THE global warming potential (GWP) index(1-3) is a measure of the relative contribution of the emissions of different greenhouse gases to the radiative forcing of the atmosphere-and thus to climate change-over a given time period. But this index does not represent the effects of climate change, and therefore does not provide an adequate basis for policy decisions about emissions reductions. This inadequacy has led to the proposal of an alternative, the economic-damage index (EDI)(4-7). This index compares the effect of different greenhouse-gas emissions on global economic welfare. Here we use a simple climate model to calculate the EDIs for a range of climate-change/greenhouse-gas emission scenarios, and compare the values to the corresponding GWPs. Although the values of these indices are, at this stage, broadly similar in both magnitude and uncertainty, the prospects of reducing these uncertainties by future research are better for the EDI.