CO2eq

CO2 equivalent (CO2e) is a metric used to compare the warming effects of different greenhouse gases (GHGs) by expressing their emissions as the amount of CO2 that would cause the same total warming over a given time horizon. It allows diverse gases to be represented on a common scale for inventorying, reporting, and policy analysis.

Calculation and units: CO2e is obtained by multiplying the mass of a gas emitted by its global warming potential (GWP) over a specified period, typically 100 years (GWP100). The result is usually reported in kilograms or tonnes of CO2e. CO2 has a GWP of 1 by definition; other gases have higher GWPs, reflecting their greater warming per unit mass over the chosen horizon.

Typical GWPs and examples: Methane (CH4) has a GWP around 28–34 for 100 years, depending on the assessment. Nitrous oxide (N2O) is about 265, and fluorinated gases vary widely, with GWPs from hundreds to tens of thousands (for example, SF6 is around 23,500). These values are periodically updated by scientific assessments, such as the Intergovernmental Panel on Climate Change (IPCC).

Applications and limitations: CO2e is widely used in greenhouse gas inventories, regulatory reporting, corporate sustainability metrics, and life cycle assessments to aggregate diverse emissions into a single metric. Limitations include sensitivity to the chosen time horizon, differences in atmospheric lifetimes and indirect effects among gases, and the fact that CO2e does not capture all environmental impacts or interactions between gases.

In summary, CO2e provides a practical, standardized way to compare and sum emissions from different greenhouse gases, while recognizing its simplifications and dependences on methodology.