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Tuesday, July 6, 2010

R. A. Betts et al., Role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming

Theoretical and Applied Climatology, 78(1-3) 157-175 (June 2004); doi: 10.1007/s00704-004-0050-y
R. A. Betts1, P. M. Cox1, M. Collins2, P. P. Harris3, C. Huntingford3 and C. D. Jones1  

¹Hadley Centre for Climate Prediction & Research, Met Office, Exeter, U.K.
²Department of Meteorology, Reading University, now at Met Office Hadley Centre, U.K.
³Centre for Ecology and Hydrology, Oxford, U.K.


A suite of simulations with the HadCM3LC coupled climate-carbon cycle model is used to examine the various forcings and feedbacks involved in the simulated precipitation decrease and forest dieback. Rising atmospheric CO2 is found to contribute 20% to the precipitation reduction through the physiological forcing of stomatal closure, with 80% of the reduction being seen when stomatal closure was excluded and only radiative forcing by CO2 was included. The forest dieback exerts two positive feedbacks on the precipitation reduction; a biogeophysical feedback through reduced forest cover suppressing local evaporative water recycling, and a biogeochemical feedback through the release of CO2 contributing to an accelerated global warming. The precipitation reduction is enhanced by 20% by the biogeophysical feedback, and 5% by the carbon cycle feedback from the forest dieback. This analysis helps to explain why the Amazonian precipitation reduction simulated by HadCM3LC is more extreme than that simulated in other GCMs; in the fully-coupled, climate-carbon cycle simulation, approximately half of the precipitation reduction in Amazonia is attributable to a combination of physiological forcing and biogeophysical and global carbon cycle feedbacks, which are generally not included in other GCM simulations of future climate change. The analysis also demonstrates the potential contribution of regional-scale climate and ecosystem change to uncertainties in global CO2 and climate change projections. Moreover, the importance of feedbacks suggests that a human-induced increase in forest vulnerability to climate change may have implications for regional and global scale climate sensitivity.

Received 13 March 2003; revised 1 September 2003; accepted 10 October 2003; published online 6 May 2004.


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