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Income and fuel price pathways are key determinants in projections of the energy system in integrated assessment models. In recent years, more details have been added to the transport sector representation in these models. To better understand the model dynamics, this manuscript analyses transport fuel demand elasticities to projected income and fuel price levels. Fuel price shocks were simulated under various scenario assumptions to isolate price effects on energy demand and create a transparent environment to compare fuel demand response. Interestingly, the models show very comparable oil price elasticity values for the projected first 10-20. years that are also close to the range described in the empirical literature. When looking at the very long term (30-40. years), demand elasticity values widely vary between models, between 0.4 and -1.9, showing either continuous demand or increased demand responses over time. The latter can be the result of long response time to fuel price shocks, availability of new technologies, and feedback effects on fuel prices. The projected transport service demand is more responsive to changes in income than fuel price pathways, corresponding with the literature. Calculating the models' inherent elasticities proved to be a suitable method to evaluate model behaviour and its application is also recommended for other models as well as other sectors represented in integrated assessment models.

Nuclear is considered as a valuable option for the decarbonization of power generation, as it is a no-carbon, yet commercially consolidated technology. However, its real prospects are uncertain, especially in the OECD countries. The main aim of this work is to explore the techno-economic implications of policy-relevant scenarios for nuclear power, designed on the actual prospects in the world regions and developed with the Integrated Assessment Model WITCH. The analysis shows that nuclear generation constantly grows over the century, even if in general the nuclear share in the global electricity mix does not significantly change over time. If constraints are applied to nuclear deployment, the contribution of this technology is compensated by renewables (mainly wind and solar PV) and, to a lower extent, by CCS. The policy costs related to nuclear phase-out are moderate, as they are almost completely compensated by innovation and technology benefits in renewables and energy efficiency. Phase-out policies applied only to the OECD regions do not entail any additional policy costs in these regions, while non-OECD regions marginally benefit from lower uranium prices.

Meeting the targets of climate change mitigation set by the Paris Agreement entails a huge transformation of the energy sector, as low- or no-carbon technologies must gradually substitute traditional, fossil-based technologies. In this perspective, the vast majority of energy analyses and scenarios project a fundamental role of Carbon Capture & Storage (CCS). However, uncertainty remains on the actual techno-economic feasibility of this technology: despite the considerable investment over the recent past, commercial maturity is yet to come. The main aim of this work is to evaluate the impacts of a progressively delayed deployment of CCS plants from a climate, energy, and economic perspective, focusing in particular on the power sector. This is carried out with the Integrated Assessment Model WITCH, exploring a wide set of long-term scenarios over mitigation targets ranging from 1.5°C to 4°C in terms of global temperature increase in 2100 with respect to the pre-industrial levels. The analysis shows that CCS will be a key mitigation option at a global level for carbon mitigation, achieving about 30% of the electricity mix in 2100 (with a homogeneous distribution across coal, gas, and biomass) if its deployment is unconstrained. If CCS deployment is delayed or forbidden, penetration cannot reach the optimal unconstrained level, resulting in a mix rearrangement, with a strong increase in renewables and, to a lesser extent, nuclear. The mitigation targets can be met, but policy costs without the implementation of CCS are from 35% to 72% higher than in the corresponding unconstrained scenarios.

Nuclear is considered as a valuable option for the decarbonization of the power generation, as it is a no-carbon, yet commercially consolidated technology. However, its real prospects are uncertain: if some countries, especially in the non-OECD area, have been extensively investing in nuclear, many OECD countries, which host the vast majority of operational reactors worldwide, feature old fleets which will not be replaced, as phase-out policies are being implemented. Research scenarios often consider polarized conditions based on either a global unconstrained nuclear development or a generalized phase-out. The main aim of this work is instead to explore the techno-economic implications of policy-relevant scenarios, designed on the actual nuclear prospects in the world regions, i.e. mainly differentiating policy constraints between the OECD and the non-OECD regions. The analysis, conducted via the Integrated Assessment Model WITCH, shows that nuclear generation constantly grows over the century, even if in general the nuclear share in the electricity mix does not significantly change over time, both at a global and at a European level. Over time, and especially if constraints are applied to nuclear deployment, the nuclear contribution is compensated by renewables (mainly wind and solar PV) and, to a lower extent, by CCS (only marginally in the EU). The policy costs related to the nuclear phase-out are not particularly high (0.4% additional global GDP loss with respect to the unconstrained policy scenario), as they are almost completely compensated by innovation and technology benefits in renewables and energy efficiency. Phase-out policies applied only to the OECD regions do not entail any additional policy costs, while non-OECD regions marginally benefit from lower uranium prices. A sudden shutdown of nuclear reactors in the OECD regions results in a doubling of these losses and gains.

This paper presents economic benefit estimates of air quality improvements in Europe that occur as a side effect of GHG emission reductions. We consider two climate policy scenarios from two representative concentration pathways (RCPs), in which radiative forcing levels are reached in 2100. The policy tool is a global uniform tax on all GHG emissions in the integrated assessment model WITCH. The resulting consumption patterns of fossil fuels are used to estimate the physical impacts and the economic benefits of pollution reductions on human health and on key assets by implementing the most advanced version of the ExternE methodology with its impact pathway analysis. The mitigation scenario compatible with $$+2\,^{\circ }\hbox {C}$$ (RCP 2.6) reduces total pollution costs in Europe by 84 %. Discounted cumulative ancillary benefits are equal to about €1.7 trillion between 2015 and 2100, or €17 per abated tonne of $$\hbox {CO}_{2}$$ in Europe. The less strict climate policy scenario (RCP 4.5) generates benefits equal to €15.5 per abated tonne of $$\hbox {CO}_{2}$$ . Without discounting, the ancillary benefits are equal to €46 (RCP 2.6) and €51 (RCP 4.5) per tonne of $$\hbox {CO}_{2}$$ abated. For both scenarios, the local benefits per tonne of $$\hbox {CO}_{2}$$ decline over time and vary significantly across countries.

In this paper, we apply two global Integrated Assessment Models (IAMs) and one detailed European electricity system model to explore the consequences of different narrative-based low-carbon scenarios on the electricity system from the global to national scale. The narratives are based on insights from socio-technical transition analysis on niche-innovations. The main aim of this exercise is to examine the solution space in low-carbon scenarios for electricity supply from the global to national scale, which is largely neglected when focusing on cost-optimal solutions only. We show that taking into account insights from socio-technical transition analysis can have large impacts on the projected transition strategy, especially regarding relatively costly technologies that currently have a high momentum. For instance, we find that the share of offshore wind in electricity generation in Europe is less than 3% or up to 27% by 2050, depending on the underlying narrative. These ranges are useful input for policy-makers, as they show the degree of flexibility in mitigation options. Furthermore, our analysis shows that combining IAMs with more detailed sectoral models illuminates the challenges on a more detailed geographical scale, for instance regarding storage requirements and the need for interconnectivity across European borders.

The abatement of non-CO2 greenhouse gases (OGHG) has proved to be of par- amount importance for reaching global mitigation targets. The modeling of their abatement is normally carried out referring to marginal abatement cost (MAC) curves, which by now represent a standard approach for such an analysis. As no evolution scenarios are available to describe future mitigation opportunities for OGHGs, exogenous technical progress factors (TP) are normally imposed, producing progressive MAC dilatation over time. The main aim of this work is to perform a sensitivity analysis evaluating climate and economic effects of imposing various TPs under different policy scenarios. The analysis shows that TP variation has a considerable impact on the climatic and economic results.

This paper describes changes to the modelling of the transport sector in the WITCH (World Induced Technical Change Hybrid) model to incorporate road freight and account for the intensity of freight with respect to GDP. Modelling freight demand based on the intensity of freight with respect to GDP allows for a focus on the importance of road freight with respect to the cost-effective achievement of climate policy targets. These climate policy targets are explored using different GDP pathways between 2005 and 2100, which are sourced from the Shared Socioeconomic Pathways (SSPs) database. Our modelling shows that the decarbonisation of the freight sector tends to occur in the second part of the century and the sector decarbonises by a lower extent than the rest of the economy. Decarbonising road freight on a global scale remains a challenge even when notable progress in biofuels and electric vehicles has been accounted for.

This paper explores the opportunities for integrating Initiative Based Learning (IBL) and Integrated Assessment Models (IAMs) in order to improve our understanding of learning in the context of societal transition pathways, and more specifically by focusing on solar PV as an energy transition technology. Our analysis shows that IAMs and IBL conceptualize learning in a very different way, and the two approaches have major structural differences with respect to the geographical as well as the temporal scale of analysis. This is also due to the different goals of the two methodologies. The aim of IAM is to develop long-term energy and technology scenarios for the next thirty to eighty years, and to describe learning processes mostly to account for future potential improvements in technologies, while IBL focuses on understanding the configuration of actors in specific institutional settings that legitimize and support specific technologies and ultimately lead to dynamics of social learning. Although ambitious forms of integration between IAMs and IBL are not feasible today, the two approaches can be used in parallel and lead to mutual enrichment via a process that we label a two-way recursive collaboration.

The penetration of Variable Renewable Energies (VREs) in the electricity mix poses serious challenges in terms of management of the electrical grids, as the associated variability and non-dispatchability are in contrast with the requirement that the load be instantaneously equalized by the generation. One of the goals of Integrated Assessment Models (IAMs) is to simulate the evolution of electricity demand and generation mix over time, therefore a proper modeling of VRE system integration is crucial. In this paper we discuss how different modeling mechanisms can profoundly impact the evolution of the electricity mix, and specifically renewable penetration. In particular, we focus on the effects of introducing a set of explicit system integration constraints in a model, WITCH, characterized by a Constant Elasticity of Substitution (CES) framework.

This paper presents estimates of the economic benefit of air quality improvements in Europe that occur as a side effect of GHG emission reductions. We consider three climate policy scenarios that reach radiative forcing levels in 2100 of three Representative Concentration Pathways (RCPs). These targets are achieved by introducing a global uniform tax on all GHG emissions in the Integrated Assessment Model WITCH, assuming both full as well as limited technological flexibility. The resulting consumption patterns of fossil fuels are used to estimate the physical impacts and the economic benefits of pollution reductions on human health and on key assets by implementing the most advanced version of the ExternE methodology with its Impact Pathway Analysis. We find that the mitigation scenario compatible with 2°C reduces total pollution costs in Europe by 76%. Discounted ancillary benefits are more than €2.5 trillion between 2015 and 2100. The monetary value of reduced pollution is equal to €22 per abated ton of CO2 in Europe. Less strict climate policy scenarios generate overall smaller, but still considerable, local benefits (14 € or 18 € per abated ton of CO2). Without discounting, the ancillary benefits are in a range of €36 to €50 per ton of CO2 abated. Cumulative ancillary benefits exceed the cumulative additional cost of electricity generation in Europe. Each European country alone would be better off if the mitigation policy was implemented, although the local benefits in absolute terms vary significantly across the countries. We can identify the relative losers and winners of ancillary benefits in Europe. In particular, we find that large European countries contribute to as much as they benefit from ancillary benefits. The scenarios with limited technology flexibility do deliver results that are similar to the full technology flexibility scenario.

The extraction and processing of unconventional oil is more energy intensive and has larger negative environmental impacts than the extraction of conventional oil. The European Union (EU) estimates that oil sands lead to 22% more emissions than conventional oil. The EU is very concerned by the potential climate and environmental impacts and has considered introducing a tax on imported unconventional oil in order to discourage its production. This study shows that a global ban on the use of unconventional oil substantially reduces global carbon dioxide emissions, but the policy is not efficient. A unilateral ban of the EU on unconventional oil has no climate benefits and it is expensive for Europe.

This paper examines how changes in an international climate regime would affect the European decarbonization strategy and costs through the mechanisms of trade, technology, and innovation. We present the results from the Energy Modeling Forum (EMF) model comparison study on European climate policy to 2050. Moving from a no-policy scenario to an existing-policies case reduces all energy imports, on average. Introducing a more stringent climate policy target for the EU only leads to slightly greater global emission reductions. Consumers and producers in Europe bear most of the additional burden and inevitably face some economic losses. More ambitious mitigation action outside Europe, especially when paired with a well-operating global carbon market, could reduce the burden for Europe significantly. Because of global learning, the costs of wind and especially solar-PV in Europe would decline below the levels observed in the existing-policy case and increased R&D spending outside the EU would leverage EU R&D investments as well.

The Energy Modeling Forum 28 (EMF28) performed a large-scale model comparison exercise to illustrate different technology pathways for cutting European greenhouse gas emissions by 80% by 2050. Focusing on selected countries (France, Germany, Italy, Sweden and UK), this paper first analyses climate and energy policy objectives and debates in the respective countries. It then compares EMF28 model results to the short-term projections of the National Renewable Energy Action Plans (NREAPs) and the long-term transformation pathway given in the European Commission’s “Energy Roadmap 2050”. It concludes that there is sufficient agreement with the NREAPs and national policies to accept the model results as conceivable scenarios. The scenarios suggest that in the future a variety of different national energy mixes will continue to reflect the different resource bases and preferences of individual Member States. In order to ensure a cost-efficient transformation, it is important to improve coordination between Member State policies and those at EU level.

The extraction and processing of unconventional oil is more energy intensive and has larger negative environmental impacts than the extraction of conventional oil. The European Union (EU) estimates that oil sands lead to 22% more emissions than conventional oil. The EU is very concerned by the potential climate and environmental impacts and has considered introducing a tax on imported unconventional oil in order to discourage its production. This study shows that a global ban on the use of unconventional oil substantially reduces global carbon dioxide emissions, but the policy is not efficient. A unilateral ban of the EU on unconventional oil has no climate benefits and it is expensive for Europe.

The abatement of non-CO2 greenhouse gases (OGHG) has proved to be of paramount importance for reaching global mitigation targets. The modeling of their abatement is normally carried out referring to marginal abatement cost (MAC) curves, which by now represent a standard approach for such an analysis. As no evolution scenarios are available to describe future mitigation opportunities for OGHGs, exogenous technical progress factors (TP) are normally imposed, producing progressive MAC dilatation over time. The main aim of this work is to perform a sensitivity analysis evaluating climate and economic effects of imposing various TPs under different policy scenarios: the analysis shows that TP variation has a considerable impact on the climatic and economic results.

This paper investigates whether an inefficient allocation of abatement, due to constraints on the use of currently available low carbon mitigation options, can promote innovation in new technologies and eventually generate welfare gains. We focus on the case of nuclear power phase out, when accounting for endogenous technical change in energy efficiency and in low carbon technologies. The analysis uses the Integrated Assessment Model WITCH, which features multiple externalities due to both climate and innovation market failures. Our results show that phasing out nuclear power stimulates additional R&D investments and deployment of infant technologies with large learning potential. The innovation benefits which this would generate and that would not otherwise be captured due to intertemporal and international externalities almost completely offset the economic costs of phasing out nuclear power. The technological change benefit depends on the stringency of the climate policy and is distributed unevenly across countries.