Nature 441, 73-76 (4 May 2006) | doi:10.1038/nature04744; Received 27 October 2005; Accepted 22 March 2006
Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing
Gabriel A. Vecchi1, Brian J. Soden2, Andrew T. Wittenberg1, Isaac M. Held1, Ants Leetmaa1 and Matthew J. Harrison1
- NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey 08540-6649, USA
- Rosenstiel School for Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149-1098, USA
Correspondence to: Gabriel A. Vecchi1 Correspondence and requests for materials should be addressed to G.A.V. (Email: Gabriel.A.Vecchi@noaa.gov).
Abstract
Since the mid-nineteenth century the Earth's surface has warmed1, 2, 3, and models indicate that human activities have caused part of the warming by altering the radiative balance of the atmosphere1, 3. Simple theories suggest that global warming will reduce the strength of the mean tropical atmospheric circulation4, 5. An important aspect of this tropical circulation is a large-scale zonal (east–west) overturning of air across the equatorial Pacific Ocean—driven by convection to the west and subsidence to the east—known as the Walker circulation6. Here we explore changes in tropical Pacific circulation since the mid-nineteenth century using observations and a suite of global climate model experiments. Observed Indo-Pacific sea level pressure reveals a weakening of the Walker circulation. The size of this trend is consistent with theoretical predictions, is accurately reproduced by climate model simulations and, within the climate models, is largely due to anthropogenic forcing. The climate model indicates that the weakened surface winds have altered the thermal structure and circulation of the tropical Pacific Ocean. These results support model projections of further weakening of tropical atmospheric circulation during the twenty-first century4, 5, 7.
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