The global warming potential—the need for an interdisciplinary retrial

Abstract

It was about 20 years ago today when Global Warming Potentials (GWP) became established as a method for comparing the climate effects of emissions of different greenhouse gases. Since then they have been going in and out of style. The GWP was originally presented as a climate analogue to the ozone depletion potential, to help assess the climate impacts of switching from chlorofluorocarbons to hydrofluorocarbons (and related molecules) (Rogers and Stephens 1988; Fisher et al. 1990). Interest in its wider utility, and in particular its use to compare the climate impact of emissions of CO2 with non-CO2 greenhouse gases, soon followed (e.g. Lashof and Ahuja 1990; IPCC 1990). The First Assessment Report (FAR) of the Intergovernmental Panel on Climate Change (IPCC 1990) tentatively embraced the concept—as the Convening Lead Author of the relevant chapter in that assessment, I was interested to re-read what we had written way-back-when; in particular, I wanted to see whether, with hindsight, I might have changed anything. I believe that we had many of the necessary caveats in place but I was particularly struck by one statement (where the square brackets are my additions for clarity): “It must be stressed that there is no universally accepted methodology for combining all the relevant factors into a single [metric] . . . A simple approach [i.e. the GWP] has been adopted here to illustrate the difficulties inherent in the concept.” But it seems that the die was cast. The IPCC retained the GWP as a metric of choice. As the Kyoto Protocol is a multi-gas treaty, it requires a method to allow parties to the protocol to place emissions of different gases on a CO2-equivalent scale. The GWP (with a 100 year time horizon) was adopted for this purpose. Indeed, it can be argued that it was the existence of the GWP (or its endorsement by the IPCC) which led to the Kyoto Protocol being a multi-gas treaty—see e.g. Skodvin (1999) for a discussion.