Re: Global warming deniers

In article <1145393941.108159.218350@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Kermit <unrestrained_hand@xxxxxxxxxxx> wrote:

[snipping away to commit a little pedantry]

Have any evidence? We have
significantly altered CO2, the main greenhouse gas, in the atmosphere.

It's actually number 2, behind water vapor. It is the number one
greenhouse gas that does not condense under terrestrial conditions,
and that is an important qualifier. If water vapor were the sole,
or strongly dominant, greenhouse gas, then we'd be a very cold place.
Any decline in temperature (say because it's night) would precipitate
water from the atmosphere, leading to further cooling, and a runaway
that direction. The noncondensing greenhouse gases, lead by CO2,
provide a floor for that process and prevent the runaway cooling.

A popular lie (whose history I and another guy have tried, somewhat
casually, to figure out) is that water vapor is 95% of the greenhouse
effect. In fact, it's more like 60-70%, see
http://www.radix.net/%7Ebobg/climate/halpern.trap.html
for more details and citations to the literature.

A different key to this business is that greenhouse absorption
does not add linearly. This is fortunate:
Current greenhouse effect is about 33 C. CO2 is something like 20%
of the greenhouse absorption. That would make for doubling CO2
to give, on its own, a warming of 6.6 C, instead of the predicted
3 C. Of those 3 C, the majority is from water vapor feedback, not
the CO2 directly. Allowing for that amplifier, the 6.6 C 'should' be
amplified to about 15 C, instead of the 3 C.

The thing is, once you have a 'lot' of a greenhouse gas, adding
more does not substantially increase the absorption at those
wavelengths. (unfortunately, it doesn't take a lot of increase in
the greenhouse effect to make for a substantial -- ice age-like --
climate changes). There are enough CO2 and H2O in the atmosphere that
increasing their concentrations only increases absorption approximately
logarithmically, hence the 3 C figure for doubled CO2 versus the
15 which would be expected linearly.

That nonlinearity also means that you can't speak of a unique
precise figure for the contribution of a given greenhouse gas,
certainly not for water vapor versus CO2. The thing here is, their
absorption bands have some overlap. If you remove all of one,
the other is perfectly able to absorb most of what the other had
been absorbing in those bands. Hence we leave it at 'something
like 60-70%' for water vapor and 'something like 12-30%' for CO2,
and get on to the scientific questions of what happens in the
full system when we (or carbon cycle variations) kick the CO2 levels.

We have reduced forests, changed the distribution and proportions of
many animals and plants, drained major rivers to a trickle, and created
large dead zones in the ocean. Altering the average temperature a few
degrees doesn't seem absurd, even if it turns out to be incorrect in
light of further evidence.

CO2 levels increased 40% at the end of last ice age (given the
logarithmic increase in absorption, it's more useful to compare
percents), and this corresponded to a 5 C increase in global mean
temperature. CO2 levels have now (2006) increased by about 35%
and will reach 40% in 5-10 years, relative to pre-industrial levels.
What, exactly, will happen is certainly a question. But it
strikes me as bizarre (in a yec sort of way) to declare that
nothing will happen. (Aside: Notice that those evil conspirator
scientists, bent on world domination and taking away everyone's
SUV, are predicting less warming for 100% increase in CO2 than
has already been observed for a 40% increase.)

--
Robert Grumbine http://www.radix.net/~bobg/ Science faqs and amateur activities notes and links.
Sagredo (Galileo Galilei) "You present these recondite matters with too much
evidence and ease; this great facility makes them less appreciated than they
would be had they been presented in a more abstruse manner." Two New Sciences

.

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