January 4, 2008

The Hadley Center Tries Again

The U.K.’s Hadley Center has issued a forecast that 2008 will come in as one of the top 10 warmest years in its 150+ year record of global average temperature. While this forecast is about as risky as predicting that the next box of a dozen doughnuts you buy will contain twelve of the one-holed wonders, the press seems enthralled by it, as virtually all major news wires ran the story under with some variant of the headline “2008 to be among hottest years on record.”

The Hadley Center does not have the greatest track record for making accurate forecasts. Recall that in early January 2007, they issued a statement proclaiming that 2007 would likely be the warmest year on record for the globe. In fact, they went as far as to assign a probability (60%) to their forecast of a record year. And, of course, this prediction was also widely covered in the press (for example, see this BBC story).

When all the numbers are in (they aren’t yet), 2007 will likely come in as around the 6th or 7th warmest year in the Hadley Center global temperature record, probably about a tenth of a degree (which is a lot) behind the record holder (1998). In other words, their forecast was way off.

Apparently stinging from this forecast bust last year, they decided to make one this year that is much broader and virtually certain to be correct.

It doesn’t take a genius (and in that light should not make any news at all—after all, we are not talking about the Darwin Awards here) to figure out that it is very likely that 2008 will be among the all-time top 10 warmest years for global temperatures. In order for 2008 to fall outside the top 10, the average temperature would have to be about 0.15ºC cooler than this year. Not impossible, but it would likely take something like a very strong La Niña (which usually only follows a strong El Niño, which we haven’t had since 1998) or a (non-predictable) major volcanic eruption to cause it to happen.

Why it is so unlikely that 2008 will not fall outside the top 10 warmest years on record? Because natural variability (as measured, in this case, by the standard deviation of the detrended Hadley Center annual global temperature record since 1977) is only about 0.08ºC. Remember that 2008 will have to be about 0.15ºC, or about 2 standard deviations, cooler than this year not to fall within the top 10. Statistically speaking, the chance that the temperature departure for one year will fall outside of 2 standard deviations from the mean is about 5%. And since we are further requiring it to fall 2 standard deviations below the mean, then the chance drops in half, or to 2.5%. Thus, based on simple statistics alone (derived from data which includes several El Niño/La Niña cycles and two major volcanic eruptions) there is only about a 1 in 40 chance that 2008 will not be among the top 10 warmest years on record. Add to the fact that there is an overall warming trend of about 0.0.18ºC/year that also has to be overcome, makes it even more unlikely that 2008 will fall outside the top 10.

That this no-brainer of a forecast is the kind of thing that makes the news these days is either a sad commentary on the state of environmental hysteria, or else is simply the result of an incredibly slow news time.

Let’s hope that it is the latter, but we’ll issue the forecast that it the former.

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