1 Introduction

Climate change in the Arctic has important regional implications because of its potential impacts to human health, ecosystems, economic interests, infrastructure, and traditional ways of life. Changes in the Arctic may also have global implications, whether because of thawing permafrost accelerating emissions of stored carbon from frozen ground [e.g., Schuur et al., 2015], reduced surface albedo adding to global warming [e.g., Holland and Bitz, 2003], or possible connections between Arctic temperature change and large‐scale weather patterns [e.g., Francis and Vavrus, 2012]. Strategies focused on mitigating Arctic climate change—in particular, strategies that mitigate Arctic temperature increases—could therefore have both regional and global benefits.

Short‐lived climate forcers (SLCFs) are a subset of greenhouse gases (GHGs) and aerosols that absorb or scatter radiation and remain in the atmosphere for relatively shorter time periods compared with other, long‐lived GHGs (e.g., carbon dioxide, CO 2 ). This group of climate forcers includes carbonaceous aerosols such as black carbon (BC) and organic carbon (OC) (atmospheric lifetimes of 3–8 days), ozone (∼22 days), and sulfate (∼4 days), and also includes species with relatively longer lifetimes such as methane (∼12 years) and some hydrofluorocarbons (typically 1–20 years). SLCFs contribute considerably to Arctic temperature change; emissions of BC, in particular, are estimated to generate approximately 0.5 K of present‐day Arctic warming, which is approximately equivalent to the projected reduction in Arctic warming attainable by 2050 under the most aggressive GHG mitigation scenario [e.g., Sand et al., 2015]. Temperature responses in the Arctic are stronger relative to global responses for all forcing agents, including SLCFs, because of Arctic amplification [e.g., Holland and Bitz, 2003]. Moreover, BC in particular may amplify Arctic temperature change because deposition onto snow and ice surfaces reduces surface albedo, causing a forcing that results in local, surface warming [e.g., Hansen and Nazarenko, 2004; Flanner et al., 2007; Jacobson, 2010].

Because of the relatively short lifetimes of these atmospheric constituents, reducing emissions of SLCFs—in particular aerosols such as BC—has been identified as a potentially fruitful avenue for slowing Arctic warming in the short term [e.g., Arctic Monitoring and Assessment Programme, 2015; Sand et al., 2015]. However, such emissions reductions must be carefully planned to achieve the desired results. BC typically has a net warming effect on Arctic temperatures, whereas co‐emitted aerosols such as OC and sulfur dioxide (SO 2 )—the precursor to atmospheric sulfate—are typically net cooling [e.g., Smith and Mizrahi, 2013; Sand et al., 2015]. As one example, recent work suggests that declining SO 2 emissions from Europe may have resulted in as much as 0.5°C of observed Arctic warming over the past 25 years [e.g., Acosta Navarro et al., 2016]. Thus, reducing emissions from sources that have higher ratios of BC to OC and SO 2 will result in greater temperature reduction benefits [e.g., Bond et al., 2013]. Furthermore, the latitude of emissions sources has a strong impact on the Arctic temperature response. BC emissions from higher latitudes tend to reside lower in the Arctic atmosphere and are more likely to deposit to local snow surfaces than emissions from lower latitudes, and therefore, typically generate a stronger Arctic temperature response per ton of emissions [e.g., Sarofim et al., 2013; AMAP, 2015]. Thus, the net Arctic impact of different emissions reduction strategies will depend on both the location and sources being targeted.

Using a multi‐model ensemble, the Arctic Monitoring and Assessment Programme (AMAP) estimated the equilibrium Arctic temperature response per unit of sustained emissions of BC, OC, and SO 2 from six sectors and seven regions [AMAP, 2015]. Using these temperature response factors, Sand et al. [2015] estimated that an aggressive, aerosol, and ozone precursor‐focused mitigation scenario could reduce Arctic warming by up to 0.2 K by 2050 compared with a “business as usual” strategy. Although the aggressive emissions reduction scenario described by Sand et al. [2015] provides a useful upper bound on potential Arctic temperature reductions from mitigation of these substances, this scenario assumes very mitigation measures and does not consider implementation costs or broader goals for long‐term GHG stabilization [e.g., van Vuuren et al., 2011a; Stohl et al., 2015].

Because any future climate change strategy must meet a wide range of objectives—including mitigating both short‐ and long‐term climate change, protecting air quality, and minimizing implementation costs—it is useful to consider the implications of a broader range of emissions reduction pathways in the context of short‐term impacts on the Arctic. This study extends the results of AMAP [2015] and Sand et al. [2015] by using the equilibrium temperature response factors from those studies to estimate the Arctic temperature changes resulting from a wider range of current and future emissions scenarios. Specifically, we used present‐day and future global emissions for BC, OC, and SO 2 from three sources: (1) two scenarios (CLE and MIT, representing a Current LEgislation and a MITigation scenario) developed for the Evaluating the Climate and Air Quality Impacts of Short‐Lived Pollutants (ECLIPSE) project [Stohl et al., 2015]; (2) each of the four representative concentration pathways (RCP8.5, RCP6.0, RCP4.5, and RCP2.6) developed for the Intergovernmental Panel on Climate Change Fifth Assessment Report [e.g., van Vuuren et al., 2011a]; and (3) a reference scenario pathway from the Global Change Assessment Model (GCAM) version 4.2 [Kim et al., 2006; Thomson et al., 2011]. Two of the above datasets represent reference case projections of future pollution control (ECLIPSE‐CLE and GCAM‐Ref), although these do differ in that the CLE scenario assumes no additional policies, while the Ref scenario assumes that additional controls are implemented as incomes increase in the future. Although we also acknowledge the contributions of other SLCFs such as ozone and methane to Arctic temperature change [e.g., Shindell et al., 2012], we do not explicitly consider those species in this analysis.

Three of the RCP scenarios (RCP6.0, RCP4.5, and RCP2.6) represent future emissions pathways that assume actions to reduce greenhouse gas emissions to reach the specified radiative forcing levels by 2100, while the fourth scenario (RCP8.5) leads to 8.5 W/m2 of radiative forcing in 2100 with forcing continuing to increase. Each of these four scenarios was developed using a different integrated assessment model (IAM)—Message for RCP8.5 [Riahi et al., 2011], the Asia‐Pacific Integrated Model (AIM) for RCP6.0 [Masui et al., 2011], GCAM for RCP4.5 [Thomson et al., 2011], and IMAGE for RCP2.6 [van Vuuren et al., 2011b]. Emissions of BC, OC, and sulfate were harmonized in the year 2000 by these four groups, but diverge after that date partly because of model differences, and partly as a consequence of different policy and technology assumptions made in order to reduce radiative forcing in the stabilization scenarios. All four RCPs assume that rising incomes will lead to more stringent air pollution controls in the future. One dataset (ECLIPSE‐MIT) illustrates strong action to limit global emissions of BC. While many of the details of these scenarios are idealized (such as assumptions of near‐term global actions to reduce GHG emissions in three RCPs, and maximum feasible reductions of BC in the ECLIPSE scenario), their use provides a wide range of near‐term results for use in this analysis. Although most of these emissions scenarios also include projections for species such as methane and nitrogen oxides, we focus our analysis on BC, OC, and sulfate as these SLCFs have the shortest atmospheric lifetimes and therefore the most immediate effects on short‐term Arctic warming.

For each of these scenarios, we estimate both present‐day, aerosol‐induced Arctic temperature change and a range of future Arctic temperature changes resulting from different assumed aerosol emissions pathways. Based on the total emissions from the different scenarios and the Arctic temperature change per unit of emissions, we also identify key combinations of regional and sectoral emissions where targeted emissions reductions could provide the largest short‐term Arctic temperature mitigation benefits.