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This study examines model-specific assumptions and projections of methane (CH4) emissions in deep mitigation scenarios generated by integrated assessment models (IAMs). For this, scenarios of nine models are compared in terms of sectoral and regional CH4emission reduction strategies, as well as resulting climate impacts. The models’ projected reduction potentials are compared to sector and technology-specific reduction potentials found in literature. Significant cost-effective and non-climate policy related reductions are projected in the reference case (10–36% compared to a “frozen emission factor” scenario in 2100). Still, compared to 2010, CH4emissions are expected to rise steadily by 9–72% (up to 412 to 654 Mt CH4/year). Ambitious CO2reduction measures could by themselves lead to a reduction of CH4emissions due to a reduction of fossil fuels (22–48% compared to the reference case in 2100). However, direct CH4mitigation is crucial and more effective in bringing down CH4(50–74% compared to the reference case). Given the limited reduction potential, agriculture CH4emissions are projected to constitute an increasingly larger share of total anthropogenic CH4emissions in mitigation scenarios. Enteric fermentation in ruminants is in that respect by far the largest mitigation bottleneck later in the century with a projected 40–78% of total remaining CH4emissions in 2100 in a strong (2 °C) climate policy case.

Japan is the sixth largest greenhouse gas emitter in 2016 and plays an important role to attain the long-term climate goals of the Paris Agreement. One of the key policy issues in Japan's energy and environmental policy arena is the energy system transition to achieve 80% emissions reduction in 2050, a current policy goal set in 2016. To contribute to the ongoing policy debate, this paper focuses on energy-related CO2 emissions and analyzes such decarbonization scenarios that are consistent with the government goals. We employ six energy-economic and integrated assessment models to reveal decarbonization challenges in the energy system. The modeling results show that Japan's mitigation scenarios are characterized by high marginal costs of abatement. They also suggest that the industrial sector is likely to have a large final energy share and significant residual emissions under the 80% reduction scenario, though it is generally thought that the transport sector would have large decarbonization challenges. The present findings imply that not only energy policy but also industrial policy may be relevant to the long-term environmental target. Given the high marginal costs exceeding those of negative emissions technologies that could place a cost ceiling, further model development would be crucial.

Integrated assessment models (IAMs) form a prime tool in informing about climate mitigation strategies. Diagnostic indicators that allow comparison across these models can help describe and explain differences in model projections. This increases transparency and comparability. Earlier, the IAM community has developed an approach to diagnose models (Kriegler (2015 Technol. Forecast. Soc. Change 90 45–61)). Here we build on this, by proposing a selected set of well-defined indicators as a community standard, to systematically and routinely assess IAM behaviour, similar to metrics used for other modeling communities such as climate models. These indicators are the relative abatement index, emission reduction type index, inertia timescale, fossil fuel reduction, transformation index and cost per abatement value. We apply the approach to 17 IAMs, assessing both older as well as their latest versions, as applied in the IPCC 6th Assessment Report. The study shows that the approach can be easily applied and used to indentify key differences between models and model versions. Moreover, we demonstrate that this comparison helps to link model behavior to model characteristics and assumptions. We show that together, the set of six indicators can provide useful indication of the main traits of the model and can roughly indicate the general model behavior. The results also show that there is often a considerable spread across the models. Interestingly, the diagnostic values often change for different model versions, but there does not seem to be a distinct trend.

In June, 2019, Japan submitted its mid-century strategy to the United Nations Framework Convention on Climate Change and pledged 80% emissions cuts by 2050. The strategy has not gone through a systematic analysis, however. The present study, Stanford Energy Modeling Forum (EMF) 35 Japan Model Intercomparison project (JMIP), employs five energy-economic and integrated assessment models to evaluate the nationally determined contribution and mid-century strategy of Japan. EMF 35 JMIP conducts a suite of sensitivity analyses on dimensions including emissions constraints, technology availability, and demand projections. The results confirm that Japan needs to deploy all of its mitigation strategies at a substantial scale, including energy efficiency, electricity decarbonization, and end-use electrification. Moreover, they suggest that with the absence of structural changes in the economy, heavy industries will be one of the hardest to decarbonize. Partitioning of the sum of squares based on a two-way analysis of variance (ANOVA) reconfirms that mitigation strategies, such as energy efficiency and electrification, are fairly robust across models and scenarios, but that the cost metrics are uncertain. There is a wide gap of policy strength and breadth between the current policy instruments and those suggested by the models. Japan should strengthen its climate action in all aspects of society and economy to achieve its long-term target. Supplementary Information The online version contains supplementary material available at 10.1007/s11625-021-00913-2.

The relatively short atmospheric lifetimes of methane (CH4) and black carbon (BC) have focused attention on the potential for reducing anthropogenic climate change by reducing Short-Lived Climate Forcer (SLCF) emissions. This paper examines radiative forcing and global mean temperature results from the Energy Modeling Forum (EMF)-30 multi-model suite of scenarios addressing CH4 and BC mitigation, the two major short-lived climate forcers. Central estimates of temperature reductions in 2040 from an idealized scenario focused on reductions in methane and black carbon emissions ranged from 0.18–0.26 °C across the nine participating models. Reductions in methane emissions drive 60% or more of these temperature reductions by 2040, although the methane impact also depends on auxiliary reductions that depend on the economic structure of the model. Climate model parameter uncertainty has a large impact on results, with SLCF reductions resulting in as much as 0.3–0.7 °C by 2040. We find that the substantial overlap between a SLCF-focused policy and a stringent and comprehensive climate policy that reduces greenhouse gas emissions means that additional SLCF emission reductions result in, at most, a small additional benefit of ~ 0.1 °C in the 2030–2040 time frame.

Macro- and sectoral-decomposition analyses were conducted using emission reduction scenarios from a global energy-system model. Emission reduction scenarios with targets of 550 ppm CO2eq and 450 ppm CO2eq, which consider variations in short-term emission fixes, up until 2030, based on extensions of the Copenhagen pledges, were selected from the AMPERE scenarios. All of the assessed emission reduction scenarios are technologically feasible through radical transformations in energy systems. Within the power sector, improvement of CO2 intensity requires wide deployment of carbon-dioxide capture and storage, nuclear power, and renewable energies. In end-use sectors, not only energy intensity improvements but also CO2 intensity improvements must be achieved by switching from fossil fuels to decarbonized energy by means of CO2 intensity improvements on the energy supply side. The feasibility of improvements in CO2 and energy intensities differs between sectors according to the types of mitigation options employed. The required carbon prices are $183/tCO2 for the 550 ppm CO2eq target and $645/tCO2 for the 450 ppm CO2eq target. When the short-term emission reduction is fixed at the level set by extensions of the Copenhagen pledges, long-term emission reductions by 2050 are more difficult to achieve because rapid and radical transformation of energy systems is required between 2030 and 2050.

This paper evaluated the impacts of climate change mitigation technology options on CO2 emission reductions and the effects of model representations regarding renewable intermittency on the assessment of reduction by using a world energy systems model. First, different diffusion scenarios for carbon dioxide capture and storage (CCS), nuclear power, and wind power and solar PV are selected from EMF27 scenarios to analyze their impacts on CO2 emission reductions. These technologies are important for reducing CO2 intensity of electricity, and the impacts of their diffusion levels on mitigation costs are significant, according to the analyses. Availability of CCS in particular, among the three kinds of technologies, has a large impact on the marginal CO2 abatement cost. In order to analyze effects of model representations regarding renewables intermittency, four different representations are assumed within the model. A simplistic model representation that does not take into consideration the intermittency of wind power and solar PV evaluates larger contributions of the energy sources than those evaluated by a model representation that takes intermittency into consideration. Appropriate consideration of renewables intermittency within global energy systems models will be important for realistic evaluations of climate change mitigation scenarios.

Technology diffusion barriers exist widely in several global warming mitigation technologies. Carbon dioxide capture and storage (CCS) is expected as a cost effective technology for ambitious CO 2 emission reduction. However, large barriers will exist when private sectors invest in CCS in the real world. In this study, a global energy systems model, which the authors refer to as DNE21+, is used to analyse this issue. Our evaluation indicates that technology diffusion barriers have a significant impact on the diffusion of CCS technology. Bottom-up type policy approach for removing the technology diffusion barriers and improvements in the liability for very long term CO 2 storage and public acceptance will be important to achieve the widespread use of CCS.

Asian countries are facing energy security issues while at the same time trying to address CO 2 mitigation. This paper analyzes the relationships between energy security and CO 2 mitigation using an energy systems model, DNE21+. The results reveal that the United States and Western Europe can reduce their CO 2 emissions while maintaining the level of energy security. In contrast, Asian countries are confronting a trade-off between energy security and CO 2 mitigation. With global CO 2 constraint, Asian countries are concentrating their energy supplies on gas imports because of smaller gas reserves and a lower capacity of carbon storage, weakening their energy security.

The objective of this paper is to address the question of what would be the real impact of energy efficiency improvements on the reduction of GHG (greenhouse gas) emissions through the deployment of energy-efficient technologies. We study the cost effectiveness of replacing current appliances with more efficient models, taking into consideration the implicit discount rate observed in people’s purchasing behavior. This is followed by a discussion of why the efficiency gap exists and how large it is. If the world were to successfully implement every negative- or zero-cost measure, the CO 2 abatement potential in the global residential and commercial sector in 2020, on a conservative estimate, would be 1.4 Gt of CO 2 , roughly equivalent to the current CO 2 emissions of India as the world fourth largest emitter. If a longer payback period is allowed, a further 1.2 Gt of opportunities, which almost amount to the current CO 2 emissions of Japan as the world’s fifth largest emitter of CO 2 , could be gained globally at below zero-cost in 2020.

This study first evaluates the pledges under the Copenhagen Accord using the DNE21+ model. Our estimates for the 2020 pledges fall collectively within the range of 46,700–49,100 Mt CO 2 -eq. Our study also finds the efforts arising from the current 2020 pledges have wide-ranging implications in terms of mitigation costs and types of actions. Based on this analysis, we seek to place the Copenhagen pledges in a long-term context, putting focus on costs and feasibility. We set up a “Carbon Prices Convergence Scenario,” assuming that all countries start from the Copenhagen commitments and gradually undertake their own individual efforts in accordance with the convergence of carbon prices toward a uniform price in 2050. Despite soaring carbon prices in most countries, total costs as share of GDP show modest increase, ranging mostly between 0% and 0.4%. We also find that there does not seem to be much difference in the degree of burden between developed and major developing countries under this scenario. Since the challenge of climate change will require significant reductions in GHG emissions in the coming decades, we need to make long lasting efforts, getting on the right track toward the ultimate goal of stabilizing GHGs.

Many of the numerous difficult issues facing the world today involve relationships entailing trade-offs and synergies. This study quantitatively assesses some alternative scenarios using integrated assessment models, and provides several indicators relating to sustainable development and climate change, such as indicators of income (per capita GDP), poverty, water stress, food access, sustainable energy use, energy security, and ocean acidification, with high consistencies among the indicators within a scenario. According to the analyses, economic growth helps improve many of the indicators for sustainable development. On the other hand, climate change will induce some severe impacts such as ocean acidification under a non-climate intervention scenario (baseline scenario). Deep emission reductions, such as to 2°C above the pre-industrial level, could cause some sustainable development indicators to worsen. There are complex trade-offs between climate change mitigation levels and several sustainable development indicators. A delicately balanced approach to economic growth will be necessary for sustainable development and responses to climate change.

Industrial energy efficiency is of paramount importance both for conserving energy resources and reducing CO2 emissions. In this paper, we compare specific energy consumption among countries in fossil power generation, steel, and cement sectors. The evaluations were conducted using common system boundaries, allocation, and calculation methods. In addition, we disaggregate within sectors, such as with blast furnace–basic oxygen furnace (BF–BOF) steel and scrap-based electric arc furnace (Scrap-EAF) steel. The results reveal that characteristics vary by sub-sector. Regional differences in specific energy consumption are relatively large in the power, BF–BOF steel, and cement sectors. For coal power generation and BF–BOF steel production, continual maintenance and rehabilitation are of key importance. We confirm these key factors identified in the previous work on our estimated numerical values. In BF–BOF steel production, corrections for hot metal ratios (pig iron production per unit of BOF crude steel production) and quality of raw materials have a large effect on the apparent specific energy consumption. Available data is not yet sufficient for straightforward evaluation of the steel and cement sectors.

This study focuses on analyses of greenhouse gas (GHG) emission reductions, from the perspective of interrelationships among time points and countries, in order to seek effective reductions. We assessed GHG emission reduction potentials and costs in 2020 and 2030 by country and sector, using a GHG emission reduction-assessment model of high resolution regarding region and technology, and of high consistency with intertemporal, interregional, and intersectoral relationships. Global GHG emission reduction potentials relative to baseline emissions in 2020 are 8.4, 14.7, and 18.9 GtCO2eq. at costs below 20, 50, and 100 $/tCO2eq., corresponding to +19, −2, and −7 %, respectively, relative to 2005. The emission reduction potential for 2030 is greater than that for 2020, mainly because many energy supply and energy-intensive technologies have long lifetimes and more of the current key facilities will be extant in 2020 than in 2030. The emission reduction potentials in 2030 are 12.6, 22.0, and 26.6 GtCO2eq. at costs below 20, 50, and 100 $/tCO2eq., corresponding to +33, +8, and −3 %, respectively, relative to 2005. Global emission reduction potentials at a cost below 50 $/tCO2eq. for nuclear power and carbon capture and storage are 2.3 and 2.2 GtCO2eq., respectively, relative to baseline emissions in 2030. Longer-term perspectives on GHG emission reductions toward 2030 will yield more cost-effective reduction scenarios for 2020 as well.

International audience This paper provides an overview of the AMPERE modeling comparison project with focus on the implications of near-term policies for the costs and attainability of long-term climate objectives. Nine modeling teams participated in the project to explore the consequences of global emissions following the proposed policy stringency of the national pledges from the Copenhagen Accord and Cancún Agreements to 2030. Specific features compared to earlier assessments are the explicit consideration of near-term 2030 emission targets as well as the systematic sensitivity analysis for the availability and potential of mitigation technologies. Our estimates show that a 2030 mitigation effort comparable to the pledges would result in a further "lock-in" of the energy system into fossil fuels and thus impede the required energy transformation to reach low greenhouse-gas stabilization levels (450 ppm CO2e). Major implications include significant increases in mitigation costs, increased risk that low stabilization targets become unattainable, and reduced chances of staying below the proposed temperature change target of 2 °C in case of overshoot. With respect to technologies, we find that following the pledge pathways to 2030 would narrow policy choices, and increases the risks that some currently optional technologies, such as carbon capture and storage (CCS) or the large-scale deployment of bioenergy, will become "a must" by 2030.

This study explores a situation of staged accession to a global climate policy regime from the current situation of regionally fragmented and moderate climate action. The analysis is based on scenarios in which a front runner coalition – the EU or the EU and China – embarks on immediate ambitious climate action while the rest of the world makes a transition to a global climate regime between 2030 and 2050. We assume that the ensuing regime involves strong mitigation efforts but does not require late joiners to compensate for their initially higher emissions. Thus, climate targets are relaxed, and although staged accession can achieve significant reductions of global warming, the resulting climate outcome is unlikely to be consistent with the goal of limiting global warming to 2 degrees. The addition of China to the front runner coalition can reduce pre-2050 excess emissions by 20–30%, increasing the likelihood of staying below 2 degrees. Not accounting for potential co-benefits, the cost of front runner action is found to be lower for the EU than for China. Regions that delay their accession to the climate regime face a trade-off between reduced short term costs and higher transitional requirements due to larger carbon lock-ins and more rapidly increasing carbon prices during the accession period., Technological Forecasting and Social Change, 90 (Part A), ISSN:0040-1625

International audience; We provide a rejoinder to a review (Rosen, 2015) of our original article "Making or breaking climate targets - the AMPERE study on staged accession scenarios for climate policy" (Kriegler et al., 2015a). We have a substantial disagreement with the content of the review, and feel that it is plagued by a number of misconceptions about the nature of the AMPERE study and the integrated assessment modeling approach employed by it. We therefore see this rejoinder as an opportunity to clarify these misconceptions and advance the debate by providing a clearer understanding of the strengths, weaknesses, and ultimately the value of integrated assessment. © 2015 Elsevier Inc.

More than half of the world's population lives in Asia, and ensuring a stable water supply is a critical issue. This study evaluates changes in the annual water withdrawal-to-availability ratio (WAR), and the major causes thereof, for each of Asian river basins under different socioeconomic development and climate change scenarios. According to our evaluation, the WAR will increase in 59%–61% of the Asian river basin areas by around 2030, as a result of population growth and the increase in per capita municipal and industrial water withdrawals. On the other hand, the WAR will decrease in 8%–16% of such areas, due to the increase in water availability associated with global warming and a decrease in per capita water agricultural withdrawal. After 2030, there will be a reduction of areas with increasing WAR because of a slowdown in the growth of both population and per capita municipal and industrial water withdrawals, while there will be an expansion of areas with decreasing WAR caused by continual decrease in per capita agricultural water withdrawal and intensified water availability. Significant measures to suppress WAR increase will differ by river basin, depending on the causes for the WAR increase. For instance, measures to deal with population increase and efforts to improve industrial and municipal water use by around 2030 will be important in the Huang He river basin. In the Indus river basin, coping with the decrease in water availability after around 2030 will be important. In addition, measures to handle population increase will be necessary.

International audience; This paper uses the EMF27 scenarios to explore the role of renewable energy (RE) in climate change mitigation. Currently RE supplies almost 20 % of global electricity demand. Almost all EMF27 mitigation scenarios show a strong increase in renewable power production, with a substantial ramp-up of wind and solar power deployment. In many scenarios, renewables are the most important long-term mitigation option for power supply. Wind energy is competitive even without climate policy, whereas the prospects of solar photovoltaics (PV) are highly contingent on the ambitiousness of climate policy. Bioenergy is an important and versatile energy carrier; however--with the exception of low temperature heat--there is less scope for renewables other than biomass for non-electric energy supply. Despite the important role of wind and solar power in climate change mitigation scenarios with full technology availability, limiting their deployment has a relatively small effect on mitigation costs, if nuclear and carbon capture and storage (CCS)--which can serve as substitutes in low-carbon power supply--are available. Limited bioenergy availability in combination with limited wind and solar power by contrast, results in a more substantial increase in mitigation costs. While a number of robust insights emerge, the results on renewable energy deployment levels vary considerably across the models. An in-depth analysis of a subset of EMF27 reveals substantial differences in modeling approaches and parameter assumptions. To a certain degree, differences in model results can be attributed to different assumptions about technology costs, resource potentials and systems integration.

International audience; Energy efficiency is one of the main options for mitigating climate change. An accurate representation of various mechanisms of energy efficiency is vital for the assessment of its realistic potential. Results of a questionnaire show that the EMF27 models collectively represent known channels of energy efficiency reasonably well, addressing issues of energy efficiency barriers and rebound effects. The majority of models, including general equilibrium models, have an explicit end-use representation for the transportation sector. All participating partial equilibrium models have some capability of reflecting the actual market behavior of consumers and firms. The EMF27 results show that energy intensity declines faster under climate policy than under a baseline scenario. With a climate policy roughly consistent with a global warming of two degrees, the median annual improvement rate of energy intensity for 2010-2030 reaches 2.3 % per year [with a full model range of 1.3-2.9 %/yr], much faster than the historical rate of 1.3 % per year. The improvement rate increases further if technology is constrained. The results suggest that the target of the United Nations' "Sustainable Energy for All" initiative is consistent with the 2-degree climate change target, as long as there are no technology constraints. The rate of energy intensity decline varies significantly across models, with larger variations at the regional and sectoral levels. Decomposition of the transportation sector down to a service level for a subset of models reveals that to achieve energy efficiency, a general equilibrium model tends to reduce service demands while partial equilibrium models favor technical substitution. © 2013 Springer Science+Business Media Dordrecht.

The term sectoral approaches has come to be frequently used in forums for global warming negotiations, particularly on a future framework. In the intensified debate on a post-Kyoto framework, the establishment of an equitable framework embracing major greenhouse gas (GHG) emitters is sought and sectoral approaches have been discussed as a possible solution. This paper therefore seeks to study the background for the current call for sectoral approaches to analyse the different stances taken by Japan, the US and the EU towards them, thus identifying the features of various types of sectoral approaches and how the can actually function.

The purpose of this paper is to present a comprehensive assessment of several alternative scenarios from the perspective of sustainable development and climate change by using a highly consistent integrated assessment model. This analysis is based on our research under the Alternative Pathways toward Sustainable Development and Climate stabilization (ALPS) project, the goal of which is to provide alternative plausible future scenarios through quantification of multiple aspects of society. On the basis of estimated pathways regarding socio-economic conditions and climate change, a range of sustainable development indicators are evaluated under various climate stabilization levels