Short term policies to keep the door open for Paris climate goals

Climate policy needs to account for political and social acceptance. Current national climate policy plans proposed under the Paris Agreement lead to higher emissions until 2030 than cost-effective pathways towards the Agreements’ long-term temperature goals would imply. Therefore, the current plans would require highly disruptive changes, prohibitive transition speeds, and large long-term deployment of risky mitigation measures for achieving the agreement’s temperature goals after 2030. Since the prospects of introducing the cost-effective policy instrument, a global comprehensive carbon price in the near-term, are negligible, we study how a strengthening of existing plans by a global roll-out of regional policies can ease the implementation challenge of reaching the Paris temperature goals. The regional policies comprise a bundle of regulatory policies in energy supply, transport, buildings, industry, and land use and moderate, regionally differentiated carbon pricing. We find that a global roll-out of these policies could reduce global CO2 emissions by an additional 10 GtCO2eq in 2030 compared to current plans. It would lead to emissions pathways close to the levels of cost-effective likely below 2 °C scenarios until 2030, thereby reducing implementation challenges post 2030. Even though a gradual phase-in of a portfolio of regulatory policies might be less disruptive than immediate cost-effective carbon pricing, it would perform worse in other dimensions. In particular, it leads to higher economic impacts that could become major obstacles in the long-term. Hence, such policy packages should not be viewed as alternatives to carbon pricing, but rather as complements that provide entry points to achieve the Paris climate goals.


Introduction
The Paris Agreement aims to collectively hold warming to well below 2 • C and pursue efforts to limit warming to 1.5 • C through progression of nationally determined climate policy plans (called nationally determined contributions, or NDCs). Nevertheless, countries have already raised their concern that the current NDCs would only slow the growth of global greenhouse gas (GHG) emissions and that short term ambition would need to be ratcheted up swiftly in order to keep the longterm goals in reach (UNFCCC 2015). This concern was further supported by recent analyses (Rogelj et al 2016). Following an NDC trajectory until 2030 would imply larger mitigation challenges in terms of the need for even faster and deeper emissions reductions after 2030 in view of an increased carbon lock-in compared to cost-effective well below 2 • C scenarios (Riahi et al 2015, Fawcett et al 2015.
Ratcheting up NDCs requires identifying concrete policies that could be effectively implemented in the real world. Economic theory has frequently emphasized the importance of carbon pricing as the leastcost policy to achieve emission reductions (Edenhofer et al 2015). However, climate policy needs also to be socially and politically acceptable while providing credible long-term pathways for climate stabilization (Vogt-Schilb and Hallegatte 2017). This requires to take into account other societal objectives, such as reducing local air pollution, in the policy choice. Implementing a carbon price alone would entail clearly visible costs that would immediately affect specific actors such as energy-intensive industries. Such actors might have the power to veto necessary policy reform and undermine the political feasibility of carbon pricing (Trebilcock 2014, Jenkins 2014. This may compel governments to look for alternative mitigation policies that may be politically more feasible but economically more costly. Despite their importance for policymakers, rigorous analyses of politically feasible policies to strengthen the NDCs to keep the Paris climate goals in reach is limited (den Elzen et al 2015, Fekete et al 2015, IEA 2015, and in the context of the 1.5 • C limit practically absent. This study investigates how rolling out a set of existing 'good practice' policies, as well as additional policies aiming to achieve carbon neutrality in individual sectors ('net zero' policies), would strengthen emissions reductions until 2030 and serve as entry points for achieving the Paris temperature goals. The novel element is to integrate such detailed policy packages until 2030 into pathways that reach longterm targets until 2100 using an integrated assessment modelling framework. This allows us to evaluate the consistency of these policy packages with the long-term Paris ambition, including to what extent they keep the door open for limiting warming to 1.5 • C (Rogelj et al 2015). Specifically, we assess how multiple dimensions that influence medium-to long-term political feasibility (Gambhir et al 2017), including transition speed, scale, and disruptiveness, are affected by the choice of short-term policy package until 2030 and the availability of carbon dioxide removal (CDR) measures.

Methods
We use a global multi-sector, multi-region integrated assessment modelling (IAM) framework, REMIND-MAgPIE (Popp et al 2014, Luderer et al 2015, Kriegler et al 2017 to assess the extent to which the strengthening of NDCs with additional policy packages would help keeping the Paris temperature goals within reach. The IAM framework consists of the energyeconomy-climate model REMIND (Bauer et al 2008, Leimbach et al 2010a, 2010b, Luderer et al 2013 coupled to the land-use model MAgPIE (Lotze-Campen et al 2008, Popp et al 2010. Both models cover the globe with 11 regions and run scenarios until the year 2100. Further details of the modeling framework can be found in the supplementary material, section S3 available at stacks.iop.org/ERL/13/ 074022/mmedia. Scenario design: in this study, we compare 13 climate policy scenarios which all assume middle-ofthe road socio-economic developments as described in Shared Socio-Economic Pathway 2 (SSP2) (Riahi et al 2017). The scenarios are differentiated along the three dimensions of near-term policy, long-term climate target and CDR availability (see table 1 for an overview of the scenario set).
The scenario set considers four different cases of near-term policy developments. The two benchmark cases of moderate and high near-term ambition are commonly used mitigation scenario designs (Fawcett et al 2015). They comprise a scenario following the conditional NDCs until 2030 and thereafter transitioning to global carbon pricing towards the Paris goals (called 'NDCs' in the following), and a scenario with a near-term phase-in (2020-2040) of cost-effective global carbon pricing to reach the Paris goals without pursuing additional policies as suggested in the NDCs ('Cost-effective pricing'). The cost-effective pricing scenario shows greater emissions reductions until 2030 due to the earlier adoption of global carbon price levels in line with the Paris goals (supplementary material figure S2). Such scenarios have been used as near-cost-optimal benchmark to evaluate the emissions gap of the NDCs (UNEP 2016). The other two near-term policy cases explored in this study represent intermediate levels of near-term ambition. These policy scenarios pursue 'Good Practice' and 'Net Zero' policy packages, respectively, on top of the conditional NDCs until 2030 and thereafter transition to cost-effective global carbon pricing to reach the Paris temperature goals. The formulation of the two policy packages is motivated below.
The NDC scenarios as well as the Good Practice and Net Zero scenarios assume that until 2030, all countries follow their respective mitigation targets and anticipate a continuation of national ambition level afterwards, and only from 2035 onwards act with full foresight towards the long-term target. Cost-effective pricing scenarios already allow for anticipation of the long-term climate target after 2020.
We consider two different long-term climate goals in the scenario design. 2 • C targets are implemented as a bound on cumulative total CO 2 emissions from 2011-2100 of 1000 GtCO 2 , implying a high likelihood (>66%) of staying below 2 • C if non-CO 2 GHGs are Table 1. Overview of the scenario set that is differentiated along the three dimensions of near-term policy (horizontal), as well as long-term climate target and CDR availability. Please note that the three 1.5 • C scenarios with limited CDR and less than optimal short-term policies cannot be solved within our modeling framework, as even with diverging high carbon prices the long-term budget is exceeded.
Cost-effectice-1.5 • C-redCDR mitigated in line with CO 2 (Clarke et al 2014). 1.5 • C targets are implemented as a more stringent bound of 400 GtCO 2 , implying a greater than 66% likelihood of holding 2100 temperatures below 1.5 • C, but allowing for temporary overshoot of this temperature limit (Luderer et al 2018). Each of the two CO 2 budget are achieved by iteratively adjusting a global carbon price that is assumed to grow with 5% p.a. until 2060 and linearly thereafter. Regionally fragmented carbon prices in 2020 (for the cost-effective scenarios) or 2030 (for the other scenarios) converge to the globally harmonized carbon price over a 20 year period (see figure S2 in the supplementary material). GHGs other than CO 2 are priced equivalently to CO 2 throughout the 21st century based on 100 year global warming potentials from IPCC's Fifth Assessment Report.
Since the large-scale deployment of CDR technologies in deep mitigation pathways has raised a number of feasibility and sustainability concerns (Smith et al 2015), we calculated the scenarios for two different assumptions on the availability of CDR technologies. The full CDR scenarios allow the full use of the potential of afforestation and BECCS as endogeneously emerging from the REMIND-MAgPIE model. In the limited CDR scenarios, we limit the total amount of global land area available for afforestation to 375 million ha, the available purpose-grown biomass to 100 EJ yr −1 , and the maximum yearly CCS injection to 8 GtCO 2 (instead of 16 GtCO 2 in the full CDR cases).
Development of policy packages: the 'good practice' and 'net zero' policy packages identified in this study constitute a significant strengthening of the policy ambition of the NDCs. An overview of the two strengthened policy packages along with sectorlevel benchmark values are presented in table 2. The implementation of these strengthened policies is often driven by multiple factors including social, economic, competitiveness and development-related factors in addition to climate policy considerations. Since many of these policies include a broader set of priorities than GHG abatement, they supplement the typical carbon pricing policies in least-cost emission scenarios (Bertram et al 2015, von Stechow et al 2015. The 'good practice' policy package assumes a global roll out of selected policies that are currently implemented successfully in some countries (Fekete et al 2015. The development of a good practice policy package for this study is an extension of (Fekete et al 2015, where benchmarks were derived for each (sub-)sector from countries that have implemented the best-in-class policies and that have resulted in significant deviation from business-as-usual emission development. By design, the good practice policy package can be regarded as implementable at least in some parts of the world because it is based on actions that some countries are already undertaking. However, policy plans and targets in some countries may not be immediately compatible with the political environment in other countries. A global roll-out of these policies would therefore need to be nationally determined and adapted to national circumstances. To this end, we assume some regional variation in the roll-out of selected policies with potentially high public costs (Inchauste and Victor 2017).
We here update and refine the 'good practice' benchmark values by examining existing policies mainly for major emitting countries, e.g. China, the EU, India, Japan and the U.S. First, existing policies were identified per (sub-)sector based on Kuramochi et al (2016) and CD-LINKS (2017), which conducted surveys to in-country experts to identify important policies for GHG emissions reductions including other relevant policies that were not primarily motivated by energy and climate policy goals. Other studies reviewed include Healy et al (2016) and den Elzen et al (2015). We then reviewed the literature on the impact of the identified policies. We also examined five-ten year historical trends of (sub-)sector-level energy and GHG emission indicators because it is often difficult, or not possible in some cases, to quantify net impact of policies. Based on this analysis, we selected policies that are effective and at the same time replicable in different parts of the world. The (sub-)sector benchmarks that are assumed achievable under the selected policies were used as 'good practice' values. Where the impact of key policies could not be directly quantified, Table 2. Overview of sector-level benchmarks under strengthened policy packages. The rationale for these benchmarks are explained in the methods section as well in the supplementary online material. Corresponding values as resulting under the NDC and least cost well below 2 • C scenarios are shown as reference and can be compared to the numbers in paranthesis for good practice and Net-zero ranges are given for benchmarks that are differentiated across regions, specifications are given in supplementary material, section S2. we selected benchmarks based on techno-economic potential studies from the literature. The 'net zero' policy package is more ambitious than the 'good practice' package, as it adds policies pushing for zero emission technologies particularly in energy end-use sectors in line with the Paris Agreement's goal to reach net zero CO 2 emissions in the second half of the century (Kriegler et al 2014, Rogelj et al 2015. It assumes global roll out of ambitious policy plans, strategies and targets that have been announced in recent years as well as a range of technoeconomic studies on deep decarbonisation pathways, and represents the level of ambition of at least some of the actors. 'Net zero' benchmark values were set only for selected (sub-)sectors that are most relevant . The selection of (sub-)sector 'net zero' policies was conducted in similar steps as with 'good practice' policies.
The result (table 2) is an indication of the rate of change that may be achievable with sector-specific policies, many of which already successfully implemented in some countries. This is different to the technical mitigation potential that is shown in other studies (UNEP 2017).
REMIND-MAgPIE implementation of policy packages: the conditional NDCs are represented in REMIND-MAgPIE by a range of sector-level targets in the energy-and land-use systems, plus regional emissions targets on total GHG excluding land-use change CO 2 emissions where applicable . In regions where the sector targets by themselves are not sufficient to meet the emissions constraint, a region-specific residual carbon price to initiate the required additional emissions reductions is imposed. The Good Practice and Net Zero policy packages also represent a range of sector-level targets, and additionally assume regionally differentiated carbon prices that exceed those resulting from the NDC emission constraints (figure S2 in the supplementary material). We decompose the effect of strengthening carbon pricing vs. strengthening sectoral policies in the supplementary material (section S1.2). Both contribute roughly equal to the strengthening of 2030 emissions reductions in the Good Practive and Net Zero cases compared to the conditional NDCs (figure S3 in the supplementary material).
All sector-specific policies in the Good Practice and Net Zero policy packages are implemented as respective lower or upper bounds or additional equations, constraining the solution space of the model. So instead of representing direct national policies (for example feed-in tariffs for renewables), the desired outcome of such policies is represented (increasing renewable shares in power generation). This approach does not yield direct insights into distributional implications of different policy instruments, or other questions of policy design (e.g. whether or not feedin tariffs, auctions, or performance standards work best for renewable support). Nevertheless, it leads to a more detailed representation of the near-term trajectories than a mere variation of carbon prices as sectoral mitigation shares are affected by the policy choice. In particular, our approach captures to what extent carbon lock-in can be avoided in the different sectors and how well upscaling of alternatives is prepared for by supporting policies. These are key features for analysing the benefits of strengthened near-term action for keeping long-term targets within reach (Bertram et al 2015).
It is important to note that efficiency targets in the buildings, transport and industry sectors are implemented by setting a maximum on total final energy use in the respective sectors. This forces the model solution away from the equilibrium energy use of the production function, leading to rather high GDP and consumption losses. These are most likely overestimated, given that some of the efficiency policies will, at least in the medium-to longer term, also have an effect on the autonomous energy efficiency improvement in these sectors which is not represented in the model.
Further information on the selection of policies as well as the translation of their impact into REMIND-MAgPIE calculations can be found in section S2 of the supplementary material. Implementability assessment: the ability to implement climate polices can be affected by a range of factors which we group in five dimensions: the speed and the scale of the transition such policies aim to induce, the disruption they cause to existing trends and patterns, their economic efficiency, and their distributional impacts on socio-economic actors. For the first four dimension we identify a small set of indicators that serve as proxies for key implementation challenges and at the same time can be meaningfully implemented in the REMIND-MAgPIE model. The fifth dimension, distributional impacts, is a critical factor for assessing the political feasibility of implementing climate policy measures. The ability of evaluating distributional impacts of mitigation pathways derived from integrated assessment models is still limited, and an active area of research (see Bauer et al (2016), for an example).
Here we look at a more narrow category, price changes for basic household goods, that are often drivers of distributional impacts.
Changes occurring at unprecedented pace (category 'speed') might entail large adjustment costs or simply overwhelm the capabilities of societies as well as legal and institutional frameworks to adapt. An obvious high-level indicator for transition speed in the energy sector is annual average emissions reduction rates from fossil fuel combustion. But, also the land use sector may face rapidly increasing demand for bioenergy and afforestation in deep mitigation scenarios.
It may be difficult to undertake large-scale changes without new strains on society and the environment (category 'scale'). Deployment of CCS has repeatedly been faced with public resistance even in the case of small-scale pilot projects. A wide variety of technically feasible CDR technologies, but also other decarbonization technologies could face similar resistance. The political acceptability of overshoot pathways relying on net negative emissions is particularly questionable in this respect. In addition, using large areas of land for afforestation or bioenergy production can be limited by sustainability concerns, such as biodiversity.
Costs that arise for concentrated interest groups, such as owners of fossil fuel reserves, coal-fired power plants, or energy intensive industries, as a result of disruptive changes in the energy system and other GHG-emitting sectors can make it politically difficult to trigger the necessary changes (Inchauste and Victor 2017) (category 'disruption'). A high-level indicator for disruptive changes is the change in CO 2 emissions growth rate from one decade to the next. In addition, we consider idle capacities of coal-fired power plants as a disruption indicator.
In terms of 'efficiency', we consider the overall macro-economic costs of mitigation policies as implied by the discounted stream of losses in household consumption. These are only direct economic costs that do not include economic benefits and co-benefits of mitigation policies from avoided damages due to reduced warming. Table 3. Overview of implementability indicators. The indicator selection is discussed in the methods section and detailed definitions are provided in section 1.3 in the supplementary material. Maxima of decadal averages are taken over the period 2020-2050 (first six indicators). Please note that a visual representation of this data that more clearly shows the relative relationships is offered in figure 3. Finally, concerns about who bears the costs of emission reductions and how quickly affected actors may be able to adapt to price increases determine whether mitigation polices are seen as equitable, which can be expected to influence their implementability (category 'price impacts'). For instance, rising food prices resulting from competition for arable land for biomass and food production could endanger food security. Energy price inceases predominantly affect low income household. We use the decadal increase in carbon prices as proxy for the price impact of climate policies. The exact definitions of the implementability indicators are described in the supplementary material.

Results
Global warming can be limited to likely below 2 • C throughout the 21st century in all four policy scenarios with both full and reduced CDR availability. Limiting warming to 1.5 • C by 2100 can also be achieved in all four policy scenarios by our modeling framework if CDR is fully available. However, when restricting CDR, 1.5 • C pathways could only be identified for the cost-effective pricing scenario introducing comprehensive carbon pricing directly after 2020. Mid-century global carbon prices are about twice as high in 1.5 • C pathways than in well below 2 • C pathways with full CDR (table S1 in the supplementary material). For both temperature goals, strengthening near term ambition from 'NDCs' to 'Net Zero' can reduce mid-century carbon prices by around 30% to levels comparable to those found in the costeffective scenarios. Restricted CDR availability rewards the strengthening of near term action more strongly and pushes 1.5 • C to the limit of what can be reached even with comprehensive carbon pricing after 2020 (Luderer et al 2013, Strefler et al 2018. Impact on emissions: the 'good practice' and 'net zero' policy scenarios provide significant additional emissions reductions in 2030 compared to the NDC scenario (figures 1 and S1). We project the NDCs to reach 43 GtCO 2 and 57 GtCO 2 equivalent emissions (including non-CO 2 GHGs) in 2030 within the range of literature estimates (Fawcett et al 2015, Rogelj et al 2016, den Elzen et al 2016, UNEP 2017, Benveniste et al 2018. The additional emissions reductions of ca. 8 GtCO 2 / 10 GtCO 2 eq in 2030 in the 'net zero'scenario (figure S3 in the supplementary material) close a large part of the emissions gap to the cost-effective scenarios in this study and the benchmark value of 40 GtCO 2 eq emissions stated in the Paris Decision (UNFCCC 2015) and based on the IPCC's Fifth Assessment Report (Edenhofer et al 2014). This is achieved with a very different policy mix than in the cost-effective carbon pricing scenarios.The mix is characterized by a substantial strengthening of technology and efficiency policies while regional carbon pricing is only moderately strengthened compared to the NDC scenario (see figure S2 in the supplementary material for regional carbon price levels in the four policy scenarios). Strengthened regulation and strengthened carbon pricing contribute roughly equal to the additional emissions reductions in 2030 (section S1.2 in the supplementary material and figure  S3). In the cost-effective pricing scenarios, emission levels fall to 30 GtCO 2 / 41 GtCO 2 eq in 2030 for the likely below 2 • C with full CDR availability, 26 GtCO 2 / 37 GtCO 2 eq for both the likely below 2 • C with restricted CDR and 1.5 • C with full CDR, and 15 GtCO 2 / 25 GtCO 2 eq for 1.5 • C with restricted CDR. One of the lowest emission pathways put forward in the literature to date reach levels of 20 Gt of CO 2 emissions in 2030 (Rockström et al 2017), in between what we obtain for the cost-effective 1.5 • C pathways with full vs. restricted CDR as well as in between the cost-effective 1.5 • C vs. 2 • C pathways with restricted CDR.
The 'Good practice' and 'Net Zero' policy scenarios mitigate the trend break in the NDC scenario between the periods 2020-2030 and 2030-2050 (figure 1, lower panel). This is also true for economic quantities like electricity sector investments (figure 2). A more steady increase in low carbon electricity investments over the next decades enhances the implementability of the electricity sector transformation compared to more rapid redirectioning of investments around 2020 (in the case of the cost-effective scenarios) or 2030 (in the case of the NDC scenario).
Implementability of pathways: we assess the political implementability of the mitigation scenarios with the indicators introduced above relating to speed, scale, efficiency, price impacts, and disruptiveness of the transition (table 2 and figure 3). They display clear trends across the four policy scenarios. The NDC scenario performs worst in almost all implementability dimensions, confirming earlier findings that a delay of mitigation action until 2030 implies disruptive changes in 2030, very large transition speeds after 2030 and substantial CDR deployment in the second half of the century to limit warming to 1.5 • C-2 • C by the end of the century (Kriegler et al 2013, Luderer et al 2013, Riahi et al 2015, Fawcett et al 2015, Strefler et al 2018. In contrast, the cost-effective pricing scenario performs best in most dimensions, with the notable exception of disruptiveness. Here it performs similar or even worse than the NDC scenario due to a rapid increase in carbon prices during the period 2020-2030. The 'Good practice' and 'Net zero' scenarios are less disruptive than both the 'NDC' (in 2030) and 'Cost effective' scenarios (see also the example of annual changes in investments in renewable power technologies, supplementary material section S.1.3.2). This points to their ability to smooth transitional breaks and serve as entry points to ratcheting up climate policy plans. However, they score less favorable than cost-effective pricing in other dimensions. While 'Good practice' and in particular 'Net zero' can mitigate the impact of delay on transition speeds compared to the 'NDC' scenario, they still require higher maximum decadal emissions reduction rates in the energy sector, faster expansion of land for afforestation and bioenergy crops, and higher CO 2 prices increases than the cost-effective scenarios. This finding holds also for the annual increase in renewable power deployment (supplementary material, section S.1.3.2). A less pronounced picture emerges for the scale indicators. While cumulative CCS use is virtually unchanged across the four policy scenarios, land use for bioenergy and afforestation and in particular the cumulative amount of net negative emissions, and thus the degree of temperature overshoot, varies from 'NDC' (highest) to 'Cost effective' (lowest). However, 'Net Zero' performs almost equally well than 'cost-effective' scenarios for likely below 2 • C, only for 1.5 • C does it lead to higher net negative emissions and land use.
The 'Good practice' and 'Net zero' scenarios also mitigate the price impacts compared to the NDC scenario, even though maximum food and carbon price increases in a single decade are still higher than in the cost-effective scenario. Notably, the two regulatory policy scenarios have similar or-in the case of 2 • C with full CDR-even higher macro-economic costs than the NDC scenario. This highlights the fact that regulatory policies can lead to lower distributional challenges associated with direct price impacts even though they incur higher macro-economic costs (Bertram et al 2015).
These rankings are robust across the three cases of the likely below 2 • C limit with full and restricted CDR availability and the 1.5 • C limit with full CDR availabilty. In general, restricting CDR availability limits-by definition-cumulative CCS and net negative emissions (scale), but increases the magnitude of    (see table 2 for definitions and temporal scope). Axes are scaled from 0 (origin) to the maximum indicator value across all scenarios specified below the indicator name. Axes are grouped according to indicator categories (see colour legend). Please note that the same data is provided in table 2 in terms of absolute values. the transition speed and disruptiveness indicators, in the cases of food and carbon prices by more than a factor of two. The food price result is counterintuitive and due to the fact that continued strong demand for biofuels keeps land demand at similar levels as for unrestricted CDR, while higher emissions prices impose an additional penalty on agricultural production (Stevanović et al 2017).
Implementation challenges of 1.5 • C pathways are larger than for likely below 2 • C pathways in all dimensions, particularly concerning scale (50%-60% more land demand for BECCS and afforestation and 110%-180% more net negative emissions) and speed (30%-70% higher maximum increase in land demand per decade for BECCS and afforestation and 30%-40% higher maximum emissions reduction rate). Generally, we find the differences in implementation challenges between 1.5 • C-2 • C to be larger than the effect of different near-term policy stringency. The benefit of strengthening early action with the 'good practice' and 'net zero' policy packages increases for restricted vs. full CDR availability and for 1.5 • C vs. likely below 2 • C particularly with regard to rapid trend breaks in CO 2 emissions (disruptiveness).

Discussion and conclusions
We find that the 'Good practice' and 'Net Zero' policy packages to strengthen the NDCs could provide a bridge towards achieving the ambition of the Paris Agreement. Although economy wide carbon pricing would be the economically most efficient policy to achieve emission reductions, it could be politically difficult to implement in the short term, for instance due to stranded assets and job losses in some sectors resulting from a strong increase of carbon prices. The policy packages consisting of a range of measures and sector targets may be favoured because of less direct visibility of mitigation costs as well as policy makers' experience with or ideological preference for non-market policies (Drews and Bergh 2016). Combinations of different policies and sector targets, such as the packages described above, could hence facilitate the implementation of the Paris Agreement. They would lead to fewer disruptive changes with less distributional implications, slower transition speeds, lower land demand and lower overshoot than following the NDCs until 2030. Without such near term strengthening of the NDCs, the temperature goals of the Paris Agreement may be no longer in reach in 2030. The policy packages might also serve to achieve a broader set of sustainable development objectives that are central for real-world policy-making (Jakob andSteckel 2016, von Stechow et al 2016).
However, with increasing ambitions the lower economic efficiency of such policy packages can be expected to aggravate the trade-offs between economic efficiency and political feasibility and become a major obstacle for the implementation of climate policies. This trade-off can be reduced if successful short-term policies result in ambitious long-term carbon pricing schemes. Hence, they should be regarded as entry points and complements to carbon pricing, not as viable alternatives in the long-term.
The study presented here is only a first step in connecting the analysis of mitigation pathways towards the Paris climate goals with an assessment of the implementability of near to medium term (2020-2050) climate action that would be consistent with these pathways. More research will be needed to better describe distributional impacts in mitigation pathways and to consolidate a set of meaningful implementability indicators for evaluating the scope of climate policies to initiate deep emissions reductions. A strengthening of current climate policy plans will be needed to keep the door open for reaching the Paris climate goals. Thus, the identification of climate policy portfolios that can serve as entry points to deep mitigation pathways is critical. Here we have shown that ambitious regulatory policy packages in combination with initially moderate, but increasingly ambitious carbon pricing could be a candidate for such entry points. Much will depend on the extent to which the climate policy portfolios can be tailored to address a broader set of sustainable development goals beyond limiting future climate change.