Re: population growth & physics ed

[jmclean@chem.ucsd.edu (James Mclean)]

Leigh Palmer says:
> Extrapolating back linearly will yield a warmer Earth than can be accounted
> for by solar heating. The aritmetic is easy, and I'll go through it for
> those silent folk who did not do the exercise. The CO2 has risen by about
> one seventh (14%) over the period in question, and the temperature has risen
> by about 0.5 K. Thus a linear relationship of the sort James suggests should
> produce a T_0 7*0.5 = 3.5 K lower than the initial temperature. The linear
> relation yields a greenhouse effect of only 3.5 K, somewhat smaller than is
> needed to keep us toasty at this distance from the Sun.The calculation of
> just how large the greenhouse effect is is something I can't find right now.
> It is considerably larger than that, but not ten times as large as I recall.
> A number would be appreciated.

Yes, this is exactly what I was trying to ask.  So say, for the sake of
argument, that the greenhouse effect (total, not just from CO2) increases
the Earth's temperature by something like 20 K.  Then we might say that
while CO2 levels have increased 14%, the greenhouse temperature enhancement
has increased by only 2.5%.

Initially I would have been happier with this than with your original
comparison, but now I'm not so sure.  It properly removes simple solar
heating from the argument.  But as you say it sweeps under the rug all the
non-linearities, etc. that should be included in the discussion.

-- 
--James McLean
jmclean@chem.ucsd.edu
post doc
UCSD