Saturday, September 24, 2005

Climate science made simple

I constantly see discussions (or should I say "discussions") of global warming which portray climate as some incredibly complex system which is impossible to understand or make meaningful predictions about. One problem (of many) is that the media does a poor job of distinguishing what parts of science are solid and widely agreed on, and what parts are still controversial. So while yes, climate is complicated, the basic logic of global warming is pretty simple.

1. Carbon dioxide traps heat. This is fairly basic physics--not something explainable in a blog to the general public, at least not without going through a lot more work that I'm willing to put in, but a senior in a good physics or chemistry program should be able to understand what's going on. In short, it's not an advanced or controversial statement. No one would ever argue about this in any context except climate.

2. Mankind has greatly increased the amount of carbon dioxide in the atmosphere. This, too, is not (or should not be) a controversial statement. When you burn things, carbon dioxide is produced in predictable ways. Industrial society burns a lot of stuff--oil, coal, etc. If you add up all the stuff we burn, and compare it to the carbon dioxide in the atmosphere, you see a significant contribution. (Predictions are that that we will have doubled the atmosphere's carbon dioxide levels in the near future.)

So given those statements, it's logical to at least provisionally conclude:

3. Mankind's activities are causing the atmosphere to trap more heat, which will cause the earth to warm.

You can do some pretty simple calculations that show that without an atmosphere, earth's average temperature would be around -20 Celsius (give or take a few degrees). The actual average temperature is about 15 Celsius. So the atmosphere warms earth by about 35 degrees Celsius. If you drastically change the amount of carbon dioxide in the atmosphere, you ought to expect to see a change in the atmosphere's effects, too. A 10% change in atmosphere properties whould, to first order, lead to a 3 degree change in earth's temperature.

I'm not going to go through all the evidence for global warming here, nor will I pretend to have adequately captured the debate. Obviously climate really is a complex system, and you get all sorts of feedback mechanisms that make it hard to predict what, exactly, the effect of a major atmospheric change would be. People have long debates over the details. But the basic picture is really not that hard to understand. Given how solid statements 1 and 2 are, it would be pretty surprising if 3 wasn't true as well. I certainly haven't *proven* 3, but the burden of proof shouldn't be on scientists to prove 3 beyond a reasonable doubt, it should be on skeptics to show how 1 and 2 don't lead to 3. Statement 3 isn't surprising. If statement 3 was wrong, that would be surprising and counterintuitive.

More simple logic applies to a topic that's been in the news recently, that being hurricanes:

1. Hurricanes are stronger and more frequent in warmer waters. Without delving into hurricane physics, you can see this just by looking at a map.

2. If earth gets warmer, oceans will get warmer too.

3. Therefore, if global warming occurs, it will increase hurricane frequency and intensity.

This is not to say that you can blame any particular storm on global warming, just that you can expect more and larger hurricanes as the earth warms. Again, I certainly haven't *proven* 3 beyond a reasonable doubt, but you can see that if 3 is wrong it would be surprising.