Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants (ECLIPSE) Policy-relevant findings

Transcription

1 1 Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants (ECLIPSE) Policy-relevant findings

2 Foreword 2 There s broad scientific consensus that climate change over recent decades is caused mainly by anthropogenic emissions of the long-lived greenhouse gas carbon dioxide (CO 2 ). CO 2 is the most important but not the only long-lived greenhouse gas, and there are also other shorter-lived substances called Short-Lived Climate Pollutants (SLCPs) which can influence the climate, especially the rates of warming in the near-term. SLCPs are also air pollutants (or precursors thereof) and thus reducing their emissions would improve air quality. One problem is, however, that some SLCPs warm the climate, whereas others cool it, and often warming and cooling SLCPs are emitted by the same sources, albeit in varying amounts. This makes quantification of their net effect very difficult. The goal of the ECLIPSE project was to quantify the impacts of SLCPs on both air quality and climate and to identify mitigation measures with co-benefits for air quality and climate policy (i.e., mitigation measures that are beneficial to both) and trade-offs (i.e., measures that improve air quality but have an undesired impact on climate, or vice versa). Having identified such measures, the project also set out to design a concrete global SLCP mitigation strategy that maximizes co-benefits and limits trade-offs. The climate problem can only be solved however if humans manage to reduce our emissions of CO 2 dramatically and immediately, especially to have lasting impact. Unfortunately, CO 2 emissions continue to increase at untenable rates. SLCP measures form an important complement to CO 2 reductions, especially to slow the pace of warming in the near-term; but should never be viewed as a replacement for urgent action on CO 2 by global leaders. The ECLIPSE project gathered some of Europe s and China s leading scientists in climate research and has made substantial progress in our understanding of SLCPs. This brochure presents a summary of our findings and I hope it will be useful for stakeholders, policy makers, and the interested public. Andreas Stohl, ECLIPSE project coordinator

3 Fact Box: Short-Lived Gases and Aerosols Considered in ECLIPSE Methane (CH 4 ) is a potent greenhouse gas with a lifetime of about nine years, which is relatively well-mixed in the atmosphere. It is also a precursor of ozone and stratospheric water vapour. Methane has both natural (e.g., wetlands) and anthropogenic sources. The latter are primarily related to the production and use of fossil fuels, livestock farming, and treatment of waste. Black carbon (BC) aerosol, commonly known as soot, is a product of incomplete combustion of fossil fuels and biomass. It causes warming through absorption of sunlight and by reducing the surface s ability to reflect sunlight when deposited on snow. Tropospheric ozone (O 3 ) is a greenhouse gas produced by chemical reactions involving methane, carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs) and NO x (nitric oxide and nitrogen dioxide). All these substances are primarily emitted by combustion processes. In addition, ECLIPSE addressed several aerosol components with a predominately cooling effect on climate: Sulphate aerosol formed from sulphur dioxide (SO 2 ), nitrate aerosol formed from nitrogen oxides and ammonia, and organic aerosol (OA) which can be directly emitted or formed from condensation of volatile organic compounds. They cause a direct cooling by scattering solar radiation and alter the radiative properties of clouds, very likely leading to further cooling. Air quality policy does not distinguish between aerosols of different type but instead considers them together. The term PM 2.5 refers to all particulate matter with diameter smaller than 2.5 micrometers. 3

4 New Scenarios for SLCP Emissions 4 ECLIPSE has developed three emission scenarios, which represent possible futures for emissions of SLCPs out to 2050: Current legislation (CLE) includes current and planned environmental laws, considering known delays and failures up to now but assuming full enforcement in the future. No further control (NFC) uses the same assumptions as CLE until 2015 but no further legislation is introduced subsequently, even if currently committed. This leads to higher emissions than in CLE for most pollutants. The ECLIPSE SLCP mitigation scenario (MIT) includes the additional measures that have both beneficial air quality and climate impact. An important finding is that the future emissions of SLCPs without assuming further policy measures are much higher than the uncertainty range resulting from the emissions used by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

5 ECLIPSE Mitigation Measures For the ECLIPSE mitigation scenario, all mitigation measures that are expected to have a positive impact on both air quality and on climate were selected into a mitigation basket that was assumed to be implemented between 2015 and The climate impacts were quantified with a climate metric (the so-called Global Temperature-change Potential, see fact box page 12) with a time horizon of 20 years (GTP 20 ). The ECLIPSE mitigation would reduce global anthropogenic emissions of methane by 50% and of BC by 80%. 5

6 The top-17 mitigation measures contribute together more than 80% of the climate benefit. Of these 80%, methane measures contribute about 47% of the benefits for the 20-year time horizon of the GTP 20 metric, while 33% are attributed to BC focused measures. Top-17 measures, ranked by importance starting from the top, are: 6 Methane measures: Oil and gas industry: Recovery and use (rather than venting or flaring) of associated gas Oil and gas industry (unconventional): Reducing emissions from unintended leaks during production (extraction) of shale gas * Coal mining: Reducing (oxidizing) emissions released during hard coal mining (ventilation air methane) Waste: Municipal waste waste paper separation, collection, and recycling Waste: Municipal food waste separation, collection and treatment in anaerobic digestion (biogasification) plants Coal mining: Hard and brown coal pre-mining emissions Degasification Gas distribution: Replacement of grey cast iron gas distribution network Waste: Industrial solid waste (food, wood, pulp and paper, textile) recovery and incineration Waste: Wastewater treatment from paper and pulp, chemical, and food industries anaerobic treatment in digester, reactor or deep lagoon with gas recovery, upgrading and use. For residential wastewater centralized collection with anaerobic secondary and/or tertiary treatment (incl. treatment with bacteria and/or flaring of residual methane) Oil and gas industry (conventional): Reducing emissions from unintended leaks during production (extraction) Copyrights: Shutterstock/NILU/Wikipedia Commons, except *) Jim Blecha 2010

7 Measures targeting BC reduction: 7 Oil and gas industry: Improving efficiency and reducing gas flaring Transport: Eliminating high emitting vehicles (super-emitters) Residential-commercial: Clean biomass cooking and heating stoves Residential-commercial: Replacement of kerosene wick lamps with LED lamps Transport: Widespread Euro VI emission standards (incl. particle filters) on diesel vehicles Industrial processes: Modernized (mechanized) coke ovens Agriculture: Effective ban of open field burning of agricultural residues

8 8 ECLIPSE SLCP Mitigation Would Substantially Improve Global Air Quality In both the current legislation and mitigation scenarios, air pollution in some regions of the world (e.g. in Europe) would be decreasing with time until 2050, whereas in other regions (e.g. in India) it would be increasing. However, relative to the current legislation scenario, the ECLIPSE mitigation basket would reduce the surface concentrations of ozone and particulate matter (PM2.5) almost everywhere and particularly in the pollution source regions. This can be seen in the figure below showing the relative difference (in %) in annual mean concentrations between the mitigation and the current legislation emission scenario for the final decade of our study ( ).

9 Impacts on Human Health 9 The reduction in pollutant concentrations by the mitigation would lead to beneficial impacts on human health, as shown here for the example of the loss of statistical life expectancy due to exposure to PM 2.5 in the EU-28 countries, the rest of Europe, China and India, for different years. Notice that large increases in the loss of life expectancy are expected in India, for all scenarios. However, this increase can be mitigated with the ECLIPSE measures by almost one year. Shutterstock

10 Beneficial Climate Impacts 10 Four different global climate models performed climate simulations until the year 2050, using both the current legislation emission scenario and the mitigation scenario. The climate warms in both cases because of rising CO 2 concentrations; however, the impact of the SLCP mitigation is given by the difference between the two, as shown in the figure below. For the final decade of the simulations ( ), global warming would be reduced by 0.22±0.07 C. This is about 10-20% of the warming expected by the IPCC (scenario RCP8.5) for the year The climate response is strongest in the Arctic, where warming would be reduced by about 0.44 C. Time evolution of differences in global mean surface temperature between transient simulations following the mitigation (MIT) and the current legislation (CLE) scenario. Negative values mean that the mitigation leads to lower temperatures than the current legislation scenario. The thick line shows the multi-model mean, whereas the shading indicates the range given by different models. Fourat, Wikipedia Commons

11 Reduced Drought in the Mediterranean The mitigation scenario led to particularly beneficial climate responses in Southern Europe (area south of the bold black line in the figure below), where the surface warming was reduced by about 0.3 C during the spring-to-autumn period and precipitation rates were increased by about 15 mm per year or more than 4% of total precipitation, compared to the current legislation scenario, for the decade Thus, the mitigation could help to alleviate expected future drought and water shortages in the Mediterranean region. 11 Precipitation difference in N 50N 40N 30N 10W 0 10E 20E 30E 40E 50E 60E mm / year Annual average differences in surface temperature (top) and precipitation (bottom) over Europe between the transient simulations based on the mitigation (MIT) and the current legislation (CLE) scenario, averaged over the last 10 years of the simulations ( ). For temperature, negative values mean that MIT has lower temperatures than CLE; for precipitation, positive values mean that MIT has more precipitation than CLE. Dots show regions where all models used agree on the sign of the difference.

12 Climate Metrics 12 Climate metrics are highly simplified models of the climate response to emission changes (see fact box) which are derived from the output of complex climate models. Their advantages are that climate impacts can be diagnosed efficiently and at low computational cost. With the metrics, the climate impact even of a single regional mitigation measure can be estimated, which would be computationally prohibitive to diagnose with full climate models. This makes the metrics attractive as a policy tool. However, it is important to show that metric-based results indeed mimic the results from global climate models. Fact Box: Climate Metrics To place the climate effect of emissions of different gases and aerosols on some kind of common scale, climate metrics are widely used. For example, the Kyoto Protocol to the United Nations Framework Convention on Climate Change is a multi-gas treaty covering a range of greenhouse gases; it uses metrics to convert emissions of methane into CO2-equivalent emissions. There is no unique way of calculating such metrics as they depend on policymaker choices of the most important time-scales and the most important parameter for characterising climate change. The Kyoto Protocol uses the 100-year Global Warming Potential (GWP 100), which is the radiative forcing due to a pulse emission of a gas, integrated over 100 years (relative to the same quantity for an equal mass emission of CO2). An alternative metric is the Global Temperature-change Potential (GTP) which is the temperature change due to an emission of a gas or aerosol particle at some time in the future. A regional equivalent of the GTP, the Regional Temperature-change Potential (RTP) can be derived which computes the temperature change in a particular region, due to emissions in different regions. The illustrations in this brochure use the 20-year GTP and time dependent RTP, but within ECLIPSE we have derived a wide-range of climate metrics for SLCPs, and also explored a novel metric, the Global Precipitation Potential, which is similar to the GTP but looks at future changes in global precipitation following an emission. Shutterstock

13 13 ECLIPSE was the first project that has designed a climate-optimized SLCP mitigation scenario and evaluated its impact both with climate metrics and with an ensemble of transient global climate model simulations. We found that for the period both approaches resulted in the same global-mean temperature difference between the mitigation and the current legislation scenario of 0.22 C as an average over four models. The figure above shows that for the period the global climate model simulations (red bars) and the metrics (blue bars) are broadly consistent even regionally, despite some differences. For instance, both methods show the strongest response in the Arctic, somewhat smaller response in the Northern Hemisphere Mid-Latitudes, yet smaller response in the tropics, and the smallest response in the Southern Hemisphere.

14 The Power of Climate Metrics 14 Once the metrics are evaluated, they can be used efficiently to quantify the time-dependent impact of regional and/or individual mitigation options. For instance, the figure below shows the total Arctic surface temperature response ( C) as a function of time by global mitigation of residential combustion (heating and cooking) in the ECLIPSE mitigation scenario and distinguishing individual SLCP components. It can be seen that reduction in Black Carbon (BC) has a cooling influence both due to its atmospheric effect and darkening of snow, while reduction in the co-emitted organic aerosol (OA) leads to warming. Other components have a small effect, leading to a net cooling of the Arctic overall. It should be recalled, however, that this cooling is superimposed over a stronger warming that is expected to result from emissions of CO 2.

15 Conclusions ECLIPSE has developed a global SLCP mitigation scenario which, if implemented over the next 15 years, would improve air quality and very likely reduce global warming at the same time. Associated air quality improvements would reduce loss of statistical life expectancy by about one month in Western Europe, two months in China, and one year in India. 15 Global mean temperature increases would be reduced by 0.22±0.07 C for the last decade of the simulation ( ), with larger reductions (0.44 C) in the Arctic. This demonstrates the cooling effect of the specific SLCP mitigation as compared to the CLE scenario. The warming reduction is largely independent of sulfur reduction measures, which would have potentially offsetting extra warming effects and for that reason are not included in the ECLIPSE mitigation measures. There are particularly beneficial climate effects in the Mediterranean where temperatures in summer would decrease and precipitation would increase, and would act to mitigate, to some extent, the large temperature increases and precipitation decreases which are expected to be primarily driven by CO 2 increases over the same period. According to our calculations, most (ca % for the decade ) of the cooling effect in our SLCP mitigation scenario is contributed by methane emission reductions. Co-benefits with air quality are strong for methane reductions, as these would lead to substantial reductions in global ozone levels as well. It needs to be emphasized that SLCP mitigation can only be a small component in a global climate mitigation strategy, especially as regards slowing the pace of warming in the near-term, since most of the global warming is caused by CO 2. If the overall climate warming is to be reduced, CO 2 emissions would have to be reduced strongly. However, climate-optimized SLCP mitigation would result in improvements of air quality and thus represents a no-regret strategy. ECLIPSE has made strong progress in understanding the impact of emissions of SLCPs on air quality and climate change, but important uncertainties remain in quantifying their impact. Further improvements in our understanding would need co-ordinated advances in observational and modelling capabilities.

16 16 ECLIPSE Partners NILU Norwegian Institute for Air Research, Kjeller Centre for International Climate and Environmental Research (CICERO), Oslo Norwegian Meteorological Institute, Oslo International Institute for Applied Systems Analysis (IIASA), Laxenburg Met Office Hadley Centre, Exeter Department of Meteorology, University of Reading, Reading Sorbonne Universités, UPMC Univ. Paris 06; Université Versailles St-Quentin; CNRS/INSU; LATMOS-IPSL, Paris Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, Crete; FORTH, ICE-HT, Platani, Patras Institute for Meteorology, University of Leipzig, Leipzig State Key Laboratory for Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing School of Environment, Tsinghua University, Beijing Norway Norway Norway Austria United Kingdom United Kingdom France Greece Germany China China Advisory Board: P. Grennfelt, S.-C. C. Lung, R. Maas, P. Pearson, O. Boucher Further information Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants A. Stohl, B. Aamaas, M. Amann, L. H. Baker, N. Bellouin, T. K. Berntsen, O. Boucher, R. Cherian, W. Collins, N. Daskalakis, M. Dusinska, S. Eckhardt, J. S. Fuglestvedt, M. Harju, C. Heyes, Ø. Hodnebrog, J. Hao, U. Im, M. Kanakidou, Z. Klimont, K. Kupiainen, K. S. Law, M. T. Lund, R. Maas, C. R. MacIntosh, G. Myhre, S. Myriokefalitakis, D. Olivié, J. Quaas, B. Quennehen, J.-C. Raut, S. T. Rumbold, B.H. Samset, M. Schulz, Ø. Seland, K. P. Shine, R. B. Skeie, S. Wang, K. E. Yttri, T. Zhu submitted to Atmos. Chem. Phys., 2015 The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/ ) under grant agreement no ECLIPSE. Photo: Front page: Shutterstock