Global Warming Worsening Impacts; Creating New ENSO ‘Flavors’

By Stephen Leahy*

UXBRIDGE, Canada, Jan 11, 2011 (Tierramérica) 

The strongest La Niña weather system in 50 years has brought historic flooding to Australia and drought to Argentina, Brazil and Uruguay, driving up food prices.

Scientists now believe climate change is likely enhancing the impacts of the famous El Niño-Southern Oscillation (ENSO), a cyclical climate phenomenon that affects weather patterns around the world.

La Niña and El Niño are, respectively, the cold and warm phases of the ENSO cycle, and form part of the system that regulates heat in the eastern tropical Pacific Ocean.

Both accompany simultaneous changes in surface ocean temperature and air pressure.

In conditions defined by climatologists as “neutral,” high air pressure predominates in the eastern Pacific, while low pressure predominates in the west.

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The difference in pressure generates the trade winds, which blow east to west over the surface of the tropical Pacific, pushing the warm waters westward. The deeper, cooler waters then surface in the east, replacing the warm waters.

During episodes of La Niña, the differences in pressure are more marked, the trade winds blow more strongly, and the cold-water currents in the eastern Pacific intensify.

On the other hand, during El Niño, high surface air pressure in the western Pacific and lower pressure on the coasts of the Americas cause the trade winds to weaken or change direction, resulting in warmer water temperatures in the eastern Pacific.

“There has been a very rapid transition from El Niño to La Niña in 2010,” Kevin Trenberth, a senior climate scientist with the National Centre for Atmospheric Research (NCAR) in the central U.S. state of Colorado, told Tierramérica. Continue reading →