MICHELE NORRIS, Host:
The National Academy of Sciences today stepped into a feud over global warming. At issue is a study that found the earth is hotter now than it's been in a thousand years. Some use that as an argument that global warming has already pushed the world into extreme climate territory. The academy panel does not dispute that humans are changing the climate, but it said the earth's climate history isn't as certain as its sometimes portrayed.
NPR's Richard Harris reports.
RICHARD HARRIS: The focus of debate is a graph which has become an icon in the political fight over global warming. It's called the hockey stick because that's what it's shaped like. It starts out as a long straight line, the handle, and then it turns deeply upwards as temperatures rise in the 20th Century.
But the Academy today looked askance at that long handle. At a briefing today, committee chair Gerald North, from Texas A&M, said they have high confidence that the last few decades have been the warmest in 400 years. But if you ask whether the past few decades have been the warmest in a thousand years, the committee uses a much weaker word.
GERALD NORTH: The committee finds it plausible.
HARRIS: And plausible is another way of saying it doesn't meet the scientific standards of certainty. That's because it's also possible they were major warm periods long ago that don't show up in the hockey stick data. Committee member Kurt Cuffey is a geographer from UC Berkeley.
KURT CUFFEY: Before about 1,600 A.D., our picture of climate history really becomes much murkier. And the primary reason it becomes much murkier is that we start losing sources of information.
HARRIS: Nobody was measuring the lengths of glaciers that long ago, for example. And old tree rings can be harder to interpret.
CUFFEY: And as you go back in time, trying to do the temperature reconstruction, you start relying more and more on data from fewer and fewer geographic locations.
HARRIS: As a result, if you include all the uncertainties, the handle of that hockey stick becomes broad and indistinct. So for one it's not possible to tell whether a heat wave known as the Medieval Warm Period was actually warmer than what we're experiencing today. Cuffey argues that's beside the point anyway.
CUFFEY: If we did know, for example, that the climate was as warm at 1000 A.D. as it is now, it would have no essential impact on our understanding of climate change in the 20th Century, the role of humans in causing it and the need to think seriously about how that may evolve in the next few centuries.
HARRIS: But this issue has taken on huge proportions because global warming skeptics have argued that the hockey stick is the main line of evidence supporting global warming and then they attacked it. The Academy report directly rejects the premise that the hockey stick is of central importance. There are stronger lines of evidence showing that humans are heating up the globe. But Myron Ebel at the Competitive Enterprise Institute says still there's something for everyone in the 155 page document.
MYRON EBEL: Well I think each side of the public policy debate will take out of it what they want to hear.
HARRIS: He hopes the report will cause the United Nations Climate Change Panel to stop using the hockey stick graph as an icon. Committee member Kurt Cuffey hopes the work will end the controversy that, in his view, blew up far out of proportion. He says what happened here is really the normal course of science. Somebody published a result and other scientists put it to the test.
CUFFEY: Science works over time as a community process, not by one genius descending from above and telling us the truth.
HARRIS: And in the case of climate history, that community now includes 12 more distinguished scientists who have given the hockey stick an extra hard look.
Richard Harris, NPR News.
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