Re: Water as a byproduct of combustion...

[Tami Bond <tami.bond@noaa.gov>]

Dear Tom,

> Puzzled.  Are you saying that additional water vapor (forget clouds for now)
> doesn't absorb proportionally to initial amounts?  That water vapor
> absorbtion is non-linear at the concentrations in the atmosphere (obviously
> becomes non-linear as absorbtion approaches 100%).  

Yes, that's what I'm saying. Some of those windows are at 100%
saturation, but not all. 

> Are you saying  that
> absorbtion of radiation in one part of the IR spectrum gives different
> heating than in another nearby part?  

No, I'm saying that there is still radiation left to absorb in some
parts of the spectrum, not in others. Absorption should all have more or
less the same effect.

> Are you saying that the contribution
> of 6-8 Gtons of CO2/yr are significant relative to the absorbtion of the
> 500,000 Gtons of water vapor in the air?

Sort of. Again, it's relative to what existed 'before', in the
'untouched' state (whatever that was). No question that H2O has a huge
effect: the planetary temperature would be something like 30 K lower
without it. But there is some radiation, e.g. 2-2.5 um, that H2O can't
touch and CO2 can. And there are some windows, e.g. 6-7 um, that are
completely saturated by H2O and it doesn't matter how much more H2O you
put up there. So yes, CO2 can have an effect even with all that water
vapor up there. 

Another issue is that controls on H2O are mostly *not* anthropogenic.
The H2O concentration is largely governed by temperature, convection,
rainfall-- natural processes. The CO2 concentration does have a
substantial dependence on anthropogenic source strength. So again, 'we'
can change concentration of CO2, while keeping H2O more or less
constant, and the radiative change from 'previous' conditions is mainly
due to CO2. (Well, this is a pretty simplistic picture... I keep being
tempted to throw caveats in...) 

> Then of course there is the long term question of whether we want to avoid
> global warming at the risk of the overdue glaciation.  (Typical interglacial
> warming - 10,000 years;  we are 12,000 years since last glacier).

Climate will change regardless of what we do. To me, the question is how
fast we want to change it, and whether the fact that it would change
anyway means that we should just do whatever we want. The
'geoengineering' possibility seems like a red herring to me; if one
pooh-poohs CO2 as a problem for current climate, how can one hope to
believe that it will offset some theoretical future cooling? We are
getting into philosophical debate here, which I am happy to continue-- I
learn something every time I go through it, and I can't stop myself
wondering about what we 'should' do!-- but we should probably take it
off-list. 

> Have you read any of the "Earth's Children" series by Jean Auel, taking
> place during  the interglacial period of 25,000-30,000 years ago?  

Yes, I have read the first 3. Liked 'Cave Bear' the best because it
seemed to have the most focus on culture and least on 'anthroporn' but
they were all enjoyable nonetheless.

Have to get some work done now!

Tami

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