Anticyclonic Warming

Spectral arguments predict that greenhouse warming from carbon dioxide should be enhanced in air masses that are low in water vapor content. In winter, these are largely the great anticyclones that dominate Siberia and northwestern North America. Observed temperatures indeed indicate an inordinate warming of these air masses, and the amount of warming is strongly predicted by the strength of the anticyclone. However, while these air masses are generally less than 150mb in depth, general circulation models largely produce warming of 750mb depth. The result is that the integrated tropospheric warming, currently predicted to be approximately 0.23°C/decade, has been overestimated by nearly an order of magnitude in the last two decades, when averaged through the troposphere.

Our analysis demonstrates that the discrepancy largely results from the fact that the cold anticyclonic warming remains confined the these air masses, rather than dispersing throughout the entire troposphere. This may not be the case for warm anticylonic warming, as is evident around the Sahara in the summer. Model parameterizations that attempt to deal with this will be difficult to devise without fundamental (and currently unknown) changes in our understanding of greenhouse warming.