But a lot of people that know a lot more than I do about this stuff seem to take the models more seriously. This forces me to take them more seriously than I otherwise would.

If you want the scientific refutation of claims try: http://www.pas.rochester.edu/~douglass/papers/Published%20JOC1651.pdf

For Antarctic ice, I was thinking of both sea ice extent and ice sheet mass:

Extent: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.anom.south.jpg

Mass: http://www.cpom.org/research/djw-ptrsa364.pdf

Do you mean Antarctic ice formation? Area or volume?

http://repository.upenn.edu/cgi/viewcontent.cgi?article=1144&context=marketing_papers

As for Arctic ice melting, that proves my point. Mean surface temperature are below those predicted by the model, Artic melting is above, Antartic _formation_ is above. Basically, they can’t predict any interesting feature of the climate system even a decade in advance.

Re: accuracy of climate models – my understanding is that while their forecasts aren’t spot on, their margin of error isn’t all that wide when applied to the climate record either. On the other hand, the recent rate of arctic ice pack melting is actually above the upper bound of what the best models predicted.

The point of my post was that if the climate models are right then we’re headed for relatively uncharted territory.

I should note that for much of the data I estimated century changes using data that spans more than centuries. For example, the ice cores can tell us that the difference in temperatures between 15,000 and 15,500 years ago, but not the centuries in between. I divide that difference by five to get the average change by century. This means that actual changes in temperature can be more volatile than what I reported above. Suppose between 15,500 and 15,400 years ago temperatures increased by 10 degrees and then in the next 400 years, they decreased by 2 degrees a century. The data would tell us that the average temp change was less than a degree a century but the actual volatility was much higher. Anyway, the bottom line is that the “1 in 3 or 4 hundred centuries” estimate is a lower bound. I don’t know how to estimate the size of this bias.

Re: Year 2000 – we hit the peak of the solar cycle in 2000, and are at or around the solar minimum right now.

There are plenty of economic models that have demonstrated some skill in predicting LA economic growth on yearly or decadal time scales. Within the bounds of that skill, you should absolutely take into account those predictions when making decadal-scale plans that depend on economic growth in LA.

The problem with climate models is they have demonstrated no forecasting skill on any time horizon, least of all centuries.