Note—On the Timing of Greenhouse Gas Emissions Reductions: A Final Rejoinder to the Symposium on “The Economics of Climate Change: The Stern Review and its Critics”

In this final rejoinder to the symposium on “The Economics of Climate Change: The Stern Review and Its Critics,” we respond to comments published in the last issue of this journal by Robert Mendelsohn, Thomas Sterner and U. Martin Persson, and John P. Weyant (Mendelsohn et al. 2008). In particular, we examine the point of debate with arguably the greatest practical importance for ongoing negotiations over an international agreement to succeed the Kyoto Protocol: namely the appropriate timing of global reductions in greenhouse gas emissions.

Too often in the past, this debate has been presented as one between the poles of “act now” and “wait-and-see”. Weyant (see Weyant's comments in Mendelsohn et al. 2008) is right to dismiss this false dichotomy. All sensible proposals concerning the appropriate trajectory for global greenhouse gas emissions entail at least some reductions in the near term, as well as efforts to promote the development of new technologies. But make no mistake, there is still room for widely divergent recommendations with potentially great ramifications.

One recommendation, which has been clearly elucidated by William Nordhaus (2007) and appears to be endorsed by both Mendelsohn and Weyant, is the “climate-policy ramp.” Under the slow policy ramp, the economically efficient climate policy entails “modest rates of emissions reductions in the near term, followed by sharp reductions in …