ECLIPSE

The EU 7th Framework Programme Collaborative Project ECLIPSE developed and assessed effective emission abatement strategies for short-lived climate pollutants (SLCPs) in order to provide sound scientific advice on measures that mitigate climate change and improve air quality at the same time.

– The current climate policy does not take into consideration a range of shortlived gases and aerosols, senior scientist Andreas Stohl explains, – and our goal was to determine their contribution to climate change and their influence on air quality by using state-of-the-art chemistry transport and climate models. While methane is included in the Kyoto Protocol, we also considered it in ECLIPSE as it is much shorter lived than carbon dioxide and also impacts air quality via formation of ozone.

Project goals

During the project, scientists from 11 institutes in Europe and China collaborated to improve understanding of the climate impact of those SLCPs.

They quantified radiative forcing and climate response due to emissions of short-lived species in various regions of the globe, and also assessed the impact on human health via changes in air quality.

Senior scientist Sabine Eckhardt explains that they also wanted to clarify possible win-win and trade-off situations between climate policy and air quality policy, while identifying a set of concrete cost-effective abatement measures for short-lived species with large co-benefits.

The scientists also evaluated model simulations of short-lived species and their long-range transport using groundbased and satellite observations, and performed case studies on key source and receptor regions (with focus on Europe, China and the Arctic).

Realistic mitigation scenario

The ECLIPSE scientists used a unique systematic concept for designing a realistic and effective SLCP mitigation scenario, and quantifying the climate and air quality impacts related to the scenario.

First they calculated the radiative forcing values for a large array of SLCPs as a function of region, season and the individual substances. Based on these radiative forcing calculations, suitable metrics were chosen to estimate the climate impact of particular SLCP emissions relative to an equal amount of CO₂ emission.

Next, they used these metrics to generate a mitigation scenario for the SLCPs that could be contrasted with the current legislation scenario. For this, the region-, season- and species-specific matrix of climate impact (as defined by the chosen metric) was used as an input to an integrated assessment model. Those emission mitigation measures with a beneficial air quality impact were then evaluated according to their expected climate benefit.

Comparing paths

– It is important to understand that emission measures typically affect several SLCP species, and often some of them are warming the climate while others are cooling, says Stohl.

– For every mitigation measure, the net effect needs to be determined by weighing the emission reduction of every SLCP with the chosen climate metric and summing over all emitted SLCP species.

Finally, we collected all measures with beneficial air quality and climate impacts in a basket defining the SLCP mitigation scenario.

The metrics, however, cannot fully quantify the climate response (e.g., changes in precipitation, or regional changes in temperature). Therefore, a second research path determined the climate response by running transient climate simulations in an ensemble of four Earth system models.

A comparison between the climate impacts expected from the metrics and those actually calculated with the transient simulations closed the loop between the first and the second research path, and allowed the scientists to evaluate the consistency of both approaches.

Challenges

There are large uncertainties in estimates of the climate effect of short-lived climate pollutants, and thus also in the effects of emission reductions related   to them. Several studies have shown that the climate impact of short-lived components can depend strongly on the location of the origin of the components. Inhomogeneity in the climate response to radiative forcing is also  important for the short-lived climate pollutants. The geographical pattern of radiative forcing due to the short-lived climate pollutants (except methane) is generally concentrated close to the source of emission. Hence, they are quite distinct from the global-scale forcing due to the long-lived greenhouse gases.

Results of ECLIPSE

ECLIPSE has identified a set of mitigation measures, which as a whole has beneficial  climate and air quality impacts. Especially methane mitigation measures offer large co-benefits as they have beneficial  climate and air quality impacts (via reductions of ozone concentrations), but reduction of BC and related emissions would also help improve air quality.

– However, the co-benefits are not as large, as the climate impacts of reducing black carbon (BC) are quite small in our suite of models, explains Stohl.

– This is largely because the semi-direct effect of BC offsets a considerable fraction of the direct aerosol radiative forcing. Realizing all ECLIPSE mitigation measures would lead to a reduced climate warming of about 0.22 K for the decade 2041-2050, and some 78-90% of that reduced warming is due to methane emission reductions.

– As CO₂ is the main driver for climate change, reduction of SLCP emissions cannot substitute CO₂ emission reductions for mitigating climate change, says Sabine Eckhardt. – However, the
SLCP measures are of a no-regret nature because of substantial improvements in air quality. Especially in developing countries, this will lead to considerable improvements in the quality of life. For instance, we estimate that in India the ECLIPSE mitigation measures would extend the life expectancy by about one year.