Evaluating the climate and air quality impacts of short-lived pollutants

Abstract

Abstract. This paper presents a summary of the work done within the European Union's Seventh Framework Programme project ECLIPSE (Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants). ECLIPSE had a unique systematic concept for designing a realistic and effective mitigation scenario for short-lived climate pollutants (SLCPs: methane, aerosols and ozone, and their precursor species) and quantifying its climate and air quality impacts, and this paper presents the results in the context of this overarching strategy. The first step in ECLIPSE was to create a new emission inventory based on current legislation (CLE) for the recent past and until 2050. Substantial progress compared to previous work was made by including previously unaccounted types of sources such as flaring of gas associated with oil production, and wick lamps. These emission data were used for present-day reference simulations with four advanced Earth system models (ESMs) and six chemistry transport models (CTMs). The model simulations were compared with a variety of ground-based and satellite observational data sets from Asia, Europe and the Arctic. It was found that the models still underestimate the measured seasonality of aerosols in the Arctic but to a lesser extent than in previous studies. Problems likely related to the emissions were identified for Northern Russia and India, in particular. To estimate the climate impacts of SLCPs, ECLIPSE followed two paths of research: the first path calculated radiative forcing (RF) values for a large matrix of SLCP species emissions, for different seasons and regions independently. Based on these RF calculations, the Global Temperature change Potential metric for a time horizon of 20 years (GTP20) was calculated for each SLCP emission type. This climate metric was then used in an integrated assessment model to identify all emission mitigation measures with a beneficial air quality and short-term (20 year) climate impact. These measures together defined a SLCP mitigation (MIT) scenario. Compared to CLE, the MIT scenario would reduce global methane (CH4) and black carbon emissions by about 50 and 80%, respectively. For CH4, measures on shale gas production, waste management and coal mines were most important. For non-CH4 SLCPs, elimination of high emitting vehicles and wick lamps, as well as reducing emissions from gas flaring, coal and biomass stoves, agricultural waste, solvents and diesel engines were most important. These measures lead to large reductions in calculated surface concentrations of ozone and particulate matter. We estimate that in the EU the loss of statistical life expectancy due to air pollution was 7.5 months in 2010, which will be reduced to 5.2 months by 2030 in the CLE scenario. The MIT scenario would reduce this value by another 0.9 to 4.3 months. Substantially larger reductions due to the mitigation are found for China (1.8 months) and India (11–12 months). The climate metrics cannot fully quantify the climate response. Therefore, a second research path was taken. Transient climate ensemble simulations with these ESMs were run for the CLE and MIT scenarios, to determine the climate impacts of the mitigation. In these simulations, the CLE scenario resulted in a surface temperature increase of 0.70±0.14 K between the years 2006 and 2050. For the decade 2041–2050, the warming was reduced by 0.22±0.07 K in the MIT scenario, and this result was in almost exact agreement with the response calculated based on the emission metrics (reduced warming of 0.22±0.09 K). The metrics calculations suggest that non-CH4 SLCPs contribute ∼22% to this response and CH4 78%. This could not be fully confirmed by the transient simulations, which attributed about 90% of the temperature response to CH4 reductions. Attribution of the observed temperature response to non-CH4 SLCP emission reductions and black carbon (BC) specifically is hampered in the transient simulations by small forcing and co-emitted species of the emission basket chosen. Nevertheless, an important conclusion is that our mitigation basket as a whole would lead to clear benefits for both air quality and climate. The climate response from BC reductions in our study is smaller than reported previously, largely because our study is one of the first to use fully coupled climate models, where unforced variability and sea-ice responses may counteract the impacts of small emission reductions. The temperature responses to the mitigation were generally stronger over the continents than over the oceans, and with a warming reduction of 0.44 K (0.39–0.49) largest over the Arctic. Our calculations suggest particularly beneficial climate responses in Southern Europe, where the surface warming was reduced by about 0.3 K and precipitation rates were increased by about 15 (6–21) mm yr-1 (more than 4% of total precipitation) from spring to autumn. Thus, the mitigation could help to alleviate expected future drought and water shortages in the Mediterranean area. We also report other important results of the ECLIPSE project.

Seasonality of global and Arctic black carbon processes in the Arctic Monitoring and Assessment Programme models

“…All models use anthropogenic emissions for BC, organic carbon, and sulphur for year 2010 from the ECLIPSE inventory, version 4a [ Stohl et al ., ; AMAP , ] and monthly varying emissions for forest and grass fires from Global Fire Emissiom Database, version 3.1 [ van der Werf et al ., ], which were converted to the model grid by each modeling group. The models were integrated for 2006–2010, with specified sea surface temperatures, sea ice concentrations, GHG concentrations, and volcanic forcings during this time period.…”

Uncertainties Caused by Major Meteorological Analysis Data Sets in Simulating Air Quality Over India

“…Aerosol processes were represented in the AERO6 module. Anthropogenic pollutant emissions were taken from Sharma et al () and Sharma et al () for India, and Evaluating the Climate and Air Quality Impacts of Short‐Lived Pollutants V5a (Stohl et al, ) for surrounding countries. Hourly biogenic emissions were estimated by the Model of Emissions of Gases and Aerosols from Nature version 2.04 (Guenther et al, ; Sakulyanontvittaya et al, ).…”

Perturbations to Global Energy Budget Due to Absorbing and Scattering Aerosols

“…This motivates modeling studies to estimate climate responses of the global‐mean temperature to the BC forcing. These studies, however, report that the temperature responses are muted (Baker et al, ; Stohl et al, ) despite a significant radiative forcing at the top of atmosphere (TOA). The BC‐induced atmospheric heating is also reported to be a source of uncertainty in future climatic change of the global precipitation (e.g., Pendergrass & Hartmann, ; Shiogama et al, ).…”

“…In contrast to BC, SF appears to have more conspicuous impacts on the global‐mean temperature (Baker et al, ; Stohl et al, ). The direct and indirect effects of SF aerosols have long been regarded as a substantial cooler to climate that can partially offset the global warming induced by long‐lived greenhouse gases (such as carbon dioxide).…”