October 5, 2006

El Niño is Back

Don’t look now but it appears an El Niño event is brewing-up in the Pacific and by Christmas of this coming year, we could be feeling the effect of this oceanic phenomenon. Imagine the potential here – pictures of floods in the Southwest, avalanches in the Rockies, mudslides in California, fires in Australia, and calamities from throughout the world. Every event will be blamed on El Niño and like clockwork, global warming will get mixed into the story.

In case you have forgotten since the last El Niño event, El Niño occurs in the equatorial Pacific Ocean. Under normal, or neutral, conditions, the trade winds in the low latitudes blow from the northeast to the southwest. In the equatorial coastal area of western South America, these winds blow off shore and create upwelling in the ocean. The upwelling brings relatively cool water to the surface (along with nutrients loved by fish) that spreads across the Pacific near the equator. If the trade winds intensify in response to pressure gradient changes in the Pacific, cold water appears creating a La Niña event. La Niña’s just fail to generate much press coverage, and most people have never heard of La Niña.

However, during the opposite phase of the Southern Oscillation, the trade winds off the coast of South America weaken, and warm water invades the eastern Pacific in the low latitudes. Such a pool of warm water is developing today, and the El Niño warnings are appearing throughout the news. Many scientists have shown that El Niño is associated with wet and warm winters from California to the Mississippi, although the statistical relationship between El Niño / La Niña indices and interannual precipitation totals is really not all that high. Furthermore, the large pool of warm water in the Pacific contributes to the global temperature, so El Niño periods tend to be associated with warmer than normal years. Linking El Niño to global warming is commonplace in the greenhouse crusade.

However, there is an exhaustive literature on this subject of global warming and the future of El Niño. The next time you see any link made between El Niño and global warming, consider what the Intergovernmental Panel on Climate Change (IPCC) has to say in their easily accessible “Summary for Policymakers.” IPCC states “Confidence in projections of changes in future frequency, amplitude, and spatial pattern of El Niño events in the tropical Pacific is tempered by some shortcomings in how well El Niño is simulated in complex models. Current projects show little change or a small increase in amplitude for El Niño events over the next 100 years.” That is hardly some ringing endorsement for more El Niño years in the future!

The El Niño – global warming link took a blow recently with a 2006 article published in Climate Dynamics entitled “Future changes of El Niño in two global coupled climate models.” The article was written by Gerald Meehl and his associates at the National Center for Atmospheric Research; Meehl and NCAR are hardly noted for greenhouse skepticism. They chose two different climate models for their experiment, and they chose those models because of their relatively outstanding ability to simulate El Niño events. They doubled and quadrupled atmospheric concentrations of carbon dioxide (CO2) and they varied the rate of increase of CO2 to be consistent with various IPCC scenarios. They compared the simulations with observed El Niño cycles and found “The amplitude of simulated present-day El Niño events in the models is comparable to observed events” – good start! A few sentences later in the conclusions they write “El Niño frequency in these experiments does not change appreciably with increased positive radiative forcing.” Imagine that – they double and quadruple CO2, the CO2 acted to warm the world (e.g., has a “positive radiative forcing”), but El Niño frequency did not change.

I know what you are thinking – maybe there will be no increase in frequency but surely there will be an increase in El Niño intensity in the future. A common measure of the severity of an El Niño event is the sea surface temperature in some well-selected part of the Pacific. Meehl et al. found that the amplitude of the standard deviations decreases “somewhat” for the doubled CO2 experiments and decreases “even more” for the quadrupled CO2 experiments. Translation – the El Niño intensity weakened as CO2 increased. The team further concluded that the reduction in amplitude “is well outside the range of inherent low frequency El Niño variability, and the reductions in amplitude for these experiments are statistically significant.” They also state that “changes of El Niño would be difficult to detect over the course of the twenty-first century, and may only emerge farther into the future with much larger forcing.” After a few sentences of caution about how their results could vary with the use of other models, they conclude “In any case, it appears that there is currently no definitive answer to the question of what will happen to El Niño in the future.”

We couldn’t say it better ourselves!

Meehl, G.A., Teng, H., and Branstator, G. 2006. Future changes of El Niño in two global coupled climate models. Climate Dynamics, 26, 549-566.




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