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Attribution of recent climate change is the effort to 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: Working Group I: The Physical Basis for Climate Change
Recent reports from the Intergovernmental Panel On Climate Change (IPCC) report have concluded that:
The panel, which represents Consensus in the Scientific Community , defines "very likely," "extremely likely," and "virtually certain" as indicating probabilities greater than 90%, 95%, and 99%, respectively. Working Group I: The Physical Basis for Climate Change KEY ATTRIBUTIONS Greenhouse gases Scientific consensus has identified concentrations. The chart at right attributes greenhouse gas Fuel s (generally Fossil Fuel s), and Agricultural byproducts (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 that frequently accompanies it. A second reason that climate change has been attributed to land use is that the Terrestrial Albedo is often altered by use, which leads to Radiative Forcing . This effect is more significant locally than globally. Intergovernmental Panel on Climate Change retrieved 26 June 2007 Livestock and land use Worldwide, livestock production occupies 70% of all land used for agriculture, or 30% of the land surface of the Earth. Food and Agricultural Organization of the U.N. retrieved 27 jun 2007 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. Specific attributions to the livestock sector include:
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. Intergovernmental Panel on Climate Change ret. 26 June 2007 Key sources to which anthropogenic aerosols are attributed "Aerosols and Climate" retrieved 26 jun 2007 include:
ATTRIBUTION OF 20TH CENTURY CLIMATE CHANGE '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 Atmosphere . This has led to increases in mean global temperature, or Global Warming . Other human effects are relevant—for example, sulphate 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 ± 0.18 ° Celsius (1.3 ± 0.32 ° 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 Record . In the 1995 second assessment report (SAR), the 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". IPCC The 2007 fourth assessment report (WG1 AR4) strengthened this finding:
Over the past five decades there has been a global warming of approximately 0.65 °C (1.17 °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 CO2, is mostly responsible for the observed warming. Evidence for this conclusion includes:
In 2001, the U.S. 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." [http://www.eia.doe.gov/oiaf/1605/ggccebro/chapter1.html [http://www.eldis.org/static/DOC8822.htm] DETECTION VS. ATTRIBUTION 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 {Link without Title} . ''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:
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 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%. Working Group I: The Physical Basis for Climate Change (italics in original) 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:
SCIENTIFIC LITERATURE AND OPINION See Also: Scientific opinion on climate change Some examples of published and informal support for the consensus view:
Some scientists do disagree with the consensus: see List Of Scientists Opposing Global Warming Consensus . For example Willie Soon and Richard Lindzen Can increasing carbon dioxide cause climate change?", Lindzen RS, 1997, PNAS 94(16) 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 CO2 increases Factors other than increased CO2 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 CO2 increases.1 2 Such results confirm that the relationship between CO2 and climate can go in both directions: changes in CO2 concentrations affect climate, while changes in climate can affect CO2 concentrations. One proposed mechanism for this effect is increased release of sequestered CO2 from oceans as circulation patterns shift, perhaps abruptly, in response to climate change.3 4 |
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