March 30, 2005

La Niñas and climate warming

This winter, relentless coastal rains and mountain snows pummeled the Pacific Southwest. Given that the target zone was green Southern California, it’s shocking that the storms were accompanied by little hype about global warming. The reason? Unlike 1998, the last stormy winter, there was no big El Niño in the central Pacific to conflate with global warming. And everyone knows (just ask Dr. Kevin Trenberth of the National Center for Atmospheric Research) there’s got to be a connection between global warming and more frequent and severe El Niños (For Kevin’s philosophy on this, look here).

But is there really a connection between warming and El Niño?

Here is what the authors of a new report published in the March 25, 2005 issue of Science magazine write:

The role of El Niño-Southern Oscillation (ENSO) in greenhouse warming and climate change remains controversial. During the warmth of the early-mid Pliocene, we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial Pacific, consistent with the prevalence of a La Niña-like state, rather than the proposed persistent warm El Niño-like conditions.

The early to mid Pliocene was a period about 3 to 4 million years ago in which temperatures in the high latitudes were about 10ºC higher than they are at present. Many people look to the Pliocene, a period when atmospheric carbon dioxide levels were thought to be about 100 ppm higher than today’s, for insight as to what the climate may be like under enhanced greenhouse conditions. When Oxford scientists R.E.M. Rickaby and P. Halloran examined Pliocene sea bed deposits for clues of the ocean state in the central Pacific, they found that La Niña, rather than El Niño, seemed to dominate.

The evidence reported by Rickaby and Halloran adds to the growing list of research that suggests that the La Niña conditions persist in the central Pacific during warmer periods (see here and here for example). Since, in general, El Niño events tend to cause more widespread weather extremes than La Niña, and since it is en vogue to attempt to link all extreme weather with global warming, naturally, the press and global warming alarmists have been quick to jump on the Kevin Trenberth-led bandwagon that global warming will lead to more and bigger El Niños. Fact is that there is precious little evidence to back up these claims and a growing amount of contrary data.

References:

Rickaby, R.E.M., and Halloran, P., 2005. Cool La Niña during the warmth of the Pliocene? Science, 307, 1948-1952.

Trenberth, K. quoted in article, El Niño and global warming: What’s the connection? UCAR Quarterly, Winter 1997.




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