Lack of Errors in the IPCC Statement for Policymakers
20 Mar, 2007 10:47 am
The 2007 IPCC Statement for Policymakers (SPM) was released in early Febuary to extensive scrutiny, which it has survived well. Few skeptics have even attempted to engage with the science it describes; here I discuss one substantive, but failed, attempt to find errors in the SPM
1. The IPCC says that "snow cover have declined on average in both hemispheres".
Pielke asserts that it is "cherry picking" because snow cover was less in the late 1980's. But this is cherry picking on Pielke's part; analogous to the assertions made by some skeptics that "global warming stopped in 1998" because global temperature hasn't increased since that year.
2. "Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system." This is probably the closest hit that Pielke makes, though the SPM statement is (of course) true. And in the context of the next sentence "Such warming causes seawater to expand, contributing to sea level rise" it makes good sense - what matters is the global average; hence complaining that this occured largely in the southern ocean is beside the point. Pielke's point that a 2006 paper finds recent cooling may well be true (though one paper is not definitive) but 2006 papers were beyond the IPCC cut-off date, as Pielke knew very well.
3. Pielke asserts that the IPCC's "The average atmospheric water vapour content has increased since at least the 1980s over land and ocean as well as in the upper troposphere. The increase is broadly consistent with the extra water vapour that warmer air can hold" conflicts with the observation of no significant change in global mean precipitation. There is no conflict: substantial changes in atmospheric water vapour (Q) can amount to no more that a fraction of one days precipitation (P): the change in Q is observable; the change in P would be below the noise level.
4. This is perhaps the strangest of the lot. Pielke objects to the statement "Mid-latitude westerly winds have strengthened in both hemispheres since the 1960s" although he sources it to his own paper on the grounds that it is inconsistent with Arctic tropospheric warming, a subject that the SPM does not even mention. This therefore cannot be an inconsistency in the SPM; and nor can it be an error, unless Pielke believes his own paper to be wrong. As Gavin Schmidt pointed out to Pielke somewhat earlier, the SPM is probably talking about the surface winds not the upper atmosphere winds anyway, in which case the point evaporates.