We have a lot of really solid evidence of significant
climate change going back at least
110 million years. There is also
evidence back 65 million years, 600,000 years,
and 500 years.
For the last 2000 years there is
Committee on Surface Temperature
Reconstructions for the Last 2,000 Years,
National Research Council, 'Surface
Temperature Reconstructions for the Last
2,000 Years', ISBN 0-309-66264-8, 196
pages, National Academies Press, 2006.
The fact that climate has gone through major changes before is the reason people are worried. If it had been stable for a billion years, we could be confident that powerful negative feedbacks keep it that way.
Instead, we see minor initial changes kicking off positive feedbacks that take things much further. Hansen's book goes into this in detail.
For the last 2000 years there is
Committee on Surface Temperature Reconstructions for the Last 2,000 Years, National Research Council, 'Surface Temperature Reconstructions for the Last 2,000 Years', ISBN 0-309-66264-8, 196 pages, National Academies Press, 2006.
still available at
http://www.nap.edu/catalog/11676.html