Earth running a fever?


The National Academy of Sciences, after reconstructing world average surface temperatures for the past 2,000 years, said last week that the data are “additional supporting evidence… that human activities are responsible for much of the recent warming.”

The academy had been asked to report to the United States Congress on how researchers were able to draw conclusions about the Earth’s climate going back thousands of years, before data was available from modern scientific instruments.

The academy’s panel of 12 experts looked at tree rings, corals, marine and lake sediments, ice cores, boreholes and glaciers.

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 panel writes.

It says the “recent warmth is unprecedented for at least the last 400 years and potentially the last several millennia,” though it was relatively warm around the year 1000, followed by a “little ice age” from about 1500 to 1850.

Between 1 A.D. and 1850, volcanic eruptions and solar fluctuations had the biggest effects on climate, says the panel. But those temperature changes “were much less pronounced than the warming due to greenhouse gas” levels by pollution since the mid-19th century.”

The National Academy of Sciences is a private agency mandated by the U.S, Congress to provide advice on scientific matters.

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