| 英文摘要: | There is growing scientific1, 2 and political3, 4 interest in the impacts of climate change and anthropogenic emissions on the Arctic. Over recent decades temperatures in the Arctic have increased at twice the global rate, largely as a result of ice–albedo and temperature feedbacks5, 6, 7, 8. Although deep cuts in global CO2 emissions are required to slow this warming, there is also growing interest in the potential for reducing short-lived climate forcers (SLCFs; refs 9,10). Politically, action on SLCFs may be particularly promising because the benefits of mitigation are seen more quickly than for mitigation of CO2 and there are large co-benefits in terms of improved air quality11. This Letter is one of the first to systematically quantify the Arctic climate impact of regional SLCFs emissions, taking into account black carbon (BC), sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs), organic carbon (OC) and tropospheric ozone (O3), and their transport processes and transformations in the atmosphere. This study extends the scope of previous works2, 12 by including more detailed calculations of Arctic radiative forcing and quantifying the Arctic temperature response. We find that the largest Arctic warming source is from emissions within the Asian nations owing to the large absolute amount of emissions. However, the Arctic is most sensitive, per unit mass emitted, to SLCFs emissions from a small number of activities within the Arctic nations themselves. A stringent, but technically feasible mitigation scenario for SLCFs, phased in from 2015 to 2030, could cut warming by 0.2 (±0.17) K in 2050. We focus on the Arctic impact of climate forcers with atmospheric lifetimes shorter than the typical hemispheric mixing times (about one month): BC and ozone precursors (CO and VOCs) that predominantly lead to warming, as well as co-emitted species that cause cooling (SO2, OC, and NOx). We omit methane and HFCs as their lifetimes are longer, although some other studies on SLCFs have included these species as well. In the Arctic, the effects of BC include both the warming from absorption of solar radiation in the atmosphere and absorption of radiation from deposition on snow/ice13, 14, 15. The Arctic warming from BC is highly variable with season of emission, physical transport into the Arctic, and the deposition to snow and ice16. In addition, processes that emit BC also co-emit other particles and gases that lead to sulphate and OC aerosols. Ozone precursors (CO, NOx and VOCs) affect climate through the formation of ozone, a potent greenhouse gas, while also changing the oxidizing capacity of the atmosphere (and thus the lifetime and levels of, for example, methane)17. Using several chemical transport models we perform detailed radiative forcing calculations from emissions of these species. Geographically, we separate emissions into seven source regions that correspond with the national groupings of the Arctic Council, the leading body organizing international policy in the region (the United States, Canada, the Nordic countries, the rest of Europe, Russia, East and South Asia, and the rest of the world). We look at six main sectors known to account for nearly all of these emissions: households (domestic), energy/industry/waste, transport, agricultural fires, grass/forest fires, and gas flaring. The models have different treatments of SLCFs, and have simulated the years 2006–2010 with prescribed sea surface temperatures. To estimate the Arctic surface temperature we apply regional climate sensitivities (RCSs), the temperature response per unit of radiative forcing for each SLCF (refs 18,19,20,21). The RCSs are defined in four broad latitude bands (60°–90° N, 28°–60° N, 28° S–28° N, 90°–28° S) to account for contributions by local and remote forcing to surface temperature changes in each band. For example, BC at midlatitudes may increase the transport of heat into the Arctic by locally warming the atmosphere and increasing the north–south temperature gradient18, 22. The RCS concept applied here accounts for this. The simulations employ anthropogenic emissions of SLCFs from the ECLIPSE emission data set V4.0a (refs 23,24) for the year 2010. Using the RCS method we estimate the total equilibrium Arctic surface temperature response to all (natural and anthropogenic) global 2010 emissions of SLCFs to be −0.44 K, with a model range of −1.02 to −0.04 K. Of this 0.48 (0.33–0.66) K is due to BC in atmosphere and snow, −0.18 (−0.30–0.03) K is due to OC, −0.85 (−0.57 to −1.29) K is due to sulphate and 0.05 (0.04–0.05) K is due to ozone. We can compare the total impact to the CMIP5 multi-model ensemble historical simulations. A cooling of −1.8 K has been estimated in the Arctic between 1913 and 2012 due to all anthropogenic forcing agents other than greenhouse gases25, whereas using the six best CMIP5 models (ranked based on the least square errors between the simulations and observations in the Arctic), a cooling trend of −0.1 K per decade from 1900 to 2005 has been reported1. These numbers are higher (negative) compared to ours, but they also include more climate forcers. Also note that our temperature response is an equilibrium result, whereas the CMIP5 calculations are from transient simulations. Figure 1 shows the annual mean Arctic surface temperature response from current emissions separated into the different emission sectors, regions and components. The largest single contribution to warming in the Arctic originates from Asian domestic emissions, followed by Russian flaring emissions. Generally, the energy sector has a cooling effect due to the relatively large direct and indirect aerosol effects of SO2 emissions. The doughnut chart in Fig. 1 reports the fractions of the Arctic warming/cooling that are due to radiative forcing within the Arctic or outside the region—showing that most of the Arctic warming effects from Asian emissions are due to radiative forcing exerted outside the Arctic, whereas most emissions from Arctic nations such as Russia and the Nordic countries affect the Arctic more directly.
| http://www.nature.com/nclimate/journal/v6/n3/full/nclimate2880.html
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