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Diminishing Return

June 27, 2007, 7:49 am

I know a number of readers are tired of my writing about climate, so I am instead taking a shot at writing a comprehensive skeptic's argument on Anthropogenic Global Warming.  A free pdf will be available for download next week, with a bound copy available for purchase at manufacturing cost.

In the mean time, Luboš Motl presents one of the core skeptics arguments, that CO2 heat absorption is a diminishing return relationship to concentration, making frequent predictions of runaway climate scenarios a real head-scratcher.

In terms of numbers, we have already completed 40% of the task to
double the CO2 concentration from 0.028% to 0.056% in the atmosphere.
However, these 40% of the task have already realized about 2/3 of the
warming effect attributable to the CO2 doubling. So regardless of the
sign and magnitude of the feedback effects, you can see that physics
predicts that the greenhouse warming between 2007 and 2100 is predicted
to be one half (1/3 over 2/3) of the warming that we have seen between
the beginning of industrialization and this year. For example, if the
greenhouse warming has been 0.6 Celsius degrees, we will see 0.3
Celsius degrees of extra warming before the carbon dioxide
concentration doubles around 2100.

It's just like when you want
your bedroom to be white. You paint it once, twice, thrice. But when
you're painting it for the sixteenth time, you may start to realize
that the improvement after the sixteenth round is no longer that
impressive.

If CO2 is not responsible for all the 0.6C of historic warming (a proposition for which there are good arguments) then future warming is even less.  Read it all for more detail, or look for my paper next week which covers this topic and many, many others in more depth.  There are lots of complications - aerosols, dimming, feedbacks - that are discussed in the paper.

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Category: Climate
  • Anon E. Mouse

    Although I agree with the conclusion, I think the weakness is that the feedback (sign and magnitude) *is* the controlling factor. Obviously, if the sign is negative, we can roll over and go back to sleep. CO2 won't drive more than a bit of temp. change. But if the sign is positive, then the uglier scenarios are possible.

    Of course, if the feedback magnitude is a constant, then, yes, any CO2 driven global warming is a pretty limited event. But if the feedback magnitude is in fact a function of temperature, then the runaway scenarios could happen. For a purely fictional example not meant to reflect reality in any way, suppose that as temperature increased, polar caps and snow cover melts, and the earth reflects less sunlight, which drives temperature upward, which melts more snow, and so on. Pretty soon we're a cool version of Venus.

    But we have hundreds of millions of years of experiments that have never shown that effect. Cut through the noise and intentional or negligent distortions of data and we know one thing for sure -- the earth is the temperature it is today despite any dinosaur killin' meteorites, volcanic what-have-yous, etc.

    Moreover, we know, from Al Gore's own charts, that temperature and CO2 have been this high before. And what happened? Temperature returned to the norm, CO2 decreased.

    Thus, a negative feedback system. The sign is negative, the magnitude is “who cares, but big enough to win.” End of freakin’ story.

  • http://blog.accentient.com Steven Borg

    I'm definitely NOT tired of your posts on global warming. In contrast to most sources, your thoughts appear to be level-headed, clear, and without the shrillness of most discussions of this topic.