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Insufficient forcing uncertainty underestimates the risk of high climate sensitivity

Author(s): Tanaka K, Raddatz T, O'Neill BC, Reick CH

Published: August, 2009

Publisher: Geophysical Research Letters

DOI: 10.1029/2009GL039642

Tags: Uncertainty, Climate Science

URL: http://www.agu.org/journals/ABS/2009/2009GL039642.shtml

Abstract: Uncertainty in climate sensitivity is a fundamental problem for projections of the future climate. Equilibrium climate sensitivity is defined as the asymptotic response of global-mean surface air temperature to a doubling of the atmospheric CO2 concentration from the preindustrial level (≈280 ppm). In spite of various efforts to estimate its value, climate sensitivity is still not well constrained. Here we show that the probability of high climate sensitivity is higher than previously thought because uncertainty in historical radiative forcing has not been sufficiently considered. The greater the uncertainty that is considered for radiative forcing, the more difficult it is to rule out high climate sensitivity, although low climate sensitivity (<2°C) remains unlikely. We call for further research on how best to represent forcing uncertainty.


Global biogeophysical interactions between forest and climate.

Author(s): Brovkin V, Raddatz T, Reick CH

Published: April, 2009

Publisher: Geophysical Research Letters

DOI: 10.1029/2009GL037543

Tags: Afforestation, Land Use Management, Climate Modelling

URL: http://www.agu.org/pubs/crossref/2009/2009GL037543.shtml

Abstract: In two sensitivity experiments using the Earth System Model of the Max Planck Institute for Meteorology (MPI‐ESM), the vegetation cover of the ice‐free land surface has been set worldwide to either forest or grassland in order to quantify the quasi‐equilibrium response of the atmosphere and ocean components to extreme land surface boundary conditions. After 400 years of model integration, the global mean annual surface temperature increased by 0.7°K and declined by 0.6°K in the forest and grassland simulations, respectively, as compared to the control simulation. Thereafter, the geographic distribution of vegetation has been allowed to respond interactively to climate. After subsequent 500 years of interactive climate‐vegetation dynamics, both forest and grassland simulations converged to essentially the same climate state as in the control simulation. This convergence suggests an absence of multiple climate‐forest states in the current version of the MPI‐ESM.


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