Climate Change Report

I recently wrote an email to a colleague with whom I've been debating global warming. We both agree that it's happening, but he thinks we do not have sufficient evidence to conclude it's manmade (via CO_2) rather than solar variation.

My email:

FYI, here's a link to a summary of the IPCC report on global warming from Wikipedia.
And here's the full text.

The summary is in a nice bulleted format with section headers, so you can skip to the parts you're most interested in. The report includes data stating that

1) atmospheric CO_2 and methane levels are higher than at any other time in the past 650,000 years, and

2) since 1750, human activities have resulted in "radiative forcing" of 1.6 W/m^2, while solar variations have resulted in only 0.12 W/m^2.

Page 11 of the full text has a graph, Figure SPM-4, which compares the observed temperature increase since 1900 with computer models assuming only natural sources, and natural plus antropogenic sources - search through the full document on the word "solar" to find relevant sections.

I don't have permission to repost his reply, so I'll try and reword it at another time.

See also this paper on ice ages, this discussion of that paper, and this discussion of that discussion.