затоплување
ml:ആഗോളതാപനം
mr:जागतिक तापमानवाढ
arz:دفا كوكبى
ms:Pemanasan global
mn:Дэлхийн дулаарал
my:ကမ္ဘာကြီး ပူနွေးလာမှု
nl:Opwarming van de Aarde
ja:地球温暖化
no:Global oppvarming
nn:Global oppvarming
oc:Escalfament global
pnb:گلوبل وارمنگ
pl:Globalne ocieplenie
pt:Aquecimento global
ro:Încălzirea globală
rm:Stgaudament global
ru:Глобальное потепление
sah:Аан дойду сылыйыыта
sq:Ngrohja globale
si:ගෝලීය උණුසුම් වීම
simple:Global warming
sk:Globálne otepľovanie
sl:Globalno segrevanje
ckb:گەرم بوونی زەوی
sr:Глобално загревање
sh:Globalno zatopljenje
su:Jagat nyongkab
fi:Ilmaston lämpeneminen
sv:Global uppvärmning
tl:Pag-init ng daigdig
ta:புவி சூடாதல்
te:భూగోళం యొక్క వేడిమి
th:ปรากฏการณ์โลกร้อน
tg:Гармшавии глобалӣ
tr:Küresel ısınma
uk:Глобальне потепління
vi:Ấm lên toàn cầu
fiu-vro:Ilma lämmämbäsminek üle ilma
zh-classical:全球暖化
war:Pagpaso han kalibutan
wuu:全球暖化
yi:גלאבאלע אנווארימונג
zh-yue:全球變暖
bat-smg:Gluobalėnis atšėlėms
zh:全球变暖
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