After a comprehensive review of climate change data, the nation's preeminent scientific body found that average temperatures on Earth had risen by about 1 degree over the last century, a development that "is unprecedented for the last 400 years and potentially the last several millennia."
The report from the National Research Council also concluded that "human activities are responsible for much of the recent warming."
Coupled with a report last month from the Bush administration's Climate Change Science Program that found "clear evidence of human influences on the climate system," the new study from the council, part of the National Academy of Sciences, signals a growing acceptance in Washington of widely held scientific views on the causes of global warming.
The council's review focused on the controversial "hockey stick" graph, which shows Earth's temperature remaining stable for 900 years then suddenly arching upward in the last century. The curve resembles a hockey stick laid on its side.
The panel dismissed critics' charges that fraud and statistical error were responsible for the graph's sharp upward swing, noting that many studies had confirmed its essential conclusions in the eight years since it was first published in the journal Nature.
"There is nothing in this report that should raise any doubts about the broad scientific consensus on global climate change ... or any doubts about whether any paper on the temperature records was legitimate scientific work," said House Science Committee Chairman Sherwood Boehlert (R-N.Y.), who requested the study in November.
The finding was a rebuke to global warming skeptics and some conservative politicians who have attacked the hockey stick as the work of overzealous scientists determined to shame the government into imposing environmental regulations on big business.
Geophysicist Michael E. Mann of Pennsylvania State University, lead author of the study that debuted the graph, said it was time "to put this sometimes silly debate behind us and move forward, to do what we need to do to decrease the remaining uncertainties."
Though scientists have cited various factors as evidence of global warming -- including the melting of polar ice caps and measurements of atmospheric carbon dioxide -- the hockey stick encapsulated the issue in an instantly recognizable way.
