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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 847 November 20, 2007 by Phillip F. Schewe
www.aip.org/pnu

EL NINO WEATHER IN A WARMER WORLD will cause a decrease in the
number of frost days in the southwestern states, an increase in
precipitation intensity in southeastern states, and an increase in
heat-wave intensity in the southern tier of states, according to a
new study.

The study looks at the weather impact of El Nino events
on weather extremes in North American if, as is often predicted,
global warming raises temperatures by a degree or two in coming
decades.

El Nino is the name for a huge ocean-atmosphere
interaction and transfer of energy across the tropical Pacific Ocean
between South America and Asia. El Nino events occur irregularly in
intervals of between two and seven years and can have a large impact
on weather in places around and beyond the Pacific basin.

Gerald Meehl (meehl@ncar.ucar.edu) and his colleagues at the National
Center for Atmospheric Research (NCAR) in Boulder, Colorado have
attempted to model what happens when El Nino events occur in a
hypothetical warmer world, especially for weather patterns in the
US.

The model, first of all, does a pretty good job of simulating
weather extremes (such as number of frost days-days when the
temperature goes below freezing---and intense precipitation) in the
world as it is now. Furthermore, the same model has been used to
demonstrate that the temperature increase over the US in recent
years has been mostly due to human-related *forcings* over and
above any natural fluctuations in effect. Giving the model a new slightly
higher base temperature, a number of specific changes in weather
extremes (during El Nino events) in the US emerge, such as those
shifts in extremes mentioned above. (Meehl et al., Geophysical
Review Letters, current issue.)