IPCC Fourth Assessment Report - Working Group I: The Physical Science Basis

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.