Rapid warming turbocharges Pacific trade winds

Rapid warming of the Atlantic Ocean has turbocharged Pacific Equatorial trade winds, new research has found. The winds have reached a level never recorded before.

The rapid warming of the Atlantic Ocean is probably caused by global warming, researchers from the University of New South Wales said. The warming has turbocharged Pacific Equatorial trade winds, which are currently at a level never seen on observed records dating from the 1860s.

The increase in these winds has caused eastern tropical Pacific cooling, amplified the Californian drought, accelerated sea level rises at a rate three times faster than the global average in the Western Pacific, and slowed the rise of global average surface temperatures since 2001.

According to the study, which is published in the journal Nature Climate Change, it may even be responsible for making El Nino events less common over the past decade due to its cooling impact on ocean surface temperatures in the eastern Pacific.

“We were surprised to find the main cause of the Pacific climate trends of the past 20 years had its origin in the Atlantic Ocean,” said co-lead author Dr Shayne McGregor from the UNSW Climate Change Research Centre and ARC Centre of Excellence for Climate System Science (ARCCSS) at UNSW. “It highlights how changes in the climate in one part of the world can have extensive impacts around the globe.”

The record-breaking increase in Pacific Equatorial trade winds over the past 20 years had, until now, baffled researchers. Trade wind intensification was considered to be a response to Pacific decadal variability. However, the strength of the winds was more powerful than expected due to changes in the Pacific sea surface temperature. Previous research had also indicated that under global warming scenarios, Pacific Equatorial Trade winds would slow down over the coming century.

The solution was found in the rapid warming of the Atlantic Ocean basin, which has created unexpected pressure differences between the Atlantic and Pacific. This has produced wind anomalies that have given Pacific Equatorial trade winds an additional push.

“The rapid warming of the Atlantic Ocean created high pressure zones in the upper atmosphere over that basin and low pressure zones close to the surface of the ocean,” said Professor Axel Timmermann, co-lead and corresponding author from the University of Hawaii.

“The rising air parcels, over the Atlantic eventually sink over the eastern tropical Pacific, thus creating higher surface pressure there. The enormous pressure see-saw with high pressure in the Pacific and low pressure in the Atlantic gave the Pacific trade winds an extra kick, amplifying their strength. It’s like giving a playground roundabout an extra push as it spins past.”

Many climate models appear to have underestimated the magnitude of the coupling between the two ocean basins, which may explain why they struggled to produce the recent increase in Pacific Equatorial trade wind trends.

But the researchers don’t expect the current pressure difference between the two ocean basins to last. When it does come to an end, they expect to see some rapid changes, including a sudden acceleration of global average surface temperatures.

Photo credit: LenDog64/ CC BY-ND 2.0

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