A new scientific paper published this week in Nature Climate Change has outlined metrics to distinguish between the impact of long and short-lived greenhouse gas emissions on rates of global warming.
Climate policies address emissions of many greenhouse gases including carbon dioxide, and others such as methane, nitrous oxide and various halogen-containing compounds. These are aggregated and traded on a CO2-equivalent basis.
So far, methods for doing the aggregation have received criticism as a tool for policy. This is because some do not relate directly to temperature and do not clearly signal the need to limit cumulative totals for long-lived gases such as CO2.
To start addressing these points, a team led by Stephen Smith of the Committee on Climate Change, working with scientists from the NERC Centre for Ecology & Hydrology, the Met Office Hadley Centre and the University of Oxford, has published the paper entitled "Equivalence of greenhouse-gas emissions for peak temperature limits".
Dr Chris Huntingford, from the NERC Centre for Ecology & Hydrology, was one of the paper co-authors. He said, "This paper sets out two metrics, for long- and short-lived greenhouse gases respectively, linking emissions of both to maximum level of global warming. By using temperature-based metrics it is now significantly easier to understand what emissions profiles could keep the planet below, for instance, the two-degrees warming threshold above pre-industrial temperature values. The metrics allow a direct method to compare cuts in longer-lived gases such as carbon dioxide, and shorter-lived ones such as methane.
Dr Huntingford continued, "As might be expected, it is the cumulative emissions of long-lived gases that influence most any peak level of warming, whereas for short-lived gases, then sustained changes to emissions rates at some future point will have most effect. This work formally characterises those two cases and any proposed future balance between them."
Full paper: "Equivalence of greenhouse-gas emissions for peak temperature limits" by Stephen M Smith, Jason A Lowe, Niel H A Bowerman, Laila K Gohar, Chris Huntingford & Myles R Allen, Nature Climate Change 2012. doi: 10.1038/NCLIMATE1496