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User:Isonomia/Global warming

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This is not an encyclopedia article. If you find this page on any site other than Wikipedia, you are viewing a mirror site. Be aware that the page may be outdated and that the user to whom this page belongs may have no personal affiliation with any site other than Wikipedia itself. The original page is located at http://en.wikipedia.org/wiki/User:Isonomia/Global_warming.
Image:HadCRUT3-temp-record.svg
Global mean surface temperature anomaly 1850 to 2007 relative to 1961–1990
Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980
Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980

Global warming is the increase in the average temperature of the Earth's near-surface air and oceans in the latter half of the 20th century.

The global average air temperature near the Earth's surface rose 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 years ending in 2005.[1] The Intergovernmental Panel on Climate Change (IPCC) concluded "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]


Contents

[edit] Terminology

The term "global warming" is a specific example of climate change, which can also refer to global cooling. In common usage, the term refers to recent warming and implies a human influence.[4] The United Nations Framework Convention on Climate Change (UNFCCC) uses the term "climate change" for human-caused change, and "climate variability" for other changes.[5] The term "anthropogenic global warming" is sometimes used when focusing on human-induced changes.

[edit] Temperature changes

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.
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.
Main article: Temperature record

[edit] 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.[6] Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).[7] 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.[8] 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.[9] Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[10][11] Temperatures in 1998 were unusually warm because the strongest El Niño in the past century occurred during that year.[12]

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,[13] 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.[14]

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.[15] Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed.[16]

[edit] Pre-human climate variations

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.
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.
Further information: Paleoclimatology
See also: Snowball Earth

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.[17]

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.[18][19]

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).

[edit] Causes

Components of the current radiative forcing as estimated by the IPCC Fourth Assessment Report.
Components of the current radiative forcing as estimated by the IPCC Fourth Assessment Report.
Main articles: Attribution of recent climate change and Scientific opinion on climate change

The Earth's climate changes in response to external forcing, including variations in its orbit around the Sun (orbital forcing),[20][21][22] volcanic eruptions,[23] and atmospheric greenhouse gas concentrations. The detailed causes of the recent warming remain an active field of research, but the scientific consensus[24][25] 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. 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 temperature increase. One such hypothesis proposes that warming may be the result of variations in solar activity.[26][27][28]

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.[29]

[edit] Greenhouse gases in the atmosphere

Main articles: Greenhouse gas and Greenhouse effect

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 lower 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.[30][31] Rather, the issue is how the strength of the greenhouse effect changes 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%.[32][33] 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. 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 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. From less direct geological evidence it is believed that CO2 values this high were last attained 20 million years ago.[34] 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.[35]

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.
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.

The present atmospheric concentration of CO2 is about 385 parts per million (ppm) by volume.[36] 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.[37] Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal, tar sands or methane clathrates are extensively used.[38]

[edit] Feedbacks

Main article: Effects of global warming#Positive feedback effects

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. Warming by the addition of long-lived greenhouse gases such as CO2 will cause more water to be evaporated into the atmosphere. Since water vapor itself acts as a greenhouse gas, the atmosphere warms further; this warming causes more water vapor to be evaporated, and so on 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 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.[39] 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.[39]

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 warming will reduce the decrease of temperature with height, 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.[40]

Another important feedback process is ice-albedo feedback.[41] 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 that could contribute to warming.[42] Similarly a massive release of CH4 from methane clathrates in the ocean could cause rapid warming, according to the clathrate gun hypothesis.

The ocean's ability to sequester carbon is 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.[43]

[edit] Solar variation

Solar variation over the last 30 years.
Solar variation over the last 30 years.
Main article: Solar variation

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.[44] 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.[45] 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.[46] 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.[47]

One predicted effect of an increase in solar activity would be a warming of most of the stratosphere, whereas greenhouse gas theory predicts cooling there [48]. The observed trend since at least 1960 has been a cooling of the lower stratosphere[49]. Reduction of stratospheric ozone also has a cooling influence, but substantial ozone depletion did not occur until the late 1970s.[50] 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.[51][52] 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.[53] Henrik Svensmark and Eigil Friis-Christensen, the main proponents of cloud seeding by galactic cosmic rays, disputed this criticism of their hypothesis.[54]


[edit] Climate models

Main article: Global climate model

[edit] Attributed and expected effects

Main article: Effects of global warming

[edit] Adaptation and mitigation

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

[edit] Social and political debate

Main articles: Global warming controversy, Politics of global warming, and Economics of global warming
See also: Climate change denial

[edit] Related climatic issues

Main articles: Ocean acidification, global dimming, and ozone depletion

[edit] See also

[edit] References

  1. ^ a b c Summary for Policymakers (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change (2007-02-05). Retrieved on 2007-02-02. “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].”
  2. ^ Hegerl, Gabriele C.; et al. (2007-05-07). Understanding and Attributing Climate Change (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change 690. Intergovernmental Panel on Climate Change. Retrieved on 2007-05-20. “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”
  3. ^ Ammann, Caspar; et al. (2007-04-06). "Solar influence on climate during the past millennium: Results from ransient simulations with the NCAR Climate Simulation Model" (PDF). Proceedings of the National Academy of Sciences of the United States of America 104 (10): 3713–3718. “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.” 
  4. ^ Climate Change: Basic Information. United States Environmental Protection Agency (2006-12-14). Retrieved on 2007-02-09. “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.”
  5. ^ United Nations Framework Convention on Climate Change, Article I. United Nations Framework Convention on Climate Change. Retrieved on 2007-01-15.
  6. ^ Working group I, section 3.2.2.2 of the 2007 IPPC page 243
  7. ^ Smith, Thomas M.; Reynolds, Richard W. (2005-05-15). "A Global Merged Land–Air–Sea Surface Temperature Reconstruction Based on Historical Observations (1880–1997)" (PDF). Journal of Climate 18 (12): 2021–2036. ISSN 0894-8755. 
  8. ^ Rowan T. Sutton, Buwen Dong, Jonathan M. Gregory (2007). "Land/sea warming ratio in response to climate change: IPCC AR4 model results and comparison with observations". Geophysical Research Letters 34. doi:10.1029/2006GL028164. 
  9. ^ Hansen, James E.; et al. (2006-01-12). Goddard Institute for Space Studies, GISS Surface Temperature Analysis. NASA Goddard Institute for Space Studies. Retrieved on 2007-01-17.
  10. ^ Global Temperature for 2005: second warmest year on record (PDF). Climatic Research Unit, School of Environmental Sciences, University of East Anglia (2005-12-15). Retrieved on 2007-04-13.
  11. ^ WMO STATEMENT ON THE STATUS OF THE GLOBAL CLIMATE IN 2005 (PDF). World Meteorological Organization (2005-12-15). Retrieved on 2007-04-13.
  12. ^ Data @ NASA GISS: GISS Surface Temperature Analysis: 2005 Summation
  13. ^ Mitchell, J. F. B.; et al. (2001-01-20). 12.4.3.3 Space-time studies. 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 on 2007-01-04.
  14. ^ Global warming in the twenty-first century: An alternative scenario - Hansen et al. 97 (18): 9875 - Proceedings of the National Academy of Sciences
  15. ^ Ruddiman, William F. (March 2005). "How Did Humans First Alter Global Climate?" (PDF). Scientific American 292 (3): 46–53. 
  16. ^ Schmidt, Gavin; et al. (2004-12-10). "A note on the relationship between ice core methane concentrations and insolation". Geophysical Research Letters 31 (23). doi:10.1029/2004GL021083. L23206. 
  17. ^ Hansen, James; et al. (2006-09-26). "Global temperature change" (PDF). PNAS 103: 14288–14293. 
  18. ^ Open University (2004-01-30). "The Open University Provides Answers on Global Warming" (PDF). Press release. Retrieved on 2007-03-04.
  19. ^ Cohen, Anthony S.; et al. (February 2004). "Osmium isotope evidence for the regulation of atmospheric CO2 by continental weathering" (PDF). Geology 32 (2): 157–160. doi:10.1130/G20158.1. 
  20. ^ Berger, A.; et al. (2005-12-10). "On the origin of the 100-kyr cycles in the astronomical forcing". Paleoceanography 20 (4). PA4019. 
  21. ^ Genthon, C.; et al. (1987-10-01). "Vostok Ice Core - Climatic response to CO2 and orbital forcing changes over the last climatic cycle". Nature 329 (6138): 414–418. 
  22. ^ Alley, Richard B.; et al. (January 2002). "A northern lead in the orbital band: north-south phasing of Ice-Age events". Quaternary Science Reviews 21 (1-3): 431–441. 
  23. ^ Robock, Alan, and Clive Oppenheimer, Eds., 2003: Volcanism and the Earth’s Atmosphere, Geophysical Monograph 139, American Geophysical Union, Washington, DC, 360 pp.
  24. ^ Joint science academies' statement: The science of climate change (ASP). Royal Society (2001-05-17). Retrieved on 2007-04-01. “The work of the Intergovernmental Panel on Climate Change (IPCC) represents the consensus of the international scientific community on climate change science”
  25. ^ "Rising to the climate challenge" (2007-10-18). Nature 449 (7164). 
  26. ^ Svensmark, Henrik (February 2007). "Cosmoclimatology: a new theory emerges". Astronomy & Geophysics 48 (1): 18-24. doi:10.1111/j.1468-4004.2007.48118.x. 
  27. ^ Forster, Piers; et al. (2007-02-05). Changes in Atmospheric Constituents and in Radiative Forcing (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change 188-193. Intergovernmental Panel on Climate Change. Retrieved on 2007-09-17.
  28. ^ Bard, Edouard; Frank, Martin (2006-06-09). "Climate change and solar variability: What's new under the sun?". Earth and Planetary Science Letters 248 (1-2): 1-14. 
  29. ^ Meehl, Gerald A.; et al. (2005-03-18). "How Much More Global Warming and Sea Level Rise" (PDF). Science 307 (5716): 1769–1772. doi:10.1126/science.1106663. 
  30. ^ IPCC WG1 AR4 Report — Chapter 1: Historical Overview of Climate Change Science (PDF). IPCC WG1 AR4 Report p97 (pdf page 5 of 36). IPCC (2007). Retrieved on 2007-10-07. “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.”
  31. ^ 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 (0 °C) 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.
  32. ^ Kiehl, J. T.; Kevin E. Trenberth (February 1997). "Earth’s Annual Global Mean Energy Budget" (PDF). Bulletin of the American Meteorological Society 78 (2): 197-208. 
  33. ^ Water vapour: feedback or forcing?. RealClimate (6 Apr 2005). Retrieved on 2006-05-01.
  34. ^ Pearson, Paul N.; Palmer, Martin R. (2000-08-17). "Atmospheric carbon dioxide concentrations over the past 60 million years". Nature 406 (6797): 695–699. doi:10.1038/35021000. 
  35. ^ Summary for Policymakers. 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 (2001-01-20). Retrieved on 2007-01-18.
  36. ^ Tans, Pieter. Trends in Atmospheric Carbon Dioxide – Mauna Loa. National Oceanic and Atmospheric Administration. Retrieved on 2008-02-15.
  37. ^ Prentice, I. Colin; et al. (2001-01-20). 3.7.3.3 SRES scenarios and their implications for future CO2 concentration. 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 on 2007-04-28.
  38. ^ 4.4.6. Resource Availability. IPCC Special Report on Emissions Scenarios. Intergovernmental Panel on Climate Change. Retrieved on 2007-04-28.
  39. ^ a b Soden, Brian J.; Held, Isacc M. (2005-11-01). "An Assessment of Climate Feedbacks in Coupled Ocean–Atmosphere Models" (PDF). Journal of Climate 19 (14). “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” 
  40. ^ Panel on Climate Change Feedbacks, Climate Research Committee, National Research Council, 2004: Understanding Climate Change Feedbacks.
  41. ^ Stocker, Thomas F.; et al. (2001-01-20). 7.5.2 Sea Ice. 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 on 2007-02-11.
  42. ^ Sample, Ian. "Warming Hits 'Tipping Point'", The Guardian, 2005-08-11. Retrieved on 2007-01-18. 
  43. ^ Buesseler, Ken O.; et al. (2007-04-27). "Revisiting Carbon Flux Through the Ocean's Twilight Zone". Science 316 (5824): 567–570. 
  44. ^ Scafetta, Nicola; West, Bruce J. (2006-03-09). "Phenomenological solar contribution to the 1900–2000 global surface warming" (PDF). Geophysical Research Letters 33 (5). doi:10.1029/2005GL025539. L05708. 
  45. ^ Stott, Peter A.; et al. (2003-12-03). "Do Models Underestimate the Solar Contribution to Recent Climate Change?". Journal of Climate 16 (24): 4079–4093. doi:10.1175/1520-0442(2003)016%3C4079:DMUTSC%3E2.0.CO;2. 
  46. ^ Marsh, Nigel; Henrik, Svensmark (November 2000). "Cosmic Rays, Clouds, and Climate" (PDF). Space Science Reviews 94: 215–230. doi:10.1023/A:1026723423896. 
  47. ^ Svensmark, Henrik (July 2000). "Cosmic Rays and Earth's Climate" (PDF). Space Science Reviews 93 (1-2): 175-185. 
  48. ^ Hegerl, Gabriele C.; et al.. Understanding and Attributing Climate Change (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change 675. Intergovernmental Panel on Climate Change. Retrieved on 2008-02-01.
  49. ^ Climate Change 2001:Working Group I: The Scientific Basis (Fig. 2.12) (2001). Retrieved on 2007-05-08.
  50. ^ Ozone History
  51. ^ Foukal, Peter; et al. (2006-09-14). "Variations in solar luminosity and their effect on the Earth's climate.". Nature. 
  52. ^ National Center for Atmospheric Research (2006-09-14). "Changes in Solar Brightness Too Weak to Explain Global Warming". Press release. Retrieved on 2007-07-13.
  53. ^ Lockwood, Mike; Claus Fröhlich. "Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature". Proceedings of the Royal Society A. doi:10.1098/rspa.2007.1880. “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.” 
  54. ^ Reply to Lockwood and Fröhlich - The persistent role of the Sun in climate forcing — Spacecenter

[edit] Further reading

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  • Hinrichs, Kai-Uwe; Laura R. Hmelo, Sean P. Sylva (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. 
  • 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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