El NinoWeather 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.)