Concerns about climate change have resulted in a need to address the whole-life atmospheric impact of infrastructure projects. But if emissions of carbon dioxide and other ‘greenhouse gases’ are to be included in overall project appraisals, what spatial and temporal boundaries should be used in assessing emissions, and how should the results be included in project decision making? This paper addresses both these issues within the context of UK legislation, proposing a global protocol for ‘carbon accounting’ based on best practice, but questioning the simplistic concept of ‘carbon pricing’ as an effective instrument of reducing emissions.