Reviewer comments on this manuscript were positive and supportive of publication. The reviewers noted some areas for clarification in the paper. Authors have responded extensively to these comments, including addition of uncertainty analysis, several citations, and comparison with observations (although the latter does not cover the whole period).

I find that this paper is nearly ready for publication. I note two aspects that should be improved:
1) The added text needs some editing by a native English speaker. The errors are not large but do affect readability.
2) Referee #1 inquired how to set the S-curve parameters. Authors have answered that question, yet they also show that the curve is set between two very distant points (1890 and 1990 in Figure 1). The timing and rate of the decreased emission factor are really unconstrained, which means that many of the trends are probably more uncertain than indicated. I do not think that authors need to alter the calculations, as it's likely that no data are available to improve confidence. Authors should at least acknowledge this issue in their discussion of uncertainty.