Re: population growth & physics ed

[palmer@sfu.ca (Leigh Palmer)]

> What conclusion can be drawn from the relative increases in temperature and
> CO2?  One implication might be that, because the relative CO2 rise is much
> larger, therefore the CO2 is not likely to be the cause of the temperature
> rise.
> But, of course, that logic is faulty.  Even if the relationship were as
> simple as T = T_0 + k *(CO2 conc), proper choices of T_0 and k could mean
> that the temperature rise is *entirely* due to the CO2, regardless of what
> the relative increases are.

That was the exercise I left for the reader. If you do that you will find
that the temperature increase above T_0 inferred in that way is much
smaller than the amount which must be accounted for by the CO2 which is
present.
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.

Of course there was no reason to expect that the effect would be linear.
The troposhere/biosphere of the Earth is in a robust state of balance. In
your (I assume chemical) terms it is heavily buffered. (Nothing disturbs me
more than the vocabulary of the ecocrazy instructing me on the "delicate
balance of nature".)

> The relative increases are an interesting fact, but in the absence of other
> information, I don't see how that fact contributes to thinking critically
> about global warming.  I therefore wasn't clear why you felt it "should
> always be pointed out".

I hope I have helped to clarify that. Thank you for pointing out that it
was not clear.

> P.S. interesting that the CO2 concentration shown in the http site you
> mention shows an annual cycle.  Does anyone know why this is?  Possibly
> aphelion and perihelion?

I was once told what the effect was likely due to, but it escapes me now.
More likely the annual variation in sea temperature. The solubility of CO2
in water varies strongly with temperature. The equilibrium concentration
of CO2 above water at ocean temperatures is about 200 ppm, far below the
current atmospheric concentration, so the CO2 is rapidly dissolving in the
sea.

Leigh