Climate Change 2007: Working Group I: The Physical Science Basis

All GWPs depend on the AGWP for CO2 (the denominator in the definition of the GWP). The AGWP of CO2 again depends on the radiative efficiency for a small perturbation of CO2 from the current level of about 380 ppm.
The species in Table 2.14 are those for which either significant concentrations or large trends in concentrations have been observed or a clear potential for future emissions has been identified. The uncertainties of these direct GWPs are taken to be ±35% for the 5 to 95% (90%) confidence range.