Earth warmest in at least 400 years, panel finds

WASHINGTON - Weighing in on the highest profile debate about global warming, the nation's premier science policy body on Thursday voiced a "high level of confidence" that Earth is the hottest it has been in at least 400 years, and possibly even the last 2,000 years.

A panel convened by the National Research Council reached that conclusion in a broad review of scientific studies, reporting that the evidence indicates “recent warmth is unprecedented for at least the last 400 years.”

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.

The report was requested last November by the chairman of the House Science Committee, Rep. Sherwood Boehlert, R-N.Y., to survey what science says about climate change over the last 2,000 years.

Last year, when the House Energy and Commerce Committee chairman, Rep. Joe Barton, R-Texas, launched an investigation of three climate scientists, Boehlert said Barton should try to learn from scientists, not intimidate them.

The Bush administration also has maintained that not enough is known about the threat to warrant new emission controls that the White House says would have cost 5 million Americans their jobs.

Boehlert said Thursday the report shows the value of having scientists advise Congress. “There is nothing in this report that should raise any doubts about the broad scientific consensus on global climate change,” he said.

INTERACTIVE The greenhouse effect How the Earth maintains a temperature conducive to life

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.

“The numerous indications that recent warmth is unprecedented for at least the last 400 years and potentially the last several millennia, in combination with estimates of external climate forcing variations over the same period, supports the conclusion that human activities are responsible for much of the recent warming,” the panel wrote.

'Hockey stick' debate
The report focused on research data criticized by warming skeptics and which was published in 2001 by the Intergovernmental Panel on Climate Change, a United Nations body that has led international warming research.

Climate scientists Michael Mann, Raymond Bradley and Malcolm Hughes had prepared the research, concluding that the Northern Hemisphere was the warmest it has been in 1,000 years. Their research included a graphic dubbed the “hockey stick” because of the way the temperature data looked when presented over time — stability followed by a sharp curve upwards over the last 140 years.

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