On a completely non-computer related note (there's been a lot of fodder for thought today), I noticed a headline that Ivan is coming back. Yeah, you read that right. Hurricane Ivan, one of the most lethal storms to hit the East Coast in a century, was pushed back out to the Atlantic, where it caught a cross stream, headed back into the Carribean, gathered strength, and seems about ready to pound the Gulf Coast as a tropical storm - oh, and the remnants of Hurrican Jeane seem poised to do the same thing.
Global warming is often taken by those unfamiliar with complex systems as a gradual warming uniformly across the world - temperatures go up by one or two or three degrees, which pushes summer up a little bit. However, this assumption can be dangerously naive. Global Warming is actually causing cooling to occur in certain portions of the world, even as the average temperature increases. What changes is something more important - the amount of energy in the system.
Complex systems are not random ones. Rather, they form regions of quasi-stability, where a particular whether pattern become apparent. Until fairly recently, the weather patterns in the Gulf of Mexico have had a certain pattern - storms would form in the Atlantic (largely because of heat, sand and contaminants picked up in the growing Sahara desert) and would move into the Caribbean, where the reasonably warm Caribbean water created a thermal gradient called a convection cell, in which cold air pushed down into a column of cold air, hit the warm Caribbean water, expanded outward as it was heated, rose in a donut shape back into the upper troposphere, where it then cools again and the pattern repeats. Because of Coriolis effects, this also begins spinning, and as more energy moves through the torus, the spin becomes faster. This is the basis of all cyclonic weather systems (i.e., most storms).
Once that Cyclone hits land, the energy that sustained it (the warm water) disappears, and the storm begins to lose energy. Usually, by the time it makes it way more than a few hundred miles, the storm has lost enough energy that it can't maintain the central column of air, and the storm dissipates. Usually. But not this time. This time, Ivan had SO MUCH energy, due to the extraordinary warmth of the Carribean, that it managed to maintain its cohesiveness even after making its way up to Pennsylvania, and once over the (warming) Atlantic, was able to reconstitute itself.
The Earth rotates, and that rotation in turn drags on storms and moves them into large circulation systems. Because most storms in the past haven't had that much energy, they fall apart far before they are significantly affected by the effect. Yet somewhere along the line, we may have entered into a new regime, a new semi-stable weather pattern, which is most ominous. If cyclones have enough energy to make a complete circuit of the Carribean circulation cell, then you have the possibility of a storm becoming a "repeat offender", persisting as a distinct entity for two, three, or four passes before entropy finally tears them apart.
What's worse, as storms re-enter the Carribbean, there is an increasing likelihood that a new storm can "cannibalize" the remaining energy of an older storm, with the effect that a Category 3 Storm gets bumped to Category 4 or 5 with regular frequency, and the likelihood increases of hypothetical Category 6, which would, by extension, have sustained winds in excess of 180 mph. To put this into perspective, Ivan's "sustained" winds topped out at 165 mph, but there were gusts within the storm that well exceeded 210 mph. A category 6 storm would have gusts in excess of 230 mph, which puts it into the regime of damage caused by a tornado (not to mention that storms of this magnetude would be spawning tornados by the dozens as such high "gusts" would be subject to incredible cyclonic pressures).
Average global temperatures have risen roughly 1 degree Celcius in the last twenty years. If existing trends continue, global temperatures will rise between three and ten degrees Celsius by the end of the century, with most computer models pointing toward the upper end of this range. That's energy going into creating even hotter water in the Caribbean and consequently even more powerful storms there. This raises the possibility of a permanent cyclonic band forming over the Southeast US, with hurricanes becoming weekly occurrences from March until November. Not a pleasant thought, to be sure ....