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Earth System Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 3 | Copyright
Earth Syst. Dynam., 8, 495-505, 2017
https://doi.org/10.5194/esd-8-495-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 05 Jul 2017

Research article | 05 Jul 2017

Non-linear intensification of Sahel rainfall as a possible dynamic response to future warming

Jacob Schewe1 and Anders Levermann1,2,3 Jacob Schewe and Anders Levermann
  • 1Potsdam Institute for Climate Impact Research, Potsdam, Germany
  • 2Institute of Physics, Potsdam University, Potsdam, Germany
  • 3Lamont-Doherty Earth Observatory, Columbia University, New York, USA

Abstract. Projections of the response of Sahel rainfall to future global warming diverge significantly. Meanwhile, paleoclimatic records suggest that Sahel rainfall is capable of abrupt transitions in response to gradual forcing. Here we present climate modeling evidence for the possibility of an abrupt intensification of Sahel rainfall under future climate change. Analyzing 30 coupled global climate model simulations, we identify seven models where central Sahel rainfall increases by 40 to 300% over the 21st century, owing to a northward expansion of the West African monsoon domain. Rainfall in these models is non-linearly related to sea surface temperature (SST) in the tropical Atlantic and Mediterranean moisture source regions, intensifying abruptly beyond a certain SST warming level. We argue that this behavior is consistent with a self-amplifying dynamic–thermodynamical feedback, implying that the gradual increase in oceanic moisture availability under warming could trigger a sudden intensification of monsoon rainfall far inland of today's core monsoon region.

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Monsoon systems have undergone abrupt changes in past climates, and theoretical considerations show that threshold behavior can follow from the internal dynamics of monsoons. So far, however, the possibility of abrupt changes has not been explored for modern monsoon systems. We analyze state-of-the-art climate model simulations and show that some models project abrupt changes in Sahel rainfall in response to a dynamic shift in the West African monsoon under 21st century climate change.
Monsoon systems have undergone abrupt changes in past climates, and theoretical considerations...
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