26 December 2014

Slowdown of Global Warming in the Early-2000s Due to Stronger Pacific Trade Winds

Summary

Despite ongoing increases in atmospheric greenhouse gases, the Earth’s global average surface air temperature has remained more or less steady since 2001.   While the negative phase of the Interdecadal Pacific Oscillation (IPO) with its cool sea surface temperatures in the tropical Pacific has been identified as a key componentof the global hiatus, it is unclear how the ocean has remained relatively cool there in spite of ongoing increases in greenhouse gases.  Here we show that a pronounced strengthening in Pacific trade winds by about 30% over the past two decades is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming via increased subsurface ocean heat uptake.  The extra uptake has come about via increased subduction in the Pacific shallow overturning cells, enhancing heat convergence in the equatorial thermocline.  At the same time, the accelerated trade winds have increased equatorial upwelling in the central and eastern Pacific, cooling SST there, which drives further cooling in other regions.  The net effect of these anomalous winds is estimated to be a cooling in the 2012 global average surface air temperature of 0.1 – 0.2°C, which can account for much of the hiatus in surface warming observed since 2001.  This hiatus could persist for much of the present decade if the trade wind trends continue, however rapid warming looks set to resume once the anomalous wind trends abate.

Contact
M. H. England
Publications
England, MH, S McGregor, P Spence, GA Meehl, A Timmermann, W Cai, A Sen Gupta, and MJ McPhaden.  2014.  "Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus."  Nature Climate Change 4: 222–227, doi:10.1038/nclimate2106.