Alternatives to the global warming potential for comparing climate impacts of emissions of greenhouse gases

The Global Warming Potential (GWP) is used within the Kyoto Protocol to the United Nations Framework Convention on Climate Change as a metric for weighting the climatic impact of emissions of different greenhouse gases. The GWP has been subjected to many criticisms because of its formulation, but nevertheless it has retained some favour because of the simplicity of its design and application, and its transparency compared to proposed alternatives. Here, two new metrics are proposed, which are based on a simple analytical climate model. The first metric is called the Global Temperature Change Potential and represents the temperature change at a given time due to a pulse emission of a gas (GTP(P)); the second is similar but represents the effect of a sustained emission change (hence GTP(S)). Both GTP(P) and GTP(S) are presented as relative to the temperature change due to a similar emission change of a reference gas, here taken to be carbon dioxide. Both metrics are compared against an upwelling-diffusion energy balance model that resolves land and ocean and the hemispheres. The GTP(P) does not perform well, compared to the energy balance model, except for long-lived gases. By contrast, the GTP(S) is shown to perform well relative to the energy balance model, for gases with a wide variety of lifetimes. It is also shown that for time horizons in excess of about 100 years, the GTP(S) and GWP produce very similar results, indicating an alternative interpretation for the GAT. The GTP(S) retains the advantage of the GWP in terms of transparency, and the relatively small number of input parameters required for calculation. However, it has an enhanced relevance, as it is further down the cause-effect chain of the impacts of greenhouse gases emissions and has an unambiguous interpretation. It appears to be robust to key uncertainties and simplifications in its derivation and may be an attractive alternative to the GWP.