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Summary: High-CO2 cloud radiative forcing feedback over both land and ocean
in a global climate model
Dorian S. Abbot,1
Matthew Huber,2,3
Gabriel Bousquet,1,4
and Chris C. Walker1
Received 17 November 2008; revised 5 January 2009; accepted 26 January 2009; published 4 March 2009.
[1] A positive feedback on high-latitude winter marine
climate change involving convective clouds has recently
been proposed using simple models. This feedback could
help explain data from equable climates, e.g., the Eocene, and
might be relevant for future climate. Here this convective
cloud feedback is shown to be active in an atmospheric
GCM in modern configuration (CAM) at CO2 = 2240 ppm
and in a coupled GCM in Eocene configuration (CCSM) at
CO2 = 560 ppm. Changes in boundary conditions that
increase surface temperature have a similar effect as increases
in CO2 concentration. It is also found that the high-latitude
winter cloud radiative forcing over land increases with
increases in surface temperature due to either increased CO2
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