Global warming hits Walker circulation

Global warming slows down wind circulation over the Pacific

 
Last Updated: Saturday 04 July 2015 | 02:50:09 AM

-- a vast system of winds over the Pacific Ocean is getting weak due to global warming, which portends ill for worldwide weather systems, including the Indian monsoon, claims a recent study.

A team of us researchers from the University Cooperation for Atmospheric Research (ucar) in Colorado has found that the Walker circulation, which pushes the Pacific Ocean's trade winds from east to west, has weakened by 3.5 per cent since the mid-1800s, and may weaken by another 10 per cent by 2100. The circulation, which spans almost half the earth, is named after British physicist Gilbert Walker, who was also the first director general of the India Meteorological Department (imd). Walker was the first scientist to establish that the Indian monsoon is affected by climate phenomena in other regions.

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Fluctuations in the circulation can affect temperatures along the Indonesian coast, a key factor for monsoon rains in India, says M Rajeevan of imd. The Walker circulation also influences El Nio.

"The Walker circulation is fundamental to climate across the globe," says Gabriel Vecchi, the lead author of the study that appeared in the May 4 issue of Nature (Vol 441, No 7089).

The ucar scientists used shipboard and land-based data as well as computer models to simulate the past and future performance of the Walker circulation, to find out how much of the effect is due to greenhouse gases emitted as a result of human activity. According to Vecchi, the answer they got was that pretty much all of it was due to global warming. "At least 80 per cent of this is attributable to human activities," he was quoted as saying by Nature.com.

Any drop (slowing down) in the Walker circulation produces an even larger reduction in the wind-forced ocean flow -- roughly twice as much in percentage terms for both the observed and projected changes, says Vecchi. In other words, if there is a 10 per cent drop in wind circulation, it can result in more than 20 per cent reduction in the ocean flow, he says.

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