The Most Controversial Chart in History, Explained
Climate deniers threw all their might at disproving the famous “hockey stick” climate change graph. Here’s why they failed.
—By Chris Mooney
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Back in 1998, a little-known climate scientist named Michael Mann and two colleagues published a paper that sought to reconstruct the planet’s past temperatures going back half a millennium before the era of thermometers—thereby showing just how out of whack recent warming has been. The finding: Recent Northern Hemisphere temperatures had been “warmer than any other year since (at least) AD 1400.” The graph depicting this result looked rather like a hockey stick: After a long period of relatively minor temperature variations (the “shaft”), it showed a sharp mercury upswing during the last century or so (“the blade”).
The report moved quickly through climate science circles. Mann and a colleague soon lengthened the shaft of the hockey stick back to the year 1000 AD—and then, in 2001, the UN’s Intergovernmental Panel on Climate Change prominently featured the hockey stick in its Third Assessment Report. Based on this evidence, the IPCC proclaimed that “the increase in temperature in the 20th century is likely to have been the largest of any century during the past 1,000 years.”
And then all hell broke loose.
Mann tells the full story of the hockey stick—and the myriad unsuccessful attacks on it—in his 2012 book The Hockey Stick and the Climate Wars: Dispatches From the Front Lines; Mann will appear at a Climate Desk Live event on May 15 to discuss this saga.
Read the rest of the article and a summary of the history here.