be found in Special Report on Emissions Scenarios. "Likely" means greater than 66% probability of being correct, based on expert judgement. Sections The report was released in four principal sections: Contribution of Working Group I (WGI): Climate Change 2007: The Physical Science Basis. Contribution of Working Group II (WGII): Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group III (WGIII): Climate Change 2007: Mitigation of Climate Change. Contribution of Working Groups I, II, and III: The Synthesis Report (SYR). Working Group I: The Physical Science Basis 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: "Warming of the climate system is unequivocal." "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." Very likely and likely mean "the assessed likelihood, using expert judgment" are over 90% and over 66%, respectively. Observations The report notes many observed changes in the Earth's climate including atmospheric composition, global average temperatures, ocean conditions, and other climate changes. Changes in the atmosphere Carbon dioxide, methane, and nitrous oxide are all long-lived greenhouse gases. "Carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values." The amount of carbon dioxide in the atmosphere in 2005 (379 ppm) exceeds by far the natural range of the last 650,000 years (180 to 300 ppm). The amount of methane in the atmosphere in 2005 (1774 ppb) exceeds by