Alexander Cockburn, a regular columnist for The Nation, begins his essay, “Is Global Warming a Sin?,” in the May 14, 2007 issue with an interesting analogy, likening the current developing (and mostly online) market in “carbon offsets” (where people assuage their guilt over their own contributions to global warming by paying others to do things that will offset the effects of their own CO2 emissions) to the medieval church’s sales of indulgences to offset sins. (I’ve encountered this basic analogy with other recent writers as well, and here, Cockburn gets the details of the analogy a bit off – he likens the current situation to the supposed role of indulgences alongside 10th century millennial fears, whereas indulgences had little or nothing to do with such 10th century fears, being mainly a much later phenomenon – though I also see the point of the [faulty] analogy – we live in a millenarian society that seems to thrive on fearing the end of the world [Y2K, terror, anthrax, dirty bombs, smallpox, avian flu, global warming], though that’s not to say that some of the feared threats, like global warming, aren’t real.)
I expected from his first paragraph that Cockburn was going to talk about problems with carbon offset schemes (there’s absolutely no accountability, there’s no clear indication that the “offset” activities actually offset buyer’s own emissions, they assuage people’s guilt without really addressing the larger problems) or perhaps the ways in which hype, fantasy, and millennial fears do play a role, alongside strong, empirically grounded science, in shaping public discourse about global warming.
Instead he proceeded to challenge the notion that there is any anthropogenic role in global warming. Certainly there is valid scientific debate about the extent of the role that human action (vs. natural causes that might be operating simultaneously) plays in overall global warming, and about the exact contribution of specific human actions compared to others. At this point, though, claiming, as Cockburn does, that “there is still zero empirical evidence that anthropogenic production of carbon dioxide is making any measurable contribution to the world’s present warming trend,” makes him decidedly the odd man out. Even George W. Bush has by now (in his last state of the union address) acknowledged the human role in global warming and the need to do something about it, though I’m not holding my breath to wait for him or his administration to take positive action on the issue.
What I was most taken aback by, though, was not his overall claim. Instead, it was the simplistic nature of his “proof.” For his proof that there is no human caused role in atmospheric CO2 accumulation and global warming, he draws solely on two graphs drawn by former meteorologist Martin Hertzberg. One graph shows global CO2 emissions beginning in 1928, with a general upward trend but some large dips (corresponding to things like major drops in economic production at the start of the Great Depression). The other shows concentration of CO2 in the atmosphere with a steadily upward trajectory. Cockburn concludes from this, “The two lines on that graph proclaim that a whopping 30 percent cut in man-made CO2 emissions didn’t even cause a 1 ppm drop in the atmosphere’s CO2. It is thus impossible to assert that the increase in atmospheric CO2 stems from people burning fossil fuels.”
There are at least two important problems with such thinking. First, for the comparison to make any sense, Cockburn and Hertzberg must be assuming that CO2 concentrations in the atmosphere are from that year’s emissions alone, which they are not. A dip in emissions for a few years, thus, would not be paired with a directly corresponding dip in CO2 concentrations. At most, you’d see a slowing in the increase of such atmospheric concentrations, which frankly is what the few numbers included in Cockburn’s column seem to indicate. Second, this simple comparison of two variables, while perhaps intuitively elegant, is an incredibly simplistic model on which to base any conclusions about global climate in general. It doesn’t even provide a sufficient basis for understanding the two variables and their relationships (to each other or to other variables), e.g. are atmospheric concentrations of CO2 simply related to total quantities emitted, or does the context of emission matter; is total warming related simply to total concentration of CO2 or more to concentrations in specific regions of the globe; are emissions concentrated in the atmosphere in their region of emission or not, and what’s the effect on climate, etc. It also doesn’t take into account any other factors that might affect global warming. In short, there’s no way you can logically and empirically conclude from Cockburn and Hertzberg’s simplistic comparison that it’s “impossible to assert that the increase in atmospheric CO2 stems from people burning fossil fuels,” much less that you’ve proved there’s no anthropogenic role in global warming.