MtCO2év

MtCO2e stands for megatonnes of CO2 equivalent and is a standard unit used to express the total climate impact of a mixture of greenhouse gases. It converts different gases to a common basis by applying their global warming potential (GWP) relative to carbon dioxide over a chosen time horizon, typically 100 years. A megatonne (Mt) equals one million metric tonnes, so MtCO2e represents one million tonnes of CO2-equivalent emissions or removals.

Calculation involves multiplying the mass of each greenhouse gas by its GWP and summing the results across all gases. For example, if a facility emits 0.5 Mt of methane (CH4) and 1 Mt of CO2, and CH4 has a GWP around 28 over 100 years, the CH4 contribution is about 14 MtCO2e, giving a total of roughly 15 MtCO2e.

Time horizon matters. The most common reference is GWP over 100 years (GWP100), but other horizons (e.g., 20 years) are used for near-term analyses. GWP values vary by gas and source (e.g., IPCC assessments), and the choice of horizon and dataset affects the final MtCO2e figure. MtCO2e is widely used in national inventories, corporate carbon footprints, climate policy targets, and scenario analyses to enable comparability across gases and sectors.

Limitations include the aggregation of gases with different lifetimes and radiative behaviors, which can obscure gas-specific dynamics. Negative MtCO2e can arise from removals or carbon sinks, and data quality directly affects reliability. While useful for overall risk assessment and target setting, MtCO2e is best interpreted alongside gas-specific information and methodological choices.