Meteorologist sees link between global warming, El Niño

Meteorologist Kevin Trenberth theorizes that much of the additional heat trapped by increasing amounts of greenhouse gases may be going into the oceans

February 23, 1999
Web posted at: 11:45 AM EST

El Niño has exhibited some peculiar behavior over the last 20 years, leading one meteorologist to hypothesize that global warming is exacerbating the effects of the weather phenomenon.

Kevin Trenberth, a meteorologist at the National Center for Atmospheric Research, notes that El Niños have been unusually frequent since the mid-1970s. That same time period has seen a dramatic rise in global temperatures, suggesting a correlation between global warming and the El Niño Southern Oscillation.

The global mean temperature peaks three to four months after the peak in El Niño, said Trenberth.

"It is no coincidence that the exceptional warmth in the first seven months of 1998 occurred as the Pacific Ocean lost heat following the peak of the 1997-98 El Niño in December 1997," he said.

During El Niños, warm water spreads across the tropical Pacific, evaporating large amounts of water vapor that release heat when the vapor condenses into clouds and rain.

Thus, El Niño events tend to transfer heat from ocean to atmosphere, warming the globe about 0.1 degree Celsius for each standard deviation of departure from average temperatures in the Southern Oscillation index, said Trenberth.

Trenberth theorizes that much of the additional heat trapped by increasing amounts of greenhouse gases may be going into the oceans. It is later released through El Niños that are larger, more frequent, or less efficient in releasing the ocean-stored heat.

The atmospheric warming induced by El Niño also helps to further dry out regions -- such as Indonesia, Australia, and parts of Africa and Brazil -- already prone to drought during an El Niño.

"Naturally occurring droughts, such as from ENSO, are likely to set in quicker, plants will wilt sooner and the droughts may become more extensive and last longer with global warming," Trenberth writes in a paper, "El Niño and Global Warming," published in the journal Current.

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