Critics of the Intergovernmental Panel on Climate Change's Special Report on Emission Scenarious claim that the use of market exchange rates rather than purchasing power parity has led to a significant upward bias in projections of greenhouse gas emissions, and hence unrealistically high future temperature. Rather than revisit the debate on the choice of exchange rates, we address a much simpler question: does the choice make a difference when it comes to projecting future temperature change? Employing a computable general equilibrium model designed to examine a variety of issues in the climate debate, we find that the answer is yes, but the difference is only minor.