What is Global warming potential? (GWP)?

The Global Warming Potential (GWP) provides a simple measure of the radiative effects of emissions of various greenhouse gases, integrated over a specified time horizon, relative to an equal mass of CO₂ emissions. The GWP with respect to CO₂is calculated using the formula:

where a_i is the instantaneous radiative forcing due to the release of a unit mass of trace gas, i, into the atmosphere, at time TR, Ci is the amount of that unit mass remaining in the atmosphere at time, t, after its release and TH is TR plus the time horizon over which the calculation is performed (100 years in this table).

http://cdiac.ornl.gov/pns/current_ghg.html