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Attribution of recent climate change is the effort to scientifically ascertain mechanisms responsible for recent changes observed in the Earth's climate, commonly known as 'global warming'. The effort has focused on changes observed during the period of instrumental temperature record, when records are most reliable; particularly in the last 50 years, when human activity has grown fastest and observations of the troposphere have become available. The dominant mechanisms (to which recent climate change has been attributed) are anthropogenic, i.e., the result of human activity. They are:〔http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9.html 〕 * increasing atmospheric concentrations of greenhouse gases * global changes to land surface, such as deforestation * increasing atmospheric concentrations of aerosols. There are also natural mechanisms for variation including climate oscillations, changes in solar activity, and volcanic activity. According to the Intergovernmental Panel on Climate Change (IPCC), it is "extremely likely" that human influence was the dominant cause of global warming between 1951 and 2010.〔 IPCC (11 November 2013): D. Understanding the Climate System and its Recent Changes, in: (Summary for Policymakers (finalized version) ), in: 〕 The IPCC defines "extremely likely" as indicating a probability of 95 to 100%, based on an expert assessment of all the available evidence.〔 IPCC (11 November 2013): Footnote 2, in: (Summary for Policymakers (finalized version) ), in: 〕 Multiple lines of evidence support attribution of recent climate change to human activities:〔 . Docket ID EPA-HQ-OAR-2009-0171. 〕 * A basic physical understanding of the climate system: greenhouse gas concentrations have increased and their warming properties are well-established.〔 * Historical estimates of past climate changes suggest that the recent changes in global surface temperature are unusual.〔 * Computer-based climate models are unable to replicate the observed warming unless human greenhouse gas emissions are included.〔 * Natural forces alone (such as solar and volcanic activity) cannot explain the observed warming.〔 The IPCC's attribution of recent global warming to human activities is a view shared by most scientists,〔 "The IPCC's conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue" (page 3).〕〔 "Most scientists agree that the warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the atmosphere ()" (page 2).〕〔 〕 and is also supported by 196 other scientific organizations worldwide〔 〕 (see also: scientific opinion on climate change). ==Background== (詳細はclimate science that are used in the following sections: Factors affecting Earth's climate can be broken down into feedbacks and forcings.〔 〕 A forcing is something that is imposed externally on the climate system. External forcings include natural phenomena such as volcanic eruptions and variations in the sun's output.〔Le Treut ''et al.'', (Chapter 1: Historical Overview of Climate Change Science ), (FAQ 1.1, What Factors Determine Earth's Climate? ), in .〕 Human activities can also impose forcings, for example, through changing the composition of the atmosphere. Radiative forcing is a measure of how various factors alter the energy balance of the Earth's atmosphere.〔Forster ''et al.'', (Chapter 2: Changes in Atmospheric Constituents and Radiative Forcing ), (FAQ 2.1, How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences? ) in .〕 A positive radiative forcing will tend to increase the energy of the Earth-atmosphere system, leading to a warming of the system. Between the start of the Industrial Revolution in 1750, and the year 2005, the increase in the atmospheric concentration of carbon dioxide (chemical formula: CO2) led to a positive radiative forcing, averaged over the Earth's surface area, of about 1.66 watts per square metre (abbreviated W m−2).〔IPCC, (Summary for Policymakers ), (Human and Natural Drivers of Climate Change ), Figure SPM.2, in .〕 Climate feedbacks can either amplify or dampen the response of the climate to a given forcing.〔 There are many feedback mechanisms in the climate system that can either amplify (a positive feedback) or diminish (a negative feedback) the effects of a change in climate forcing. Aspects of the climate system will show variation in response to changes in forcings.〔 〕 In the absence of forcings imposed on it, the climate system will still show internal variability (see images opposite). This internal variability is a result of complex interactions between components of the climate system, such as the coupling between the atmosphere and ocean (see also the later section on Internal climate variability and global warming).〔Albritton ''et al.'', (Technical Summary ), (Box 1: What drives changes in climate? ), in .〕 An example of internal variability is the El Niño-Southern Oscillation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Attribution of recent climate change」の詳細全文を読む スポンサード リンク
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