February 2, 2007

IPCC Fourth Assessment Report

IPCC releases the Working Group I Summary for Policymakers

Government representatives spent the week approving the summary line by line, so the text released that Friday was both a scientific assessment and an intergovernmentally approved document.

2 February 2007, in Paris

The IPCC released the Summary for Policymakers of Working Group I's contribution to the Fourth Assessment Report in Paris on 2 February 2007, under the title Climate Change 2007: The Physical Science Basis. Representatives of 113 governments had approved the text line by line over the preceding week.

The summary declared warming of the climate system "unequivocal," citing observed temperature increases, widespread melting of snow and ice, and rising average sea level.

Two judgments, not one

Attribution carried its own calibrated phrase. The summary concluded that most observed global-average warming since the mid-20th century was "very likely" caused by the observed increase in anthropogenic greenhouse-gas concentrations — with "very likely" defined as greater than 90% assessed probability.

That threshold had strengthened since 2001, when the comparable conclusion was only "likely." The estimated global surface-temperature increase from 1906 to 2005 was given as 0.74 °C, with a 90% interval of 0.56–0.92 °C.

One volume of the assessment

This was not the complete Fourth Assessment Report. The other working-group contributions and the Synthesis Report had not yet been released, and the full AR4 cycle was scheduled for completion later in 2007.

Working Group I, co-chaired by Susan Solomon and Dahe Qin, assessed observations, causes and projections; impacts and mitigation belonged to the other working groups. The wider AR4 process drew on more than 3,500 experts from more than 130 countries.

Sources

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