Comparing the climate effect of emissions of short- and long-lived climate agents

Abstract

Multi-gas climate agreements require a metric by which emissions of gases with different lifetimes and radiative properties can be placed on a common scale. The Kyoto Protocol to the United Nations Framework Convention on Climate Change uses the global warming potential (GWP) as such a metric. The GWP has attracted particular criticism as being inappropriate in the context of climate policy which seeks to restrict warming below a given target, because it gives equal weight to emissions irrespective of the target and the proximity to the target. The use of an alternative metric, the time-dependent global temperature change potential (GTP), is examined for its suitability and the prospects for it including very short-lived species. It retains the transparency and relative ease of use, which are attractive features of the GWP, but explicitly includes a dependence on the target of climate policy. The weighting of emissions using the GTP is found to be significantly dependent on the scenarios offuture emissions and the sensitivity of the climate system. This may indicate that the use of any GTP-based weighting in future policymaking would necessitate regular revisions, as the global-mean temperature moves towards a specified target.

Comparison of physically- and economically-based CO<sub>2</sub>-equivalences for methane

“…3.5 where we discuss structural uncertainties. The 100-yr GTP for methane (3.9 and 6.2 with and without CH 4 conversion to CO 2 ) is much lower than the 100-yr GWP (25.2 and 27.2), as already noted by Shine et al (2007) and Gillett and Matthews (2010). The methane GDPs estimated from the central values of the parameters are 24.3 and 26.3 without and with the CH 4 conversion to CO 2 , respectively.…”

“…The cost-effective temperature change potential introduced by Johansson (2012) can be seen as a simplified version of this metric that reduces to the GTP before the climate target is reached but can be extended beyond that. Shine et al (2007) introduced a time horizon that is a function of the proximity to a target year, which makes the physical metric dynamic, and reproduces qualitatively the results of Manne and Richels (2001).…”

“…Neither the GWP, nor the GTP introduced by Shine et al (2005Shine et al ( , 2007) is a straightforward special case of Eq. (3).…”

“…Physically-based metrics compare the relative effects of forcing agents in terms of a physical quantity of the climate system, such as the cumulative radiative forcing in the case of the GWP or the global mean surface temperature change in the case of the global temperature change potential (GTP, Shine et al, 2005Shine et al, , 2007. Socio-economically-based metrics compare the relative costs of forcing agents on the climate system.…”

Potential climate forcing of land use and land cover change

“…The percentage of anthropogenic RF attributable to LULCC activities is likely to decrease in the future, even as the magnitude of the RF could increase by up to 1.0 W m −2 from 2010 to 2100. The lifetime and distribution of short-lived species makes simplification difficult in terms of equating CO 2 RF to other constituents (Shine et al, 2007), but simple approaches of controlling cumulative carbon should account for the 2 to 3 times enhancement of the LULCC RF over long time periods per unit CO 2 emitted relative to other sources of CO 2 .…”