Eastern Pacific surface cooling and the mysterious ?global-warming hiatus?

[Emily]

http://www.nature.com/news/climate-change-the-case-of-the-missing-heat-1.14525

Climate change: The case of the missing heat

Sixteen years into the mysterious ?global-warming hiatus?, scientists are piecing together an explanation.
Jeff Tollefson
15 January 2014

The biggest mystery in climate science today may have begun, unbeknownst to anybody at the time, with a subtle weakening of the tropical trade winds blowing across the Pacific Ocean in late 1997. These winds normally push sun-baked water towards Indonesia. When they slackened, the warm water sloshed back towards South America, resulting in a spectacular example of a phenomenon known as El Ni?o. Average global temperatures hit a record high in 1998 ? and then the warming stalled.

For several years, scientists wrote off the stall as noise in the climate system: the natural variations in the atmosphere, oceans and biosphere that drive warm or cool spells around the globe. But the pause has persisted, sparking a minor crisis of confidence in the field. Although there have been jumps and dips, average atmospheric temperatures have risen little since 1998, in seeming defiance of projections of climate models and the ever-increasing emissions of greenhouse gases. Climate sceptics have seized on the temperature trends as evidence that global warming has ground to a halt. Climate scientists, meanwhile, know that heat must still be building up somewhere in the climate system, but they have struggled to explain where it is going, if not into the atmosphere. Some have begun to wonder whether there is something amiss in their models...

http://www.nature.com/nclimate/journal/v4/n3/full/nclimate2106.html

Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus

Matthew H. England, Shayne McGregor, Paul Spence,
Gerald A. Meehl, Axel Timmermann, Wenju Cai, Alex Sen Gupta,
Michael J. McPhaden, Ariaan Purich & Agus Santoso

Nature Climate Change 4, 222?227 (2014)
doi:10.1038/nclimate2106

Received 11 September 2013
Accepted 18 December 2013
Published online 09 February 2014
Corrected online 14 February 2014

Despite ongoing increases in atmospheric greenhouse gases, the Earth?s global average surface air temperature has remained more or less steady since 2001. A variety of mechanisms have been proposed to account for this slowdown in surface warming. A key component of the global hiatus that has been identified is cool eastern Pacific sea surface temperature, but it is unclear how the ocean has remained relatively cool there in spite of ongoing increases in radiative forcing. Here we show that a pronounced strengthening in Pacific trade winds over the past two decades?unprecedented in observations/reanalysis data and not captured by climate models?is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming through increased subsurface ocean heat uptake. The extra uptake has come about through 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, lowering sea surface temperature there, which drives further cooling in other regions. The net effect of these anomalous winds is 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 is expected to resume once the anomalous wind trends abate.