Measurement of greenhouse gas emissions

The emissions inventory reports emissions of carbon dioxide, methane, nitrous oxide, and the four F-gases (hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride, and nitrogen trifluoride). Overall emissions are given as a single figure, measured in megatonnes or kilotonnes of carbon dioxide equivalent (MtCO₂e or KtCO₂e), by weighting non-carbon dioxide gases by their global warming potential (GWP). The GWP of a greenhouse gas is defined as its warming influence relative to that of carbon dioxide over a 100 year period. For example, the global warming potential of methane over 100 years is 21, meaning that each tonne of methane emitted causes the same level of warming over 100 years as 21 tonnes of CO₂. Approximately 99% of equivalent emissions in Scotland’s transport sector are due to CO₂, therefore a breakdown of emissions by greenhouse gas is not included in this report.