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  eems like in the '90s, El Niño just didn't want to go away. El Niño, an unusual rise in sea-surface temperatures in the equatorial Pacific Ocean, visited three times from 1990 to 1995. In between, temperatures never went quite back to normal, as if it were all one long El Niño. This has led to some intriguing but speculative discussion about the possible link between rising global temperatures and the apparent increase in El Niños.

El Nino
A weather map reveals the wide range and impact of El Niño.
One respected climate scientist who has gone out on a limb about the global warming-El Niño connection is Kevin Trenberth, a climatologist at the National Center for Atmospheric Research in Boulder, Colorado. He thinks that El Niño may function as a kind of pressure release valve on the tropics. In an era of global warming, Trenberth says, ocean currents and weather systems might not be able to bleed off all the heat pumped into the tropical seas. Periodically, it has to get rid of the excess that builds up, he suggests, and that safety valve is El Niño.

Since 1976, there have been seven El Niños. Based on the most reliable records, which go back 120 years, we would have expected to see only five, Trenberth says. Could the recent upturn be part of a natural cycle or some kind of oddball blip on the climate radar screen?

One factor hampering efforts to clear up the confusion is the inadequacy of the computer simulations that scientists use to study El Niño and global warming. For one thing, the models used to predict the potential consequences of global warming are not set up to predict changes that occur on the relatively small scales of time and space on which El Niño operates. Nor do the models do an adequate job of simulating certain key aspects of climate, such as the effects of cloud cooling and the feedbacks between the oceans and atmosphere. So, for the moment, the theorized connection between El Niño and global warming is still in the realm of speculation.

-- By Daniel Pendick

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