How did the IPCC form a consensus that evidence of global warming is “unequivocal?”
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Each IPCC report explains the basis of its conclusions in great detail. For example, the 2007 statement that “warming of the climate system is unequivocal” is explained on in the Summary for Policymakers from Working Group I and in further detail in the full report on page 5. The full statement is: “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.” The supporting observations (of which there are many) include global temperature trends at the surface and aloft, increased atmospheric water vapor, declines in mountain glaciers and snow cover in both hemispheres, and documented increases in ocean temperature since the 1960s to depths of at least 10,000 feet.
More Information: IPCC Assessment reports
Principles Governing IPCC Work