tCO2e

tCO2e stands for metric tons of carbon dioxide equivalent. It is a unit used to express the overall climate impact of greenhouse gases by converting each gas to an equivalent amount of CO2 based on its global warming potential (GWP). The total CO2e is calculated by summing the products of each gas’s mass and its GWP over a chosen time horizon, most commonly 100 years (GWP100). This makes heterogeneous emissions comparable in a single metric.

Common gases included in CO2e calculations are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and several fluorinated gases. For example, using GWP100, 1 tonne of CH4 is about 28 tCO2e and 1 tonne of N2O is about 265 tCO2e, though exact numbers depend on the specific GWP values used.

Global warming potentials are provided by the IPCC and vary with the time horizon and the assessment version. Because GWPs are estimates, the resulting tCO2e figures depend on the chosen horizon and data sources. Despite this, tCO2e is widely used to aggregate emissions in corporate inventories, product life cycle assessments, and regulatory reporting, enabling comparison and aggregation of different emission sources.

Limitations include sensitivity to the chosen time horizon and GWP values, the potential for oversimplification of complex climate processes, and the fact that it is a bookkeeping unit rather than a direct physical measurement. Nonetheless, tCO2e remains a standard unit for communicating and comparing climate impact across fuels, processes, and products.