There is a recent paper on the role of water vapor in the climate system which presents an much needed broadening beyond the role of carbon dioxide as the dominant climate forcing, as is emphasized in the 2007 IPCC WG report [and thanks to Faisal Hossain for alerting us to it!] .The paper is
Schneider, T., P. A. O’Gorman, and X. J. Levine (2010), WATER VAPOR AND THE DYNAMICS OF CLIMATE CHANGES, Rev. Geophys., 48, RG3001, doi:10.1029/2009RG000302.
The abstract reads
“Water vapor is not only Earth’s dominant greenhouse gas. Through the release of latent heat when it condenses, it also plays an active role in dynamic processes that shape the global circulation of the atmosphere and thus climate. Here we present an overview of how latent heat release affects atmosphere dynamics in a broad range of climates, ranging from extremely cold to extremely warm. Contrary to widely held beliefs, atmospheric circulation statistics can change nonmonotonically with global-mean surface temperature, in part because of dynamic effects of water vapor. For example, the strengths of the tropical Hadley circulation and of zonally asymmetric tropical circulations, as well as the kinetic energy of extratropical baroclinic eddies, can be lower than they presently are both in much warmer climates and in much colder climates. We discuss how latent heat release is implicated in such circulation changes, particularly through its effect on the atmospheric static stability, and we illustrate the circulation changes through simulations with an idealized general circulation model. This allows us to explore a continuum of climates, to constrain macroscopic laws governing this climatic continuum, and to place past and possible future climate changes in a broader context.”
The finding that
“Contrary to widely held beliefs, atmospheric circulation statistics can change nonmonotonically with global-mean surface temperature…”
reinforces what we have reported on; e.g. see
that it is the atmospheric and ocean regional circulation patterns [rather than a global average of any climate metric] that matters in terms of such societally and environmentally important events such as droughts, floods etc. While the Schneider et al 2009 paper still emphasizes a global perspective (since they use an idealized global circulation model), their conclusion regarding atmospheric circulations is a message that the new IPCC assessment needs to heed.