More on global warming

I noted a couple of days ago that the economic argument on Kyoto has largely been won. The BCA shift to a neutral position reflects the fact that the economic costs of Kyoto will be small. Warwick McKibbin <a href="”>continues to argue (PDF file) that his alternative provides a better way of dealing with uncertainty about implementation costs, and he makes some good points. In my view, Warwick’s arguments are more applicable to the design of a substantial post-Kyoto initiative than to the first steps involved in Kyoto itself.

It might be useful to point to some developments in the scientific debate, with the warning that, like most bloggers, I’m not an expert on most of the relevant issues.

The most impressive evidence against the global warming hypothesis (GWH) has been the satellite data, which originally showed a strong cooling trend, directly contrary to the evidence of surface-level warming. The inconsistency was partially resolved when Matthias Schabel and Frank Wentz pointed out that the measurements, taken by a team led by John Christy at the University of Alabama, had failed to account properly for the gradual decay of satellite orbits. When this adjustment was made, the satellite data showed a weak upward trend. There’s been a bit of back and forth adjustment since then, but now Schabel and Wentz have struck again with a statistical analysis (PDF file that brings the satellite data much closer to the ground-level, though there is still a gap between the trends. This research is still unpublished, and no doubt there will be more debate, but it looks as though the contradiction between the data sets has been reduced to a minor anomaly, which will be resolved in due course. As Schabel and Wentz note in their abstract, this is bad news for critics of the standard modelling of water vapor feedbacks, who have relied heavily on the satellite data.

A second area of contention has concerned events at the poles. I tend not to put too much weight on this because I’ve formed the impression that polar climates are inherently highly variable, poorly understood and subject to severe measurement problems. This impression has been reinforced by what I’ve seen over the last year or so, which seems to have something for everybody. On the one hand, the spectacular break up of an ice-shelf recently gave rise to this report suggests that sea-level rise may proceed more rapidly than was previously thought. On the other hand, large parts of Antarctica appear to be cooling, not warming, which is not what the GW models predict.

Although it often seems as if these issues will never be resolved, at least one hypothesis should be subject to a conclusive test in the next few years. A number of sceptics have argued that the high global temperatures of recent years are due to the combination of variable solar activity and the El Nino cycle. No-one disputes the importance of El Nino, but the solar cycle idea is rejected by most climatologists.

Sceptic John Daly points out that the peak of solar activity has passed, which he says should imply declining global temperatures over the next few years. Obviously it would be good for all of us if he was right – on the standard version of the GWH, serious environmental damage seems inevitable even if we implement then extend Kyoto.

If, as I expect, we see a continuation of the warming trend, an acceptance by Daly and others that their hypothesis had been refuted might help to mobilise serious action.

Unfortunately, there is always the intermediate possibility of data that is not conclusive either way. Murphy’s Law suggests that this is what we’ll get.