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Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants

Final Report Summary - ECLIPSE (Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants)

Executive Summary:
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 un-accounted 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 ad-vanced 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 par-ticular. 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 months 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±0.7 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±0.9 K). It was also expected from the metrics that non-CH4 SLCPs would contribute ~22% to this response and CH4 78%, however this could not be fully confirmed by the transient simula-tions, which attributed about 90% of the temperature response to CH4 reductions, for reasons discussed in the paper. 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 we find a strong semi-direct effect offsetting the direct BC aerosol radiative effect. 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 warm-ing was reduced by about 0.3 K and precipitation rates were increased by about 15 (6-21) mm/yr (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.
Project Context and Objectives:
ECLIPSE aims to develop and assess effective emission abatement strategies for short-lived climate agents in order to provide sound scientific advice on how to mitigate climate change while improving the quality of air. Current climate policy does not consider a range of short-lived gases and aerosols, and their precursors (including nitrogen oxides, volatile organic compounds, sulphate, and black carbon). These nevertheless make a significant contribution to climate change and directly influence air quality. There are fundamental scientific uncertainties in characterizing both the climate and air quality impacts of short-lived species and many aspects (for example, the regional dependence) are quite distinct to those for the longer-lived climate gases already included in the Kyoto Protocol. ECLIPSE brings together 11 institutes with established and complementary expertise for a closely
co-ordinated 3 year programme. It will build on existing knowledge and use state-of-the-art chemistry and climate models to improve understanding of key atmospheric processes (including the impact of short-lived pecies on cloud properties) and characterize existing uncertainties; evaluate model simulations of short-lived species and their long-range transport using ground-based and satellite observations; perform case studies on key source and receptor regions (focused on Southeastern Europe, China and the Arctic); quantify the radiative forcing and climate response due to short-lived species, incorporating the dependence on where the species are emitted; refine the calculation of climate metrics, and develop novel metrics which, for example, consider rate of climate warming and go beyond using global-mean quantities; clarify possible win-win and trade-off situations between climate policy and air quality policy; identify a set of concrete cost-effective abatement measures of short-lived species with large co-benefits.

Project Results:
The United Nations Framework Convention on Climate Change (UNFCCC) requires climate policies to ‘be cost-effective so as to ensure global benefits at the lowest possible cost’ and that ‘policies and measures should ... be comprehensive … [and] … cover all relevant sources, sinks and reservoirs’. This was made operational by the Kyoto Protocol, which sets limits on emissions of six different greenhouse gases (GHGs), or groups of GHGs – carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs) and sulfur hexafluoride (SF6). Collectively these are often known as “the Kyoto gases” or the “Kyoto basket” . CO2 is the most important anthropogenic driver of global warming, with additional significant contributions from CH4 and N2O. However, other anthropogenic emissions capable of causing climate change are not covered by the Kyoto Protocol. Some are covered by other protocols, e.g. emissions of chlorofuorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are regulated by the Montreal Protocol, because of their role in stratospheric ozone (O3) depletion. But there are others, notably several short-lived components that give strong contributions to climate change that are excluded from existing climate agreements.
During ECLIPSE we investigate climate and air quality impacts of the emissions of CH4, which has a lifetime of about 9±1 years and a number of much shorter-lived components (atmospheric lifetimes of months or less) which directly or indirectly (via formation of other short-lived species) influence the climate :
• Methane is a greenhouse gas roughly 26 times stronger than CO2 on a per molecule basis at current concentrations. It is relatively well-mixed in the atmosphere and has both natural and anthropogenic sources. It is also a precursor of O3 and stratospheric water vapour.
• Black carbon (BC, also commonly known as soot), a product of incomplete combustion of fossil fuels and biomass, affects climate via several mechanisms. It causes warming through absorption of sunlight and by reducing surface albedo when deposited on snow. BC also affects clouds, with a consequent (but highly uncertain) impact on their distribution and radiative properties
• Tropospheric O3 is a greenhouse gas produced by chemical reactions from the emissions of the precursors CH4, carbon monoxide (CO), non-CH4 volatile organic compounds (NMVOCs) and nitrogen oxides (NOx). Emissions of these same precursors also impact on hydroxyl radical (OH) concentrations with further impacts especially on CH4.
• Several components have cooling effects on climate, mainly sulphate aerosol formed from sulphur dioxide (SO2) and ammonia (NH3), nitrate aerosol formed from NOx and NH3, and organic aerosol (OA) which can be directly emitted or formed from gas-to-particle conversion of NMVOCs. They cause a direct cooling by scattering solar radiation and alter the radiative properties of clouds, very likely leading to further cooling.
We refer to these substances as short-lived climate pollutants (SLCPs) as they also have detrimental impacts on air quality, directly or via formation of secondary pollutants. Notice that we include the precursors of O3 and secondary aerosols in our definition of SLCPs. We also include CH4 in our study even though it is included in the Kyoto Protocol, because of its relatively short lifetime compared to that of CO2 and its importance for air quality via the formation of O3. We do not include HFCs in our definition of SLCPs, as they have no significant impact on air quality and can be regulated from a climate policy perspective alone. For SLCPs, on the other hand, cost-effective environmental policy measures should be designed such that they optimize both the climate and air quality responses. In some instances, control of the emissions of a species is expected to reduce future warming and improve air quality at the same time – a “win-win” situation: in others, the control of emissions may be conflicting, in the sense that it could increase warming while improving air quality (or vice versa) – in this case, emission control involves a “trade-off” between the impacts.
The net climate impact since pre-industrial times of all short-lived components other than CH4 together is very likely to be cooling due primarily to sulphate aerosols. Whilst SLCP reductions are clearly beneficial for air quality, elimination of all current non-CH4 SLCP emissions would thus very likely lead to extra warming. Nevertheless, targeted emission reductions of selected SLCPs which cause warming (either directly or via formation of secondary species) have the potential to reduce global warming on a short timescale, as well as improving air quality. They may also reduce the rate of warming (Myhre et al., 2011; Shindell et al., 2012) that is important, for example, for the adaptation of ecosystems to climate change (as recognized by UNFCCC Art. 2) and is expected to accelerate in the near future (Smith et al., 2015). Reducing these selected SLCP emissions might be effective to help avoid (or at least delay) certain undesired impacts of climate change (e.g. rapid sea ice loss in the Arctic). At least, optimized SLCP emission reductions could help to reduce the undesired extra climate warming caused by air quality policy measures that often do not consider climate impacts.
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.
ECLIPSE has come to a number of important scientific conclusions, which are also of high relevance for climate and air quality policy:
• ECLIPSE has created a new inventory for anthropogenic SLCP emissions, including scenarios for the future. An important finding is the large range of possible future developments of anthropogenic SLCP emissions, which even for a single future energy pathway substantially exceeds the range of SLCP emissions given in IPCC’s RCPs. The large range results from the uncertainties of future air quality policies, as well as from the expected level of implementation and enforcement of existing policies
• Detailed comparisons between measured and modelled distributions of aerosol, O3 and other SLCP gases have shown that for many substances the models are in good agreement with available observations. The model performance of the ESMs is similar to that of CTMs. For BC, in particular, the agreement between models and measurements has improved for the Arctic (Eckhardt et al., 2015), which is partly the result of accounting for emissions from gas flaring and emission seasonality. Outside the Arctic, a reduction of the BC lifetime led to improvements. Nevertheless, our comparisons suggest underestimates of BC and aerosol precursor emissions in high-latitude Russia and in India. Furthermore, it was found that SO2 concentrations are overestimated and CO concentrations are underestimated by the models at the surface in Asia and Europe during summer and autumn. The CO underestimate is likely associated with a too short CO lifetime in the models. Ozone, on the other hand, is generally overestimated at rural locations. Such discrepancies may affect model responses to emission perturbations and thus radiative forcing.
• Earth System Models can reproduce the accelerated upward trend of surface temperature over Europe that was observed when aerosol precursor emissions were reduced in the 1990s (leading to solar brightening), after a period of emission growth in the 1960s-1980s (leading to solar dimming).
• ECLIPSE performed detailed multi-model calculations of RF for all considered SLCP species, as a function of emission region and season. It is found that the absolute values of specific RF for aerosols are generally larger in summer than in winter. An important new finding is that the semi-direct effect on clouds, although highly uncertain, can potentially offset a considerable fraction of the direct positive RF of BC. This, together with reduced BC lifetimes, causes the net RF for BC calculated in ECLIPSE to be only weakly positive, which is different from most previous studies.
• NOx emissions affect the concentrations of O3, CH4 and nitrate aerosols. The first effect leads to positive RF, while the latter two cause negative RF. We have quantified all these effects and can state with confidence that the current net RF of global historical NOx emissions is negative. The forward looking metrics GWP and GTP for NOx are negative as well, except for short time horizons.
• ECLIPSE had a focus on calculation and testing of emission metrics, which led to a better understanding of existing metrics, further development of the applications of the RTP concept and introduction of new metric concepts such as the Global Precipitation change Potential (GPP). After careful consideration of the alternatives, we chose a 15-year ramp-up version (i.e. assuming a linear implementation of measures) of the GTP20 metric for designing a SLCP mitigation scenario.
• The GTP20 metric was implemented into the GAINS model to compile a basket of all mitigation measures (MIT) that had beneficial impacts on both air quality and climate. We find that the 17 most important mitigation measures would contribute more than 80% of the climate benefits according to the GTP20 metric. The top measures both for CH4 and BC mitigation are to prevent the venting (for CH4) and flaring (for BC) of gas associated with the oil production. For CH4, measures on shale gas production, waste management and coal mines were also important. For non-CH4 SLCPs, elimination of high emitting vehicles and wick lamps, as well as reducing emissions from coal and biomass stoves, agricultural waste, solvents and diesel engines were also important.
• The MIT scenario would reduce global anthropogenic emissions of CH4 and BC by 50% and 80%, respectively. As a result of co-control with BC, emissions of OA would also be reduced by 70%, whereas emissions of CO2 and SO2 would hardly be changed. Based on the GTP20 metric, the CO2-equivalent emissions (including CO2 emissions) would be decreased by about 70% in the year 2030, with about 56% of the decrease caused by CH4 measures and 44% caused by non-CH4 SLCP measures.
• The mitigation scenario would reduce surface concentrations of O3 and PM2.5 globally compared to the CLE scenario, with BC reductions of more than 80% in some areas. We estimate that in the EU the loss of statistical life expectancy due to air pollution will be reduced from 7.5 months in 2010 to 5.2 months in 2030 in the CLE scenario. The MIT measures would reduce statistical life shortening by another 0.9 months. Substantially larger reductions in life shortening due to the mitigation are found for China (1.8 months) and India (11-12 months).
• Climate impacts of SLCP emissions were simulated with four ESMs with full ocean coupling. Equilibrium simulations that removed all land-based anthropogenic emissions of SO2, BC and OA in turn showed robust global-mean increase in surface temperatures of 0.69 K (0.40-0.84 K) for SO2 removal and smaller warming for OA removal (Baker et al., 2015). The global mean temperature response to BC removal was slightly negative: -0.05 K (-0.15 to 0.08 K). The relatively small global response to BC emission reductions was attributed to a strong but uncertain semi-direct effect, which partly offsets the direct aerosol radiative effect.
• Climate impacts of the MIT scenario were investigated with ESM ensemble transient simulations of both the CLE and MIT scenario. Multi-model ensemble mean global mean surface temperature in the CLE scenario increased by 0.70±0.14 K between the years 2006 and 2050. The ensemble mean global mean surface warming for the last decade of the simulation (2041-2050) was, however, 0.22±0.07 K weaker for the MIT scenario, demonstrating the effect of the SLCP mitigation. The response was strongest in the Arctic, with warming reduced by about 0.44 K (0.39-0.49 K).
• In the context of developing climate policies, there are other climate parameters than global annual mean temperature that are of relevance. The MIT scenario led to particularly beneficial climate responses in Southern Europe, where the surface warming was reduced by about 0.3 K from spring to autumn and precipitation rates were increased by about 15 (6-21) mm/yr (15 mm/yr corresponding to more than 4% of total precipitation), compared to the CLE scenario. Thus, the mitigation could help to alleviate expected future drought and water shortages in the Mediterranean region.
• Additional ESM transient simulations, which only included the CH4 emission reductions, led to a global warming reduction that amounted to about 90% of the reduction produced by the simulations using the full set of measures. This suggests that the net climate benefits from the non-CH4 SLCP mitigation measures in terms of global annual mean temperature change are very limited. Nevertheless, if implemented as such, the mitigation package as a whole would have beneficial impacts on both air quality and climate, and for the latter, also in other climate variables than global annual mean temperature change such as regional changes in temperature and precipitation.
• For the first time, ECLIPSE compared the temperature response to an SLCP mitigation scenario as it is given by climate metrics (using the ARTP method) and as it is simulated with transient ESM simulations. This is crucial for the application of metrics, which – because of their simplicity and flexibility – are very relevant in a policy context where they can substitute full ESM simulations which are expensive and impractical for small perturbations. Both approaches give a global mean reduced warming of the surface temperatures by 0.22 K (and similar uncertainty ranges) for the period 2041-2050. Also the large-scale pattern of the response (with strongest warming reductions in the Arctic) is reproduced similarly by both methods, even though the agreement is less good than for the global mean.
• The metrics-based approach and the transient model simulations agree less well on the relative contribution of CH4 and non-CH4 SLCP mitigation measures to the reduced warming. While the metrics-based approach suggests that the non-CH4 measures account for 22% of the global-mean temperature response for 2041-2050, the transient simulations result in a contribution from non-CH4 measures of only about 10%. One reason for this disagreement is that many of the BC-related measures included in the mitigation basket were relatively OC-rich and this makes their net temperature response extremely uncertain, especially when aerosol indirect effects are considered. Furthermore, differences in how the forcing through the semi-direct effect of BC is accounted for likely contribute.
• Most of the cooling effect in our SLCP mitigation scenario is contributed by CH4 reductions, leaving only minor benefits with respect to near-term global mean climate warming from reducing non-CH4 SLCPs. The possible co-benefits between air quality policy (which mainly addresses non-CH4 SLCPs) and climate policy are therefore more limited than expected and probably only exist for those sources with the highest BC/OA emission ratios. To the contrary, clear co-benefits were found for CH4 mitigation, which reduces climate warming and improves air quality via reduced surface O3 concentrations.



Potential Impact:
In the framework of the ECLIPSE project the impacts of SCLCPs were quantified, both on air pollution and chlimate change. Mitigation measures with co-benefits for air quality and climate policy were identified. A brochure, which has as target group stakeholders, plicy makers and the interested public will be available for distribution. This is the most important knowledge transfer from ECLIPSE to the decision makers.
The coordinator of ECLIPSE was also involved in summarizing and reviewing current understanding of air quality and climate to update existing policies with the latest science. Those findings have been collected in a book “Air Quality –Review” published by the European Union in 2013. Later the most important/relevant findings of ECLIPSE in relation to this were presented at the “Air Quality and Climate Change stakeholders meeting”, 2nd December 2014 in Brussels
The one-day stakeholder meeting was dedicated to Air Quality and Climate Change research and policy implications derived from the EU research projects ACCENT+, PEGASOS, MACC, ECLAIRE, ACCESS, and ECLIPSE.
Some of the ECLIPSE partners also have active involvement in the AMAP (Arctic Monitoring and Assessment Program, http://www.amap.no/) activities (Expert group for SLCF). Model simulations, which were based on exactly the same settings as in ECLIPSE were used to enlarge the model ensemble and therefore decrease uncertainties of the results.
Not only the AMAP community, but also other EU-projects as well as many international group made use of the ECLIPSE dataset. The data can be downloaded on the ECLIPSE website or from the ECCAD-Gaia database (http://eccad.sedoo.fr/). ECLIPSE emissions used in model runs to analyse data collected as part of the EU ACCESS project –for analysis of flights to Svalbard which encountered Siberian pollution. We also used the ECLIPSE emissions within the French ANR CLIMSLIP (Climate Impacts of Short-lived Pollutants and Methane in the Arctic) project.
ECLIPSE also collaborated with the EU research project PEGASOS, LIMITS, ECLAIRE – which lead to joint publication like “K. Tsigaridis et al.: The AeroCom evaluation and intercomparison of organic aerosol”. ECLIPSE also supported contributions to meetings on an IGAC/IGBP Air Pollution and Climate initiative.

Having Chinese partners in the project also enforced the collaboration with China. There was a paper done with Chinese evaluating the NOx projections. Tsinghua worked with GAINS to develop scenarios for this paper and continues to use it and present the paper results. The collaboration with the same group continues beyond ECLIPSE and follows now something that got out of the ECLISPE too which is potential role of NH3 in formation of PM in China and since they have no policy yet to control NH3 then it is possibly an emerging research area; in fact already manifested itself in few papers in recent years and now also World Bank is interested and got IIASA and Tsinghua on board of their project that will look into this.
After the Stohl et al article about Arctic and black carbon has been published, there was some coverage in Austrian radio (FM4) http://fm4.orf.at/stories/1726307/. – “A black future for the Arctic?” , which focused on BC climate impacts.
ECLIPSE scenarios have been used with several students of the IIASA Young Scientists Summer Program (YSSP) and will continue to be used (http://www.iiasa.ac.at/web/home/education/yssp/about.html). Also the cooperation with South Africa on the development of the GAINS model and work with students within the respective program (http://www.iiasa.ac.at/web/home/education/sa-yssp/about.html) will make use of the ECLIPSE scenarios. Also at the ACCESS summer school, French ECLIPSE researchers got involved.
Educational publishing company Pearson Education in the United Kingdom contacted us (June 2014) asking for a permission to use one of the figures (Figure 1 'Sectorial trend in global, China, and Indian SO2 emissions since 1990') from the Klimont, Smith, Cofala (2013, ERL) paper about global SO2 development in a new educational textbook Exploring Science Year 8 by Mark Levesley that they produce. Prof Danny Harvey from the Department of Geography at the University of Toronto (Canada) asked to use the results from the at above paper (Klimont et al, 2013, ERL) in his university lectures. (December 2014)
To communicate/discuss the key finding of ECLIPSE with the scientific community 34 manuscripts in reviewed journals were submitted/published and scientist had 60 presentations on international conferences, which had a focus on ECLIPSE topics.
ECLIPSE researchers also had active involvement in the EMEP activity: Transboundary particulate matter, photo-oxidants, acidifying and eutrophying components. (http://emep.int/publ/reports/2014/EMEP_Status_Report_1_2014.pdf)
The development of the EMEP/MSC-W model has also been supported by the EU FP7 projects MACC-II, TRANSPHORM, ECLAIRE, ECLIPSE, PEGASOS, and IMPACT2C, the Nordic Council of Ministers, the Norwegian Space Centre and the Norwegian Ministry of the Environment.
There was also a strong link with the Task Force on Hemispheric Transport of Air Pollution (TF HTAP), which is an international scientific cooperative effort to improve the understanding of the intercontinental transport of air pollution across the Northern Hemisphere.

List of Websites:
eclipse.nilu.no
Andreas Stohl
NILU - Norwegian Institute for Air Research
P.O. Box 100
N-2027 Kjeller

Tel.: +47 6389 8035
Fax: +47 6389 8050
Email: ast@nilu.no
Webpages: www.nilu.no www.nilu.no/andreas/

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