The carbon dioxide equivalent describes the combined global warming potential of different greenhouse gas emissions.
Different greenhouse gases have different global warming potentials (GWPs). The Intergovernmental Panel on Climate Change (IPCC) publishes GWP indices for greenhouse gases in its assessment reports.
The GWPs of other greenhouse gases are proportional to the global warming potential of carbon dioxide, set at 1. For example, the global warming potential of methane relative to carbon dioxide over 100 years is 28.