Fourth Assessment Report

Climate Change 2007, the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change (IPCC), is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for adaptation and mitigation. The report is the largest and most detailed summary of the climate change situation ever undertaken, produced by thousands of authors, editors, and reviewers from dozens of countries, citing over 6,000 peer-reviewed scientific studies.

It supersedes the Third Assessment Report (2001), and is superseded by the Fifth Assessment Report.

The headline findings of the report were: "warming of the climate system is unequivocal", and "most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."

The report was released in four principal sections:

The full WGI report was published in March 2007, and last updated in September of that year. It includes a Summary for Policymakers (SPM), which was published in February 2007, and a Frequently Asked Questions section.

This section of the report, Climate Change 2007: The Physical Science Basis, assessed current scientific knowledge of "the natural and human drivers of climate change" as well as observed changes in climate. It looked at the ability of science to attribute changes to different causes, and made projections of future climate change.

It was produced by 676 authors (152 lead authors, 26 review editors, and 498 contributing authors) from 40 countries, then reviewed by over 625 expert reviewers. More than 6,000 peer-reviewed publications were cited.

Before being approved, the summary was reviewed line by line by representatives of 113 governments during the 10th session of WGI, in January to February 2007.

On the issue of global warming and its causes, the SPM states that:

Very likely and likely mean "the assessed likelihood, using expert judgment" are over 90% and over 66%, respectively.

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