CNN.com - Study: Earth 'likely' hottest in 2,000 years - Jun 22, 2006:
Combining that information gave the panel "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," the academy said.
Overall, the panel agreed that the warming in the last few decades of the 20th century was unprecedented over the last 1,000 years, though relatively warm conditions persisted around the year 1000, followed by a "Little Ice Age" from about 1500 to 1850.
The scientists said they had less confidence in the evidence of temperatures before 1600. But they considered it reliable enough to conclude there were sharp spikes in carbon dioxide and methane, the two major "greenhouse" gases blamed for trapping heat in the atmosphere, beginning in the 20th century, after remaining fairly level for 12,000 years.
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