The construction of new fossil fuel energy infrastructure implies a commitment to burn fossil fuels and therefore produce CO _2 emissions for several decades into the future. The recent letter by Davis and Socolow (2014 Environ. Res. Lett. http://dx.doi.org/10.1088/1748-9326/9/8/084018 9 http://dx.doi.org/10.1088/1748-9326/9/8/084018 ) highlights the current and growing commitment to future emissions, and argues that this emission commitment should be accounted for at the time of new construction. The idea of accounting for future committed emissions associated with current energy policy decisions is compelling and could equally be applied to other aspects of the fossil fuel supply chain, such as investing in the development of new fossil fuel reserves. There is evidence, for example, that oil reserves are growing faster that the rate of extraction, implying a growing future emissions commitment that is likely incompatible with climate mitigation targets.