CO2 Equivalent
The CO2 equivalent (CO2e) is a comparison unit that converts the climate impact of different greenhouse gases into the impact of carbon dioxide via their global warming potential (GWP), enabling them to be accounted for on a single common basis.
The CO2 equivalent (abbreviated CO2e or CO2-eq) is the central measurement and comparison metric in greenhouse gas accounting. Because gases other than carbon dioxide - such as methane (CH4), nitrous oxide (N2O) and fluorinated gases (F-gases) - also contribute to global warming, yet differ greatly in their warming effect per tonne, their quantities are converted into an equivalent amount of CO2 using the so-called global warming potential (GWP). This produces a single, comparable figure in tonnes of CO2 equivalent (t CO2e) that captures the entire climate impact of a company, product or process.
The conversion is performed by multiplying the emitted quantity of a gas by its GWP factor. Methane, for example, has a GWP of roughly 28 to 30 over a 100-year time horizon (GWP100), and nitrous oxide a GWP of about 265 to 273 - so one tonne of methane corresponds to around 28 tonnes of CO2 equivalent. The applicable GWP values are defined by the Intergovernmental Panel on Climate Change (IPCC) in its assessment reports and are updated periodically; reporting must therefore state which IPCC values and which time horizon underlie the inventory, in order to ensure comparability and traceability.
In sustainability reporting, the CO2 equivalent is the mandatory unit for disclosing greenhouse gas emissions. Under CSRD reporting, ESRS E1 (Climate change) requires gross emissions to be reported by Scope 1, 2 and 3, along with total emissions in tonnes of CO2 equivalent, methodologically based on the Greenhouse Gas Protocol. National rules such as the German Greenhouse Gas Emissions Trading Act and EU instruments like the Emissions Trading System (EU ETS) also settle emissions in CO2 equivalents. Correct, documented application of the GWP factors is therefore a prerequisite for an audit-proof greenhouse gas inventory.
Legal Basis
ESRS E1 (Delegated Regulation (EU) 2023/2772); Greenhouse Gas Protocol (Corporate Standard); IPCC Assessment Reports (GWP values); Kyoto Protocol (Annex A greenhouse gases)
Practical Example
A compliance officer at a mid-sized food producer prepares the greenhouse gas inventory for the company's first CSRD report. In addition to the natural gas burned in the boilers (CO2), she records methane emissions from wastewater treatment and nitrous oxide from the company vehicle fleet. To report the total impact under ESRS E1, she multiplies each gas quantity by the relevant GWP100 factor from the current IPCC report and sums the results into a single figure in tonnes of CO2 equivalent. In the methodology documentation she notes the IPCC report and time horizon used, so that the auditor can follow the calculation and confirm it as part of the limited assurance engagement.