Reframing non-CO2 climate mitigation approaches to limit global warming

About a decade ago, our thinking on climate mitigation dramatically changed with the concept of carbon budgets. This made clear that reducing CO2 emissions was not enough - we had to eliminate them completely or simply reach our maximum budget (and temperature) more slowly.

My vision for this fellowship is to bring a similar sea-change in attitude towards non-CO2 contributors to global warming, especially short-lived pollutants like methane. As with the carbon budget concept, the missing piece currently is a simple and transparent way to accurately represent the complexities of the climate.

With the Paris Agreement, countries have agreed on a global aspiration to limit global warming to well below 2C. Some countries, cities, sector organisations and companies have announced 'net zero' targets, or at least have emissions reductions targets. However, these targets are currently not enough combined to achieve the Paris temperature goal. Further, in most cases they are ambiguous with regard to the details of the target. Not only does this cause uncertainty in analysing the expected global warming from achieving the targets, it suggests that detailed plans of action are not in place.

A critical element of my research is to bring in one of the key uncertainties, short-lived climate pollutants, such as methane and aerosol, into an evaluation framework. Traditional methods used to calculate 'CO2-equivalence' do not accurately represent methane's potent and short lived impact on climate. My proposed work using 'CO2-warming-equivalence' (CO2-we) will enable methane's strong short-lived, and much weaker long-lived, impacts to be assessed. This means temperature impacts in 2030, 2050 and 2100 can all be accurately evaluated within one framework for short and long lived pollutants. The 'CO2-warming-equivalence' method is designed to identify the CO2 emissions that would generate the same warming over time as the original methane emission. I will use CO2-we to define the concept of an 'all forcing budget', analogous to the 'carbon budget', which is used by the UK government to limit CO2 emissions. (A 'forcing' is anything that disturbs the climate system's energy balance.)

The key elements of this programme are:

-Metrics for climate mitigation: I will further develop my work on CO2-we to incorporate all GHG fluxes, aerosol and albedo change, and into a budget framework. The metrics used will be updated and developed to ensure they reproduce the latest understanding from complex climate models for all forcings.

-Climate policy: CO2-we will be used as a tool to explore several concepts in climate policy, including a temperature-based fair share analysis for all GHG emissions and countries' national targets under the Paris Agreement. Qualitative methods will be used to investigate the definition of and intention behind organisation-level net-zero (or equivalent) climate targets.

-Climate mitigation in the agricultural sector: I will work with stakeholders to develop a new model for assessing mitigation options in the agricultural sector. This will be based on previous work carried out in Cranfield, combined with the metrics described above, and practical knowledge from farmers as to what is feasible on farm. This research will reflect the impact of agriculture on temperature, which most methods do not at present assess.

The tools developed in this programme will enable decision makers to accurately evaluate the impact of different actions on temperature over different timescales, to help the decision making process. Unless decision makers are using climate models to simulate mitigation actions, this is currently not an analysis that is available to them. My tools will be quicker and simpler to run than even simple climate models currently are, thus making the analysis available even in the absence of computing skills.