Re: global warming and sea level rise

From: Robin Hanson (
Date: Thu Jul 19 2001 - 07:43:20 MDT

Hal Finney writes:
> >
> 102599.htm
>This is a very ambitious study, combining a climate model with an economic
>model. I can't help being skeptical about whether the researchers have
>bitten off more than they can chew.

Wow. An extropian complaining that an elaborate analysis of the future
just still isn't detailed enough to inform our choices. :-) Of course
by this standard virtually no extropian analysis is good enough either.
We have no models of anywhere near this detail for the social implications
of nanotech, AI, uploads, space colonization, etc, which are subjects of
constant discussion here. My attitude is to draw tentative conclusions
from whatever is the best analysis in an area.

>.. Nordhaus ... "three
>box" model (atmosphere, biosphere, ocean) is much simpler than the full
>models being run. He says that he gets about the same results, but if
>so then that would suggest that the more complex models aren't really
>necessary, wouldn't it?

No, a more complex model can *validate* a simpler one. If I show you a
simple model of a ball bouncing and you complain that it doesn't take
into account air friction, if I then show that you get pretty much the
same results with a more complex model, that allows me to get away with
the simpler model in future discussions. I don't have to always use the
most complex possible model.

>His economic model seems even more questionable. ...
>... But how much credibility
>does a model have which assumes only one commodity, no significant
>international trade, and that technology and population growth are
>independent of economic activity? ...

Lots of credibility. But as usual, you have to have some expertize
in an area like this in order to judge what sort of approximations
in a model are reasonable. I'm nowhere as expert as Nordhaus on
this, but I know enough to see why these are reasonable
approximations for his purposes.

>TFP growth is assumed to slow gradually over the next three
>centuries until eventually stopping. ...
>For those interested in pursuing it, his model is available for
>download as an Excel spreadsheet. It would be interesting to plug in
>some more aggressive growth scenarios and see if it alters his results

Yes, as usual the effective way to challenge one model is with
another model.

Robin Hanson
Asst. Prof. Economics, George Mason University
MSN 1D3, Carow Hall, Fairfax VA 22030-4444
703-993-2326 FAX: 703-993-2323

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