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Thursday, January 6, 2011

Getting it wrong: George White's argument against AGW (Pt 1)

George White mounts an argument;that the theory of global warming fails certain essential emperical tests. Specifically, he argues the temperature increase in the lower troposphere is to low to be consistent with global warming over the period of satellite observations; and that climate sensitivity is, at most, about one sixth of that determined by the IPCC.

Considering the former argument first, he writes:
"The first prediction of AGW to fail, is that a 20% increase in CO2 is expected to cause an increase in the average global temperature of about 0.8°C. Detecting trends in satellite data is difficult for many reasons. Year to year differences can exceed 1°C, global seasonal variability exceeds 3.5°C, hemispheric seasonal variability exceeds 12°C and discontinuities arise as the data from different satellites is merged, however; a 25 year trend this large should be evident and it's not."

The first and most immediate problem with this argument is that it gets the facts wrong. CO2 concentrations have not increased by 20% over the "25+" years of satellite observations. In fact, in the 30 years from 1979 (the first full year of satellite temperature observations) to 2008, CO2 concentrations increased from 336.85 ppm to 385.34 ppm, or 14.4%(annual average as measured at Mauna Loa). Over a 25 year interval, the increase is closer to 12%. White has made a 66% error in one of the best known numbers in climate science.

If we correct for that error, and use the IPCC benchmark climate sensitivity of 2.8 degrees C per doubling of CO2, then it is easy to determine the predicted increase in temperature over the 30 years, which turns out to be 0.54 degrees C. For the 25 years, it is 0.46 degrees C. Although much less than White's calculated figure, these are still sufficiently large figures that we would expect to detect them in the temperature record. For ease of comparison, I will turn both figures into trends, and expressed as trends, both turn out to be around 0.018 degrees C per year.

For comparison, here are the trends in the temperatures, with two sigma error bars, of the five most frequenty used temperatue indices:
(From Tamino)

Very clearly, the predicted rate of temperature increase, at 0.018 degrees C/year, lies well within the error bars of all five data sets. Clearly, and contrary to White, the temperature record does not disconfirm the prediction. White, in fact, has no argument. Importantly, White's argument fails not because the data is inconclusive, or too noisy(indeed, the data emphatically refutes the null hypothesis that the climate is not warming). Rather, White's argument fails because the temperature data is what we would expect assuming global warming due to CO2 forcing and feedbacks alone, and with no temperature lags. White fails to realize this becausehis prediction, which amounts to a trend of 0.032 degrees C/year, is completely incorrect.

The caveatts are important. In fact, recent global temperature increases have been driven by other green house gasses in addition to CO2 which enhance the warming, but also by aerosols which have a cooling effect. The combined effect is very close to the effect of CO2 alone over the period from 1750 to 2005, but that is happen-stance, and it could have been quite different (and probably is over the period since 1980). Further, due to the thermal capacity of the oceans, only 66% of the heating due to global warming is expected to be realized within a few decades of the initial forcing, with the full effect not being realized for millenium. This is called Thermal Lag, and it is a major factor in the short term responce to global warming.
(Net forcings from 1750 to 2005, IPCC AR4)

While it is clear that White is aware of the issue of Thermal Lag - it is the primary point of discussion in his essay - it is not clear that he is aware of the other factors.  He refers to the noisy data, but the source of that noise is short term variations in solar irradiance, such as those generated by the sunspot cycle, and changes in circulation patterns in the ocean and atmosphere, such as those associated with the El Nino Southern Oscillation. The upshot is that White's first argument is conceptually flawed. It is not possible to make a sensible prediction of future global temperatures without considering all forcings, positive and negative, and attempting to do so based on just one forcing is little better than a shot in the dark.

So, White's first argument fails both because he got his facts wrong, and because of conceptual confusion. Both of these failings also characterize his second argument. Indeed, in formulating his second argument, virtually every single "fact" he appeals to that I fact checked was wrong in detail, and often by significant amounts.  These flaows mean that White does not show what he thinks he shows, even if his basic argument were not flawed; but as his second argument cannot show what it purports to show, the errors turn out to be irrelevant.  Therefore I will deal with White's conceptual confusion first, in my next post; and leave the errors of fact to another post after that.

1 comment:

  1. Tom,
    Go to and near the bottom there are links to the ppt, which is different from what I think you have on White.