Balancing Short- and Long-lived Climate Pollutant Mitigation: Clearer Metrics are Critical

Abstract:

We propose a new standard for reporting Global Warming Potentials (GWPs) that is central to climate policy debates and decision-making. GWPs are an essential element of policy analysis and policymaking, and are even built into legal structures that regulate “carbon dioxide equivalents.” However, the current reporting convention is misleading because it hides the divergence between short and long-term interests inside a single timescale. We propose using two timescales everywhere, as an inseparable pair. This makes explicit one of the principal issues in climate policy: the temporal tradeoffs of benefits among actions that reduce emissions of a suite of climate pollutants.

Policymakers often treat GWPs as if they were a value-neutral technocratic measure, while in fact the choice of timescales, at the heart of the GWP, is central to the political battles over climate policy. At its most basic, cutting emissions of pollutants with different radiative properties and atmospheric lifetimes yields climate benefits that vary in the near- and long-term. Battles such as that between coal and natural gas rest on this distinction.

The most common form of GWP is based on a 100 year time integral, but this timescale conceals near-term impacts. On the other hand, opting instead for a 20 year time integral ignores climate impacts after 20 years. A distinguished list of scientists and economists has attempted to come up with improved metrics that incorporate the range of timescales into a single value. Our proposal abandons this quest. There is no “right” answer to the underlying dispute, but there is a right answer for policy analysis: use two time constants together, similar to the way that systolic and diastolic blood pressures, latitude and longitude, and city and highway gas mileage are reported together. This strategy will provide much needed clarification to myriad climate change solution-related decisions.