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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

Sure is cold out there, unusually so. By “unusual,” I mean the temperature is on the low end of the observed temperatures from previous winters.

Of course, we don’t have any more than about 100 years of reliable measurements, so it’s possible that the freeze we’re experiencing now isn’t as unusual as we suspect. But, anyway, it still sure is cold.

If you recall, a lot of global warming models predicted it would be hot and not cold, and to risk redundancy, it sure is cold. Does this dissonance between the models’ predictions and what is actually happening mean that those models are wrong?

No. But it sure as ice doesn’t mean that they are right.

Here’s the thing: No matter how cold the winter is, no matter how much snow falls, the global warming models will not be disproved. In technical language, they cannot be falsified by the observations.

Another way to say this is that the winter we’re seeing is consistent with what the models have been predicting. Again — does this consistency mean that the models are right and that the theories of man-made warming are true?

No.

Consistency is such a weak criterion that almost any imaginable theory of climate will produce predictions that are consistent with observations. The term is probabilistic: It means that what actually happens had to have some chance of occurring according to a model. If global warming climate models said, “It is impossible that this winter will see temperatures below X,” and temperatures did, in fact, drop below this threshold, then the models would be inconsistent with the observations. The model would be falsified.

But global warming climate models never make statements like that. They say that any temperature is possible, even if this possibility is low. Certain temperatures have probabilities as low as you like, but they are never precisely zero. (To anticipate an objection: “that number was practically zero” is logically equivalent to “she was practically a virgin.”)

Man-made global warming is just one of many possible theories of climate. Another is the Business-as-Usual Theory (BUT), which states that whatever happened last year will more or less happen this year, and so on into the future.

The winter we’re seeing is consistent with the BUT, which like the man-made global warming theory, never says any temperature is impossible. Further, BUT is corroborated more strongly by this winter than is the man-made warming theory. BUT’s predictions are closer to what we actually see.

“Stop right there, Briggs! You’re making the classical mistake of confusing weather with climate. The global warming models make predictions of climate and not weather. This winter doesn’t mean anything!”

I am not making that mistake, and it is you who are confused. Weather is climate. More specifically, aggregations of weather are climate. Means, averages, and distributions of daily weather comprise climate. That is, climate is a statistical phenomenon and depends for its existence on defining a reference time frame.

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.

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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