The growing awareness of the challenge of climate change has led to much discussion in recent years of the need to reduce emissions of greenhouse gases (GHGs). There are many issues associated with this agenda, and the NAO has reported on two of them last year (the accuracy of emissions forecasting and the use of cost-eff ectiveness analysis). But the ability to measure and report GHG emissions accurately is a fundamental requirement underpinning any form of analysis and forecasting. This briefing, produced for the Environmental Audit Committee, aims to throw light on this process.