It’s an old chestnut of those who would argue against relying on computer models to try to understand the trajectory of climate over the next century. ” We can?t predict the weather a week in advance. How can we do it 100 years in advance?”

William Connolley has an excellent explanation of the way in which the argument glibly misunderstands the issue:

A better analogy is with throwing a (fair) die: you can’t predict whether the next throw will be 1, 2, 3, 4, 5 or 6; yet you can be fairly sure that if you throw it 1000 times you’ll get very bored. Sorry: If you throw it 1000 times, the average throw will be close to 3.5. And to pursue this a bit more, if you make the die a bit unfair (by, say, making the 6 twice as likely to come up) then you still can’t predict what the next throw will be. But you can be sure that the long-term average will go up to… thinks… about 4 1/3.

But I wondered: is this just a straw man? Does anyone really make this argument? Not to worry. Tech Central Station (in the person of none other an eminence than James Glassman himself) comes through again:

We know how difficult it is to predict the weather for tomorrow; so, how are we going to predict the climate 100 years from now?

Thanks, Jim.

update: In rereading this, I realize another point that needs to be made. I’m not trying to use this as a defense of climate models. There are plenty of good reasons to think carefully about the use of climate models in formulating public policy. You’ve got to be careful in understanding both their strengths and limitations. This is merely meant to point out the vacuousness of one particular rhetorical trick used in an attempt to knock them down.