This June 2006 report concludes that "there is sufficient evidence from tree rings, retreating glaciers, and other 'proxies' to say with confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years. ... There is less confidence in reconstructions of surface temperatures from 1600 back to A.D. 900." Includes an audio briefing and link to the full report. From the National Academy of Sciences.