Long Cao, G. Bala & Ken Caldeira, Geophys. Res. Lett., 38 (2011), Why is there a short-term increase in global precipitation in response to diminished CO2 forcing?

Geophysical Research Letters, 38 (2011) L06703; doi: 10.1029/2011GL046713

Why is there a short-term increase in global precipitation in response to diminished CO₂ forcing?

Long Cao (Department of Global Ecology, Carnegie Institution, Stanford, CA, U.S.A.), Govindasamy Bala (Center for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, and Divecha Center for Climate Change, Indian Institute of Science, Bangalore, India) and Ken Caldeira (Department of Global Ecology, Carnegie Institution, Stanford, CA, U.S.A.)

Abstract

Recently, it was found that a reduction in atmospheric CO₂ concentration leads to a temporary increase in global precipitation. We use the Hadley Center coupled atmosphere-ocean model, HadCM3L, to demonstrate that this precipitation increase is a consequence of precipitation sensitivity to changes in atmospheric CO₂ concentrations through fast tropospheric adjustment processes. Slow ocean cooling explains the longer-term decrease in precipitation. Increased CO₂ tends to suppress evaporation/precipitation whereas increased temperatures tend to increase evaporation/precipitation. When the enhanced CO₂ forcing is removed, global precipitation increases temporarily, but this increase is not observed when a similar negative radiative forcing is applied as a reduction of solar intensity. Therefore, transient precipitation increase following a reduction in CO₂-radiative forcing is a consequence of the specific character of CO₂ forcing and is not a general feature associated with decreases in radiative forcing.

Received 10 January 2011; accepted 28 February 2011; published 24 March 2011.

Citation: Cao, L., G. Bala, and K. Caldeira (2011), Why is there a short-term increase in global precipitation in response to diminished CO₂ forcing?, Geophys. Res. Lett., 38, L06703, doi:10.1029/2011GL046713.

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