A safe, but misleading, prediction about global warming

Reuters’s, on 3 January, had this headline, “2008 to be in top 10 warmest years say forecasters.”

A quote:

2008 will be slightly cooler than recent years globally but will still be among the top 10 warmest years on record since 1850 and should not be seen as a sign global warming was on the wane, British forecasters said.

Where to start? First, the anemic forecast. Suppose the global mean temperature is, as predicted by several models, increasing, though this increase is subject to fluctuation from year to year, such that for one or two years the temperature might actually decrease, but in the long run, the temperature will still increase. Call this scenario the increasing temperature climate. It is important to emphasize that the increasing climate schema is consistent with both a significant man-made component and with the change being due to external causes. Now suppose, as has also been proposed, that the global mean temperature instead followed this cartoon, depicting a cyclically-changing climate:

Global mean temperature cartoon

This cartoon (and those based on other potential climate scenarios) is also consistent with either man-made climate changes or with the changes being due to external causes. It is just that, in this picture, the man-made component is harder to quantify. This is because of the trivial truth that man must influence the climate (see this), and that this influence will either be trivial or significant.

So it is a tautology to say that either man-made global warming is significant or it is not. One of those conditions must be true. It is also observed that the global mean temperature is correlated from year to year, so it is a fact that the temperature is somewhat constrained, in the sense that we will see little change from year to year, no matter whether mad-made global warming is significant or not, and regardless whether a general increasing or a cyclic climate holds.

Lastly, it is also the case that the global mean temperature has been increasing since the late 1990s until 2006. In 2007, the temperature decreased.

So the prediction that “2008 will be in the 10 ten warmest years” has an overwhelming probability of being true regardless whether man-made global warming is significant or not, and regardless whether an increasing or cyclic climate holds. That is, no matter what, this prediction is probably true, and it is useless as its intent was to give indirect evidence that the increasing climate scenario holds and that the man-made component of global warming is significant. It does neither such thing. Presenting this prediction as news is a clever debating tactic, but it is misleading, because the alternatives are not presented, even though the forecast is just as much evidence for them.

“‘The fact that 2008 is forecast to be cooler than any of the last seven years does not mean that global warming has gone away,’ said Phil Jones, director of climate research at UEA.” Jones is right, partially. But he forgot to say, “That fact the 2008 is forecast to be cooler than any of the last seven years also means that it might true that the climate is cyclic and that man has no real influence on it.”

This forecast is not additional evidence that an increasing climate or that man-made global warming holds.

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