Carbon dioxide equivalent
Carbon dioxide equivalent (CO2e) is a unit for comparing the climate effect of different greenhouse gases by converting their amounts using global warming potential values relative to carbon dioxide, usually over a stated time horizon. It lets emissions of several gases be reported as one comparable total.
In simple terms
Greenhouse gases do not affect the climate equally or persist for the same length of time. A selected global warming potential and time horizon provide a conversion factor. Multiply each gas’s mass by that factor, then add the converted amounts. A carbon footprint or life cycle assessment can express its result in kilograms or tonnes of CO2e. CO2e is a comparison convention; it does not mean different gases cause identical physical responses.
Why it matters
A common unit lets an inventory combine gases, compare sources, and track a total without hiding which gases were emitted. The selected global warming potential and time horizon still matter, so a credible result identifies the calculation basis rather than presenting CO2e as a context-free measurement.
Example
For example, a greenhouse gas inventory can multiply the mass of methane emitted by its selected global warming potential, report the result in tonnes of CO2e, and add it to similarly converted emissions. The inventory should also identify the global warming potential source and time horizon.
How it differs
Global warming potential
Global warming potential is the conversion factor for a gas over a selected time horizon; carbon dioxide equivalent is the converted amount produced by applying that factor.
Carbon footprint
A carbon footprint is the calculated greenhouse gas total for a defined subject and boundary; CO2e is the comparison unit commonly used to express that total.