IPCC's purpose is to evaluate the state of climate science as a...

IPCC's purpose is to evaluate the state of climate science as a basis for informed policy action, primarily on the basis of peer-reviewed and published scientific literature, It does not carry out research nor does it monitor climate related data or other relevant parameters. It bases its assessment mainly on peer reviewed and published scientific/technical literature.
Look here,
http://www.ipcc.ch/about/procd.htm