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ERROR: type should be string, got "https://doi.org/10.1007/s10584-019-02490-x\nClimatic Change (2020) 162:1913–1927 https://doi.org/10.1007/s10584-019-02490-x\nClimatic Change (2020) 162:1913–1927 Ken Oshiro, et al. [full author details at the end of the article] Received: 31 October 2017 /Accepted: 4 July 2019\n# The Author(s) 2019\n/Published online: 20 July 2020 This article is part of a Special Issue on 'National Low-Carbon Development Pathways' edited by Roberto\nSchaeffer, Valentina Bosetti, Elmar Kriegler, Keywan Riahi, Detlef van Vuuren, and John Weyant.\nElectronic supplementary material The online version of this article (https://doi.org/10.1007/s10584-019-\n02490-x) contains supplementary material, which is available to authorized users. Abstract This study assesses Japan’s mid-century low-emission pathways using both national and global\nintegrated assessment models in the common mitigation scenario framework, based on the\ncarbon budgets corresponding to the global 2 °C goal. We examine high and low budgets, equal\nto global cumulative 1600 and 1000 Gt-CO2 (2011–2100) for global models, and 36 and 31 Gt-\nCO2 (2011–2050) in Japan for national models, based on the cost-effectiveness allocation\nperformed by the global models. The impacts of near-term policy assumption, including the\nimplementation and enhancement of the 2030 target of the nationally determined contribution\n(NDC), are also considered. Our estimates show that the low budget scenarios require a 75%\nreduction of CO2 emissions by 2050 below the 2010 level, which is nearly the same as Japan’s\ngovernmental 2050 goal of reducing greenhouse gas emissions by 80%. With regard to near-\nterm actions, Japan’s 2030 target included in the NDC is on track to meet the high budget\nscenario, whereas it is falling short for the low budget scenario, which would require emission\nreductions immediately after 2020. Whereas models differ in the type of energy source on\nwhich they foresee Japan basing its decarbonization process (e.g., nuclear- or variable renew-\nable energy-dependent), the large-scale deployment of low-carbon energy (nuclear, renewable,\nand carbon capture and storage) is shared across most models in both the high and low budget\nscenarios. By 2050, low-carbon energy represents 44–54% of primary energy and 86–97% of\nelectricity supply in the high and low budget scenarios, respectively. Keywords Carbon budget . Integrated assessment model . Mitigation . Nationally determined\ncontribution . Paris agreement 1 Introduction The Paris Agreement sets a goal to limit the average global temperature increase to well below\n2 °C and to pursue efforts to limit the rise to 1.5 °C above pre-industrial levels. However,\naccording to several studies that have been performed using integrated assessment models 1914 Climatic Change (2020) 162:1913–1927 (IAMs), the collection of greenhouse gas (GHG) emissions implied by the nationally deter-\nmined contributions (NDCs) is not on track with the optimal pathways toward the 2 °C goal\n(Rogelj et al. 2016; van Soest et al. 2017b; Vandyck et al. 2016). In particular, Fujimori et al. (2016a) emphasize the effectiveness of the review and revision of current NDCs in Asian\ncountries. In addition, since the Paris Agreement parties are encouraged to formulate long-term\nlow-emission development strategies, some parties have already submitted their mid-century\nstrategies, including the emission reduction target by 2050. Some national and regional IAMs\nhave been utilized to assess the NDCs and national mid-century pathways (Iyer et al. 2017;\nPye et al. 2017). y\nJapan was the sixth-largest emitter of GHGs in 2016, accounting for about 3% of global\nemissions, with about 88% of national GHG emissions being CO2 (Olivier et al. 2017). Japan’s\nenergy and climate policies were reformed after the nuclear accident in 2011 (see International\nEnergy Agency 2016 for more detail), and Japan has set its NDC target to a GHG emissions\nreduction of 26% below the 2013 level by 2030, with the long-term goal of an 80% GHG\nemissions reduction by 2050. National IAMs have assessed the ambition of these national\ngoals (Akimoto et al. 2015; Kuramochi et al. 2017; Masui et al. 2014; Sano et al. 2016), and\nsome of them have explored the feasibility of enhancing this ambition (Oshiro et al. 2017). Sugiyama et al. (2019) employed multiple Japanese IAMs and explored the sectoral mitigation\nchallenges to achieve the long-term decarbonization goal in Japan. These exercises are useful\nin that they are based on a bottom–up analysis that considers the national context; however,\nthey are generally performed based on the national target expressed as an annual emission\nreduction. Thus, their implications for the national decarbonization strategy in the context of\nthe global climate goals of the Paris Agreement are still unclear. 2.1 Models Seven global IAMs and two national IAMs covered by the CD-LINKS1 project were included\nin this study (Electronic Supplementary Material [ESM] Table S1). Although there are several\nnational models in Japan, two models, namely AIM/Enduse[Japan] (Oshiro and Masui 2015)\nand DNE21+ (Akimoto et al. 2010; RITE 2015) were selected in this study because of their\ntime horizons corresponding to the mid-century pathways and experiences in the international\nmodel intercomparison project that focused both on the NDC and the national 2050 target in\nJapan (Akimoto et al. 2015; Spencer et al. 2015). For the global models, namely AIM/CGE\n(Fujimori et al. 2017a, b), COPPE-COFFEE (Rochedo 2016), DNE21+, GEM-E3 (Capros\net al. 2014; E3MLab 2017), IMAGE (Stehfest et al. 2014; van Vuuren et al. 2017), POLES\n(Keramidas et al. 2017), and REMIND-MAgPIE (Kriegler et al. 2017), we included as many\nmodels as possible so as to consider uncertainties in the national mid-century low-emission\npathways in the context of the 2 °C goal. Whereas this study focuses mainly on the emission\npathways by 2050 in Japan, the global models cover the second half of this century to assess\nthe carbon budget associated with the 2 °C goal (see Section 2.2). The models differ in terms\nof model type and solution algorithm as well as regional coverage. As shown in ESM\nTable S1, most intertemporal models simply considered the budgets constraint, while the\nrecursive dynamic models assumed emission or carbon tax trajectory over time. Because\nDNE21+ performs both national and global analyses under different scenario protocols, the\nmodel versions are referred to as DNE21+ (national) and DNE21+ (global) throughout this\nstudy. 1 CD-LINKS: Linking Climate and Development Policies—Leveraging International Networks and Knowledge\nSharing (www.cd-links.org) 1 Introduction In addition, we explored the implications of mid-century national mitigation\nstrategies in the context of the long-term climate goals mentioned in the Paris Agreement. national emission pathways and the global climate goal was considered. The most recent\nnational policies in Japan, including the implementation of the NDC and other related policies\non energy mix, were also taken into consideration so as to inform the global stocktake\nprocedure. In addition, we explored the implications of mid-century national mitigation\nstrategies in the context of the long-term climate goals mentioned in the Paris Agreement. 1 Introduction Given the country’s share of the global GHG emissions, several global IAMs include Japan\nas one individual region, and these have explored the level of national emissions that would\ncorrespond to the global 2 °C goal (Akimoto et al. 2010; Fujimori et al. 2016b; Luderer et al. 2012; van Ruijven et al. 2012; van Sluisveld et al. 2013). Previously, the Asian Modeling\nExercise provided the implications for national mid-century emissions pathways for Asian\ncountries, including Japan, based on multi-model intercomparison. Calvin et al. (2012) shows\nthe range of CO2 emissions in Japan among the different IAMs. However, very stringent\nmitigation scenarios, such as those implied by the well-below 2 °C goal, were not considered. More recently, van Soest et al. (2017a) assessed the emission pathways in 11 major economies,\nincluding Japan, using global models, and indicated that the national emission pathways\nestimated vary significantly across models. Aldy et al. (2016) explored economic impacts of\nthe NDCs in the seven major economies, including Japan, by using multiple global models,\nand indicated that economic impact varies among models. Although the results of these studies\nare useful to gain an understanding of the uncertainties in national low-emission pathways\ncorresponding to the global mitigation target, it is necessary to study their impact on national\nenergy system and mitigation costs more explicitly in order to inform national mid-century\nstrategy in the context of the Paris Agreement. On the other hand, the national scenario assessments have been conducted based on\nframeworks that did not consider the harmonization between national and global models. In\nthis study, we bridge the gap by assessing mid-century low-emission pathways in Japan,\nlinking the scenarios from multiple global and national IAMs in a common scenario frame-\nwork, with the aim to inform the national mid-century strategy in the context of the global 2 °C\ngoal. The long-term carbon budgets were used as a boundary condition to link the scenarios\nderived from national models with those of global models so that the consistency between the Climatic Change (2020) 162:1913–1927 1915 national emission pathways and the global climate goal was considered. The most recent\nnational policies in Japan, including the implementation of the NDC and other related policies\non energy mix, were also taken into consideration so as to inform the global stocktake\nprocedure. 2.2 Carbon budgets In this study, we used the carbon budget as the boundary condition to link the scenarios\nof global and national models in accordance with the modeling protocol of CD-LINKS. The global models used global carbon budgets of 1600 and 1000 Gt-CO2, including\nagriculture, forestry, and other land use (AFOLU) emissions between 2011 and 2100,\nwhich roughly correspond to a 50 and 67% chance, respectively, of keeping the temper-\nature increase below 2 °C by the end of this century (Luderer et al. 2018). The national\nmodels used the national budgets between 2011 and 2050, which were set at 36 and 31\nGt-CO2, respectively, based on the global models results under a cost-effective allocation\nand the discourse between the national and global modeling teams. Because most of CO2\nwas emitted by energy and industrial processes in Japan (United Nations Framework 1916 Climatic Change (2020) 162:1913–1927 Convention on Climate Change 2017), the national budgets include CO2 emissions from these\nsectors. Although non-CO2 emissions are not constrained explicitly, CO2 equivalent prices are\nimplemented for the emissions of non-CO2 gases as well. It should be noted that carbon budgets\nin this study are derived from only the global models’ result and, therefore, they are not\nassociated with specific climate policies in Japan or with the consequences of international\nnegotiations. Also, the national budgets may vary with different effort-sharing schemes. Although this study does not focus on these areas in detail, Van den Berg et al. (2019) do\nexplore extensively national budgets and pathways under several effort-sharing schemes. 2.3 Scenario design In order to incorporate the most recent national policies, including the NDC, and the global\nlong-term mitigation goal in the context of the Paris Agreement, seven scenarios were\nexamined based on the near-term emissions conditions and the long-term high and low budgets\n(Table 1). For near-term policy dimensions, a reference scenario without any explicit climate policies\n(NoPOL) and following two policy scenarios were examined. National Policies implemented\n(NPi) took the current energy and climate policies until 2020 into consideration, whereas this\nscenario has no explicit emission constraints in the near-term. NDC considered policies\nadditional to those represented in NPi, which reflect policies or targets included in Japan’s\nNDC until 2030 as well as the emissions reduction target by 2030. In the NPi and NDC\nscenarios, there was a protocol specifying that the rates of emissions reductions relative to the\nNoPOL or NPi scenarios in 2030 should be kept constant after 2030. For the technological conditions, the most recent national energy and climate policies were\nconsidered based on the CD-LINKS climate policy database (NewClimate Institute et al. 2016). For example, in the NDC and NDC1600/1000 scenarios, most models included the\nnational 2030 target, which is to increase the share of nuclear and renewable energy to 20–\n22% and 22–24% of total electricity generation, respectively. However, given the uncertainties\nof policy perspectives, especially those for nuclear power in Japan, the assumptions on the\ntechnological conditions were not fully harmonized so as to be able to consider several options\nand possibilities for energy system transformation. The detailed assumptions by the models are\nsummarized in ESM Table S3. Assumptions regarding socio-economic conditions were also\nnot fully harmonized in order to reflect both structural and parametric uncertainties to a range\nof the results. 2.3 Scenario design For example, the assumed population and economic growth differed across Table 1 Scenario design based on the near-term emissions conditions and the long-term budgets\nNear-term policies\nLong-term CO2 budgets\nNone\nHigh\nLow\nNo policy\nNoPOL\n–\n–\nNPi\nNPi\nNPi1600\nNPi1000\nNDC\nNDC\nNDC1600\nNDC1000\nNoPOL Reference scenario without any explicit climate policies, NPi National Policies implemented, NDC\nnationally determined contribution\nTh hi h\nd l\nb d\nt\nl t\n1600\nd 1000 Gt CO\nti\nl\nb t\n2011\nd 2100 f\nth Table 1 Scenario design based on the near-term emissions conditions and the long-term budgets The high and low budgets are equal to 1600 and 1000 Gt-CO2, respectively, between 2011 and 2100 for the\nglobal models, and between 36 and 31 Gt-CO2, respectively, between 2011 and 2050 for the national modelsy 1917 Climatic Change (2020) 162:1913–1927 models. A large gap was observed between the national and global models because the global\nmodels refer to other scenario frameworks, such as shared socio-economic pathways, while\nnational models refer to the government’s official economic prospects, which are more\noptimistic for economic growth (ESM Fig. S1 Table S4). models. A large gap was observed between the national and global models because the global\nmodels refer to other scenario frameworks, such as shared socio-economic pathways, while\nnational models refer to the government’s official economic prospects, which are more\noptimistic for economic growth (ESM Fig. S1 Table S4). 3.1 Emissions The cumulative CO2 emissions over the periods of 2011–2050 and 2051–2100 among the\nmodels are shown on Fig. 1. With regard to the global models, although the median across the\nmodels is almost consistent with the national budgets, cumulative emissions between 2011 and\n2050 vary to some extent across the models. In addition, the range of cumulative emissions by\n2050 also differs by the different near-term policies. For example, cumulative emissions in the\nNDC1000 scenario were found to exceed the carbon budget in some models; therefore, this\nscenario is characterized by a deeper emission reduction in the second half of this century, and\neven the net removal of CO2 between 2051 and 2100. A discussion of the effort-sharing\nschemes in the global models and an assessment of the longer-term pathways are beyond the\nscope of this study; however, it should be noted that uncertainties remain in the number of\nnational budgets. Although the trajectories after 2050 are not the main focus of this study, the global 1000 Gt-\nCO2 budgets scenario suggests that cumulative emissions in Japan in the second half of this\ncentury need to be nearly zero. In particular, if near-term emissions follow the level of the\nNDC, the net removal of CO2 would be required in the second-half of the century in the global\n1000 Gt-CO2 scenario, which is equivalent to about 4.1 Gt-CO2 (median), because cumulative\nemissions in the first half of the century exceed the national budget by 2100. Fig. 1 Cumulative CO2 emissions from energy and industrial processes over the period of 2011–2050 and 2051–\n2100 in Japan. Boxes indicate the full ranges, while the horizontal line segments show the median values of\nglobal model results. The horizontal lines (solid and dashed) represent high and low budgets (36 and 31 Gt-CO2),\nrespectively. NoPOL Reference scenario without any explicit climate policies, NPi National Policies implement-\ned, NDC nationally determined contribution, 1600, 1000 global carbon budgets of 1600 and 1000 Gt-CO2,\nrespectively Fig. 1 Cumulative CO2 emissions from energy and industrial processes over the period of 2011–2050 and 2051–\n2100 in Japan. Boxes indicate the full ranges, while the horizontal line segments show the median values of\nglobal model results. The horizontal lines (solid and dashed) represent high and low budgets (36 and 31 Gt-CO2),\nrespectively. 3.1 Emissions NoPOL Reference scenario without any explicit climate policies, NPi National Policies implement-\ned, NDC nationally determined contribution, 1600, 1000 global carbon budgets of 1600 and 1000 Gt-CO2,\nrespectively Fig. 1 Cumulative CO2 emissions from energy and industrial processes over the period of 2011–2050 and 2051–\n2100 in Japan. Boxes indicate the full ranges, while the horizontal line segments show the median values of\nglobal model results. The horizontal lines (solid and dashed) represent high and low budgets (36 and 31 Gt-CO2),\nrespectively. NoPOL Reference scenario without any explicit climate policies, NPi National Policies implement-\ned, NDC nationally determined contribution, 1600, 1000 global carbon budgets of 1600 and 1000 Gt-CO2,\nrespectively 1918 Climatic Change (2020) 162:1913–1927 The CO2 emissions pathways in Japan over the period of 2010–2050, and their ranges\nacross the models in 2030 and 2050, are depicted in Fig. 2. The figures for total GHG\nemissions and detailed results can be found in ESM Fig. S2, Table S5 and S6. Because the\ntrend in the emission reduction from 2010 is broadly consistent between CO2 and GHGs, we\nmainly focus on CO2 emissions in this section. CO2 emissions in the NoPOL and NPi\nscenarios remain almost stable, and their reductions in 2050 from the 2010 level are 8%\n(median; full range −17 to 33%) and 14% (full range −4 to 34%), respectively. In the NDC\nscenario, CO2 emissions continue to fall after 2030 in most models, decreasing by 29% (full\nrange 10–45%) in 2050 with respect to the 2010 level. Additional mitigation efforts are required to meet the carbon budget that corresponds to the\nglobal climate objective of keeping the temperature rise below 2 °C. To meet the high budget,\nthe median CO2 emission reduction reaches 61% below the 2010 level (full range 35–74%) by\n2050. In these scenarios the emissions of total GHGs also fall by 63% (median 33–76%) (see\nESM Fig. S2). The low budget scenarios (both NDC100 and NPi1000), as well as the high\nbudget scenarios, require a substantial emission reduction, which is equivalent to a 75% (full\nrange 47–89%) reduction by 2050 below the 2010 level. As shown in ESM Fig. S2, a similar\ntrend is observed in the reduction of total GHG emissions, where the median reduction in 2050\nis 73% (range 45–91%) below the 2010 level. 2 Because Japan’s long-term goal does not specify any base-year, these numbers are not directly comparable.\nAccording to UNFCCC (2017), GHG emissions (without land use, land-use change, and forestry (LULUCF) in\nJapan accounted for about 1.27, 1.39, and 1.30 Gt-CO2-equivalents in 1990, 2005, and 2010, respectively. 3.1 Emissions This reduction is broadly similar to the national\nlong-term goal in Japan to reduce GHG emissions by 80%.2 For the sectoral CO2 emissions, while emissions from the energy demand sectors vary\nacross models, all models show rapid and significant emissions reduction in the energy\nsupply sector in 2050 (Fig. 2, bottom, ESM Fig. S3). In particular, energy supply is\nnearly decarbonized by 2050 in the low budget scenarios (median 93–97% reduction\nbelow 2010). In the energy demand sectors, the median CO2 emissions in the low budget\nscenarios are reduced by 59–64% by 2050 relative to 2010, while those in the high\nbudget scenarios are halved in this period. With regard to the near-term policy dimension, in the high budget scenarios, the\nmedian CO2 emissions in 2030 in the NPi1600 scenario (−24% below 2010) are almost\nidentical to those in the NDC1600 scenario (−23% below 2010), suggesting that Japan’s\nNDC is broadly on track to meet the emission pathway corresponding to the global 1600\nGt-CO2 budget. In contrast, given the stringency of the carbon budget in the low budget\nscenarios, median CO2 emissions in the NPi1000 scenario fall by 34% (full range 14–\n39%) by 2030, whereas the NDC1000 scenarios show a 23% reduction. Although all\nmodels explored the pathways to meet the low budget with no additional effort beyond\nthe NDC by 2030, these pathways involve a rapid emission reduction after 2030. Figure 3 shows that the average annual changes in CO2 emissions in the NDC1000\nscenario represent −5.2 and −6.1% (median) over the periods of 2030–2040 and 2040–\n2050, respectively, whereas in the NPi1000 scenario, the corresponding figures are −4.4\nand −4.7%, respectively. Consequently, the median CO2 emissions in the NDC1000\nscenario reach the same extent as those in the NPi1000 scenario by 2035, and are lower\nafter 2040 (Fig. 2). For the last half-century, Japan’s economy has experienced such\ndrastic changes only in the oil crisis in the 1970s and 1980s and in the global economic\nrecession at the end of 2000. Climatic Change (2020) 162:1913–1927 1919 Fig. 2 Top left panel shows the pathways of annual CO2 emissions from energy and industrial processes in Japan\nfor the various scenarios. Lines indicate the median values, and ranges indicate the first to third quartiles of the\nresults. The gray line indicates the historical emissions trajectory from 1990 taken from UNFCCC (2017). 3.1 Emissions The\ndotted line shows the full range of the results. Top, right panel shows the range of annual CO2 emissions in 2030\nand 2050. Boxes indicate the full range, and the horizontal line segments show the median. Plots indicate the\nresults of each model. Bottom panels show the range of sectoral direct CO2 emissions in 2030 and 2050. The\ndashed line shows the 2010 level\ng (\n) Fig. 2 Top left panel shows the pathways of annual CO2 emissions from energy and industrial processes in Japan\nfor the various scenarios. Lines indicate the median values, and ranges indicate the first to third quartiles of the\nresults. The gray line indicates the historical emissions trajectory from 1990 taken from UNFCCC (2017). The\ndotted line shows the full range of the results. Top, right panel shows the range of annual CO2 emissions in 2030\nand 2050. Boxes indicate the full range, and the horizontal line segments show the median. Plots indicate the\nresults of each model. Bottom panels show the range of sectoral direct CO2 emissions in 2030 and 2050. The\ndashed line shows the 2010 level 3.2 Energy system The empty circles shown in the right panel indicate the historical annual changes between 1970 and 2015\ntaken from European Commission’s Joint Research Centre (JRC)/Netherlands Environmental Assessment\nAgency (PBL) (2016). Changes of > 2% per year are not shown a\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\n2020−2030\n−10%\n−8%\n−6%\n−4%\n−2%\n0%\n2%\nAnnual rate of changes in CO2 emissions (%/yr) Fig. 3 Average annual rate of changes in CO2 emissions from energy and industrial processes by decade in\nJapan. The empty circles shown in the right panel indicate the historical annual changes between 1970 and 2015\ntaken from European Commission’s Joint Research Centre (JRC)/Netherlands Environmental Assessment\nAgency (PBL) (2016). Changes of > 2% per year are not shown drastic emission reductions in the energy supply sector, about 86% (full range 72–100%) and\n97% (full range 77–100%) of electricity comes from low-carbon energy sources by 2050 in the\nhigh and low budget scenarios, respectively. Especially in the low budget scenarios, electricity\nis nearly decarbonized by 2050 and, in some scenarios, net CO2 emissions from electricity\nbecome negative due to the deployment of bioenergy with CCS (BECCS). With regard to the\nnear-term, more than 60% of electricity comes from low-carbon sources in 2030 in the\nNPi1000 scenario, without depending on CCS (the share of each low-carbon energy can be\nfound in ESM Figs. S5, S6). The development of the shares of various energy sources in the primary energy supply and\nelectricity generation in the high and low budget scenarios over the period of 2010–2050 is\nshown in Fig. 4 (bottom). In both the high and low budget scenarios, fossil fuel without CCS is\nsubstituted by low-carbon energies over time; however, the share of the low-carbon energy\nsource varies among all models, both national and global. The share of nuclear and renewables\nin primary energy in 2050 ranges from 5 to 23% and from 14 to 39%, respectively, in the\nNDC1000 scenario (see ESM Table S7 for more detail). 3.2 Energy system In both the high and low budget scenarios, upscaling of low-carbon energies, including\nnuclear, renewable, and carbon capture and storage (CCS), is a key mitigation option for the\nmost models (Fig. 4, top, ESM Fig. S4). While the share of low-carbon energy accounts for\nabout 10 and 6% of the total primary energy supply in 2010 and 2015, respectively, the median\nshare in 2050 increases to 44% (full range 25–61%) and 54% (full range 42–75%) in the high\nand low budgets scenarios, respectively. In addition, the share of low-carbon energy has to be\napproximately tripled over the period of 2030–2050 both in the high and low budget scenarios. A more rapid increase is required if the emissions by 2030 follow the NDC. To achieve this Climatic Change (2020) 162:1913–1927 1920 a\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\na\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\na\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\nHistorical (1970−2015)\n2020−2030\n2030−2040\n2040−2050\n−10%\n−8%\n−6%\n−4%\n−2%\n0%\n2%\nAnnual rate of changes in CO2 emissions (%/yr)\nModel\nA\na\nC\nd\nD\nG\nI\nP\nR\nAIM/CGE\nAIM/Enduse[Japan]\nCOPPE−COFFEE\nDNE21+(national)\nDNE21+(global)\nGEM−E3\nIMAGE\nPOLES\nREMIND−MAgPIE\nScenario\nNoPOL\nNPi\nNDC\nNDC1600\nNPi1600\nNDC1000\nNPi1000\nFig. 3 Average annual rate of changes in CO2 emissions from energy and industrial processes by decade in\nJapan. Climatic Change (2020) 162:1913–1927 1921 Fig. 4 Top panels show upscaling of low-carbon energies in the primary energy supply and electricity generation\nin 2030 and 2050 in Japan. Low-carbon energies include nuclear, renewables, carbon capture and storage (CCS),\nand imported hydrogen. The dashed line shows the historical data in 2010 and 2015 taken from the International\nEnergy Agency (2017). Bottom panels show the development of the share of energy sources over the period of\n2010–2050. Empty circles indicate the share in 2010. Model markers and the shaded areas show the share in\n2050\nClimatic Change (2020) 162:1913–1927\n1921 Fig. 4 Top panels show upscaling of low-carbon energies in the primary energy supply and electricity generation\nin 2030 and 2050 in Japan. Low-carbon energies include nuclear, renewables, carbon capture and storage (CCS),\nand imported hydrogen. The dashed line shows the historical data in 2010 and 2015 taken from the International\nEnergy Agency (2017). Bottom panels show the development of the share of energy sources over the period of\n2010–2050. Empty circles indicate the share in 2010. Model markers and the shaded areas show the share in\n2050 Fig. 4 Top panels show upscaling of low-carbon energies in the primary energy supply and electricity generation\nin 2030 and 2050 in Japan. Low-carbon energies include nuclear, renewables, carbon capture and storage (CCS),\nand imported hydrogen. The dashed line shows the historical data in 2010 and 2015 taken from the International\nEnergy Agency (2017). Bottom panels show the development of the share of energy sources over the period of\n2010–2050. Empty circles indicate the share in 2010. Model markers and the shaded areas show the share in\n2050 the final energy consumption by 2050. The buildings sector is characterized by a large-scale\ndeployment of low-carbon energies; especially in the low budget scenarios this accounts for almost\n80% by 2050, while energy demand reduction is moderate in this sector. 3.2 Energy system Some models are characterized by the\nconservative assumption of nuclear and CCS accounting for ≤20% of the primary energy\nsupply, together with a dependency on renewables. In contrast, other models depend largely on\nnuclear and/or CCS, while the share of renewables in the primary energy supply remains at <\n20% in 2050. The detailed results on the low-carbon energy share can be found in ESM\nTables S7 and S8. The range of the share of CCS is relatively wider compared with other\nenergy sources in 2050, reflecting the different assumptions among models. The change in the energy demand from 2010 onward and the share of low-carbon carriers are\nsummarized in Fig. 5 and ESM Fig. S7–S9. Although the final energy consumption varies greatly\nacross the models, the median drops to 20 and 26% in the high and low budget scenarios,\nrespectively, by 2050. In particular, a large-scale reduction in energy demand is observed in\ntransportation sector by 2050 (median−41% below 2010 in low budget scenarios). In addition, the\nshare of low-carbon carriers, such as renewables, electricity, hydrogen, and heat, is increased with\nthe more stringent carbon budget in 2050. In the low budget scenarios, this share exceeds half of Climatic Change (2020) 162:1913–1927 3.3 Mitigation costs The relationship between carbon prices and emission reductions in 2050 relative to those in\n2010, and the net present value (NPV) of mitigation costs expressed as a fraction of the\nbaseline gross domestic product (GDP) for the period of 2021–2050 are shown in Fig. 6. 3.3 Mitigation costs Although carbon prices of each model should not be directly compared because the level of\nemission reduction in 2050 is different depending on the model, the stringency of the carbon Climatic Change (2020) 162:1913–1927 1922 a\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\na\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\n2030\n2050\n0.0\n0.2\n0.4\n0.6\n0.8\n1.0\n1.2\n1.4\nFinal energy consumption (2010=1)\nFinal energy, indexed to 2010\na\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\na\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\n2030\n2050\n0%\n20%\n40%\n60%\n80%\n100%\nShare of low−carbon carrier (%)\nShare of low−carbon energy carrier\na\ndAI\nP\nC\nD\nR\na\ndAI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR\na\nd\nA\nI\nP\nC\nD\nR\na\nd\nA\nI\nP\nC\nD\nRG\na\nd\nA\nI\nP\nC\nD\nRG\nad\nA\nI\nPCDR\na\nd\nA\nI\nPCDR\nG\na\nd\nA\nI\nPCDRG\na\nd\nA\nI\nPC\nD\nR\na\nd\nA\nI\nPC\nD\nR\na\nd\nA\nI\nPCD\nR\nG\na\nd\nA\nI\nPCDR\nG\na\nd\nA\nI\nP\nC\nD\nR a\nd\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR a\nd\nA\nI\nP\nC\nD\nR\nad\nA\nI\nP\nC\nD\nR\nG\nad\nA\nI\nP\nC\nD\nR\nG\nIndustry\nBuildings\nTransportation\n0.0\n0.2\n0.4\n0.6\n0.8\n1.0\n1.2\n1.4\nFinal energy consumption (2010=1)\nad\nA\nI\nP\nC\nD\nR\nad\nA\nI\nP\nC\nD\nR\nG\nad\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nIP\nC\nD\nR\nad\nA\nI\nP\nC\nD\nR\na\nd\nA\nIP\nC\nD\nRG\na\ndAIP\nC\nD\nRG\na\ndA\nI\nP\nCD\nR\na\ndA\nI\nP\nCD\nR\nG a\nd\nAI\nP\nCD\nRG a\nd\nA\nI\nP\nC\nD\nR a\nd\nA\nI\nP\nC\nD\nR\na\nd\nA\nI\nPC\nD\nR\nG\na\nd\nA\nI\nPC\nD\nR\nG\nad\nA\nI\nPC\nDR a\nd\nA\nI\nPC\nDRG\na\ndA\nI\nPCDRG\na\nd\nA\nI\nPCDR\na\nd\nA\nI\nPCDR\na\nd\nA\nI\nPC\nD\nR\nG\na\nd\nA\nI\nPC\nD\nR\nG\nIndustry\nBuildings\nTransportation\n0%\n20%\n40%\n60%\n80%\n100%\nShare of low−carbon carrier (%)\nModel\nA\na\nC\nd\nD\nG\nI\nP\nR\nAIM/CGE\nAIM/Enduse[Japan]\nCOPPE−COFFEE\nDNE21+(national)\nDNE21+(global)\nGEM−E3\nIMAGE\nPOLES\nREMIND−MAgPIE\nScenario\nNoPOL\nNPi\nNDC\nNDC1600\nNPi1600\nNDC1000\nNPi1000\nFig. 3.3 Mitigation costs Bottom panels show the change in final\nenergy consumption indexed to the 2010 level and share of low-carbon energy carriers by sector in 2050\nClimatic Change (2020) 162:1913–1927\n1922 a\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\na\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\n2030\n2050\n0%\n20%\n40%\n60%\n80%\n100%\nShare of low−carbon carrier (%)\nShare of low−carbon energy carrier Share of low−carbon energy carrier a\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\n2050\nd to 2010 a\na\na\na\na\na\na\nd\nd\nd\nd\nd\nd\nd\nA\nA\nA\nA\nA\nA\nA\nI\nI\nI\nI\nI\nI\nI\nP\nP\nP\nP\nP\nP\nP\nC\nC\nC\nC\nC\nC\nC\nD\nD\nD\nD\nD\nD\nD\nR\nR\nR\nR\nR\nR\nR\nG\nG\nG\nG\n2030\n0.0\n0.2\n0.4\n0.6\n0.8\n1.0\n1.2\n1.4\nFinal energy consumption (2010=1)\nFinal energy, indexed Share of low−carbon carrier (%) ad\nA\nI\nP\nC\nD\nR\nad\nA\nI\nP\nC\nD\nR\nG\nad\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nIP\nC\nD\nR\nad\nA\nI\nP\nC\nD\nR\na\nd\nA\nIP\nC\nD\nRG\na\ndAIP\nC\nD\nRG\na\ndA\nI\nP\nCD\nR\na\ndA\nI\nP\nCD\nR\nG a\nd\nAI\nP\nCD\nRG a\nd\nA\nI\nP\nC\nD\nR a\nd\nA\nI\nP\nC\nD\nR\na\nd\nA\nI\nPC\nD\nR\nG\na\nd\nA\nI\nPC\nD\nR\nG\nad\nA\nI\nPC\nDR a\nd\nA\nI\nPC\nDRG\na\ndA\nI\nPCDRG\na\nd\nA\nI\nPCDR\na\nd\nA\nI\nPCDR\na\nd\nA\nI\nPC\nD\nR\nG\na\nd\nA\nI\nPC\nD\nR\nG\nIndustry\nBuildings\nTransportation\n0%\n20%\n40%\n60%\n80%\n100%\nShare of low−carbon carrier (%) a\ndAI\nP\nC\nD\nR\na\ndAI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR\na\nd\nA\nI\nP\nC\nD\nR\na\nd\nA\nI\nP\nC\nD\nRG\na\nd\nA\nI\nP\nC\nD\nRG\nad\nA\nI\nPCDR\na\nd\nA\nI\nPCDR\nG\na\nd\nA\nI\nPCDRG\na\nd\nA\nI\nPC\nD\nR\na\nd\nA\nI\nPC\nD\nR\na\nd\nA\nI\nPCD\nR\nG\na\nd\nA\nI\nPCDR\nG\na\nd\nA\nI\nP\nC\nD\nR a\nd\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR\nG\na\nd\nA\nI\nP\nC\nD\nR a\nd\nA\nI\nP\nC\nD\nR\nad\nA\nI\nP\nC\nD\nR\nG\nad\nA\nI\nP\nC\nD\nR\nG\nIndustry\nBuildings\nTransportation\n0.0\n0.2\n0.4\n0.6\n0.8\n1.0\n1.2\n1.4\nFinal energy consumption (2010=1) Share of low−carbon carrier (%) Share of low−carbon carr Fig. 3.3 Mitigation costs 5 Range of the change in final energy consumption relative to 2010 (top, left) and the share of low-carbon\nenergy carriers in the total final energy supply (top, right) in Japan. Low-carbon energy carriers include\nelectricity, heat, and hydrogen and renewables (biomass, solar, and geothermal) in accordance with the definition\nin the Intergovernmental Panel on Climate Change (IPCC) (2014). 3.3 Mitigation costs CO2 price\nIP\nG\nadD\nAR\nIP\nG\na\nd\nD\nA\nR\nI\nP\na\nd\nD\nA\nR\nI\nP\na\nd\nD\nA\nR\nI\nP\nG\na\nd\nD\nA\nR\nI\nP\nG\nad\nD\nA\nR\n0.0%\n0.5%\n1.0%\n1.5%\n2.0%\n2.5%\n3.0%\nNPi\nNDC\nNDC1600\nNPi1600\nNDC1000\nNPi1000\n% of discounted baseline GDP\nPolicy cost indicator\nGDP Loss\nAdditional Total Energy System Cost\nEquivalent Variation\nArea under MAC Curve\nMitigation cost (NPV, 2021−2050)\nModel\nA\na\nC\nd\nD\nG\nI\nP\nR\nAIM/CGE\nAIM/Enduse[Japan]\nCOPPE−COFFEE\nDNE21+(national)\nDNE21+(global)\nGEM−E3\nIMAGE\nPOLES\nREMIND−MAgPIE\nFig. 6 Left panel shows the reduction of CO2 emissions relative to 2010 versus the price of carbon in 2050\nacross the various scenarios, and the range of the price of carbon in Japan. Right panel shows the range of the net\npresent value (NPV) mitigation costs accumulated over the period of 2021–2050 relative to the NPi scenario as a\nfraction of baseline gross national product (GDP), discounted at the rate of 5%. Mitigation costs indicators are\ndifferent among models Emissions reduction vs. CO2 price CO2 price (US$2010/t−CO2) Fig. 6 Left panel shows the reduction of CO2 emissions relative to 2010 versus the price of carbon in 2050\nacross the various scenarios, and the range of the price of carbon in Japan. Right panel shows the range of the net\npresent value (NPV) mitigation costs accumulated over the period of 2021–2050 relative to the NPi scenario as a\nfraction of baseline gross national product (GDP), discounted at the rate of 5%. Mitigation costs indicators are\ndifferent among models budget scenarios for most models, although the full range is similar with the high budget\nscenarios (0.1–2.1%). With regard to carbon price, a large gap is observed, especially among the national and\nglobal models(ESM Fig. S10a). One plausible reason for this gap is that the national models\nresult in a deeper emissions reduction in 2050, especially for AIM/Enduse[Japan], and they\nassume larger economic growth than the global models. In addition, the national model\nconsiders regional specific barriers, such as constraints on electricity interconnections across\nsub-regions in Japan for AIM/Enduse[Japan], which would exacerbate the challenge to inte-\ngrate variable renewable energies (VREs). 3.3 Mitigation costs 5 Range of the change in final energy consumption relative to 2010 (top, left) and the share of low-carbon\nenergy carriers in the total final energy supply (top, right) in Japan. Low-carbon energy carriers include\nelectricity, heat, and hydrogen and renewables (biomass, solar, and geothermal) in accordance with the definition\nin the Intergovernmental Panel on Climate Change (IPCC) (2014). Bottom panels show the change in final\nenergy consumption indexed to the 2010 level and share of low-carbon energy carriers by sector in 2050 budget has a large impact on the level of the carbon price for all models. In the high budget\nscenarios, the median carbon price is projected to be 110 US$/t-CO2 by 2050 (full range 65–\n261 US$/t-CO2) and 141 US$/t-CO2 (full rang: 36–431 US$/t-CO2) in the NPi1600 and\nNDC1600 scenarios, respectively. Although cumulative mitigation costs (NPV) over the\nperiod 2021–2050 are also not directly comparable as the models report different cost\nindicators, they range from 0.1 to 2.0% of the baseline GDP in the high budget scenarios. In contrast, to meet the more stringent carbon budget, the low budget scenarios require an\nadditional effort compared with the NDC and the high budget scenarios. The median carbon\nprice in the NDC1000 scenario rises to 497 US$/t-CO2 (full range 133–2093 US$/t-CO2) in\n2050, while in the NPi1000 scenario it represents 376 US$/t-CO2 (full range 151–1073 US$/t-\nCO2). NPV mitigation cost in the low budget scenarios also becomes higher than the high Climatic Change (2020) 162:1913–1927 1923 D GG\nP\nII\nP\nR\nD\nR\nD\nd\nd D\nA\na\nA\na\nR\nI\nA\nR\nD\nP A\nP\nI\nd\nRR\naDa\nA\nI\nGdPP\nGd\nI\na\nd\na\n0%\n20%\n40%\n60%\n80%\n0\n500\n1000\n1500\n2000\nCO2 emissions reduction from 2010\nCO2 price (US$2010/t−CO2)\nScenario\nNPi\nNDC\nNDC1600\nNPi1600\nNDC1000\nNPi1000\nEmissions reduction vs. 3.3 Mitigation costs It should also be noted that cumulative mitigation\ncosts for some global models, such as DNE21+ (global), IMAGE, and REMIND-MAgPIE, in\nthe NDC scenarios are smaller than those in the NPi scenarios, especially in the low budget\nscenarios. This is in contrast to the national models and is generally associated with the higher\ncarbon budgets in the NDC scenarios between 2011 and 2050, which are compensated for in the\nsecond half of this century in these global models (Fig. 1). Whereas the differences in the carbon\nbudget between the NDC and NPi scenarios are moderate for IMAGE, this model shows a large\ndifference in the annual mitigation costs in 2030 between the NDC1000 and NPi1000 (ESM\nFig. S10b), thus the cumulative cost in NPi1000 is still higher compared with the NDC1000. 4 Discussion and conclusion In this study we explored the low-emission pathways up to 2050 in Japan based on the\nstringent carbon budgets suggested by the 2 °C goal and the latest national climate policies\nand subsequently identified the following implications for the national mid-century strat-\negies. As shown in Fig. 2, the NDC policies are consistent with the high budget scenario, 1924 Climatic Change (2020) 162:1913–1927 effectively keeping the country on track. The low budget scenarios suggest that the\nnational 2050 goal to reduce GHG emissions by 80% can be considered to be an effective\nmilestone in the context of the global 2 °C goal because the level of emissions reduction in\n2050 in these scenarios is almost consistent with the national 2050 goal. Nevertheless, the\nmitigation effort for low budget scenarios would be significantly too weak without\nadditional mitigation action beyond the NDC after 2030. For most models,\ndecarbonization of the energy supply is observed in 2050 in the low budget scenarios. In terms of energy systems, both the national and global models suggest that a transfor-\nmation of the energy system is a key aspect of all scenarios. However, the energy sources\nmainly used for decarbonization differ across models: nuclear, CCS, or renewable ener-\ngies. Mitigation costs are generally increased in the scenarios with stringent carbon\nbudgets for most models, whereas there is a wide variety among models, especially\nbetween the national and global models. However, the following factors should be considered carefully. First, the emission pathways\nof the low budget scenarios entail huge challenges for achieving the rapid reduction of and\nassociated transformation in the energy system. For example, the rate of emissions reduction\nbetween 2030 and 2050 in the NDC1000 scenario corresponds to about 6% per year. Over the\nlast half-century, Japan’s economy has only experienced such drastic changes during the oil\ncrisis and the global economic recession. It should also be noted that increasing the mitigation\neffort in 2030 would also be challenging, requiring the integration of more VREs and the\nrestarting of nuclear power plants. For example, the NPi1000 scenario would require an\nincrease in the share of low-carbon electricity generation to more than 60% by 2030, without\ndepending on CCS. Second, there are still large uncertainties in the national budgets which were derived from\nthe global models as shown in Fig. 1. 4 Discussion and conclusion In addition, the range of the carbon budget would be\nwider when other effort-sharing schemes are considered, such as those based on equity and\ncapability; for example, national budgets result in 6–39 Gt-CO2 over the period of 2011–2050,\nwith a global carbon budget of 1000 Gt-CO2 under the various effort-sharing approaches (van\nden Berg et al. 2019). Also, emission pathways by 2050 are associated with those in the second\nhalf of this century. Although this study mainly focused on the national scenarios by 2050, it\nwould also be useful to explore the national pathways in the second half of this century when\nconsidering the possibility of large-scale negative emissions and the impact of emissions\novershoot by 2050. Third, in some indicators a gap between the national and global models is observed. For\nexample, the carbon prices in the national models tend to be higher than those in the global\nmodels. One reason for these differences would be derived from the representation of specific\ncircumstances in Japan, such as limitations in integrating VREs. This gap emphasizes the\nimportance of the further development of national model exercises, not only by using bottom–\nup models with fixed demand but also top–down models, such as AIM/CGE[Japan] and\nDEARS, that incorporate specific regional circumstances, and the utilization of these experi-\nences in the assessment of global models. Fourth, to meet the high and low budgets, it is necessary to transform the energy system as\nshown in most models’ results, while taking into account the levels of technological uncer-\ntainty in Japan. In this study, the share of renewables, nuclear, and fossil fuel CCS in primary\nenergy and electricity generation vary significantly across the models, reflecting technological\nuncertainties as well as the model structure (Fig. 4). This variation suggests that there are\nvarious options for energy system transformation in Japan that correspond to the global 2 °C Climatic Change (2020) 162:1913–1927 1925 goal. Nevertheless, several barriers remain, such as the limited potential of carbon sequestra-\ntion, the integration of VREs, the costs of these technologies, and the uncertainties regarding\nnuclear power availability. goal. Nevertheless, several barriers remain, such as the limited potential of carbon sequestra-\ntion, the integration of VREs, the costs of these technologies, and the uncertainties regarding\nnuclear power availability. References Akimoto K, Sano F, Homma T et al (2010) Estimates of GHG emission reduction potential by country, sector,\nand cost. Energy Policy 38:3384–3393. https://doi.org/10.1016/j.enpol.2010.02.012 Akimoto K, Sano F, Homma T et al (2010) Estimates of GHG emission reduction potential by country, sector,\nand cost. Energy Policy 38:3384–3393. https://doi.org/10.1016/j.enpol.2010.02.012 Akimoto K, Tehrani BS, Sano F et al (2015) MILES (Modelling and Informing Low Emissions strategies)\nproject. Japan policy paper: a joint analysis of Japan's INDC. http://www.iddri. org/Publications/Collections/Analyses/MILES_Japan%20Policy%20Paper.pdf. Accessed 11 Oct 2017 Akimoto K, Tehrani BS, Sano F et al (2015) MILES (Modelling and Informing Low Emissions strategies)\nproject. Japan policy paper: a joint analysis of Japan's INDC. http://www.iddri. org/Publications/Collections/Analyses/MILES_Japan%20Policy%20Paper.pdf. Accessed 11 Oct 2017 g\ny\n_ p\ny\np\np\nAldy J, Pizer W, Tavoni M et al (2016) Economic tools to promote transparency and comparability in the Paris\nagreement. Nat Clim Chang 6:1000–1004. https://doi.org/10.1038/nclimate3106 g\ng\np\ng\nvan den Berg N, van Soest HL, den Elzen M et al (2019) Implications of various effort-sharing approaches for\nnational carbon budgets and emission pathways. Clim Chang. https://doi.org/10.1007/s10584-019-02368-y Calvin K, Clarke L, Krey V et al (2012) The role of Asia in mitigating climate change: results from the Asia\nmodeling exercise. Energy Econ 34[Suppl 3]:S251–S260. https://doi.org/10.1016/j.eneco.2012.09.003 g\ngy\n[\npp\n]\np\ng\nj\nCapros P, Paroussos L, Fragkos P et al (2014) Description of models and scenarios used to assess European\ndecarbonisation pathways. Energ Strat Rev 2:220–230. https://doi.org/10.1016/j.esr.2013.12.008 g\ngy\npp\n]\np\ng\nj\nCapros P, Paroussos L, Fragkos P et al (2014) Description of models and scenarios used to assess Europ\nd\nb\ni ti\nth\nE\nSt t R\n2 220 230 htt\n//d i\n/10 1016/j\n2013 12 008 Capros P, Paroussos L, Fragkos P et al (2014) Description of models and scenarios used to assess European\ndecarbonisation pathways. Energ Strat Rev 2:220–230. https://doi.org/10.1016/j.esr.2013.12.008\nE3MLab (2017) GEM-E3 model m Manual http://www e3mlab ntua gr/e3mlab/GEM%20-%20E3%20 Capros P, Paroussos L, Fragkos P et al (2014) Description of models and scenarios used to assess European\ndecarbonisation pathways. Energ Strat Rev 2:220–230. https://doi.org/10.1016/j.esr.2013.12.008\nE3MLab (2017) GEM-E3 model m Manual. http://www.e3mlab.ntua.gr/e3mlab/GEM%20-%20E3%20 E3MLab (2017) GEM-E3 model m Manual. http://www.e3mla\nManual/GEM-E3_manual_2017.pdf. Accessed 19 Oct 2017 (\n)\np\nManual/GEM-E3_manual_2017.pdf. Accessed 19 Oct 2017 p\ng\nManual/GEM-E3_manual_2017.pdf. Accessed 19 Oct 2017 European Commission’s Joint Research Centre (JRC)/Netherlands Environmental Assessment Agency (PBL)\n(2016) Emission Database for Global Atmospheric Research (EDGAR), release version 4.3.2. http://edgar. jrc.ec.europe.eu. 4 Discussion and conclusion To explore the national development pathways corresponding to the global climate\ngoal, it would be effective to link the scenarios from national and global IAMs in the\ncommon framework based on a carbon budget approach. In the context of the imple-\nmentation of the Paris Agreement, these exercises would be meaningful not only for\ndeveloping the national low-emission strategy but also for developing the global\nstocktake procedure. Acknowledgements This work is part of a project that has received funding from the European Union’s\nHorizon 2020 research and innovation programme under grant agreement No. 642147 (CD-LINKS). KO, SF,\nand TM are grateful for the support of the Environment Research and Technology Development Fund (2-1702)\nprovided by the Environmental Restoration and Conservation Agency. SF is grateful for the support of the Japan\nSociety for the Promotion of Science (JSPS) KAKENHI Grant Number JP16K18177. Compliance with ethical standards Disclaimer The views expressed are purely those of the writer and may not in any circumstances be regarded as\nstating an official position of the European Commission. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International\nLicense (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and repro-\nduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a\nlink to the Creative Commons license, and indicate if changes were made. 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Affiliations Ken Oshiro1 & Keii Gi2 & Shinichiro Fujimori1,3,4 & Heleen L. van Soest5,6 & Christoph\nBertram7 & Jacques Després8 & Toshihiko Masui3 & Pedro Rochedo9 & Mark Roelfsema5 &\nZoi Vrontisi10 Ken Oshiro1 & Keii Gi2 & Shinichiro Fujimori1,3,4 & Heleen L. van Soest5,6 & Christoph\nBertram7 & Jacques Després8 & Toshihiko Masui3 & Pedro Rochedo9 & Mark Roelfsema5 &\nZoi Vrontisi10 * Ken Oshiro\nkoshiro@athehost.env.kyoto-u.ac.jp * Ken Oshiro\nkoshiro@athehost.env.kyoto-u.ac.jp * Ken Oshiro\nkoshiro@athehost.env.kyoto-u.ac.jp 1\nKyoto University, C1-3, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto, Japan 2\nResearch Institute of Innovative Technology for the Earth, 9-2 Kizugawadai, Kizugawa, Kyoto, Japan 3\nNational Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki, Japan 4\nInternational Institute for Applied System Analysis (IIASA), Schlossplatz 1, 2361 Laxenburg, Aust 5\nPBL Netherlands Environmental Assessment Agency, P.O. Box 30314, 2500 GH The Hague,\nThe Netherlands 6\nCopernicus Institute of Sustainable Development, Utrecht University, P.O. Box 80.115, 3508 TC Utrecht,\nThe Netherlands 7\nPotsdam Institute for Climate Impact Research, P.O. Box 601203, 14412 Potsdam, Germany 8\nEuropean Commission, Joint Research Centre (JRC), Calle Inca Garcilaso 3, 41092 Seville, Spain 9\nCOPPE, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco C, Sala 211, Ilha do Fundão,\nRio de Janeiro, RJ 21941-972, Brazil 10\nE3M-Lab, Institute of Communication and Computer Systems, National Technical University of Athens, 9,\nIroon Politechniou Street, 15 773 Zografou Campus, Athens, Greece"