Intergovernmental Panel on Climate Change

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The Intergovernmental Panel on Climate Change (IPCC) is a United Nations-affiliated committee established in 1988. As of August 2013, the panel had 195 government representatives, according to the IPCC's website. The panel's stated purpose is "to provide policymakers with regular assessments of the scientific basis of climate change, its impacts and future risks, and options for adaptation and mitigation."

The IPCC's authors, contributors, and editors assess existing scientific literature on climate change by organizing, reviewing, and publishing what are known as the panel's Assessment Reports, which summarize scientific, technical, social, and political information for governments and policymakers on climate change-related issues, including both scientific claims and policy recommendations. The IPCC does not conduct original research, establish or operate its own climate models, or measure climate and weather phenomena.

Background

The United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) established the IPCC in 1988. The panel's stated role is "to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to the understanding of climate change, its impacts and future risks, and options for adaptation and mitigation." The IPCC is composed of representatives from United Nations (UN) and WMO member countries. As of August 2013, the panel had 195 government representatives, according to the IPCC's website. Scientists are involved voluntarily with the panel as authors, contributors, and reviewers for the IPCC's published reports. The panel receives and approves nominations for these roles from member governments.

The IPCC is composed of three working groups and one task force: Working Group I is responsible for gathering, assessing, and publishing the physical science of climate change; Working Group II is responsible for analyzing and explaining climate change impacts and adaptation; and Working Group III is responsible for drafting and explaining climate change mitigation efforts. The stated mission of the IPCC's task force is "to develop and refine a methodology for the calculation and reporting of national greenhouse gas emissions and removals."

Terms and definitions

See also: Greenhouse gases and global warming

Climate is a combination of normally prevailing weather conditions averaged over decades, centuries, or longer periods of time. These conditions include air pressure, atmospheric conditions, humidity, temperature, precipitation, cloudiness, fog, frost, sunshine, winds, and more. By contrast, weather is a combination of the same conditions in an area or region over shorter periods of time, such as days, weeks, or months. The earth's climate system is affected by several factors, including the atmosphere; volcanic eruptions; snow; ice; oceans and other bodies of water; land surface; biological organisms, including human beings, wildlife, and vegetation; changes in Earth's orbit; and changes to the sun.

Climate change can refer to significant or large-scale changes in land surface and ocean temperature, precipitation, storm and wind patterns, or other weather-related events that can occur over a long period of time, including decades, centuries, and millennia. In the public debate, the term climate change may be used interchangeable with the theory that human activity since the Industrial Revolution contributes to and/or is responsible for global warming and subsequent changes in the climate. This theory states that global warming will occur when concentrations of greenhouse gases (heat-trapping gases) such as carbon dioxide, water vapor, and methane rise and thus keep more heat in the atmosphere than can escape into space and/or be absorbed on Earth. More heat in the atmosphere, less absorption of greenhouse gases on Earth, solar and volcanic activity may contribute to an increase in global average surface temperatures.

Global warming refers to a gradual increase in global surface temperatures and the temperature of the Earth's atmosphere. Global warming is associated with the greenhouse effect that is produced when the Earth's surface and atmosphere absorbs solar energy and reradiates the energy back into space. A portion of the absorbed energy is emitted by land and oceans, absorbed by the Earth's atmosphere, and reradiated back to the Earth. The greenhouse effect is one of several climate forcings, which are the major drivers of Earth's climate, alongside solar activity, volcanic eruptions, and aerosols.

IPCC Assessment Reports

The IPCC publishes assessment and special reports covering scientific, technological, social, and economic information related to climate change. Its assessment reports, referred to as IPCC Assessment Reports, include projections of future climate change based on existing scientific literature and different scenarios involving the trajectory of greenhouse gas emissions and other factors that affect global climate. The IPCC does not conduct original research, establish or operate its own climate models, or measure climate and weather phenomena.

IPCC assessments are drafted by lead authors, contributing authors, and reviewers. The panel receives nominations for these roles from member governments. According to the IPCC, authors and contributors are selected based on expertise and "to reflect a range of scientific, technical and socio-economic views and backgrounds." In writing and publishing its assessment reports, the IPCC reviews and incorporates literature from scientific journals, governmental reports, studies from industry and research universities, reports from international organizations, and literature presented at academic conferences.

The IPCC's Fifth Assessment Report (published between 2013-2014) included 831 individuals as lead authors, coordinating authors, and review editors. These individuals were selected from 3,598 nominations for the three working groups (some individuals were nominated for more than one working group).

Stance on climate change

In five Assessment Reports (published in the years 1990, 1995, 2001, 2007, and 2013-2014), the IPCC endorsed its conclusion that, in its view, human-induced greenhouse gas (GHG) emissions were the main contributors to global warming and thus would likely drive climate change in the 21st century. The IPCC's Fourth Assessment Report (2007) endorsed the following conclusions on climate change:

• "Global GHG emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004."
• "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic [human-caused] GHG concentrations."
• "Continued GHG emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century."

Support and opposition

Summarized below are the views of those who support and oppose the IPCC's evaluation of human-caused climate change.

Support

• In an online article, the Union of Concerned Scientists, whose stated mission is to adopt “rigorous, independent science to work to solve our planet’s most pressing problems,” argued that the IPCC's process of writing and reviewing its Assessment Reports ensures that the reports are scientifically credible because the panel considers "the range of scientific opinion on climate change fairly." In addition, the article supported the IPCC's stance on providing "several channels for input from experts along the entire spectrum of opinion, including global warming contrarians." The article's authors concluded, "The inclusive process by which IPCC assessments are developed and accepted by its members results in reports of exceptional scientific credibility."
• In a December 2012 article posted at Skeptical Science, a self-described nonprofit science education organization whose stated goal is "to explain what peer reviewed science has to say about global warming," Dana Nuccitelli argued that global surface temperature projections in the IPCC's Assessment Reports have been credible and confirmed by observational data. Nuccitelli cited the second IPCC Assessment Report's (published in 1995) projected rate of warming of 0.14°C (Celsius) per decade from 1990 to 2012 compared to an observed warming rate of 0.15°C per decade from 1990 to 2012. Nuccitelli also cited the IPCC's third report (from 2001) showing a projected warming rate of 0.16°C per decade from 1990 to 2012 compared to an observed warming rate of 0.15°C per decade for the same period. Nuccitelli concluded, "The IPCC has thus far done remarkably well at predicting future global surface warming."
• David Titley, director of the Center for Solutions to Weather and Climate Risk at Pennsylvania State University, argued in December 2015 that the IPCC's conclusion that human-induced greenhouse gases are responsible for global warming is based on "a combination of multiple, independent sources of data." Titley cited the warming effect of human-caused carbon dioxide CO₂ emissions from 1750 to 2011, which he argued accounted for approximately 42 percent of the total warming influence from human-caused emissions during this period. Titley further argued that the reduced rate of warming observed between 1998-2013 did not alter the claim that human-caused greenhouse gas emissions predominantly drive global warming and climate. Titley argued that human-induced climate change theory is based on observations and measurements accepted by organizations other than the IPCC, including major national academies of science in the United Kingdom, China, India, Russia, Brazil, and the United States. Titley concluded, "The basis of the science of climate change is exceptionally well-understood and can be—and has been—applied by many researchers inside and outside the government."

Opposition

• Judith Curry, former Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, argued in December 2015 that the IPCC's conclusion to attribute global warming since 1950 to human activity is contradicted by other data, such as data showing a slower rate of warming from 1998-2013 compared to the IPCC's 2007 projections. Curry also argued that the IPCC did not have adequate explanations for previous variations in global climate, including the warming period from 1910-1945 and a period of slower warming between 1945-1975. Additionally, Curry claimed that the general warming trend since the year 1800 cannot be explained by the human-induced greenhouse gas emissions, which Curry argued counted against the IPCC's claim that human activity is likely responsible for warming since 1950. Curry concluded that "these three points substantially reduces the confidence that we should place in the IPCC’s attribution of warming since 1950 to human causes."
• In its 2016 study critiquing the theory of human-caused climate change and global warming, the Nongovernmental Panel on Climate Change (NIPCC), a self-described panel of scientists and scholars who "are not predisposed to believe climate change is caused by human greenhouse gas emissions", argued that the IPCC's Assessment Reports are "not balanced or accurate summaries of the current state of climate science." The study's authors argued that the IPCC does not adequately consider alternative hypothesis that may contradict the conclusion that human-induced greenhouse gas emissions are primarily responsible for global warming and that human-induced global warming is dangerous. The authors concluded, "In contradiction of the scientific method, IPCC assumes its implicit hypothesis is correct and that its only duty is to collect evidence and make plausible arguments in the hypothesis’s favor." The study's authors instead argued that "currently observed changes in global climate indices and the physical environment" are the result of natural variability in the Earth's climate.
• David Botkin, professor emeritus of the Department of Ecology, Evolution, and Marine Biology at the University of California, Santa Barbara, argued in May 2014 that the U.S. National Climate Assessment (a U.S. government report mandated by Congress) and the IPCC's Assessment Reports assume that "climate warming forecast by the global climate models is happening and will continue to happen and grow worse." Botkin argued that climate model forecasts cited by the IPCC do not match observational data, particularly two temperature datasets collected by satellites and balloons released into the atmosphere. Botkin further claimed that the IPCC process of collecting and reviewing large amounts of scientific literature may lead scientists to "misinterpret specific papers, fail to understand where the major observational gaps are, and have trouble making an accurate list of citations and all sources of information."

See also

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  Greenhouse gas

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  Climate change

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  Methane

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  Carbon dioxide