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American Association for the Advancement of Science

El Niño events are currently unpredictable

Georgia Tech researchers work underwater to remove cores from living coral colonies growing on Fanning Island in the central Pacific. In the laboratory, these “modern” cores provide records of the most recent period of climate changes for comparison to the fossil coral climate reconstructions.
[Image courtesy of Roland Klein, Norwegian Cruise Lines]

Some climate events, like monsoon seasons, are thought to be influenced by greenhouse gases. But, so far, researchers have not been able to tie a quirk in the global climate, known as the El Niño-Southern Oscillation (ENSO), to any other natural or human-made processes. The ENSO occurs roughly every five years, and it warms large stretches of the Pacific Ocean while influencing rainfall around the world.

Now, after studying fossil coral records spanning the last 7000 years, Kim Cobb and colleagues from the U.S. and China suggest that ENSO's behavior still can't be tied to global warming. The researchers sampled corals from Christmas and Fanning Islands in the tropical Pacific Ocean and found that ENSO behavior followed no clear pattern during the past 7000 years.

The ENSO's behavior is certainly more variable today than it has been in recent history but it's not completely unique, they say. The researchers' findings disagree with some current models that suggest ENSO responds to radiation from the Sun that gets trapped by greenhouse gases. In light of their results, Cobb and the other researchers say that—even if it exists—a link between ENSO behavior and global warming may be difficult to prove.