The panel of top climate scientists told lawmakers that the Earth is running a fever and that “human activities are responsible for much of the recent warming.” Their 155-page report said average global surface temperatures in the Northern Hemisphere rose about 1 degree F during the 20th century...From the press release:
Many scientists tie warming temperatures to rising emissions of certain gases like carbon dioxide. While essential to survival, carbon dioxide has seen a spike as fossil fuels are burned by cars and factories, leading to concerns that it and other gases are exacerbating the greenhouse effect that keeps Earth inhabitable.
There is sufficient evidence from tree rings, boreholes, retreating glaciers, and other "proxies" of past surface temperatures to say with a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years, according to a new report from the National Research Council. Less confidence can be placed in proxy-based reconstructions of surface temperatures for A.D. 900 to 1600, said the committee that wrote the report, although the available proxy evidence does indicate that many locations were warmer during the past 25 years than during any other 25-year period since 900.(Thanks Fred Turner)