Hockey Stick on Ice
Politicizing the science of global warming.
Friday, February 18, 2005 12:01 a.m. EST
On Wednesday National Hockey League Commissioner Gary Bettman canceled the season, and we guess that’s a loss. But this week also brought news of something else that’s been put on ice. We’re talking about the “hockey stick.”
Just so we’re clear, this hockey stick isn’t a sports implement; it’s a scientific graph. Back in the late 1990s, American geoscientist Michael Mann published a chart that purported to show average surface temperatures in the Northern Hemisphere over the past 1,000 years. The chart showed relatively minor fluctuations in temperature over the first 900 years, then a sharp and continuous rise over the past century, giving it a hockey-stick shape.
Mr. Mann’s chart was both a scientific and political sensation. It contradicted a body of scientific work suggesting a warm period early in the second millennium, followed by a “Little Ice Age” starting in the 14th century. It also provided some visually arresting scientific support for the contention that fossil-fuel emissions were the cause of higher temperatures. Little wonder, then, that Mr. Mann’s hockey stick appears five times in the Intergovernmental Panel on Climate Change’s landmark 2001 report on global warming, which paved the way to this week’s global ratification–sans the U.S., Australia and China–of the Kyoto Protocol.
Yet there were doubts about Mr. Mann’s methods and analysis from the start. In 1998, Willie Soon and Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics published a paper in the journal Climate Research, arguing that there really had been a Medieval warm period. The result: Messrs. Soon and Baliunas were treated as heretics and six editors at Climate Research were made to resign.
Still, questions persisted. In 2003, Stephen McIntyre, a Toronto minerals consultant and amateur mathematician, and Ross McKitrick, an economist at Canada’s University of Guelph, jointly published a critique of the hockey stick analysis. Their conclusion: Mr. Mann’s work was riddled with “collation errors, unjustifiable truncations of extrapolation of source data, obsolete data, geographical location errors, incorrect calculations of principal components, and other quality control defects.” Once these were corrected, the Medieval warm period showed up again in the data.
This should have produced a healthy scientific debate. Instead, as the Journal’s Antonio Regalado reported Monday, Mr. Mann tried to shut down debate by refusing to disclose the mathematical algorithm by which he arrived at his conclusions. All the same, Mr. Mann was forced to publish a retraction of some of his initial data, and doubts about his statistical methods have since grown. Statistician Francis Zwiers of Environment Canada (a government agency) notes that Mr. Mann’s method “preferentially produces hockey sticks when there are none in the data.” Other reputable scientists such as Berkeley’s Richard Muller and Hans von Storch of Germany’s GKSS Center essentially agree.
We realize this may all seem like so much academic nonsense. Yet if there really was a Medieval warm period (we draw no conclusions), it would cast some doubt on the contention that our SUVs and air conditioners, rather than natural causes, are to blame for apparent global warming.
There is also the not-so-small matter of the politicization of science: If climate scientists feel their careers might be put at risk by questioning some orthodoxy, the inevitable result will be bad science. It says something that it took two non-climate scientists to bring Mr. Mann’s errors to light.
But the important point is this: The world is being lobbied to place a huge economic bet–as much as $150 billion a year–on the notion that man-made global warming is real. Businesses are gearing up, at considerable cost, to deal with a new regulatory environment; complex carbon-trading schemes are in the making. Shouldn’t everyone look very carefully, and honestly, at the science before we jump off this particular cliff?