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Actually, Weather Is Climate

It is statistically appropriate to point to this year's frigidity as evidence that the theory of man-made global warming is suspect.

by
William M. Briggs

Bio

January 22, 2010 - 12:00 am
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For instance, if “climate” is defined as the yearly mean temperature, then this year’s cold winter will produce a yearly mean temperature that is colder than average (as long as the coming summer isn’t abnormally hot: winter, of course, overlaps two calendar years and a hot summer can balance out a cold winter in the yearly mean).

So it is appropriate to point to this year’s frigidity as evidence that the theory of man-made global warming is suspect. If “climate” is defined as the decadal mean temperature, then this year’s cold winter will push the decadal mean lower. And it is still acceptable to point to this year’s winter as evidence against the man-made global warming theory.

Just as it was appropriate when the media trumpeted each and every “record setting high!” as evidence for that theory.

The difference is that one day’s temperature has little influence on a yearly mean — it is just one out of 365 other numbers that make up the average. One day’s temperature is thus weak evidence for or against any theory of climate.

But a slew of months with higher- or lower-than-average temperatures will push that yearly mean higher or lower. A season’s mean temperature is stronger evidence for or against any climate theory than is a day’s.

Back in the 1990s, when the yearly mean temperatures were increasing, this was touted as evidence for the man-made global warming — but those years’ temperatures also corroborated the Business-as-Usual theory. Which theory was better?

For the past decade, we have had a string of years with mostly decreasing temperatures. This is strong evidence against the man-made global warming theory, but pretty good testimony for the BUT. So far, the BUT theory is winning on points (there are other climate theories the BUT doesn’t beat). This doesn’t mean that BUT is true and that the man-made global warming theory is false, but it does suggest that this is so.

You can’t have it both ways. It is a mistake to extol evidence that supports the man-made global warming theory and to cry foul when presented with evidence which weakens that theory.

That so many do this says more about their desires than it does about any theory of climate.

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William M. Briggs is a statistical consultant in New York and San Francisco. He is an American Meteorological Society member and serves on their Probability & Statistics Committee. His specialty is on the philosophy of evidence, forecast evaluation, and marketing.
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