Many people do believe that global warming
will affect the poles more than the tropics, thus decreasing the earth's temperature gradient. However, at the same time, more general energy is going into the system. Therefore, i tend to believe that global warming will increase convective precipitation
such as summer thunderstorms, 'monsoonal
' patterns associated with differential land and ocean heating, and other generally localized storms such as hurricane
s - while decreasing the severity of the fronts associated with the polar jet stream
in the temperate areas. What this will mean is more violent localized storms, with possible long periods of drought in temperate areas such as the Midwest
where most precipitation comes from interractions with the polar jet stream. This being said, i agree with the premise stated by Ja Son that the weather may become more severe in some ways.
I think the best way to predict the effects of warmer climates is to look back at times when the climate was warmer. In the time of the dinosaurs, the climate was warmer, in part because all the carbon which was later locked up in oil was still cycling through the systems of the earth. (until humans found it and started burning it again) At this time, there were no ice caps and no deserts. The earth was dominated by large shallow seas and vast swamps and jungles. Tropical forests grew as far north as England. These conditions might be conductive to great biodiversity in some areas... but they are probably not very good for us humans, a species which prefers drier grassland areas.
Incidentally, the El Nino pattern does not actually decrease hurricanes.. it just changes where they occur. In El Nino, the hurricanes in the Atlantic become less intense, but hurricanes in the east Pacific become much more abundant and intense. In fact, in the summer of 1997, a hurricane obtained such strength that it almost was able to strike Los Angeles still as a catergory 1 storm.. but the steering currents of the atmosphere prevailed and moved it harmlessly out to sea.
Also, El Nino is not a net warming of the Earth's waters, it is just a warning in some areas. In El Nino patterns, the water is actually cooler than normal near southeastern Asia, causing monsoons to fail and massive droughts.