Here are a couple of more references on decarbonization:

John Whitehead shows a trend decline of about 2 percent per year in the U.S.(we are decarbonizing faster than most of the world).

Jesse Ausubel (last chart) shows a graph which, eyeballing it, seems to show a decline in the same general range as Nordhaus assumes, about 1 percent per year, or somewhat less.

In my previous post, I pointed out that world GDP is almost 50 times what it was in 1900. Adjusting for decarbonization of GDP, on a worldwide basis we are still spewing out 25 times as much as we were back then.

To restate my question. Human activity, as measured by GDP, is 50 times what it was in 1900. It is 10 times what it was in 1950. The total amount of global warming from 1900 to 1950 was about the same as between 1950 and now. How do you reconcile those two facts?

(i) the sensitivity of global temperature to human activity has fallen, nearly offsetting the huge increase in human activity. If this is so, I wish we understood why. Decarbonization is not enough to explain it. It seems like a hugely important issue.

or (ii) most of the global warming earlier in the century is random noise. But now that human activity is as high as it is, things are really cooking (so to speak). But that means that it’s pointless to try to calibrate your global climate model to the 1900-1975 period. It’s really the last 30 years of data that are all the meaningful information that we have to work with. Given the huge annual variation, we effectively have about 3 data points (you have to take about a 10-year average to smoothe out annual noise). There are an awful lot of curves that you can construct that go through three points.

I turned off comments on this post, but you are welcome to add to the discussion on the previous entry.