Dan Rather
DECEMBER'S ARRIVAL brought to an official close the busiest hurricane season on record. But it seems that someone forgot to tell Mother Nature, as Hurricane Epsilon disregarded the calendar to become an unprecedented 14th hurricane and 26th named storm - in a storm season that has run out of actual names. Meanwhile, amid growing concern over global warming - concern that has been intensified by extreme weather - we've been hearing strange warnings that Europe may be at risk of slipping into a mini ice age.
Just what is going on out there?
COMPLEX SYSTEMS
What is going on is a demonstration of one of the most complex systems imaginable -- weather on a planetary scale. Like all complex systems, its parts and processes are interrelated. And like most complex systems, the ways in which these parts are interrelated are often very subtle. Saying that one or another factor causes a given weather event is often a scientifically unsatisfying way of looking at it; where weather is concerned, it is usually more accurate to talk about one factor influencing another.
So what is influencing the bizarre weather that we saw at the close of last year's storm season, and throughout the whole of this year's extended season? Researchers at the National Oceanic and Atmospheric Administration (NOAA) believe that global warming is not the culprit, despite the intuitive connection that many have made because of the key role that warm ocean water plays in hurricane formation.
CULPRIT
The real culprit behind 'Katrina', 'Rita' and 'Epsilon', too, says NOAA, is the "tropical multi-decadal signal," a naturally occurring fluctuation of Atlantic ocean temperatures with hot and cold cycles that can take decades to complete.
Some folks pointed to this year's spate of hurricanes as proof-in-pudding evidence that global warming's effects were not only with us, but also dramatic and deadly. The danger in demagoging the issue of global warming in this way is that some people might now conclude that, since this does not appear to be true, global warming might neither exist nor pose a real threat. But singling out a group of hurricanes as caused by global warming makes as little sense as does drawing conclusions about global warming based on a week or two of unseasonably hot or warm weather.
The best way to think of global warming - and we ought to be thinking about it, because it is real and is already changing our planet - is as an influence on the context in which weather takes place. Is it exerting an influence on the multi-decadal system that lies behind our very active hurricane seasons? Perhaps, but that influence can be extremely hard, if not impossible, to pin down.
INFLUENCE
One place where scientists do believe they are seeing global warming's influence is along the European coast. The ocean current known as the Gulf Stream brings warm waters from the tropics north, giving nations such as England and France a milder climate than they might otherwise enjoy at such high latitudes. But the Gulf Stream is weakening because, scientists think, of the large volumes of fresh, cold water being dumped into the ocean by the rapid melting of the Greenland and Arctic ice sheets.
Scientists studying the phenomenon think it could likely drop average temperatures in Britain by a degree centigrade during the next decade. This may not seem like a lot, but in the interdependent system that is weather, a little bit of change can have outsize effects down the line. That global warming can contribute to regional cooling may come as a surprise, but no more of a surprise than a hurricane in December.
Dan Rather is a former television
broadcaster.
