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Global warming, convective threshold and false thermostats
Author(s) -
Williams Ian N.,
Pierrehumbert Raymond T.,
Huber Matthew
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl039849
Subject(s) - climatology , convection , radiative forcing , environmental science , forcing (mathematics) , cloud cover , climate model , thermostat , atmospheric sciences , climate change , sea surface temperature , global warming , meteorology , geology , physics , cloud computing , thermodynamics , oceanography , computer science , operating system
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.