Re: population growth & physics ed

[palmer@sfu.ca (Leigh Palmer)]

> Hi!
> There's just a note I'd like to add to the general discussion about
> greenhouse effects. Quoting John Gribbin's

John Gribbin, coauthor of "The Jupiter Effect"? Is he your authority?
I think you could choose better. Gribbin is a science popularizer, not
a specialist in one of the related fields.

> "Hothouse Earth", pg.131,"Even
> doubling the amount of carbon dioxide in the atmosphere...only increases
> the amount of heat trapped by the greenhouse effect by an average of four
> watts per square meter.  The increase is so small because the
> concentration of carbon dioxide is so large that most of the heat trying
> to escape from the earth in the waveband from thirteen to seventeen
> micrometers is trapped already- radiation that has been trapped by one
> carbon dioxide molecule cannot be trapped by another one.

Doubling the amount of CO2 in the atmosphere will not increase the power
density of the "heat trapped" one bit. I think what he should say is that
it would reduce the power radiated directly away from Earth's surface
without being absorbed by the atmosphere by four watts per square meter.
Of course no heat is "trapped" at all; almost exactly as much radiation
is radiated away from Earth as is absorbed by Earth from the Sun.

> But even this
> modest increase in the strength of the greenhouse effect will cause the
> world to warm slightly, and this will evaporate more water vapor from the
> oceans.  Because it absorbs across the infrared spectrum, and because it
> is released from the seas in large quantities as the world warms, water
> vapor is the single most important greenhouse gas.

Yes, and by an order of magnitude more than CO2 in greenhouse effectiveness.

> The modest warming
> caused by a carbon dioxide doubling releases water vapor, which warms the
> world a little more and releases more water vapor....studies show the
> water vapor feedback effect amplifies the temperature increase by a
> factor of three..."

Well, let us in on those studies, please. Experts differ on the
importance and even the sign of water vapor effects brought on by
changes in CO2 concentration. Gribbin has chosen only one point of
view, it seems. Judging by his track record I think I'll hang back
a bit on making my judgment. Some experts think that water vapor
increase will produce increased cloud cover which will lower Earth's
overall albedo in the visible, diminishing the amount of energy
absorbed. This negative feedback accounts for the remarkable
stability of the temperature of Earth in the current era, so they
say. The system is homeostatic, it seems, in this particular state.

> ...I think it's time for a heck of a
> lot more research on this topic, with the willingness to make societal
> adjustments in the interest of long term survival, if necessary.

Exactly my sentiments! I would add that there is no reason to take any
costly steps until after "a heck of a lot more research on this topic"
has been done, wouldn't you agree?

Leigh