Archive for July, 2010

An Excellent Question!

July 1, 2010

From here.

how can the variability seen in the numbers calculated by GCMs be assigned to be weather.  If the numbers are weather, then it is clear that it cannot be the correct weather.  If climate is taken to be the average of weather, how can the average of the weather calculated by GCMs be expected to have any fidelity to actual future states of the Earth’s climate systems.

I have long wondered myself, why is it that if climate is average weather, and long term weather prediction is not possible, that the average of unpredictable weather is somehow predictable? The only thing I can think of, is that weather is assumed to be distributed around mean that it is entirely a deviation from, that no matter what the weather is, averaged over a long enough period the same “climate” emerges. This requires, however, that the system somehow “knows” that it needs to make up for when it was too cold or too hot because of weather, with enough of the opposite kind of variation to maintain the mean the same. But if the weather is truly random, how can it possibly be certain that it would, in fact, always tend back to the mean? I suppose one could also allow for the mean over a long enough period to be close to the “climate” but not necessarily there, in which case climate is not perfectly predictable, but within some reasonable limits, can be almost predicted. But the only other problem I can think of with this reasoning, is that the physical processes which determine climate, the crucial feedbacks of clouds and water vapor, are critically dependent on processes involving weather systems, on short timescales. If the behavior of weather systems is not predictable, how can the feedback processes be predicted?

Believe it or not, I really am honestly confused by this, and would like to know. My view has always been that means are determined by their components, not the other way around, and in that way I view climate as determined by the weather, not the other way around, and as a related issue, I would like to know if anyone thinks I am way off base on this.


July 1, 2010

Even though nobody asked, I thought that people might like to know a little bit about my philosophy of science. I suppose you could say that am an Idealist, a believer in the purist, high minded ideas of Karl Popper and the idea that science is about (gosh) testing hypotheses. Thinking of it like a sentence “Scientists test hypotheses” you need the subject (a hypothesis which makes predictions which can be checked against observations/experiments), the verb (having a hypothesis is one thing, science needs actually testing of it), and of course the subject is also crucial (someone actually has to formulate the hypotheses, and do the actual testing. But I don’t think this is really enough to describe the way I view science. No, I think that there is more to it than that, because a crucial element is missing. With very few exceptions, the only way to talk about testing hypotheses is if their predictions are “measurable”. You cannot hope to test do science without mathematics, and given the limitations mere mortals often face when it comes to establishing unequivocal certainty, you almost certainly will need statistics. I guess what I am saying is that at least this element of my view of science was best expressed by Lord Kelvin, and also by the computer scientist John McCarthy:

All Science Is Numbers.~Lord Kelvin

He who refuses to do arithmetic is doomed to talk nonsense.~John McCarthy

For readers: what do you think defines science as an idea, as a practice, as way of learning about the universe?