Chipping away at the global warming uncertainty

ResearchBlogging.orgGiven just how much we don't understand about the Earth's climate, it's understandable that a newcomer to the science of global warming would doubt that we are capable of predicting much of anything. Many a climate change pseudoskeptic makes this argument, which can be compelling, but only if you don't understand how science works. A paper in this week's Nature Geoscienceis a perfect example of why so many people who otherwise consider themselves skeptics, people like me, find the anthropogenic explanation for climate change so persuasive. It's not so much what we know as the trends associated with what we don't that are so convincing.

The paper, "Warming maximum in the tropical upper troposphere deduced from thermal winds" by Yale climatologists Robert J. Allen and Steven C. Sherwood, gets rid of yet another discrepancy between what's been observed and what our climate models tell us to expect. A couple of years ago it was satellites that had been mis-calibrated. Last week it was the 1945 cooling trend, which turned out to be an artifact of different methods of recording ocean temperatures. This time it's problems with weather balloons, annoyingly called "radiosondes" by those who get to play with them.

Here's Allen and Sherwood's description of the problem:

...most analyses of radiosondes continue to show less warming of the tropical troposphere since 1979 than reported at the surface. At least one satellite dataset also implies this. By contrast, theoretical and model expectations indicate that the troposphere should warm somewhat faster than the surface.

Now, some observers might be surprised to learn that this sort of thing was still considered a problem. Weren't these anomalies dispatched a while back? After all, reports like a 2006 study of temperature trends by a US government panel noted that

This significant discrepancy no longer exists because errors in the satellite and radiosonde data have been identified and corrected. New data sets have also been developed that do not show such discrepancies.

But such dismissals weren't enough for everyone. Climatologists, it would seem, can be stubborn folk. Allen and Sherwood are two such characters. Attempts to resolve the problems didn't impress them, particularly the satellite data rejigging.

... errors inherent in correction procedures (that is, structural uncertainty) could be sufficient to explain differences between expected and reported warming, but this has not been conclusively demonstrated. Thus, doubts remain about whether the tropical atmosphere has behaved as predicted.

So they turned to a proxy for atmospheric temperatures that they say comes with fewer complicating factors and therefore produces less uncertainty. That proxy is wind speed. Measuring wind at different altitudes and running the data through a mathematical procedure known as the "thermal-wind equation" should give us a good idea of what the temperatures in the upper reaches of the troposphere (more or less that portion of the atmosphere where humans can breathe) really are. Fortunately, the wind and temperature measurements, although taken by the same balloons, are independent. After applying the equation, they conclude that:

... our data do not seem to be consistent with a lack of upper-tropospheric warming in the tropics. The degree of warming remains fairly uncertain, but is within the range simulated by climate models, albeit with some discrepancies near the tropopause [top of troposphere].


Most importantly, we conclude that observed changes in wind seem to be consistent with those predicted by models given sampling and other uncertainties.

Time after time, discrepancies that produce uncertainty are being whittled away. And every time, the new results are consistent with computer models that say the planet is getting warmer because of fossil-fuel emissions. Uncertainty remains, but it's much smaller. And both the persistence of uncertainty and it's diminished magnitude are hallmarks of good science. The trend is almost always in the same direction. It's what you would expect if the science was robust.

And that's why I'm not a global warming denier.

Allen, R.J., Sherwood, S.C. (2008). Warming maximum in the tropical upper troposphere deduced from thermal winds. Nature Geoscience, 1(6), 399-403. DOI: 10.1038/ngeo208


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James - I think I know at least a little about how science works. And I'm a bit confused about your take on how uncertainty gets whittled away. There's no way to know before the uncertainties are actually addressed that the result is going to be a reduction in the uncertainty attaching to a particular hypotheses. Sure, that's how it works with robust theories; but again, you don't know the theory is robust until after the fact.

By bob koepp (not verified) on 05 Jun 2008 #permalink

My reasons for not being a denialist are:

1) Science has a great track record.

2) I don't understand climatology enough to judge it.

3) Even in areas I feel competent enough to disagree with the mainstream, I don't expect society at large to suddenly start listening to me.

4) The denialists act just like creationists. They camp outside of the mainstream of science, hold themselves responsible only to each other, and then launch attacks targeted at people not qualified to judge the issue.

5) Almost all of the dissent comes from the extreme end of the political Right. Political extremists of all stripes play fast and loose with the truth, and the neo-cons have been the worst in recent years.

6) The idea of gambling with the human race (or at least a significant portion thereof) in the name of the economy just leaves me feeling unclean.

By James M. Jensen II (not verified) on 14 Jun 2008 #permalink

Please explain how the "scientific" conclusion is that there is a cause-effect relationship between the "observed"/"confirmed" warming trend and the use of fossil fuels by humans. I think this is the most glaring flaw in the"science" presented. The conclusion is a hammer-nail relationship. What else (other than the fossil fuel use) was both legitimately observed and at the same time included in the hypothesis/conclusion equation?

By Kevin S. Gareau (not verified) on 17 Jun 2008 #permalink