The need for clarity in the composition of greenhouse gas targets set by countries has been underlined in a guest post for Carbon Brief by Professor Myles Allen of the University of Oxford and Priestley Centre director Piers Forster.
The post, which discusses a new study in Nature Climate Change by the authors and colleagues from Oslo, Reading and Wellington, sets out an improved method for accounting for short-lived climate pollutants, such as methane and black carbon, against CO2 when setting future climate targets.
This is important in terms of global temperature targets, which are aligned with emissions through a metric (GWP100) based on trapped atmospheric heat over 100 years. While GWP100 is a ready reckoner of the impact of the greenhouse gas mix 20-40 years after emission, it is shown to over-value the role of short-lived pollutants over longer periods. This could, in turn, lead to ‘Faustian bargains’ being made, as prioritising the reduction of short-lived pollutants over all-important CO2 reductions could mean we miss global temperature targets.
The metric is the basis of most countries’ INDCs for the Paris Climate Change Agreement, which aims to keep warming ‘well below’ the agreed threshold of 2C. The authors suggest that, to remove ambiguity, CO2 and other greenhouse gases be accounted for separately by all countries, which should specify both their timeline for getting to net zero CO2 and their means of controlling methane and other short-lived climate pollutants.
The Washington Post also features the study, explaining the confusing role played by methane in global temperature targets, the importance of curbing carbon dioxide relative to methane emissions and why timing is all.