Open thread, Nov. 02 - Nov. 08, 2015

MrMind

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If it's worth saying, but not worth its own post (even in Discussion), then it goes here.

Notes for future OT posters:

1. Please add the 'open_thread' tag.

2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)

3. Open Threads should be posted in Discussion, and not Main.

4. Open Threads should start on Monday, and end on Sunday.

Why, then, are you talking about the models' fit when answering the question of whether the "climate models can predict weather changes over long term periods" (emphasis mine)?

What other way is there? Building a time machine?

How else can you estimate the suitability of models in making predictions than testing their past predictions on current data?

What other way is there?

The usual plain-vanilla way is to use out-of-sample testing -- check the model on data that neither the model nor the researchers have seen before. It's common to set aside a portion of the data before starting the modeling process explicitly to serve as a final check after the model is done.

In the cases where the stability of the underlying process in in doubt, it may be that there is no good way other than waiting for a while and testing the (fixed in place) model on new data as it comes in.

The characteristics of the model's fi... (read more)

5Salemicus11y

One possible answer is to look at how the then-state-of-the-art models in (say) 1990, 1995, 2000, etc, predicted temperature changes going forwards. The answer, in point-of-fact, is that they consistently predicted a considerably greater temperature rise than actually took place, although the actual temperature rise is just about within the error bars of most models. Now, there are two plausible conclusions to this: * Those past mistakes have been appropriately corrected into today's models, so we don't need to worry too much about past failures. * This is like Paul Samuelson's economics textbook, which consistently (in editions published in the 50s, 60s, 70s and 80s) predicted that the Soviet Union would overtake the US economy in 25 years.