Global warming potential (GWP) is the heat absorbed by any greenhouse gas in the atmosphere, as a multiple of the heat that would be absorbed by the same mass of carbon dioxide (CO2). GWP is 1 for CO2. For other gases it depends on the gas and the time frame. Some gases, like methane, have large GWP, since a ton of methane absorbs much more heat than a ton of CO2. Some gases, again like methane, break down over time, and their heat absorption, or GWP, over the next 20 years is a bigger multiple of CO2 than their heat absorption will be over 100 or 500 years. Values of GWP are estimated and updated for each time frame as methods improve.
Carbon dioxide equivalent (CO2e or CO2eq or CO2-e) is calculated from GWP. It can be measured in weight or concentration. For any amount of any gas, it is the amount of CO2 which would warm the earth as much as that amount of that gas. Thus it provides a common scale for measuring the climate effects of different gases. It is calculated as GWP times amount of the other gas. For example if a gas has GWP of 100, two tons of the gas have CO2e of 200 tons, and 1 part per million of the gas in the atmosphere has CO2e of 100 parts per million.
Estimates of GWP values over 20 and 100 years are periodically compiled in reports from the Intergovernmental Panel on Climate Change.