2 posts tagged “climate modeling”

Real Climate had a pretty good article a few weeks ago about Edward Lorenz, who recently died.  The article speaks of Lorenz's butterfly effect, atmospheric modeling, and chaotic systems.

The article is definitely worth reading, but I found the last two paragraphs very insightful:

...how can climate be predictable if weather is chaotic? The trick lies in the statistics. In those same models that demonstrate the extreme sensitivity to initial conditions, it turns out that the long term means and other moments are stable. This is equivalent to the 'butterfly' pattern seen in the figure above being statistically independent of how you started the calculation. The lobes and their relative position don't change if you run the model long enough. Climate change then is equivalent seeing how the structure changes, while not being too concerned about the specific trajectory you are on.

Another way of saying it is that for the climate problem, the weather (or the individual trajectory) is the noise. If you are trying to find the common signal that is a signature of a particular forcing then averaging over a number of simulations with different weather works rather well. (There is a long standing quote in science - "one person's noise is another person's signal" which is certainly apropos here. Climate modellers don't average over ensemble members because they think that weather isn't important, they do it because it gives robust estimates of the signal they are usually looking for.)

I am not sure how true this really is, but it is certainly an interesting read.  Here is a tidbit (make sure you read the whole article):

Climate modeling needs a professional, peer-reviewed journal devoted exclusively to the codes employed and to mishaps in modeling. I propose that it be titled the Journal of Climate Codes and Failures. All other journals in the field of climate research would accept a manuscript submitted to them only if the authors could prove that they had simultaneously submitted their reports of code changes, incidents and mishaps to JCCF. All parties would then be aware of the problems involved in climate modeling. They would have created a system enabling them to learn from their mistakes. As it stands, they cannot learn, because all accidents are swept under the rug. In my mind that is unprofessional. Worse, I consider it unforgivable. Just think of it: a scientific discipline that has arranged things such that its members CANNOT learn! Truly inconceivable!