Climate change
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Instrumental_Temperature_Record.png/280px-Instrumental_Temperature_Record.png)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Global_Warming_Map.jpg/280px-Global_Warming_Map.jpg)
Global warming is the increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation.
The global average air temperature near the Earth's surface rose 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 year period ending in 2005, which is higher than the earlier estimate of 0.6 ± 0.2 °C for the period ending in 2000.[1] The Intergovernmental Panel on Climate Change (IPCC) concludes "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations"[1] via the greenhouse effect. Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward.[2][3] These basic conclusions have been endorsed by at least 30 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. While individual scientists have voiced disagreement with some of the main conclusions of the IPCC, the overwhelming majority of scientists working on climate change are in agreement with them.[4]
Climate model projections summarized by the IPCC indicate that average global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the 21st century.[1] The range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if greenhouse gas levels are stabilized. The delay in reaching equilibrium is a result of the large heat capacity of the oceans.[1]
Increasing global temperature will cause sea level to rise, and is expected to increase the intensity of extreme weather events and to change the amount and pattern of precipitation. Other effects of global warming include changes in agricultural yields, trade routes, glacier retreat, species extinctions and increases in the ranges of disease vectors.
Remaining scientific uncertainties include the amount of warming expected in the future, and how warming and related changes will vary from region to region around the globe. There is ongoing political and public debate worldwide regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to its expected consequences. Most national governments have signed and ratified the Kyoto Protocol, aimed at reducing greenhouse gas emissions.
Terminology
The term "global warming" is a specific example of the broader term climate change, which can also refer to global cooling. In common usage, the term refers to recent warming and implies a human influence.[5] The United Nations Framework Convention on Climate Change (UNFCCC) uses the term "climate change" for human-caused change, and "climate variability" for other changes.[6] The term "anthropogenic global warming" is sometimes used when focusing on human-induced changes.
Causes
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/88/Mauna_Loa_Carbon_Dioxide.png/280px-Mauna_Loa_Carbon_Dioxide.png)
The Earth's climate changes in response to external forcing, including variations in its orbit around the sun (orbital forcing),[7][8][9] volcanic eruptions, and atmospheric greenhouse gas concentrations. The detailed causes of the recent warming remain an active field of research, but the scientific consensus[10][11] identifies elevated levels of greenhouse gases due to human activity as the main influence. This attribution is clearest for the most recent 50 years, for which the most detailed data are available. Some other hypotheses departing from the consensus view have been suggested to explain the observed increase in mean global temperature. One such hypothesis proposes that warming may be the result of variations in solar activity.[12][13][14]
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 0.5 °C (0.9 °F) would still occur.[15]
Greenhouse gases in the atmosphere
The greenhouse effect was discovered by Joseph Fourier in 1824 and was 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 atmosphere and surface.
Existence of the greenhouse effect as such is not disputed. Naturally occurring greenhouse gases have a mean warming effect of about 33 °C (59 °F), without which Earth would be uninhabitable.[16][17] Rather, the issue is how the strength of the greenhouse effect is changed when human activity increases the atmospheric concentrations of some greenhouse gases.
On Earth, the major greenhouse gases are water vapor, which causes about 36–70% of the greenhouse effect (not including clouds); carbon dioxide (CO2), which causes 9–26%; methane (CH4), which causes 4–9%; and ozone, which causes 3–7%.[18][19] Some other naturally occurring gases contribute very small fractions of the greenhouse effect; one of these, nitrous oxide (N2O), is increasing in concentration owing to human activity such as agriculture. The atmospheric concentrations of CO2 and CH4 have increased by 31% and 149% respectively above pre-industrial levels since 1750. Molecule for molecule, methane is a more effective greenhouse gas than carbon dioxide, but its concentration is much smaller so that its total radiative forcing is only about a fourth of that from carbon dioxide. 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. From less direct geological evidence it is believed that CO2 values this high were last attained 20 million years ago.[20] Fossil fuel burning has produced about 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.[21]
The present atmospheric concentration of CO2 is about 383 parts per million (ppm) by volume.[22] Future CO2 levels are expected 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, but may be ultimately limited by the availability of fossil fuels. 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.[23] Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal, tar sands or methane clathrates are extensively used.[24]
Feedbacks
The effects of forcing agents on the climate are complicated by various feedback processes.
One of the most pronounced feedback effects relates to the evaporation of water. In the case of warming by the addition of long-lived greenhouse gases such as CO2, the initial warming will cause more water to be evaporated into the atmosphere. Since water vapor itself acts as a greenhouse gas, this causes still more warming; the warming causes more water vapor to be evaporated, and so forth until a new dynamic equilibrium concentration of water vapor is reached with a much larger greenhouse effect than that due to CO2 alone. Although this feedback process involves 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.[25] 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. Nevertheless, cloud feedback is second only to water vapor feedback and is positive in all the models that were used in the IPCC Fourth Assessment Report.[25]
Another important feedback process is ice-albedo feedback.[26] 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.
Positive feedback due to release of CO2 and CH4 from thawing permafrost, such as the frozen peat bogs in Siberia, is an additional mechanism contributing to warming.[27] A massive release of CH4 from methane clathrates could cause rapid warming, according to the clathrate gun hypothesis.
The ocean's ability to sequester carbon is expected to decline as it warms, because the resulting low nutrient levels of the mesopelagic zone limits the growth of diatoms in favor of smaller phytoplankton that are poorer biological pumps of carbon.[28]
Solar variation
![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/0d/Solar-cycle-data.png/280px-Solar-cycle-data.png)
A few papers suggest that the Sun's contribution may have been underestimated. Two researchers at Duke University, Bruce West and Nicola Scafetta, have estimated that the Sun may have contributed about 45–50% of the increase in the average global surface temperature over the period 1900–2000, and about 25–35% between 1980 and 2000.[29] A paper by Peter Stott and other researchers 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.[30] 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.
A different hypothesis is that variations in solar output, possibly amplified by cloud seeding via galactic cosmic rays, may have contributed to recent warming.[31] 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.[32]
One predicted effect of an increase in solar activity would be a warming of the stratosphere; however, the observed effect since at least 1960 has been a cooling of the lower stratosphere, which is one of the predicted results of greenhouse gas warming.[33] Reduction of stratospheric ozone also has a cooling influence, although substantial ozone depletion did not occur until the late 1970s. 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.[1] In 2006, Peter Foukal and other researchers from the United States, Germany, and Switzerland found no net increase of solar brightness over the last thousand years. Solar cycles led to a small increase of 0.07% in brightness over the last 30 years. This effect is far too small to contribute significantly to global warming.[34][35] A 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.[36] Henrik Svensmark and Eigil Friis-Christensen, the main proponents of cloud seeding by galactic cosmic rays, disputed the findings of Lockwood and Fröhlich.[37]
Temperature changes
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/2000_Year_Temperature_Comparison.png/280px-2000_Year_Temperature_Comparison.png)
Recent
Global temperatures on both land and sea have increased by 0.75 °C (1.35 °F) relative to the period 1860–1900, according to the instrumental temperature record. This measured temperature increase is not significantly affected by the urban heat island effect.[38] Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).[39] 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.[40] Since the Northern Hemisphere has more land mass than the Southern Hemisphere it warms faster; also there are extensive areas of seasonal snow cover subject to the snow-albedo feedback. Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the asymmetry of warming as the major gases are essentially well-mixed 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.[41] Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[42][43]
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,[44] 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.[45]
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.[46] Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed.[47]
Pre-human climate variations
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Ice_Age_Temperature.png/280px-Ice_Age_Temperature.png)
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.[48]
A rapid buildup of greenhouse gases caused 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.[49][50]
Sudden releases of methane from clathrate compounds (the clathrate gun hypothesis) have been hypothesized as a cause for 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
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Global_Warming_Predictions.png/280px-Global_Warming_Predictions.png)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/ad/Global_Warming_Predictions_Map.jpg/280px-Global_Warming_Predictions_Map.jpg)
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 underlying system (climate). These models predict that the effect of adding greenhouse gases is to produce a warmer climate.[51] 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 1.1 °C to 6.4 °C (2.0 °F to 11.5 °F) by the end of the 21st century, relative to 1980–1999.[1] 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.[52] 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.
Most global climate models, when run to project future climate, are forced by imposed greenhouse gas scenarios, generally one from the IPCC Special Report on Emissions Scenarios (SRES). Less commonly, models may be run by adding a simulation of the carbon cycle; this generally shows a positive feedback, though this response is uncertain (under the A2 SRES scenario, responses vary between an extra 20 and 200 ppm of CO2). Some observational studies also show a positive feedback.[53][54][55]
The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem.[56] There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability.
Attributed and expected effects
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Glacier_Mass_Balance.png/280px-Glacier_Mass_Balance.png)
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 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,[57] 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 being attributed in part to global warming.[58] While changes are expected for overall patterns, intensity, and frequencies, it is difficult to attribute specific events 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.[59]
Increasing deaths, displacements, and economic losses projected due to extreme weather attributed to global warming may be exacerbated by growing population densities in affected areas, although temperate regions are projected to experience some minor benefits, such as fewer deaths due to cold exposure.[60] 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.[58] 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, but that the detection of long-term trends is complicated by the quality of records prior to routine satellite observations. The summary also states that there is no clear trend in the annual worldwide number of tropical cyclones.[1]
Additional anticipated effects include sea level rise of 110 to 770 millimeters (0.36 to 2.5 ft) between 1990 and 2100,[61] repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increased intensity of 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.[62] However, few mechanistic studies have documented extinctions due to recent climate change[63] and one study suggests that projected rates of extinction are uncertain.[64]
Economic
Some economists have tried to estimate the aggregate net economic costs of damages from climate change across the globe. Such estimates have so far failed to reach 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).[60] 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 1%, and that in a worst-case scenario global per capita consumption could fall 20%.[65] 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,[66] while others have supported the general attempt to quantify economic risk, even if not the specific numbers.[67][68]
In a summary of economic cost associated with climate change, the United Nations Environment Programme emphasizes the risks to insurers, reinsurers, and banks of increasingly traumatic and costly weather events. Other economic sectors likely to face difficulties related to climate change include agriculture and transport. Some limited studies suggest developing countries, rather than the developed world, are at greatest economic risk.[69]
Security
In November 2007, the Center for Strategic and International Studies and the Center for a New American Security published a report highlighting the national security effects of climate change.[70] These security effects include increased competition for resources between countries, mass migration from the worst affected areas, challenges to the cohesion of major states threatened by the rise in sea levels, and, as a consequence of these factors, an increased risk of armed conflict, including even nuclear conflicts.
Adaptation and mitigation
The broad agreement among climate scientists that global temperatures will continue to increase has led nations, states, corporations and individuals to implement actions to try to curtail global warming or adjust to it. Many environmental groups encourage 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.[71][72]
There has also been business action on climate change, including efforts at increased energy efficiency and limited moves towards use of alternative fuels. One important innovation has been the development of greenhouse gas emissions trading through which companies, in conjunction with government, agree to cap their emissions or to purchase credits from those below their allowances.
The world's primary international agreement on combating global warming is the Kyoto Protocol, an amendment to the United Nations Framework Convention on Climate Change (UNFCCC) negotiated in 1997. The Protocol now covers more than 160 countries globally and over 55% of global greenhouse gas emissions.[73] 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.[74]
Claiming "serious harm" to the United States economy and the exemption of "80 percent of the world, including major population centers" like China and India, from the treaty, George W. Bush contends that the Kyoto Protocol is an unfair and ineffective means of addressing global climate change concerns.[75] Still, various state, local, and regional governments within the United States have begun their own initiatives to indicate support and compliance with the Kyoto Protocol on a local basis. For example, the Regional Greenhouse Gas Initiative is a state-level emissions capping and trading program involving eight Northeastern U.S. states, which was founded on December 20, 2005.[76]
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.[77]
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% increase and 3% decrease in global gross domestic product.[78]
Social and political debate
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![](http://upload.wikimedia.org/wikipedia/commons/thumb/6/6b/GHG_by_country_2000.svg/280px-GHG_by_country_2000.svg.png)
Over the past several years, public perceptions and attitudes concerning the causes and importance of global warming have changed.[79] Increased awareness of the scientific findings surrounding global warming has resulted in political and economic debate. Poor regions, particularly Africa, appear at greatest risk from the suggested effects of global warming, while their actual emissions have been negligible compared to the developed world.[80] At the same time, developing country exemptions from provisions of the Kyoto Protocol have been criticized by the United States and Australia, and have been used as part of the rationale for continued non-ratification by the U.S.[81] In the Western world, the idea of human influence on climate and efforts to combat it have gained wider acceptance in Europe than in the United States.[82][83]
The issue of climate change has sparked debate weighing the benefits of limiting industrial emissions of greenhouse gases versus the resultant impact on economic activity. There has been discussion in several countries about the cost of adopting cleaner alternative energy sources in order to reduce carbon emissions.[84] Organizations and companies such as the American Petroleum Institute and ExxonMobil, represented by individuals such as Philip Cooney and some think tanks such as the Competitive Enterprise Institute, have campaigned to downplay the risks of climate change.[85][86][87][88] Environmental groups and some public figures have launched campaigns emphasizing the risks. Some fossil fuel companies have recently scaled back such efforts[89] or called for policies to reduce global warming.[90]
Another point of debate is the degree to which newly developed economies such as India and China should be expected to constrain their emissions. China's gross national CO2 emissions are expected to exceed those of the U.S. within the next few years, and may have already done so according to a 2006 report.[91] 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.[92] India, also one of the biggest sources of industrial emissions, has made similar assertions.[93] However, the U.S. contends that if they must bear the cost of reducing emissions, then China should do the same.[94]
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.[95] 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,[96] and is projected to decrease by a further 0.14 to 0.5 units by 2100 as the ocean absorbs more CO2.[1][97] 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.[98]
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 twentieth 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.[1]
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
References
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The updated 100-year linear trend (1906 to 2005) of 0.74°C [0.56°C to 0.92°C] is therefore larger than the corresponding trend for 1901 to 2000 given in the TAR of 0.6°C [0.4°C to 0.8°C].
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Recent estimates (Figure 9.9) indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the seconds half of the 20th century, with a small net cooling from the combined effects of solar and volcanic forcings
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However, because of a lack of interactive ozone, the model cannot fully simulate features discussed in (44)." "While the NH temperatures of the high-scaled experiment are often colder than the lower bound from proxy data, the modeled decadal-scale NH surface temperature for the medium-scaled case falls within the uncertainty range of the available temperature reconstructions. The medium-scaled simulation also broadly reproduces the main features seen in the proxy records." "Without anthropogenic forcing, the 20th century warming is small. The simulations with only natural forcing components included yield an early 20th century peak warming of ≈0.2 °C (≈1950 AD), which is reduced to about half by the end of the century because of increased volcanism.
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However, the overwhelming majority of scientists who work on climate change agree on the main points
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In common usage, 'global warming' often refers to the warming that can occur as a result of increased emissions of greenhouse gases from human activities.
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To emit 240 W m–2, a surface would have to have a temperature of around –19 °C. This is much colder than the conditions that actually exist at the Earth's surface (the global mean surface temperature is about 14 °C). Instead, the necessary –19 °C is found at an altitude about 5 km above the surface.
{{cite web}}
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at position 62 (help) - ^ 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 32 °F 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.
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Interestingly, the true feedback is consistently weaker than the constant relative humidity value, implying a small but robust reduction in relative humidity in all models on average" "clouds appear to provide a positive feedback in all models
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ignored (help) - ^ Svensmark, Henrik (2000). "Cosmic Rays and Earth's Climate" (PDF). Space Science Reviews. 93 (1–2): 175–185. Retrieved 2007-09-17.
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Our results show that the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified.
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Cohen, Anthony S. (2004). "Osmium isotope evidence for the regulation of atmospheric CO2 by continental weathering" (PDF). Geology. 32 (2): 157–160. doi:10.1130/G20158.1. Retrieved 2007-03-04.
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Torn, Margaret (2006-05-26). "Missing feedbacks, asymmetric uncertainties, and the underestimation of future warming". Geophysical Research Letters. 33 (10). L10703. Retrieved 2007-03-04.
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Harte, John (2006-10-30). "Shifts in plant dominance control carbon-cycle responses to experimental warming and widespread drought". Environmental Research Letters. 1 (1). 014001. Retrieved 2007-05-02.
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Scheffer, Marten (2006-05-26). "Positive feedback between global warming and atmospheric CO2 concentration inferred from past climate change" (PDF). Geophysical Research Letters. 33. doi:10.1029/2005gl025044. Retrieved 2007-05-04.
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Stocker, Thomas F. (2001-01-20). "7.2.2 Cloud Processes and Feedbacks". Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. Retrieved 2007-03-04.
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(help) - ^ McMichael AJ, Woodruff RE, Hales S (2006). "Climate change and human health: present and future risks". Lancet. 367 (9513): 859–69. doi:10.1016/S0140-6736(06)68079-3. PMID 16530580.
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(help) - ^ Church, John A. (2001-01-20). "Executive Summary of Chapter 11". Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. Retrieved 2005-12-19.
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(help) - ^ 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).
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(help)CS1 maint: multiple names: authors list (link) - ^ "Climate Control: a proposal for controlling global greenhouse gas emissions" (PDF). Sustento Institute. Retrieved 2007-12-10.
- ^ Monbiot, George. "Rigged - The climate talks are a stitch-up, as no one is talking about supply" (HTML). Retrieved 2007-12-22.
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(help) - ^ Climate talks face international hurdles, by Arthur Max, Associated press, 5/14/07.
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(help) - ^ Weart, Spencer (2006), "The Public and Climate Change", in Weart, Spencer (ed.), The Discovery of Global Warming, American Institute of Physics, retrieved 2007-04-14
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Revkin, Andrew (2007-04-01). "Poor Nations to Bear Brunt as World Warms". The New York Times. Retrieved 2007-05-02.
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Brahic, Catherine (2006-04-25). "China's emissions may surpass the US in 2007". New Scientist. Retrieved 2007-05-02.
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Crampton, Thomas (2007-01-04). "More in Europe worry about climate than in U.S., poll shows". International Herald Tribune. Retrieved 2007-04-14.
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(help) - ^ "Summary of Findings". Little Consensus on Global Warming. Partisanship Drives Opinion. Pew Research Center. 2006-07-12. Retrieved 2007-04-14.
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(help) - ^ "EU agrees on carbon dioxide cuts". BCC. 2007-03-09. Retrieved 2007-05-04.
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(help) - ^ Begley, Sharon (2007-08-13). "The Truth About Denial". Newsweek. Retrieved 2007-08-13.
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Sandell, Clayton (2007-01-03). "Report: Big Money Confusing Public on Global Warming". ABC. Retrieved 2007-04-27.
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(help) - ^ "Global Warming Resolutions at U.S. Oil Companies Bring Policy Commitments from Leaders, and Record High Votes at Laggards" (Press release). Ceres. April 28, 2004. Retrieved 2007-07-27.
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(help); "Group: China surpassed US in carbon emissions in 2006: Dutch report". Reuters. 2007-06-20. Retrieved 2007-10-16.{{cite news}}
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(help) - ^ China: US should take lead on climate, by Michael Casey, Associated Press, 12/7/07.
- ^ India's glaciers give grim message on warming, by Somni Sengupta, 7/17/07, New York Times via oregonlive.com.
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Jacobson, Mark Z. (2005-04-02). "Studying ocean acidification with conservative, stable numerical schemes for nonequilibrium air-ocean exchange and ocean equilibrium chemistry" (PDF). Journal of Geophysical Research. 110 (D7). doi:10.1029/2004JD005220. D07302. Retrieved 2007-04-28.
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Caldeira, Ken (2005-09-21). "Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean". Journal of Geophysical Research. 110 (C09S04): 1–12. Retrieved 2006-02-14.
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Raven, John A.; et al. (2005-06-30). "Ocean acidification due to increasing atmospheric carbon dioxide" (ASP). Royal Society. Retrieved 2007-05-04.
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(help)
Further reading
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/24/Wikinews-logo.svg/40px-Wikinews-logo.svg.png)
- Amstrup, Steven C. (2006-04-27). "Recent observations of intraspecific predation and cannibalism among polar bears in the southern Beaufort Sea". Polar Biology. 29 (11): 997–1002. doi:10.1007/s00300-006-0142-5.
{{cite journal}}
: Check date values in:|date=
(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Association of British Insurers (2005-06). Financial Risks of Climate Change (PDF).
{{cite book}}
: Check date values in:|year=
(help) - Barnett, Tim P. (2005-11-17). "Potential impacts of a warming climate on water availability in snow-dominated regions". Nature. 438 (7066): 303–309. doi:10.1038/nature04141.
{{cite journal}}
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(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Behrenfeld, Michael J. (2006-12-07). "Climate-driven trends in contemporary ocean productivity" (PDF). Nature. 444 (7120): 752–755. doi:10.1038/nature05317.
{{cite journal}}
: Check date values in:|date=
(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Choi, Onelack (May 2005). "The Impacts of Socioeconomic Development and Climate Change on Severe Weather Catastrophe Losses: Mid-Atlantic Region (MAR) and the U.S." Climate Change. 58 (1–2): 149–170. doi:10.1023/A:1023459216609.
{{cite journal}}
: Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Dyurgerov, Mark B. (2005). Glaciers and the Changing Earth System: a 2004 Snapshot (PDF). Institute of Arctic and Alpine Research Occasional Paper #58. ISSN 0069-6145.
{{cite book}}
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ignored (|author=
suggested) (help) - Emanuel, Kerry A. (2005-08-04). "Increasing destructiveness of tropical cyclones over the past 30 years" (PDF). Nature. 436 (7051): 686–688. doi:10.1038/nature03906.
{{cite journal}}
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(help) - Hansen, James (2005-06-03). "Earth's Energy Imbalance: Confirmation and Implications" (PDF). Science. 308 (5727): 1431–1435. doi:10.1126/science.1110252.
{{cite journal}}
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(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Hinrichs, Kai-Uwe (2003-02-21). "Molecular Fossil Record of Elevated Methane Levels in Late Pleistocene Coastal Waters". Science. 299 (5610): 1214–1217. doi:10.1126/science.1079601.
{{cite journal}}
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(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Hirsch, Tim (2006-01-11). "Plants revealed as methane source". BBC.
{{cite news}}
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(help) - Hoyt, Douglas V. (1993–11). "A discussion of plausible solar irradiance variations, 1700–1992". Journal of Geophysical Research. 98 (A11): 18, 895–18, 906.
{{cite journal}}
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(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Kenneth, James P. (2003-02-14). Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis. American Geophysical Union.
{{cite book}}
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(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help)CS1 maint: year (link) - Keppler, Frank (2006-01-18). "Global Warming - The Blame Is not with the Plants". Max Planck Society.
{{cite news}}
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ignored (|author=
suggested) (help) - Kurzweil, Raymond (2006–07). "Nanotech Could Give Global Warming a Big Chill" (PDF). Forbes / Wolfe Nanotech Report. 5 (7).
{{cite journal}}
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(help) - Lean, Judith L. (2002–12). "The effect of increasing solar activity on the Sun's total and open magnetic flux during multiple cycles: Implications for solar forcing of climate". Geophysical Research Letters. 29 (24). doi:10.1029/2002GL015880.
{{cite journal}}
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(help); Cite has empty unknown parameter:|1=
(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Lerner, K. Lee (2006-07-26). Environmental issues : essential primary sources. Thomson Gale. ISBN 1414406258.
{{cite book}}
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(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - McLaughlin, Joseph B. (2005-10-06). "Outbreak of Vibrio parahaemolyticus gastroenteritis associated with Alaskan oysters". New England Journal of Medicine. 353 (14). New England Medical Society: 1463–1470.
{{cite journal}}
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ignored (|author=
suggested) (help)(online version requires registration) - Muscheler, Raimund (2005-07-28). "Climate: How unusual is today's solar activity?" (PDF). Nature. 436 (7012): 1084–1087. doi:10.1038/nature04045.
{{cite journal}}
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(help); Unknown parameter|coauthors=
ignored (|author=
suggested) (help) - Oerlemans, J. (2005-04-29). "Extracting a Climate Signal from 169 Glacier Records" (PDF). Science. 308 (5722): 675–677. doi:10.1126/science.1107046.
{{cite journal}}
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(help) - Oreskes, Naomi (2004-12-03). "Beyond the Ivory Tower: The Scientific Consensus on Climate Change" (PDF). Science. 306 (5702): 1686. doi:10.1126/science.1103618.
{{cite journal}}
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(help) - Purse, Bethan V. (February 2005). "Climate change and the recent emergence of bluetongue in Europe". Nature Reviews Microbiology. 3 (2): 171–181. doi:10.1038/nrmicro1090.
{{cite journal}}
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ignored (|author=
suggested) (help) - Revkin, Andrew C (2005-11-05). "Rise in Gases Unmatched by a History in Ancient Ice". The New York Times.
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(help) - Ruddiman, William F. (2005-12-15). Earth's Climate Past and Future. New York: Princeton University Press. ISBN 0-7167-3741-8.
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(help) - Ruddiman, William F. (2005-08-01). Plows, Plagues, and Petroleum: How Humans Took Control of Climate. New Jersey: Princeton University Press. ISBN 0-691-12164-8.
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(help) - Solanki, Sami K. (2004-10-23). "Unusual activity of the Sun during recent decades compared to the previous 11,000 years" (PDF). Nature. 431: 1084–1087. doi:10.1038/nature02995.
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ignored (|author=
suggested) (help) - Solanki, Sami K. (2005-07-28). "Climate: How unusual is today's solar activity? (Reply)" (PDF). Nature. 436: E4–E5. doi:10.1038/nature04046.
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ignored (|author=
suggested) (help) - Sowers, Todd (2006-02-10). "Late Quaternary Atmospheric CH4 Isotope Record Suggests Marine Clathrates Are Stable". Science. 311 (5762): 838–840. doi:10.1126/science.1121235.
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(help) - Svensmark, Henrik (2007-02-08). "Experimental evidence for the role of ions in particle nucleation under atmospheric conditions". Proceedings of the Royal Society A. 463 (2078). FirstCite Early Online Publishing: 385–396. doi:10.1098/rspa.2006.1773.
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suggested) (help)CS1 maint: year (link)(online version requires registration) - Walter, K. M. (2006-09-07). "Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming". Nature. 443 (7107): 71–75. doi:10.1038/nature05040.
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ignored (|author=
suggested) (help) - Wang, Y.-M. (2005-05-20). "Modeling the sun's magnetic field and irradiance since 1713" (PDF). Astrophysical Journal. 625: 522–538. doi:10.1086/429689.
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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
- Outgoing Longwave Radiation pentad mean – NOAA Climate Prediction Center
- 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'
- NASA Finds Sun-Climate Connection in Old Nile Records
- News in Science - Night flights are worse for global warming
- Educational
- Climate change at HowStuffWorks
- What Is Global Warming? – Simulation 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
- Daily global temperatures and trends from satellites – Interactive graphics from NASA
- The Pew Center on global climate change
- Governments
- 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
- IPS Inter Press Service – Independent news on global warming and its consequences.
- Gateway to the UN System's Work on Climate Change
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