Is there any merit to the studies that show that historical CO2 levels lag behind temperature, and not lead them?
Yes, there’s merit to those studies, says Peter Hildebrand, Director of the Earth Science Division at NASA’s Goddard Space Flight Center, responding to a question from Twitter.
In the pre-industrial age, the CO2 response to temperature was that the temperature would go up and CO2 would go up. Or if the temperature went down, CO2 would go down. Because when the temperature rose, the whole biosphere revved up and emitted CO2. So we understand that process.
In the post-industrial age, the opposite is true. Increasing CO2 in the atmosphere is leading to increased temperature. So two different things happened, one pre-industrial, where temperature was driving the CO2, and post-industrial, where CO2 was driving temperature. Which means a completely different physical-biological process is going on.