Global warming, convective threshold and false thermostats
Abstract
We demonstrate a theoretically expected behavior of the tropical sea surface temperature probability density function (PDF) in future and past (Eocene) greenhouse climate simulations. To first order this consists of a shift to warmer temperatures as climate warms, without change of shape of the PDF. The behavior is tied to a shift of the temperature for deep convection onset. Consequently, the threshold for appearance of high clouds and associated radiative forcing shifts along with temperature. An excess entropy coordinate provides a reference to which the onset of deep convection is invariant, and gives a compact description of SST changes and cloud feedbacks suitable for diagnostics and as a basis for simplified climate models. The results underscore that the typically skewed appearance of tropical SST histograms, with a sharp drop-off above some threshold value, should not be taken as evidence for tropical thermostats.
Keywords
convection, cloud, feedback
Date of this Version
2009
DOI
10.1029/2009GL039849
Repository Citation
Williams, Ian N.; Pierrehumbert, Raymond T.; and Huber, Matthew, "Global warming, convective threshold and false thermostats" (2009). Department of Earth, Atmospheric, and Planetary Sciences Faculty Publications. Paper 89.
http://dx.doi.org/10.1029/2009GL039849
Volume
36
Issue
21
Pages
L21805-L21805
Link Out to Full Text
http://www.agu.org/pubs/crossref/2009/2009GL039849.shtml