Abstract
The South Pacific Convergence Zone (SPCZ) is the largest rainband in the Southern Hemisphere and provides most of the rainfall to southwest Pacific island nations. In spite of various modelling efforts, it remains uncertain how the SPCZ will respond to greenhouse warming. Using a hierarchy of climate models we show that the uncertainty of SPCZ rainfall projections in present-generation climate models can be explained as a result of two competing mechanisms. Higher tropical sea surface temperatures lead to an overall increase of atmospheric moisture and rainfall whereas weaker sea surface temperature gradients dynamically shift the SPCZ northeastward and promote summer drying in areas of the southwest Pacific. On the basis of a multi-model ensemble of 76 greenhouse warming experiments and for moderate tropical warming of 1–2 °C we estimate a 6% decrease of SPCZ rainfall with a multi-model uncertainty exceeding ±20%. For stronger tropical warming exceeding 3 °C, a tendency for a wetter SPCZ region is identified.
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Acknowledgements
This work was supported by the Office of Science (BER) US Department of Energy, Grant DE-FG02-07ER64469, by the US National Science Foundation under grant 1049219 and by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). S.M. and M.H.E. were supported by the Australian Research Council. M.L. was supported by the Institut de Recherche pour le Developpement. W.C. was supported by the Australian Climate Change Science Program and the CSIRO Office of Chief Executive Science Leader programme. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. The KNMI Climate Explorer, Netherlands, provided CMIP data from their Web site at http://climexp.knmi.nl/. We acknowledge the International Centre for Theoretical Physics, Italy, for hosting an influential workshop on Hierarchical Modelling of Climate and providing the ICTP idealized atmospheric GCM.
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The paper was written by M.J.W., A.T. and K.S. Experiments were carried out by M.J.W., A.T., K.S. and S.M. All authors contributed to interpreting the results, improving the methodology and refining the paper.
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Widlansky, M., Timmermann, A., Stein, K. et al. Changes in South Pacific rainfall bands in a warming climate. Nature Clim Change 3, 417–423 (2013). https://doi.org/10.1038/nclimate1726
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DOI: https://doi.org/10.1038/nclimate1726
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