What are the "modest levels of first-world consumption" in the estimates you mention? And how recent are these estimates? There are many factors that likely will contribute to a smaller first-world footprint, e.g. http://fivethirtyeight.com/features/americans-will-burn-less...
This has a survey of capacity estimates on page 10. I took the median of those, which more or less matched the sources I've encountered over the past year.
Two of the estimates have years associated with them: 1994 and 1999. The survey itself was published in 2013 so didn't have the data available that fivethirtyeight cited. I think it's time for researchers to update their capacity estimates.
This has a survey of capacity estimates on page 10. I took the median of those, which more or less matched the sources I've encountered over the past year.