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Six hundred years ago, the world was warm. Or maybe it wasn’t. What’s the truth? Beware. This question has recently been elevated from a mere scientific quandary to one of the hot (or cold) issues of modern politics. Argue in favor of the wrong answer and you risk being branded a liberal alarmist or a conservative Neanderthal. Or you might lose your job.

Six editors recently resigned from the journal Climate Research because of this issue. Their crime: publishing the article “Proxy Climatic and Environmental Changes of the Past 1,000 Years,” by W. Soon and S. Baliunas of the Harvard-Smithsonian Center for Astrophysics.

Without passing judgment on this particular paper, I can still point out that our journals are full of poor papers. If editors were dismissed every time they published one, they would all be out of work within a month or two. What made the Soon and Baliunas situation different is that their paper attracted enormous attention. And that’s because it threw doubt on the hockey stick.

If you don’t know what the hockey stick is, do a Google search, including the word “climate.” You’ll learn that it is the nickname for a remarkable graph that has become a poster child for the environmental movement. Published by M. Mann and colleagues in 1998 and 1999, the plot showed that the climate of the Northern Hemisphere had been remarkably constant for 900 years until it suddenly began to heat up about 100 years ago-right about the time that human use of fossil fuels began to push up levels of atmospheric carbon dioxide. The overall shape of the curve resembled a hockey stick laying on its back-a straight part with a sudden bend upwards near the end.

The hockey stick was turned from a scientific plot into the most widely reproduced picture of the global warming discussion. The version below comes from the influential 2001 report of the Intergovernmental Panel on Climate Change (IPCC). The hockey stick figure appears five times in just the summary volume alone.

Soon the graph acquired a very effective sound bite: 1998 was the warmest year in the last thousand years. This carried a compelling conclusion: global warming is real; humans are to blame; we must do something-hurry and ratify the Kyoto treaty on limitations of fossil fuel emissions. Yet some scientists urged caution, a go slow approach. As a wise man once warned, “do not let the merely urgent interfere with the truly important.”

There was a minor scientific glitch. The hockey stick contradicted previous work that had concluded that there had been a “medieval warm period.” In fact, it disagreed with a plot published by the IPCC itself a decade earlier (in its 1990 report) that showed pronounced warm temperatures from the years 1000 to 1400.

Such inconsistencies are common in science, and scientists love them. They mean more work, maybe a little public attention (which can’t hurt funding), and the excitement that comes with the effort to resolve uncertainty. The Soon and Baliunas paper was part of this process. Their paper presented all the data in favor of the medieval warm period.

The debate grew. Critics of Soon and Baliunas charged that their paper wasn’t balanced; because it consisted of a compilation of data showing warming at different locations at different times, the criticism went, the work was not a valid refutation of the hockey stick analysis, which had combined a much larger set of data. That was a valid concern, but it didn’t necessarily mean that the Soon and Baliunas results should be ignored. It simply meant that the issue was still open.

Meanwhile, critics excoriated Climate Research for allegedly failing to vet the Soon and Baliunas paper properly. The publisher, a German company called Inter-Research, agreed, leading to the resignation of the journal’s editor-in-chief and, eventually, five other editors.

Then last month the situation became even more complex. S. McIntyre and R. McKitrick published a paper in Energy and Environment with a detailed critique of the original hockey stick work. They stated bluntly that the original Mann papers contained “collation errors, unjustifiable truncations of extrapolation of source data, obsolete data, geographical location errors, incorrect calculations of principal components, and other quality control defects.” Moreover, when they corrected these errors, the medieval warm period came back-strongly. Mann, et al., disagreed. They immediately posted a reply on the Web, with their criticism of McIntyre and McKitrick’s analysis.

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