In his talk to thousands of scientists this week at the American Geophysical Union, Dr. Richard Alley, perhaps the best communicator" of all climatologists today, explained with a wonderfully simple metaphor why changes in levels of carbon dioxide in the atmosphere slightly lag behind changes in global temperature.
It's important because this fact seems to challenge the cause and effect relationship between carbon dioxide and global temps. Alley opened his talk by quoting from a letter than an alum recently wrote the university for which he works, Penn State. The alum complained that for his work on global warming, Alley "should be dealt with severely to prevent such shameful activities in the future," and pointed to this lag between changes in the levels of CO2 and changes in global atmosphere as the "shameful" part of Alley's argument.
Here's Alley's example. If he was to overspend on his credit card, his credit card company would delightedly raise the interest rate he is charged on the debt he owes. This would in not too long a time raise the amount of debt he owes the company. But nonetheless, the overspending would come first, and so one could argue that the raise in the rate of interest lags the change in the level of debt, and hence there is no cause and effect relationship between debt and interest.
But as anyone who has ever dealt with debt knows, the interest rate is "the big control knob" on the amount of debt an individual owes, in another of Alley's wonderfully simple metaphors.
Similarly, changes in C02 track changes in global temperatures extremely well, but don't necessarily precede changes in temperature. They lag, slightly. This doesn't change the fact that CO2, more than any other factor, controls global temps…
Kit Stolz 
CO2 concentrations cannot reach into the past and increase the temperature.
Doesn’t debunk GW or AGW, doesn’t even mean manmade environmental change doesn’t cause warming.
Alley’s credit card company doesn’t go back and retroactively increase either his limit or rate either. There’s a reason it is called cause and effect.
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I like the nuance you bring to the argument, Mr. Dawg, and I like the fact that you’re reading me to disagree with me.
But the argument that CO2 isn’t the control knob because a rise in temperatures slightly precedes the beginning of a rise in CO2 overlooks the constant back and forth between output of CO2 and other greenhouse gases and the constant uptake by the oceans, by rock weatherization, and so on.
I’m not going to go to another metaphor to make the point, but just say that in any such finely balanced system, with big shifts over deep time (as in the familiar chart above) it’s really not surprising. The same Quaternary factor that produces a warming produces a shift in CO2 production or re-uptake, which amplifies the warming already began. (In Alley’s metaphor, overspending which produces a higher interest rate.) The point can be made scientifically, as in below, but I like Alley’s method better, as we all live with budgets, and all know how easily can get out of balance, and how quickly that imbalance can become serious.
http://icebubbles.ucsd.edu/Publications/CaillonTermIII.pdf
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I hate to ask this but… Can you guys slow down a little and explain exactly how it’s possible for CO2 to cause global warming yet the data show that CO2 increases follow temperature increases? I just don’t understand how that is possible. What are the other factors that link the two?
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First, although the lag of 800 years or so sounds like a lot to us humans, to our planet it’s but a blink of an eye.
To put it in human terms, if you’re on a bike, and you begin to coast down a slight hill, you may have to pedal a bit to get some speed before gravity kicks in, but that doesn’t mean that gravity (and its feedback, acceleration) has no effect.
Still, I can almost hear skeptics at this point say “Correlation is not causation!”
True, but for us ordinary non-mathematicians, to understand the causation means understanding the grand unfolding of planetary history. We have to think more like a continent and less like a human.
On a continental scale, a slight shift in the tilt of the planet (which is one of the Milankovich cycles) brings the Northern Hemisphere more under the influence of the sun, or less so, which makes ice ages less likely, or more so.
Scientists have found that this slight shift (the beginning of the downhill) is amplified by feedbacks on the ground, in the oceans, and in the atmosphere. More ice leads to greater albedo (whiteness) at the poles, which leads to more cold, deeper ice, less polar vegetation, less CO2, and, over the course of thousands of years, a migration of ice southward. Contrastingly, more sun on the northern pole leads to more vegetation, less whiteness, and, over deep time, changes in the atmosphere, which leads to more warmth, which leads to warmer oceans, and so on.
And that’s not even mentioning plankton, or the Gaia effect.
Scientists know this is how it works partly from the paleo record of the deep past, and partly because they can only reproduce what happened on our planet over that time in mathematical models by adding in the amplifying feedbacks of atmospheric changes.
Hope that helps.
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