The Earth as a Pot of Water
We got slagged by an ugly, pelting, ice-and-slush snowstorm last weekend, just as my parents arrived for a visit. It was a final gesture of winter weather from a winter that had largely been absent from the year. We topped 70°F on two separate occasions this year, and, while we had some heavy rains, this was only the second snow; the first didn’t reach us until early March.
With the attention global warming has been getting in the news, it’s not surprising to see people discussing weather oddities in terms of global warming, whether positively or negatively. Freakishly warm January weather makes shopkeepers and bus riders insist global warming is responsible; freakishly late snow makes them announce global warming is exaggerated. Neither method of thinking is correct, and not just because the data sample is too small to be meaningful.
Even laymen understand that a single three-day heat wave does not a global warming trend make. Still, there is a sense that, if the world is warming, then the weather will get steadily hotter from year to year. On the scale of a lifetime, this is broadly correct, but, if the world is rapidly heating up, what we should really expect to see is wild swings in the weather.
Imagine a pot of water. If you take a spoon and stir it steadily around the pot, you will disturb the water considerably for a few seconds, but as you continue to stir, the water will settle into a consistent pattern of behavior, namely circling the pot with your spoon. Because your spoon will not stir the water with perfect precision, and because fluids, like water, are chaotic media (that is, small changes in one region can generate large and unpredictable changes elsewhere), you will create small eddies in the rotating water. But because your spoon continues to stir regularly, such eddies will quickly be re-assimilated into the overall pattern of circling water.
The earth is similar to this pot, although its behavior is more complex, because the range of input is more complex than a single spoon. Regional differences of heating, such as between land and water, or polar and equatorial latitudes, drive the weather’s engine, along with some input from the earth’s rotation. The interactions between these regions are chaotic, because the weather exists in fluid media—the air and water. But because the sun heats regions more or less consistently from day to day, and from year to year, the flow of these fluids has built up considerable momentum. The seas and atmosphere continue to rotate at a consistent speed, and in a consistent direction, producing consistent weather. Hiccups occasionally erupt when the natural variation of any cycle swings to an extreme, but the critical point to note is that these hiccups are infrequent and short-term, lasting little more than a year at most, and occurring every few years on a continental land mass. Irregularities are quickly drawn into the slow, predictable swirling of the usual weather patterns, just as a chance swirl in the pot disappears into the general rotation.
If the patterns by which the sun heats the earth change, however, hiccups in the weather will not be drawn back into the normal weather patterns, because the thermodynamic engine which powers the weather is no longer pulling the weather in the same direction it used to. Indeed, the new rhythms will themselves create such disturbances, just as you would create a lot of turbulence if you started stirring the spoon in a different direction in the pot of water. The planetary equivalent of this turbulence is freak weather, which can be hot or cold, according to the particular path and point of origin of the turbulence.
That’s the kind of thing we’ve been observing of late. Instead of a devastating flood every few years, we’re seeing two or three floods every year, somewhere in the world. Instead of a vicious blizzard somewhere in the country every year or three, we’re seeing multiple blizzards every year, accompanied by equally freakish warm pockets elsewhere in the country at the same time. Hurricane count is up by a factor of five. The weather is no better or worse than it was in my childhood, but even in my lifespan, it’s become more extreme. And that’s something to worry about when considering the hazards of global warming.