Monday, May 02, 2011

Climate vs. Weather

OK, folks, I feel compelled to weigh in on this. I'm tired of people looking at individual weather phenomenon (Katrina, the recent tornadoes in the south, cold winters, heat waves) and declaring a connection to (or a refutation of) global warming.

It's apples and oranges. Weather and climate are different things.

Allow me the analogy to a roulette wheel in a casino. Imagine that when the wheel is spun, you knew the exact velocity and position of the wheel. You then use that to predict which number will be pointed to at any given moment, using the basic laws of physics. You predict what number will be at the top in 2 seconds, 4 seconds, 6 seconds, and so forth. Your prediction for 2 seconds will likely be pretty good. But due to imprecision in your measurements, your prediction for 4 seconds will not be OK but not as good as the 2-second prediction, for 6 seconds will be not as good as the 4-second prediction, you will not be terribly accurate at all at predicting the final resting number of the wheel. (If you want the details for why the predictive ability falls off, it is due to chaos theory.)

This is analogous to predicting the weather. A roulette wheel is of course far simpler than the weather (and doesn't have nearly the chaos-inducing non-linear variables), so in practice you'd do a lot better than a weather forecaster, but the principle is the same (and this is, after all, an analogy). In particular, you can see that predicting the roulette wheel (weather) gets significantly more difficult as time passes.

If the casino made its money "predicting" the roulette wheel, they'd lose money like crazy and go out of business quickly. But of course, we know empirically that as a rule casinos have a bit of a habit of making, not losing, money.

Why? Simple: they're not predicting the weather, they're looking at the climate. If predicting the weather is analogous to predicting the outcome of given roulette wheel spin, looking at the climate is analogous to predicting the AVERAGE outcome of MANY roulette wheel spins. In other words, it's looking at the statistics of the system rather than any individual outcome.

In the case of the roulette wheel, we know that over the long time, a fair roulette wheel will end on red a little less than half of the time, on black a little less than half of the time, and occasionally on 0 or 00. And that "little less than half" is where they make all of their money at the roulette table.

In the same way, climate is not about individual weather events, it's what the statistical averages and trends are in temperature, precipitation, etc. Having a "warming" climate doesn't mean that winter snowfall stops, or that we have nothing but heat waves and no cold snaps. But it does mean that over a long-ish period of time, when these things are averaged out, there are measurable trends in the statistics.

One heat wave, one hurricane, one deep freeze - it is impossible and thus meaningless to say that any of these would or would not have happened without climate change, or that any such event proves or disproves climate change theories.

This is like saying that 4 spins of the roulette wheel which, in a row, yield 4 reds somehow "proves" that the odds of the roulette wheel favor red. Assuming the wheel is not rigged or flawed, this proves nothing of the sort. People who make similar claims relating weather to climate are doing everyone a disservice by saying so. Climate science has its flaws, but its model and accuracy will be refined and improved in the aggregate, not by the individual weather event.

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