Re: Global warming test

"George O. Bizzigotti" <gbizzigo@xxxxxxxxxx> wrote in message
news:1eeh33ltr5sqlo6dvk0a921nq95rj1bm40@xxxxxxxxxx
On Tue, 1 May 2007 17:45:20 -0700, "Mark Test" <MARKT38@xxxxxxxxxxxx>
wrote:

[much snippage]

Am I correct in stating that nearly 99% of CO2 is made naturally?

It's hard to put precisely unless one has a very specific definition
of "made naturally." Fossil fuel burning, which is the most
significant human contribution, released 5.3 Pg of carbon per year in
the 1980s. This goes on against a background carbon cycle that totals
210 Pg carbon per year (120 Pg cycles between the land and atmosphere
and 90 Pg cycles between the ocean and atmosphere). Thus the human
perturbation amounts to 2.6% of the natural cycle., and so in a given
year one might say that 97.4% of the CO2 is "made naturally."

Got it.

On the other hand, the concentration of CO2 in the atmosphere has
risen from close to 280 ppm in 1800 to 367 ppm in 1999, The increase
is mostly due to human activities. On this basis, one might equally
well state that only 76% of the CO2 currently in the atmosphere is
"made naturally."

Any increase of volcanic activity during this same time-frame?
"Only 76% is made naturally"...OK...so only 24% is from man.

I use these two examples to illustrate that although the carbon cycle
and historical CO2 concentrations are reasonably well understood, it
is difficult to reduce that understanding to a single number. Although
one could create the impression of disagreement (some say it's 76%
whereas others say it's over 97%) because the single value is much
more dependant on semantics and definition, most scientists agree on
the underlying technical understanding.

So, nature makes more CO2 than man....a significant amount more.
You see, where a layman like me is scratching his head....how can
man who contributes from 3-24% of the world's CO2 be the sole
cause for climate change? (I know you don't say we're the sole
cause...but Al Gore does.)

Did the IPCC use water vapor in its climate models?

Yes. I should also point out that strictly speaking, the IPCC doesn't
have "its" climate models. The IPCC reviews results from climate
modeling published in the peer-reviewed literature. The IPCC is a
large interdisciplinary panel of experts, only some of whom run
climate models, and their reviews are based on the entire body of
literature, not all of which is published by IPCC members.

Got it.....I was told that many models don't factor in water vapor.
Thanks for setting me straight.

The reason water is not widley considered a greenhouse pollutant is
that it has a relatively short residence time in the atmosphere; water
gets removed as rain in something like 10 days on average, whereas
changes in CO2 levels persist for decades to centuries. Water levels
are included in the climate models; the vapor is a greenhouse gas,
whereas clouds lead to the opposite effect (cooling) as demonstrated
by the contrail article cited by Mr. Test. Evaportation from the
oceans and rainfall tend to keep water vapor levels roughly constant
despite anthropogenic effects.

The bottom line is that whereas water vapor levels are roughly
constant, CO2 levels are increasing, and it's the amount of change
that is the issue rather than the baseline amount.

The fact remains that water vapor is the number one greenhouse gas,
and to ignore it alarms me.

I did not mean to give the impression that water is ignored. Rather,
the role of human activities on the amount of water in the atmosphere
is indirect, whereas the role of CO2 is direct. Human production of
extra CO2 increases CO2 level in the atmosphere which causes
additional greenhouse effect. In contrast, all things being equal,
human production of extra water doesn't significantly increase water
levels in the atmosphere because the extra water falls out as rain.

The "all things being equal" qualifier is there because the water
content of the atmosphere is more dependent on temperature than on
human activities. As temperature increases, more water goes into the
atmosphere, but evaporation from the ocean dwarfs evaporation due to
human activity. That's why the current models all consider water vapor
levels and the effects of clouds.

I would argue that water should not be considered a greenhouse
pollutant even though it is a greenhouse gas because human activities
do not significantly affect the global* amount of water in the
atmosphere and the direct contribution of water to the greenhouse
effect. CO2 is different, because human activities do increase the
level of CO2 and result in greenhouse warming. Humans can manage the
degree of greenhouse effect by how much CO2 they emit; the amount of
water they emit is much less consequential.

*It has local effects, as anyone who has walked a golf course in the
desert can attest. Globally, it's a wash (pardon the pun) because it
simply means more rain somewhere else or at some other time.

BTW, CO2 levels last for decades to
centuries? Which is it? If we know how long H2O stays in the air,
surely we know to the second how long CO2 stays in the air.

It's not that simple. Scientists have measured rates for the various
processes that add or remove CO2 from the air. "Residence time" is a
convenient but imprecise indicator of how long an "average" CO2
molecule might remain in the atmosphere. It is imprecise because of
the number of individual processes that need to be considered (many of
which depend on CO2 levels in different ways), and because the
calculation is much more complex than summing a column of figures. The
imprecise "decades to centuries" is useful as an indicator that CO2 is
much more long-lived than water; however, the precise understanding
comes at the level of the individual processes. Unfortunately, it's
difficult to summarize those individual processes in a Usenet post
(chapters if not entire books have been written), so for this venue
one is left with only the rough order-of-magnitude residence time.

For what its worth, the water residence time is similarly imprecise;
"something like 10 days" was also meant to cover a rather broad range.
Even if a few days to a month or two sounds more precise than decades
to centuries, it's not.

Thanks for the info.....very good stuff.

Mark



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