Oxford Martin Programme on

Climate Pollutants

The Challenge

For policy makers to make informed decisions to mitigate against climate change, the effects of different climate pollutants on warming must be compared against each other.

Carbon dioxide is the main driver of anthropogenic climate change. Other climate pollutants, including methane and nitrous oxide, contribute half as much warming again, and will become more important as carbon dioxide emissions are reduced. However, many of these other pollutants are short-lived, unlike carbon dioxide. Methane has a half-life of around a decade, so although the immediate effect of a molecule of methane on temperature is stronger, in 50 years the impact will be much smaller.

How do we compare the different forcing agents when they cause different amounts of warming over different time periods? Currently, governing bodies use approved metrics, for example, “global warming potential”. This programme will investigate how to improve these metrics and their use for informing policy. Some are used for purposes for which they were not originally designed, and can in some cases provide misleading results.

The key questions this programme will answer are:

  • Are the climate metrics used in international agreements fit-for-purpose?
  • Are there better climate metrics than those being used?

The programme will compare whether different metrics are useful in relating anthropogenic emissions to impacts on climate. The work will look at metrics that are currently used in international agreements and schemes, as well as new metrics that are being proposed.

Under ambitious mitigation scenarios, the effects of short-lived climate pollutants become more important, as carbon dioxide emissions are reduced. The programme will investigate the role of different climate pollutants under different scenarios for reducing carbon emissions towards net zero.

This programme will demonstrate new ways of evaluating the climate response to different mitigation scenarios. This will enable policy makers to make informed decisions about the best course of action to achieve their climate goals especially under ambitious targets following from the Paris Agreement.

featured publication

Ensuring that offsets and other internationally transferred mitigation outcomes contribute effectively to limiting global warming

This paper published as an accepted manuscript in Environmental Research Letters, shows that a simple “do no harm” principle regarding the choice of metrics to use in internationally transferred mitigation outcomes can be used to guard against an offset agreement that involves exchanging greenhouse gases with different lifetimes increasing global warming on some timescales. This may also be applicable in other contexts such as voluntary and compliance carbon markets.

The paper also shows that both approximate and exact “warming equivalent” exchanges are possible, but present challenges of implementation in any conventional market.

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Python notebook for calculation of warming-equivalent emissions, Supplementary code and datafile to reproduce figures in the article "Ensuring that offsets and other internationally transferred mitigation outcomes contribute effectively to limiting global warming"

Python notebook Supplementary data