On Wednesday I trekked to the 12th monthly meeting of the Secret Science Club, an informal lecture series in the basement of Union Hall, a bar in Brooklyn. The speaker this month was William Schlesinger, a biogeochemist and the new president of a think tank called the Institute of Ecosystem Studies. (The special drink was a "climate cooler," which was a pleasant if mild rum punch.) Schlesinger gave a good introductory-level talk on the basics of global warming: where the carbon dioxide's coming from, what it does in the atmosphere (with the requisite inside-a-car-on-a-hot-day slide), how we might decrease our CO2 production, etc. Due to time constraints, he only got to briefly mention his recent research, which focuses on how trees and soil affect CO2 levels, and vice versa. After the talk I had a couple of questions, and I posed one to him, but I don't think he exactly got what I was getting at. During the talk, Schlesinger showed one graph that showed a fairly close correlation between GDP growth and the change in CO2 output from the U.S. for a few decades in the 20th century. Then he showed another graph that showed a very tight correlation between atmospheric CO2 and global population over the 20th century, if I recall. So how do you reconcile these? I realize that these two constraints don't inherently and necessarily conflict—what happens in the U.S. could be independent of what's happening across the globe. But the spirit of the two graphs did seem to clash: one implicitly argued that CO2 output tracked with economic growth, and the other implicitly argued that CO2 in the atmosphere tracked with population. The distinction seems important to me because most median population projections (whose accuracy is another question) for the 21st century say that population growth will flatten out around 10 billion people around 2050. And if atmospheric CO2 really does track closely with global population, does that mean that even if we continue on our current pathetic regulatory course, CO2 levels will also level off in 2050? That level would still be high enough to cook us all silly, but if we want to respond appropriately to the problem we should pin down the projection as much as possible. Any DiscoBlog readers know how to forecast the atmospheric conditions for our li'l planet 50 years out?