It is time to stop quivering in our boots in pointless fear of the future and just roll up our sleeves and build it.
- Ray Pierrehumbert

Wednesday, June 27, 2007

How Do We Know We're Not Wrong?

All sincere doubters ought to consider Naomi Oreskes' excellent overview of the state of knowledge about anthropogenic climate change in specific, and about how we collectively come to know anything about anything in general.

Thanks to Andrew Dessler and Grist for the link.


Anonymous said...

I found the attached presentation interesting, but unconvincing. I’ll preface my remarks by saying that I’m not a “denier”; I’m on-record (in a cover story in National Review) as accepting that AGW is real.

Here are some obvious issues:

Pages 11 and 49 show a chart of temperature reconstructions going back about 1,000 years. This is very similar-looking to the North Report for the NAS, which I take to represent consensus opinion. It’s interesting that if you use the proxy reconstruction lines for the whole period, and not a splice of the actuals for the modern period (which seems to me to be the accurate way to estimate change unless you believe there is very different relationship between proxies and actuals in prior periods than the modern era, in which case the proxies seem pretty suspect and you ought to throw out the whole comparison) that as North said “It looks like more of a bow than a hockey stick”. That is, current temperature proxies are extraordinarily close to what they were in about the year 1000. even more interesting is that the purple proxy line (which by visual inspection and from memory, so nobody call me on this, is the Esper 2002 tree ring proxy study), the first derivative of modern temperatures isn’t even that impressive, as you had a very similar run-up in temperatures over a comparable period between about 850 and 1000.

Page 64 is pretty amateurish – “many model-based predictions have come true”. Really, I have a causal model for predicting the winner of baseball games – the team that bats first wins. Look at this long list of predictions that my model has made correctly.

Pages 65 – 69 use the intense 2005 hurricane season as confirmation of predictions. 1. Too bad about 2006. 2. There is a reason that hypotheses are subject to falsification tests rather than confirmation tests.

Page 81. Proof by lack of proven alternatives. ‘nuff said

Beyond all of this snarking, I think the really important point that she misses is that climate models that make predictions that can only be tested for a single instance (one world with lack of regional granularity) over 30+ years resist falsification tests. This isn’t to say that they mist be wrong, just that difficulty in establishing predictive certainty of the kind we can get is, say, classical physics is inherent to our current understanding of the science.

Jim Manzi

Michael Tobis said...

Thanks for sticking around, Jim.

I've taken on your tree-ring reconstruction question as a blog entry here. I'll have more to say about your other points soon.