Attribution of recent climate change 3201 222119456 2008-06-27T17:27:05Z Quadell 57108 Converting [1] to <ref>, and/or misc fixes, typos fixed: byproducts → by-products using [[Project:AutoWikiBrowser|AWB]] {{pp-semi-indef}} {{See|Global warming|Climate change|Climate change denial}} '''Attribution of recent climate change''' is the effort to [[scientific method|scientifically ascertain]] mechanisms responsible for relatively recent changes observed in the [[Earth]]'s [[climate]]. The effort has focused on changes observed during the period of [[instrumental temperature record]], when records are most reliable; particularly on the last 50 years, when human activity has grown fastest and observations of the upper atmosphere have become available. The dominant mechanisms to which recent climate change has been attributed all result from human activity. They are:<ref name=WG1-2007-AR4>{{Cite web | title = Working Group I: The Physical Basis for Climate Change | publisher = [[Intergovernmental Panel on Climate Change|IPCC]] | url = http://ipcc-wg1.ucar.edu/wg1/wg1-report.html}}</ref> *increasing [[atmosphere|atmospheric]] concentrations of [[greenhouse gas]]es *global changes to land surface, such as [[deforestation]] *increasing atmospheric concentrations of [[aerosol]]s. Recent reports from the [[Intergovernmental Panel on Climate Change]] (IPCC) report have concluded that: *"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."<ref name=WG1-2007-SPM>{{Cite book | title = Working Group I: The Physical Basis for Climate Change (Summary for Policymakers) | publisher = [[Intergovernmental Panel on Climate Change|IPCC]] | date = 2007 | isbn = 978 0521 88009-1 | url = http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf}}</ref> *"From new estimates of the combined anthropogenic [[radiative forcing|forcing]] due to greenhouse gases, [[aerosol]]s, and [[land use|land surface changes]], it is ''extremely likely'' that human activities have exerted a substantial net warming influence on climate since 1750."<ref name=WG1-2007-AR4/> *"It is ''virtually certain'' that anthropogenic aerosols produce a net negative [[radiative forcing]] (cooling influence) with a greater magnitude in the [[Northern Hemisphere]] than in the [[Southern Hemisphere]].<ref name=WG1-2007-AR4/> The panel, which represents [[Scientific opinion on climate change|consensus]] in the [[scientific community]], defines "very likely," "extremely likely," and "virtually certain" as indicating probabilities greater than 90%, 95%, and 99%, respectively.<ref name=WG1-2007-AR4/> ==Key attributions== ===Greenhouse gases=== [[Image:Greenhouse Gas by Sector.png|thumb|350px|right]] Scientific consensus has identified [[carbon dioxide]] as the dominant [[greenhouse gas]] forcing. (The dominant greenhouse gas overall is [[water vapor]]. Water vapor, however, has a very short atmospheric lifetime (about 10 days) and is very nearly in a dynamic equilibrium in the atmosphere, so it is not a [[radiative forcing|forcing]] gas in the context of global warming.<ref name="rc_wv">{{cite web |url=http://www.realclimate.org/index.php?p=142 |title=Water vapour: feedback or forcing? |accessdate=2008-04-07 |last=Schmidt |first=Gavin A. |date=2005-04-06 |work= |publisher=[[RealClimate]]}}</ref>) [[Methane]] and [[nitrous oxide]] are also major forcing contributors to the [[greenhouse effect]]. The [[Kyoto Protocol]] lists these together with [[Hydrofluorocarbons]] (HFCs), [[Perfluorocarbons]] (PFCs), and [[Sulphur hexafluoride]] (SF6),<ref name=kyoto>{{Cite web | title = The Kyoto Protocol | publisher = [[UNFCCC]] | url = http://unfccc.int/resource/docs/convkp/kpeng.html}}</ref> which contribute to climate change primarily by interfering with atmospheric [[ozone]] concentrations. The chart at right attributes anthropogenic greenhouse gas [[emissions]] to eight main economic sectors, of which the largest contributors are [[power stations]] (many of which burn [[coal]] or other [[fossil fuel]]s), [[industry|industrial]] processes (among which [[cement]] production is a dominant contributor<ref name=WG1-2007-TS>{{Cite book | title = Working Group I: The Physical Basis for Climate Change (Technical summary) | publisher = [[Intergovernmental Panel on Climate Change|IPCC]] | date = 2007 | isbn = 978 0521 88009-1 | url = http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_TS.pdf}}</ref>), [[transportation]] [[fuel]]s (generally [[fossil fuel]]s), and [[agriculture|agricultural]] by-products (mainly methane from [[enteric fermentation]] and nitrous oxide from [[fertilizer]] use). ===Land use=== Climate change is attributed to [[land use]] for two main reasons. While 66% of anthropogenic [[carbon dioxide|CO<sub>2</sub>]] emissions over the last 250 years have resulted from burning fossil fuels, 33% have resulted from changes in land use, primarily [[deforestation]].<ref name=WG1-2007-TS/> Deforestation both reduces the amount of carbon dioxide absorbed by deforested regions and releases greenhouse gases directly, together with aerosols, through [[slash and burn|biomass burning]] that frequently accompanies it. A second reason that climate change has been attributed to land use is that the [[albedo|terrestrial albedo]] is often altered by use, which leads to [[radiative forcing]]. This effect is more significant locally than globally.<ref name=WG1-2007-TS/> ====Livestock and land use==== Worldwide, livestock production occupies 70% of all land used for agriculture, or 30% of the ice-free land surface of the Earth.<ref name=livestock>{{Cite book | title = Livestock's Long Shadow | date = 2006 | publisher = Food and Agricultural Organization of the U.N. | isbn = 9251055718 | url = http://www.virtualcentre.org/en/library/key_pub/longshad/A0701E00.pdf}}</ref> Scientists attribute more than 18% of anthropogenic greenhouse gas emissions to livestock and livestock-related activities such as deforestation and increasingly fuel-intensive farming practices.<ref name=livestock/> Specific attributions to the livestock sector include: *9% of global [[carbon dioxide]] emissions *35-40% of global [[methane]] emissions (chiefly due to [[enteric fermentation]] and [[manure]]) *64% of global [[nitrous oxide]] emissions, chiefly as a result of [[fertilizer]] use.<ref name=livestock/> ===Aerosols=== With virtual certainty, scientific consensus has attributed various forms of climate change, chiefly cooling effects, to [[aerosol]]s, which are small particles or droplets suspended in the atmosphere.<ref name=WG1-2007-FM>{{Cite book | title = Working Group I: The Physical Basis for Climate Change (Front matter) | publisher = [[Intergovernmental Panel on Climate Change|IPCC]] | date = 2007 | isbn = 978 0521 88009-1 | url = http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_FrontMatter.pdf}}</ref> Key sources to which anthropogenic aerosols are attributed<ref>{{Cite web | title = Aerosols and Climate | last = Geerts | first = B. | url = http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/aerosol&climate.html}}</ref> include: *biomass burning such as [[slash and burn]] deforestation. Aerosols produced are primarily [[black carbon]]. *industrial [[air pollution]], which produces [[soot]] and airborne [[sulfate]]s, [[nitrate]]s, and [[ammonium]] *dust produced by [[land use]] effects such as [[desertification]] == Attribution of 20th century climate change ==<!-- This section is linked from [[Global warming controversy]] --> {{IPCC}} [[Image:Climate Change Attribution.png|250px|right|thumb|One [[global climate model]]'s reconstruction of temperature change during the 20th century as the result of five studied forcing factors and the amount of temperature change attributed to each.]] Over the past 150 years human activities have released increasing quantities of [[greenhouse gas]]es into the [[Earth's atmosphere|atmosphere]]. This has led to increases in mean global temperature, or [[global warming]]. Other human effects are relevant—for example, sulphate [[Particulate|aerosol]]s are believed to lead to cooling—and natural factors also contribute. According to the [[historical temperature record]] of the last century, the Earth's near-surface air temperature has risen around 0.74 [[Plus-minus sign|±]] 0.18&nbsp;°[[Celsius]] (1.3 ± 0.32&nbsp;°[[Fahrenheit]]). A historically important question in climate change research has regarded the relative importance of human activity and non-[[anthropogenic]] causes during the period of [[instrumental temperature record|instrumental record]]. In the 1995 Second Assessment Report (SAR), the [[Intergovernmental Panel on Climate Change|IPCC]] made the widely-quoted statement that "The balance of evidence suggests a discernible human influence on global climate". The phrase "balance of evidence" suggested the (English) common-law standard of proof required in civil as opposed to criminal courts: not as high as "beyond reasonable doubt". In 2001 the Third Assessment Report (TAR) refined this, saying "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities".<ref name=WG1-2001-SPM>{{Cite book | title = Working Group I: The Physical Basis for Climate Change (Summary for Policymakers) | date = 2001 | publisher = [[IPCC]] | page = 7 | url = http://www.grida.no/climate/ipcc_tar/wg1/007.htm}}</ref> The 2007 fourth assessment report (WG1 AR4) strengthened this finding: *"Anthropogenic warming of the climate system is widespread and can be detected in temperature observations taken at the surface, in the free atmosphere and in the oceans. Evidence of the effect of external influences, both anthropogenic and natural, on the climate system has continued to accumulate since the TAR."<ref name=WG1-2007-TS/> Over the past five decades there has been a global warming of approximately 0.65&nbsp;°C (1.17&nbsp;°F) at the Earth's surface (see [[historical temperature record]]). Among the possible factors that could produce changes in global mean temperature are internal variability of the climate system, external forcing, an increase in concentration of greenhouse gases, or any combination of these. Current studies indicate that the increase in greenhouse gases, most notably CO<sub>2</sub>, is mostly responsible for the observed warming. Evidence for this conclusion includes: * Estimates of internal variability from climate models, and reconstructions of past temperatures, indicate that the warming is unlikely to be entirely natural. * Climate models forced by natural factors ''and'' increased greenhouse gases and aerosols reproduce the observed global temperature changes; those forced by natural factors alone do not<ref>http://www.grida.no/climate/ipcc_tar/wg1/007.htm</ref>. * "Fingerprint" methods indicate that the pattern of change is closer to that expected from greenhouse gas-forced change than from natural change.<ref>http://www.grida.no/climate/ipcc_tar/wg1/460.htm</ref> * The plateau in warming from the 1940s to 1960s can be attributed largely to sulphate aerosol cooling.<ref>http://www.grida.no/climate/ipcc_tar/wg1/figspm-4.htm</ref> In 2001, the U.S. [[United States National Academy of Sciences|National Academy of Sciences]] released a report supporting the IPCC’s conclusions regarding the causes of recent climate change. It stated, "Greenhouse gases are accumulating in Earth’s atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes are also a reflection of natural variability."<ref>http://www4.nationalacademies.org/onpi/webextra.nsf/web/climate?OpenDocument</ref><ref>http://www.eia.doe.gov/oiaf/1605/ggccebro/chapter1.html</ref><ref>http://www.eldis.org/static/DOC8822.htm</ref> == Detection vs. attribution == [[Image:GHG per capita 2000.svg|thumb|400px|Per capita greenhouse gas emissions by country including land-use change]] Detection and attribution of climate signals, as well as its common-sense meaning, has a more precise definition within the climate change literature, as expressed by the IPCC<ref>http://www.grida.no/climate/ipcc_tar/wg1/443.htm#1211</ref>. ''Detection'' of a signal requires demonstrating that an observed change is statistically significantly different from that which can be explained by natural internal variability. ''Attribution'' requires demonstrating that a signal is: * unlikely to be due entirely to internal variability; * consistent with the estimated responses to the given combination of anthropogenic and natural forcing * not consistent with alternative, physically plausible explanations of recent climate change that exclude important elements of the given combination of forcings. Detection does not imply attribution, and is easier than attribution. Unequivocal attribution would require controlled experiments with multiple copies of the climate system, which is not possible. Attribution, as described above, can therefore only be done within some margin of error. For example, the IPCC's [[IPCC Fourth Assessment Report|Fourth Assessment Report]] says "it is ''extremely likely'' that human activities have exerted a substantial net warming influence on climate since 1750," where "extremely likely" indicates a probability greater than 95%.<ref name=WG1-2007-AR4/> Following the publication of the Third Assessment Report (TAR) in 2001, "detection and attribution" of climate change has remained an active area of research. Some important results include: * A review of detection and attribution studies by the International [[Ad hoc|Ad Hoc]] Detection and Attribution Group<ref>{{Cite journal | title = Detecting and Attributing External Influences on the Climate System: A Review of Recent Advances | first = T. | last = Barnett | coauthors = et al. | journal = Journal of Climate | volume = 18 | issue = 9 | date = May 2005 | pages = 1291–1314 | url = http://www.llnl.gov/tid/lof/documents/pdf/315840.pdf | doi = 10.1175/JCLI3329.1}}</ref> found that "natural drivers such as solar variability and volcanic activity are at most partially responsible for the large-scale temperature changes observed over the past century, and that a large fraction of the warming over the last 50 yr can be attributed to greenhouse gas increases. Thus, the recent research supports and strengthens the IPCC Third Assessment Report conclusion that 'most of the global warming over the past 50 years is likely due to the increase in greenhouse gases.'" * Multiple independent reconstructions of the [[temperature record of the past 1000 years]] confirm that the late 20th century is probably the warmest period in that time * Two papers in Science in August 2005<ref>{{Cite web | title = Et Tu LT? | date = [[2007-08-11]] | publisher = RealClimate.org |last=Schmidt |first=Gavin A. | url = http://www.realclimate.org/index.php?p=170}}</ref><ref>{{Cite web | title = The tropical lapse rate quandary | date = [[2007-08-11]] | publisher = RealClimate.org |last=Schmidt |first=Gavin A. | url = http://www.realclimate.org/index.php?p=179}}</ref> resolve the problem, evident at the time of the TAR, of [[troposphere|tropospheric]] temperature trends. The UAH version of the record contained errors, and there is evidence of spurious cooling trends in the radiosonde record, particularly in the tropics. See [[satellite temperature measurements]] for details; and the 2006 US CCSP report.<ref>{{Cite journal | title = Temperature Trends in the Lower Atmosphere - Understanding and Reconciling Differences (Executive Summary) | last = Wigley | first = Tom M. L. | coauthors = et al. | publisher = [[National Oceanic and Atmospheric Administration|NOAA]] | date = [[2006-05-02]] | url = http://www.climatescience.gov/Library/sap/sap1-1/finalreport/sap1-1-final-execsum.pdf}}</ref> * Barnett and colleagues say that the observed warming of the oceans "cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two [[anthropogenic]]ally forced climate models," concluding that "it is of human origin, a conclusion robust to observational sampling and model differences"<ref>{{Cite journal | first = Tim P. | last = Barnett | coauthors = et al. | title = Penetration of Human-Induced Warming into the World's Oceans | date = [[2005-07-08]] | journal = Science | volume = 309 | issue = 5732 | pages = 284–287 | url = http://www.sciencemag.org/cgi/content/abstract/309/5732/284 | doi = 10.1126/science.1112418 <!--Retrieved from url by DOI bot--> | pmid = 15933161}}</ref> * Bratcher and Giese <ref>{{Cite journal | title = Tropical Pacific Decadal Variability and Global Warming | last = Bratcher | first = Amy J. | coauthors = Giese, Benjamin S. | date = [[2002-10-08]] | publisher = [[Geophysical Research Letters]] | volume = 29 | issue = 19 | pages = 24–1 to 24–4 | url = http://www.agu.org/pubs/crossref/2002/2002GL015191.shtml | doi = 10.1029/2002GL015191, <!--Retrieved from url by DOI bot-->}}</ref> observed conditions that "could be an indication of a climate regime shift to pre-1976 conditions." Bratcher and Giese conclude: "The results presented here do not preclude the possibility that anthropogenic sources of greenhouse gases have contributed to global warming. However the results do indicate that the human forced portion of global warming may be less than previously described." == Scientific literature and opinion ==<!-- This section is linked from [[Climate change]] --> {{Main|Scientific opinion on climate change}} Some examples of published and informal support for the consensus view: * The attribution of climate change is discussed extensively, with references to peer-reviewed research, in [http://www.grida.no/climate/ipcc_tar/wg1/439.htm chapter 12] of the IPCC TAR, which discusses [http://www.grida.no/climate/ipcc_tar/wg1/443.htm#1211 The Meaning of Detection and Attribution], [http://www.grida.no/climate/ipcc_tar/wg1/456.htm Quantitative Comparison of Observed and Modelled Climate Change], [http://www.grida.no/climate/ipcc_tar/wg1/458.htm Pattern Correlation Methods] and [http://www.grida.no/climate/ipcc_tar/wg1/460.htm Optimal Fingerprint Methods]. *An essay<ref>http://www.sciencemag.org/cgi/content/full/306/5702/1686</ref> in [[Science (journal)|''Science'']] surveyed 928 [[Abstract (summary)|abstracts]] related to climate change, and concluded that most journal reports accepted the [[Scientific opinion on climate change|consensus]]. This is discussed further in [[scientific opinion on climate change#Surveys|scientific opinion on climate change]]. * A recent paper (Estimation of natural and anthropogenic contributions to twentieth century temperature change, [[Simon Tett|Tett SFB]] et al., JGR 2002), says that "Our analysis suggests that the early twentieth century warming can best be explained by a combination of warming due to increases in greenhouse gases and natural forcing, some cooling due to other anthropogenic forcings, and a substantial, but not implausible, contribution from internal variability. In the second half of the century we find that the warming is largely caused by changes in greenhouse gases, with changes in sulphates and, perhaps, volcanic aerosol offsetting approximately one third of the warming."<ref>http://groups-beta.google.com/group/sci.environment/msg/aa8521b67cd216ac?dmode=source</ref> * In 1996, in a paper in [[Nature (journal)|''Nature'']] titled "A search for human influences on the thermal structure of the atmosphere", [[Benjamin D. Santer]] et al. wrote: "The observed spatial patterns of temperature change in the free atmosphere from 1963 to 1987 are similar to those predicted by state-of-the-art climate models incorporating various combinations of changes in carbon dioxide, anthropogenic sulphate aerosol and stratospheric ozone concentrations. The degree of pattern similarity between models and observations increases through this period. It is likely that this trend is partially due to human activities, although many uncertainties remain, particularly relating to estimates of natural variability." * Some scientists noted for their somewhat skeptical view of global warming accept that recent climate change is mostly anthropogenic. [[John Christy]] has said that he supports the [http://www.agu.org/sci_soc/policy/climate_change_position.html American Geophysical Union (AGU) declaration], and is convinced that human activities are the major cause of the global warming that has been measured.<ref>http://sfgate.com/cgi-bin/article.cgi?file=/c/a/2003/12/18/MNGNV3PH9D1.DTL&type=printable</ref> Some scientists do disagree with the consensus: see [[list of scientists opposing global warming consensus]]. For example [[Willie Soon]] and [[Richard Lindzen]]<ref>{{Cite journal | title = Can increasing carbon dioxide cause climate change? | last = Lindzen | first = Richard S. | date = [[1997-08-05]] | journal = Proceedings of the National Academy of Sciences | volume = 94 | issue = 16 | doi = 10.1073/pnas.94.16.8335 | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=33750 | pages = 8335 | pmid = 11607742}}</ref> say that there is insufficient proof for anthropogenic attribution. Generally this position requires new physical mechanisms to explain the observed warming; for example "Climate hypersensitivity to solar forcing?", Soon W et al., 2000, Annales Geophysicae-Atmospheres Hydrospheres and Space Sciences 18(5). == Findings that complicate attribution to CO<sub>2</sub> == === Warming sometimes leads CO<sub>2</sub> increases === Factors other than increased CO<sub>2</sub> concentrations can initiate warming or cooling episodes (see e.g., [[orbital forcing]]). The ice core record shows that on some occasions temperature starts rising hundreds of years before CO<sub>2</sub> increases.<ref>{{Cite journal | last = Indermühle | first = Andreas | coauthors = Monnin, Eric; Stauffer, Bernhard; Stocker, Thomas F.; Wahlen, Martin | date = 2000 | title = Atmospheric CO2 concentration from 60 to 20 kyr BP from the Taylor Dome ice core, Antarctica | journal = [[Geophysical Research Letters]] | volume = 27 | url = http://www.climate.unibe.ch/~stocker/papers/indermuehle00grl.pdf}}</ref><ref>{{Cite journal | last = Fischer | first = Hubertus | coauthors = Wahlen, Martin; Smith, Jesse; Mastroianni, Derek; Deck, Bruce | date = 1999 | title = Ice core records of atmospheric CO2 around the last three glacial terminations | journal = [[Science (journal)|Science]] | volume = 283 | doi = 10.1126/science.283.5408.1712 | url = http://www.sciencemag.org/cgi/content/abstract/sci;283/5408/1712 | pages = 1712 | pmid = 10073931}}</ref> Such results confirm that the relationship between CO<sub>2</sub> and climate can go in both directions: changes in CO<sub>2</sub> concentrations affect climate, while changes in climate can affect CO<sub>2</sub> concentrations. One proposed mechanism for this effect is increased release of sequestered CO<sub>2</sub> from oceans as circulation patterns shift, perhaps abruptly, in response to climate change.<ref>{{Cite journal | last = Skinner | first = L.C. | date = 2006 | title = Glacial – interglacial atmospheric CO2 change: a simple “hypsometric effect” on deep-ocean carbon sequestration? | journal = [[Climate of the Past Discussions]] | volume = 2 | url = http://www.clim-past-discuss.net/2/711/2006/cpd-2-711-2006.pdf}}</ref><ref>{{Cite journal | last = Paillard | first = Didier | date = 2000 | title = Glacial Cycles: Toward a New Paradigm | journal = [[Reviews of Geophysics]] | volume = 39 | issue = 3 | url = http://www.geog.ox.ac.uk/~mnew/teaching/Online_Articles/paillard_rev_geophys_2001.pdf}}</ref> A more speculative and polemical inference sometimes drawn is that the causal relationship between temperature rises and global CO<sub>2</sub> concentrations is only one-way, so that historical increases in CO<sub>2</sub> have been nothing more than the product of independently rising temperatures.<ref>http://en.wikipedia.org/wiki/The_Great_Global_Warming_Swindle</ref> However, a strictly "one-way" view of the relationship between CO<sub>2</sub> and temperature contradicts basic results in physics, specifically the fact that the absorption and emission of infrared radiation by CO<sub>2</sub> increases as its atmospheric concentration increases.<ref>{{Cite book |last = Liou |first = K.N. |title = An Introduction to Atmospheric Radiation (2nd ed) |publisher = Academic Press |year = 2002 |isbn = 978-0124514515}} </ref><ref>{{Cite journal |last = Staley |first = D.O. |coauthors = G.M. Jurica |journal = Journal of Applied Meteorology |date = 1970 |title = Flux emissivity tables for water vapor, carbon dioxide and ozone |volume = 9 |pages = 365–372 |url = http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0450(1970)009%3C0365%3AFETFWV%3E2.0.CO%3B2 | doi = 10.1175/1520-0450(1970)009 <!--Retrieved from url by DOI bot--> |year = 1970}} </ref> First principles as well as empirical observation suggest that positive feedbacks from CO<sub>2</sub> concentrations amplify warming initially caused by other factors: <blockquote>Close analysis of the relationship between the two curves [i.e., temperature and CO<sub>2</sub>] shows that, within the uncertainties of matching their timescales, the temperature led by a few centuries. This is expected, since it was changes in the Earth’s orbital parameters (including the shape of its orbit around the Sun, and the tilt of Earth’s axis) that caused the small initial temperature rise. This then raised atmospheric CO2 levels, in part by outgassing from the oceans, causing the temperature to rise further. By amplifying each other’s response, this “positive feedback” can turn a small initial perturbation into a large climate change. There is therefore no surprise that the temperature and CO2 rose in parallel, with the temperature initially in advance. In the current case, the situation is different, because human actions are raising the CO2 level, and we are starting to observe the temperature response.<ref>http://www.antarctica.ac.uk/about_bas/news/news_story.php?id=178</ref> </blockquote> Present CO<sub>2</sub> levels greatly exceed the range found in the ice core data. Isotopic analysis of atmospheric CO<sub>2</sub> confirms that fossil fuel burning is the source of most of the CO<sub>2</sub> increase, unlike during prior interglacial periods.<ref>{{Cite journal | last = Schimel | first = D. | date = 1996 | title = CO2 and the carbon cycle, pp.76-86 in Climate Change 1995: The Science of Climate Change. J.T. Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg and K. Maskell (eds), Cambridge University Press 1996.}}</ref> As noted above, models that include increased CO<sub>2</sub> levels when simulating recent climate match the observed data far better than those that do not.<ref name=WG1-2007-SPM/> === Warming on other planets? === {{main|extraterrestrial atmospheres}} Over the last two decades proxy evidence of local or planetary warming has been observed on [[Mars]], <ref name=mars-melt>{{Cite news | title = Mars Melt Hints at Solar, Not Human, Cause for Warming, Scientist Says | first = Kate | last = Ravilious | publisher = National Geographic News | date = [[2007-02-28]] | url = http://news.nationalgeographic.com/news/2007/02/070228-mars-warming.html}}</ref> [[Pluto]],<ref name=pluto-warming>{{Cite news | title = Pluto is undergoing global warming, researchers find | date = [[2002-10-09]] | publisher = [[Massachusetts Institute of Technology|MIT]] | url = http://web.mit.edu/newsoffice/2002/pluto.html}}</ref> [[Jupiter]], <ref>{{Cite news | title = New Storm on Jupiter Hints at Climate Change | first = Sara | last = Goudarzi | publisher = Space.com | date = [[2006-05-04]] | url = http://www.space.com/scienceastronomy/060504_red_jr.html}}</ref> and [[Neptune]]'s largest moon [[Triton (moon)|Triton]].<ref>{{Cite news | title = MIT researcher finds evidence of global warming on Neptune's largest moon | date = [[1998-06-24]] | publisher = [[Massachusetts Institute of Technology|MIT]] | url = http://web.mit.edu/newsoffice/1998/triton.html}}</ref> It has sometimes been asserted in the popular press that this points to a solar explanation for the recent warming on Earth.<ref>{{Cite news | title = Sun to Blame for Global Warming | first = John | last = Carlisle | date = June 1998 | publisher = [[The National Center for Public Policy Research]] | url = http://www.nationalcenter.org/NPA203.html}}</ref> Physicist [[Khabibullo Abdusamatov]] claims that [[solar variation]] has caused global warming on Earth,<ref>{{Cite journal | title = About the long-term coordinated variations of the activity, radius, total irradiance of the Sun and the Earth's climate | first = Habibullo I. | last = Abdussamatov | journal = Proceedings of the International Astronomical Union | date = June 2004 | volume = 223 | url = http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=288608 | doi = 10.1017/S1743921304006775 <!--Retrieved from url by DOI bot--> | pages = 541–542}}</ref> and that the coincident warmings "can only be a straightline consequence of the effect of the one same factor: a long-time change in solar irradiance."<ref>{{Cite news | title = Look to Mars for the truth on global warming | last = Solomon | first = Lawrence | authorlink = Lawrence Solomon | date = [[2007-02-02]] | publisher = [[National Post]] | url = http://www.canada.com/nationalpost/story.html?id=edae9952-3c3e-47ba-913f-7359a5c7f723&k=0 | accessdate = 2007-03-02}}</ref> This view is not accepted by other scientists. Planetary physicist Colin Wilson responded, "His views are completely at odds with the mainstream scientific opinion," and climate scientist Amato Evan stated, "the idea just isn't supported by the theory or by the observations."<ref name=mars-melt/> Charles Long of [[Pacific Northwest National Laboratory]], who studies radiative transfer, says "That's nuts...It doesn't make physical sense that that's the case."<ref>{{Cite news | title = Sun Blamed for Warming of Earth and Other Worlds | date = [[2007-03-12]] | first = Ker | last = Than | publisher = LiveScience.com | url = http://www.livescience.com/environment/070312_solarsys_warming.html}}</ref> [[Jay Pasachoff]], an astronomy professor at [[Williams College]], said that Pluto's global warming was "likely not connected with that of the Earth. The major way they could be connected is if the warming was caused by a large increase in sunlight. But the solar constant—the amount of sunlight received each second—is carefully monitored by spacecraft, and we know the Sun's output is much too steady to be changing the temperature of Pluto."<ref name=pluto-warming/> Instead, scientific opinion is that these changes are caused by other factors, such as orbital irregularities or (in the case of Mars) changes in [[albedo]] as a result of dust storms<ref>{{Cite journal | first = Lori K. | last = Fenton | coauthors = ''et al.'' | title = Global warming and climate forcing by recent of albedo changes on Mars | date = [[2007-04-05]] | journal = [[Nature (journal)|Nature]] | volume = 446 | issue = 7136 | doi = 10.1038/nature05718 | url = http://humbabe.arc.nasa.gov/~fenton/pdf/fenton/nature05718.pdf | pages = 646–649 | accessdate = 2007-05-09}}</ref>. == References == * Le Quéré, ''How much of the recent ''CO<sub>2</sub>'' increase is due to human activities?'', 2005<ref>http://www.realclimate.org/index.php?p=160</ref> ==Footnotes== {{Reflist}} == See also == {{EnergyPortal}} [[Aviation and climate change]] == External links == *[http://www.realclimate.org/ RealClimate] - Blog on current climate change issues by active climatologists *"The Climate of Man", ''The New Yorker'' (2005): [http://www.newyorker.com/printables/fact/050425fa_fact3 Part 1], [http://www.newyorker.com/printables/fact/050502fa_fact3 Part 2], [http://www.newyorker.com/printables/fact/050509fa_fact3 Part 3] *[http://www.sciencebits.com/CO2orSolar Anthropogenic or Solar?] by Shaviv *[http://publishing.royalsociety.org/media/proceedings_a/rspa20071880.pdf Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature] by Mike Lockwood and Claus Frohlich *[http://www.epa.gov/climatechange US EPA climate change and global warming website] {{global warming}} [[Category:Global warming]]