On the relationship between metrics to compare greenhouse gases – the case of IGTP, GWP and SGTP

Metrics for comparing greenhouse gases are analyzed, with a particular focus on the Integrated Temperature Change Potential (IGTP) following a call from IPCC to investigate this metric. It is shown that GWP and IGTP are asymptotically equal when the time horizon approaches infinity. The difference between IGTP and GWP is estimated for different greenhouse gases using an upwelling diffusion energy balance model with different assumptions on the climate sensitivity and the parameterization governing the rate of ocean heat uptake. It is found that GWP and IGTP differ by some 10% for CH4 (for a time horizon of less than 500 years), and the relative difference between GWP and IGTP is less for gases with a longer atmospheric life time. Further, it is found that the relative difference between IGTP and GWP increases with increasing rates of ocean heat uptake and increasing climate sensitivity. Finally, it is shown that IGTP is equivalent to the Sustained Global Temperature change Potential (SGTP) under standard assumptions when estimating GWPs, i.e. a constant background temperature and a constant background concentration of greenhouse gases