In message , Retief
writes
On Mon, 6 Nov 2006 09:23:23 +0000, John Beardmore
wrote:

All the GH gases are equivalent to CO2 of 430 ppm.

This is simply not true:

http://www.profc.udec.cl/~gabriel/tu...cp1/1-11-2.gif

Clearly these different gases have different absorption spectra, and
can never be "equivalent to CO2"...

They can have a net thermal effect similar to CO2.

They absorb at different wavelengths, and they absorb at different
efficiencies. No, they are not similar.

They are similar in that they are greenhouse gasses.

They are similar in they cause net amounts of energy to be retained
which affects temperature. That they absorb different amounts at
different wave lengths doesn't mean that different amounts of various
green house gasses can't achieve the same energy retention / temperature
increase as some particular amount of CO2.


The technique demonstrated by claiming "equivalence" is called
"begging the question" (a well known logical fallacy).

Well - you begged it - you got an answer.


But if "net thermal effect" is what the comparison is all about, why
don't you compare it to something people can see and touch -- say, a
burning candle?

Could do, but it interesting to compare the 'potency' of various
greenhouse gasses, and if CO2 is the one with the biggest effect, it's
not surprising that people adopt it as a bench mark, but contribution to
heat retention and heat flows are calculated. Candle power would be
rather a small unit to use though.


"This is equivalent to XXX extra candles burning per
square mile of Earth's surface"... Oh, but then you wouldn't be able
to fold in the CO2 boogeyman...

Not a matter of any particular bogey - just causes, effects and
mitigation.


That is, the response of CO2 to a shifting spectrum is different than
the other gases.

What do you mean by a "shifting spectrum" ?

The sun behaves approximately as a black body. If the sun increases
in temperature (and output), the spectrum shifts towards the blue (and
increased UV).

OK - and how significant do you claim this is ?


And NOAA notes that the solar emission spectrum has changed:
http://www1.ncdc.noaa.gov/pub/data/p...olar_variabili
ty/lean2000_irradiance.txt

"Estimated increases since 1675 are 0.7%, 0.2% and 0.07% in broad
ultraviolet, visible/near infrared and infrared spectral bands, with
a total irradiance increase of 0.2%."

So ?

So, many of those other (so-called "equivalent") greenhouse gases also
interact with incoming solar flux,

So far so good.


and thus those gases are NOT
_equivalent_ to CO2. Their behavior is qualitatively and quantitively
different.

Yes - they all cause different amounts of heat to be retained per
amount of greenhouse gas released, but that doesn't mean that the total
heat retained can't be represented as being equivalent to a particular
amount of carbon dioxide.


BTW, from a historical standpoint, we are at a very low atmospheric
CO2 concentration...

http://en.wikipedia.org/wiki/Image:P...on_Dioxide.png

Not from a human civilization standpoint. What does it matter what happened
millions of years ago? Heck, why not go back to the big bang -- CO2
was zero
then!

Oh, you mean that the Earth supports no life, because a "climate
catastrophe" (as you predict impending) has exterminated all life,
when those past CO2 concentrations went up to an estimated 5-6000 ppm?

I's sure that if he'd intended to say something stupid and out of
context he could have managed it without your help !

He has asserted that CO2 will cause a global catastrophe. And we can
examine this claim by looking at historical records. You even quoted
Lloyd Parker's question "What does it matter what happened millions of
years ago?"

Indeed! Why do we believe that increasing CO2 will be any more
catastrophic than it was a million years ago?

Well, you mentioned a figure of 6000 ppm I believe. How well would you
cope physiologically at that concentration ?


Again, current CO2 levels are exceptionally low, compared to past
history.

Geological history yes, but as I understand it, not human history.


And we note that those high levels did not exterminate life
on Earth.

Which doesn't mean humanity would have survived. I suggest that if,
warming aside, 6000 ppm CO2 concentrations pose a major physiological
challenge to us and other animals, that in itself is a global
catastrophe.


Cheers, J/.
--
John Beardmore