A Tug-of-War Over La Niña

Dick writes about Earth and planetary science for Science magazine.

All government researchers agree that La Niña--the unusual cooling of the tropical Pacific blamed for triggering everything from floods in Mozambique to drought in the United States--will eventually die. They just can't agree when. In dueling announcements released yesterday and today, NASA and the National Oceanic and Atmospheric Administration (NOAA) are at loggerheads over whether La Niña is about to fade away or will linger into the fall. It's not a moot question: At stake is the strength of the Atlantic hurricane season, which La Niña can boost.

Although both agencies are looking at the same observations from the Pacific, they see different fates for La Niña. David Adamec, an oceanographer at NASA's Goddard Space Flight Center in Greenbelt, Maryland, points to the recent warming of surface waters in the eastern tropical Pacific and of deeper waters toward the central Pacific as evidence that La Niña is on its way out. "NOAA is responsible for the climate forecasts for the U.S.," he respectfully notes; but the abnormal coolness of subsurface water has been halved since this time last year, he says. That rapid rise in temperature is a "big change." At its current rate of fading, La Niña could be gone by midsummer, Adamec says.

But Vernon Kousky of NOAA's Climate Prediction Center (CPC) in Camp Springs, Maryland, begs to differ. "I think they've come out a bit prematurely," he says. "There's enough La Niña in place that it's not going to die as quickly as NASA has it." With "a fairly large volume of cool water" still beneath the surface, Kousky and the CPC today called for La Niña to weaken only over the next 6 months (www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory). That would mean that it has a chance to bolster the number and intensity of hurricanes during the upcoming Atlantic season, as it did last year.

Longtime El Niño and La Niña watcher Eugene Rasmusson of the University of Maryland, College Park (and formerly of NOAA), doesn't see big changes looming in the Pacific either. He suspects that NOAA "is right on target." One thing's for sure, he says: The stirrings in the Pacific "will keep everybody on their toes."

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