August 4, 2014
Strengthening Of Pacific Trade Winds Attributed To Warming In The Atlantic
redOrbit Staff & Wire Reports - Your Universe Online
Climate scientists have finally solved the mystery as to why the equatorial Pacific trade winds, which were expected to get weaker due to increasing greenhouse gas levels, have actually gotten stronger in recent years.
For more than a decade, experts have wondered why the trade winds have behaved in contrast to climate models and become supercharged since the early 1990s. The phenomenon, according to a team of US and Australian scientists, is the result of recent rapid warming in the Atlantic Ocean likely due to global climate change.
Writing in the August 3 online edition of the journal Nature Climate Change, researchers explain that the Pacific trade winds are currently blowing at unprecedented levels, surpassing all records dating back to the 1860s. As a result, sea level rise in the western Pacific has been accelerated, which has an impact not just on the regional climate but global conditions as well.
“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,” co-lead author Dr. Shayne McGregor from the ARC Centre of Excellence for Climate System Science (ARCCSS) at the University of New South Wales said in a statement Sunday. “It highlights how changes in the climate in one part of the world can have extensive impacts around the globe.”
“We saw that the rapid Atlantic surface warming observed since the early 1990s, induced partly by greenhouse gasses, has generated unusually low sea level pressure over the tropical Atlantic,” he added. “This, in turn, produces an upward motion of the overlying air parcels. These parcels move westward aloft and then sink again in the eastern equatorial Pacific, where their sinking creates a high pressure system.”
The resulting difference in pressure between the Atlantic and the Pacific strengthened the Pacific trade winds, noted Dr. McGregor. The increase in the winds has caused cooling in the eastern tropical Pacific region, amplified the California drought, and slowed the increase of global average surface temperatures over the last 13 years.
The increased intensity of these winds, previously believed to be a response to Pacific decadal variability, could also be responsible for reducing the frequency of El Niño events over the past decade by cooling ocean surface temperatures in the eastern Pacific, University of New South Wales and University of Hawaii researchers said.
“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,” co-lead author and Hawaii professor Axel Timmermann said. “It's like giving a playground roundabout an extra push as it spins past.”
“Our study documents that some of the largest tropical and subtropical climate trends of the past 20 years are all linked: Strengthening of the Pacific trade winds, acceleration of sea level rise in the western Pacific, eastern Pacific surface cooling, the global warming hiatus, and even the massive droughts in California,” added co-author Malte Stuecker of the University of Hawaii Meteorology Department.
Co-author Matthew England from the University of New South Wales noted that it “will be difficult to predict when the Pacific cooling trend and its contribution to the global warming hiatus will come to an end. The natural variability of the Pacific, associated for instance with the El Niño-Southern Oscillation, is one candidate that could drive the system back to a more even Atlantic–Pacific warming situation.”