Climate Change Mitigation Scenarios Research Articles

System-level effects of increased energy efficiency in global low-carbon scenarios: A model comparison

Supporting investments in energy efficiency is considered a robust strategy to achieve a successful transition to low-carbon energy systems in line with the Paris Agreement. Increased energy efficiency levels are expected to reduce the need for supply-side investments in controversial technologies, such as carbon dioxide capture and storage (CCS) and nuclear energy, and to induce a downward push on carbon prices, which may facilitate the political and societal acceptance of climate policies, without adversely affecting living comfort and sustainable development. In order to fully reap these potential benefits, economies need to design policy packages that balance emission reduction incentives on both the demand and the supply side. In this paper we carry out a model-comparison exercise, using two well-established global integrated assessment models, PROMETHEUS and TIAM-ECN, to quantitatively analyze the global system-level effects of increased energy efficiency in the context of ambitious post-COVID climate change mitigation scenarios. Our results confirm the expected benefits induced by higher energy efficiency levels, as in 2050 global carbon prices are found to decline by 10%–50% and CO2 storage from CCS plants is 13%–90% lower relative to the “default” mitigation scenarios. Similarly, enhanced energy efficiency reduces the additional average yearly system costs needed globally in 2050 to achieve emission reductions in line with the Paris Agreement. These additional costs are estimated to be of the order of 2 trillion US$ – or 1% of global GDP – in a well-below-2 °C scenario, and can be reduced by 6–30% with the adoption of higher energy efficiency standards. While the two models project broadly consistent future trends for the energy mix in the various scenarios, the effects may differ in magnitude due to intrinsic differences in how the models are set up and how sensitive they are to changes in energy efficiency and emission reduction targets.

Assessing global climate change mitigation scenarios from a power system perspective using a novel multi-model framework

There is a debate regarding the suitability of global integrated assessment models (IAMs) for long-term planning exercises of the global energy system. This study informs this debate from a power system perspective and proposes a methodological framework for soft-linking of global IAMs with detailed global power system models. With the proposed open-source framework, the scenario results from IAMs can be fed into a power system model to assess given scenarios with enhanced modelling resolution. Results from these simulations can be redirected to the IAM through iterative bi-directional soft-linking. A proof of concept application is presented by linking global IAM MESSAGEix-GLOBIOM with global power system model PLEXOS-World. Among others, the results suggest that the assumption of unconstrained electricity flows inside large regional copperplates without internal network constraints causes an overestimation of the potential of variable renewables within MESSAGEix-GLOBIOM. We propose areas for informed improvements in MESSAGEix-GLOBIOM and for IAMs in general.

Heat stress, labor productivity, and economic impacts: analysis of climate change impacts using two-way coupled modeling

Climate change affects various fundamental human activities, and understanding the consequences of its impacts is essential. Among them, heat stress considerably affects economic conditions. Furthermore, when analyzing the socioeconomic impacts of climate change, both socioeconomic and climate systems must be considered simultaneously, though such studies are scarce. This study aimed to evaluate the socioeconomic impacts of changes in labor productivity due to heat stress (measured by wet bulb globe temperature) under various climate change scenarios through a new modeling framework that coupled a computable general equilibrium model and an Earth system model of intermediate complexity to realize the interactions between the two systems through the relationship between heat stress and labor productivity. Results indicated that labor productivity declined as climate change progressed (particularly in hot and humid regions), driving a gradual decline in total global gross domestic product (GDP). Although regional GDP largely decreased where labor productivity considerably declined, it slightly increased in some areas because of a comparative advantage brought about by the difference in the impact on labor productivity by region. Consequently, carbon dioxide (CO2) emissions and concentrations and the resulting temperature were slightly reduced when examining the impact of climate change on labor productivity. These tendencies were similar in both business-as-usual and climate change mitigation scenarios, but the overall impacts were smaller under the latter. There was a limited impact on CO2 emissions, CO2 concentrations, and temperature via integrated socioeconomic and climate systems. However, this study focused on only a single channel of the various interactions between the two systems. For a more complete evaluation of the impacts of climate change, further development of the integrated model is required.

Impacts of climate change mitigation and clean cooking access on future childhood stunting in India

BACKGROUND AND AIM: Many children in India face the double health burden of high exposure to ambient (AAP) and household air pollution. Although climate change mitigation is expected to decrease AAP, climate policies could increase the cost of clean fuels. We aimed to quantify the impacts of climate change mitigation and clean cooking access on future childhood stunting in India. METHODS: We linked 2015-2016 Demographic Health Survey data with satellite-based particulate matter (PM2.5) data to estimate the association between in-utero exposure to ambient PM2.5, cooking fuel type, and stunting among children 5 years. Ambient PM2.5 and clean cooking access were projected under global climate change mitigation scenarios in line with the 2°C Paris Agreement target and a range of national energy access scenarios with an integrated assessment model. We used a modified substitution estimator approach to estimate the number of children with stunted growth under each scenario in 2030 and 2050 according to state and urbanicity and accounting for demographic change. RESULTS:In-utero exposure to ambient PM2.5 significantly increased the odds of child stunting (OR: 1.04, 95%CI: 1.05-1.03 per 10 μg/m3 increase in PM2.5) and clean compared to polluting cooking fuel decreased the odds of stunting (OR: 0.86, 95%CI: 088-0.84) in confounder-adjusted models. Under the 2°C target and a range of policies to support clean energy access, national average exposure to ambient PM2.5 was 45.9 μg/m3 and clean cooking access was 74% -97% in 2050 compared to 57.4 μg/m3 and 91%-99% under business-as-usual. Reductions in AAP under the 2°C Paris Agreement target prevented stunting in 1 million children in rural and 0.8 million in urban areas in India in 2050 compared to business-as-usual. CONCLUSIONS:Air pollution reductions achieved by meeting the Paris Agreement target combined with policies to offset increased costs of clean cooking could contribute to improved linear growth in young children in India. KEYWORDS: co-benefits, clean cooking access, childhood stunting

Empirical testing of the visualizations of climate change mitigation scenarios with citizens: A comparison among Germany, Poland, and France

While scenarios are used extensively for communication about climate change mitigation, little is known about the interpretation of these scenarios by citizens. We conducted a cross-country empirical evaluation of scenario visualizations for global mitigation, using online surveys in Germany (N = 379), Poland (N = 223), and France (N = 225). Each respondent received visualizations of the required changes in global carbon dioxide emissions and composition of electricity supply (fossil fuels, nuclear, and renewable sources) for limiting global warming to 1.5 °C. We evaluated the effects of respondents’ demographics, prior beliefs, numeracy, and graph literacy on the reading accuracy and knowledge gains from the visualizations. We also included an experimental between-groups design on visualization format, where four groups received different graph formats (steep or gradual graphs with depictions of uncertainty ranges or scenario ensembles) and the fifth group received a table. Results showed that higher education level, numeracy, and graph literacy increased reading accuracy in all countries, while age reduced them. Respondents with prior beliefs about climate change mitigation that matched the information in the visualizations had also higher reading accuracy and knowledge gains. While the effects of different visualization formats were comparatively minor, customizing formats according to demographic and country differences was used to reduce adverse effects from these differences. These results emphasize the need to design visualizations that match characteristics of the intended audience and could inform better communication of climate change mitigation scenarios to non-expert audience.

What future for primary aluminium production in a decarbonizing economy?

Aluminium is an energy intensive material with an environmental footprint strongly dependent on the electricity mix consumed by the smelting process. This study models prospective environmental impacts of primary aluminium production according to different integrated assessment modeling scenarios building on Shared Socioeconomic Pathways and their climate change mitigation scenarios. Results project a global average carbon intensity ranging between 8.6 and 18.0 kg CO2 eq/kg in 2100, compared to 18.3 kg CO2 eq/kg at present, that could be further reduced under mitigation scenarios. Co-benefits with other environmental indicators are observed. Scaling aluminium production impacts to the global demand shows total emission between 1250 and 1590 Gt CO2 eq for baseline scenarios by 2050 while absolute decoupling is only achievable with stringent climate policy changing drastically the electricity mix. Achieving larger emission reductions will require circular strategies that go beyond primary material production itself and involve other stakeholders along the aluminium value chain.

Disentangling the Impacts of Anthropogenic Aerosols on Terrestrial Carbon Cycle During 1850-2014.

Aerosols have a dimming and cooling effect and change hydrological regimes, thus affecting carbon fluxes, which are sensitive to climate. Aerosols also scatter sunlight, which increases the fraction of diffuse radiation, increasing photosynthesis. There remains no clear conclusion whether the impact of aerosols on land carbon fluxes is larger through diffuse radiation change than through changes in other climate variables. In this study, we quantified the overall physical impacts of anthropogenic aerosols on land C fluxes and explored the contribution from each factor using a set of factorial simulations driven by climate and aerosol data from the IPSL‐CM6A‐LR experiments during 1850–2014. A newly developed land surface model which distinguishes diffuse and direct radiation in canopy radiation transmission, ORCHIDEE_DF, was used. Specifically, a subgrid scheme was developed to distinguish the cloudy and clear sky conditions. We found that anthropogenic aerosol emissions since 1850 cumulatively enhanced the land C sink by 22.6 PgC. Seventy‐eight percent of this C sink enhancement is contributed by aerosol‐induced increase in the diffuse radiation fraction, much larger than the effect of the aerosol‐induced dimming. The cooling of anthropogenic aerosols has different impacts in different latitudes but overall increases the global land C sink. The dominant role of diffuse radiation changes found in this study implies that future aerosol emissions may have a much stronger impacts on the C cycle through changing radiation quality than through changing climate alone. Earth system models need to consider the diffuse radiation fertilization effect to better evaluate the impacts of climate change mitigation scenarios.

Meta-analysis of leaf area index, canopy height and root depth of three bioenergy crops and their effects on land surface modeling

The expected large-scale expansion of biofuel production in climate change mitigation scenarios calls for improvements in the representation of bioenergy crops in land surface models. Leaf area index (LAI), canopy height (CH) and root depth (RD) are key parameters that regulate exchanges of heat and moisture between land and atmosphere. This study performs a meta-analysis combining unique data from 34 observational studies and 14 countries to estimate monthly variability in LAI, CH, and RD of three main bioenergy crops: miscanthus (MSC), switchgrass (SWG), and reed canary grass (RCG). Using the Community Land Model v.5.0 and the results from the meta-analysis, we also tested the effects that variability in parameterization of LAI and CH have on key components of the surface energy budget, relative to prescribed values. Results from the meta-analysis show a strong seasonality of LAI and CH, with mean (± one standard error) LAI values at the peak summer month of 6.05 ± 0.84, 5.56 ± 0.75, and 5.39 ± 1.15 m2/m2, and maximum CH of 246 ± 23, 147 ± 16, and 156 ± 10 cm, for MSC, SWG, and RCG, respectively. These values are typically larger than the default parameterizations in CLM. Information on RD was limited and average values are 172 ± 56, 165 ±46, and 193 ± 11 cm, for MSC, SWG, and RCG, respectively. The seasonal cycles of latent heat, sensible heat and surface albedo are primarily affected by the range of LAI values, and less sensitive to variability in CH. Relative to the default values, higher LAI values increase latent heat and decrease sensible heat, with the highest absolute changes in summer. They also decrease surface albedo in winter months due to a larger snow masking effect. Our results offer a basis to compare experimental work and modelling studies, improve parameterization in land surface models, and identify the importance of vegetation structure parameters to evaluate key climate processes in response to bioenergy crops.

Health impacts of fine particles under climate change mitigation, air quality control, and demographic change in India

Despite low per capita emissions, with over a billion population, India is pivotal for climate change mitigation globally, ranking as the third largest emitter of greenhouse gases. We linked a previously published multidimensional population projection with emission projections from an integrated assessment model to quantify the localised (i.e. state-level) health benefits from reduced ambient fine particulate matter in India under global climate change mitigation scenarios in line with the Paris Agreement targets and national scenarios for maximum feasible air quality control. We incorporated assumptions about future demographic, urbanisation and epidemiological trends and accounted for model feedbacks. Our results indicate that compared to a business-as-usual scenario, pursuit of aspirational climate change mitigation targets can avert up to 8.0 million premature deaths and add up to 0.7 years to life expectancy (LE) at birth due to cleaner air by 2050. Combining aggressive climate change mitigation efforts with maximum feasible air quality control can add 1.6 years to LE. Holding demographic change constant, we find that climate change mitigation and air quality control will contribute slightly more to increases in LE in urban areas than in rural areas and in states with lower socio-economic development.

Alternative carbon price trajectories can avoid excessive carbon removal

The large majority of climate change mitigation scenarios that hold warming below 2 °C show high deployment of carbon dioxide removal (CDR), resulting in a peak-and-decline behavior in global temperature. This is driven by the assumption of an exponentially increasing carbon price trajectory which is perceived to be economically optimal for meeting a carbon budget. However, this optimality relies on the assumption that a finite carbon budget associated with a temperature target is filled up steadily over time. The availability of net carbon removals invalidates this assumption and therefore a different carbon price trajectory should be chosen. We show how the optimal carbon price path for remaining well below 2 °C limits CDR demand and analyze requirements for constructing alternatives, which may be easier to implement in reality. We show that warming can be held at well below 2 °C at much lower long-term economic effort and lower CDR deployment and therefore lower risks if carbon prices are high enough in the beginning to ensure target compliance, but increase at a lower rate after carbon neutrality has been reached.

Why the shared socioeconomic pathway framework has not been useful for improving climate change mitigation policy analysis

Numerous ways to improve the usefulness of climate change mitigation scenarios that rely on the Shared Socioeconomic Pathway (SSP) framework that was developed over the last 10 years have been suggested. The problem with these proposals is that the diagnosis of what has led to the inability of integrated assessment modelers to properly analyze mitigation policies is wrong. The first main problem with the past use of the SSP-based mitigation scenarios is that few input variables for what is supposed to be the same SSP are given the same numerical values by different modeling teams. The more significant problem with the way in SSP-based mitigation scenarios have been used to analyze mitigation policies is that the different integrated assessment models (IAMs) have very different structures and functions. Thus, even if all the input variables comprising a single SSP had the same numerical values, the scenario results from running such a SSP through different IAMs would be quite different, leading to different understandings of the usefulness of different mitigation policies. This situation can be avoided by developing just two or three more detailed and improved IAMs focused on the critical next 10–20 years for mitigating climate change.

The land–energy–water nexus of global bioenergy potentials from abandoned cropland

Bioenergy is a key option in climate change mitigation scenarios. Growing perennial grasses on recently abandoned cropland is a near-term strategy for gradual bioenergy deployment with reduced risks for food security and the environment. However, the extent of global abandoned cropland, bioenergy potentials and management requirements are unclear. Here we integrate satellite-derived land cover maps with a yield model to investigate the land–energy–water nexus of global bioenergy potentials. We identified 83 million hectares of abandoned cropland between 1992 and 2015, corresponding to 5% of today’s cropland area. Bioenergy potentials are 6–39 exajoules per year (11–68% of today’s bioenergy demand), depending on multiple local and management factors. About 20 exajoules per year can be achieved by increasing today’s global cropland area and water use by 3% and 8%, respectively, and without production inside biodiversity hotspots or irrigation in water-scarce areas. The consideration of context-specific practices and multiple environmental dimensions can mitigate trade-offs of bioenergy deployment. Bioenergy from grasses is a key option to mitigate climate change. This study finds that recently abandoned cropland could help meet 11–68% of today’s bioenergy demand.

Decomposition analysis of per capita emissions: a tool for assessing consumption changes and technology changes within scenarios

Recent studies show that behaviour changes can provide an essential contribution to achieving the Paris climate targets. Existing climate change mitigation scenarios primarily focus on technological change and underrepresent the possible contribution of behaviour change. This paper presents and applies a methodology to decompose the factors contributing to changes in per capita emissions in scenarios. With this approach, we determine the relative contribution to total emissions from changes in activity, the way activities are carried out, the intensity of activities, as well as fuel choice. The decomposition tool breaks down per capita emissions loosely following the Kaya Identity, allowing a comparison between the contributions of technology and consumption changes among regions and between various scenarios. We illustrate the use of the tool by applying it to three previously-published scenarios; a baseline scenario, a scenario with a selection of behaviour changes, and a 2 °C scenario with the same selection of behaviour changes. Within these scenarios, we explore the contribution of technology and consumption changes to total emission changes in the transport and residential sector, for a selection of both developed and developing regions. In doing so, the tool helps identify where specifically (i.e. via consumption or technology factors) different measures play a role in mitigating emissions and expose opportunities for improved representation of behaviour changes in integrated assessment models. This research shows the value of the decomposition tool and how the approach could be flexibly replicated for different global models based on available variables and aims. The application of the tool to previously-published scenarios shows substantial differences in consumption and technology changes from CO2 price and behaviour changes, in transport and residential per capita emissions and between developing and developed regions. Furthermore, the tool’s application can highlight opportunities for future scenario development of a more nuanced and heterogeneous representation of behaviour and lifestyle changes in global models.

Mapping Multi-Level Policy Incentives for Bioenergy With Carbon Capture and Storage in Sweden

Bioenergy with carbon capture and storage (BECCS) is considered a key mitigation technology in most 1.5–2.0°C compatible climate change mitigation scenarios. Nonetheless, examples of BECCS deployment are lacking internationally. It is widely acknowledged that widespread implementation of this technology requires strong policy enablers, and that such enablers are currently non-existent. However, the literature lacks a more structured assessment of the “incentive gap” between scenarios with substantive BECCS deployment and existing policy enablers to effectuate BECCS deployment. Sweden, a country with progressive climate policies and particularly good preconditions for BECCS, constitutes a relevant locus for such examinations. The paper asks to what extent and how existing UN, EU, and Swedish climate policy instruments incentivize BECCS research, development, demonstration, and deployment in Sweden. The analysis is followed by a tentative discussion of needs for policy reform to improve the effectiveness of climate policy in delivering BECCS. Drawing on a tripartite typology of policy instruments (economic, regulatory, and informational) and the ability of these instruments to create supply-push or demand-pull, the article finds that: (1) no instruments create a demand-pull to cover operational expenditure; (2) economic instruments provide partial support for research and the capital expenditure associated with demonstration, and; (3) regulatory instruments provide partial clarity on environmental safeguards and responsibilities. A few regulatory barriers also continue to counteract deployment. The article concludes that the existing policy mix requires considerable reform if BECCS is to contribute substantially to the Swedish target for net-zero emissions. Continued effort to dismantle regulatory barriers must be complemented with a strong demand-pull instrument that complements the current focus on supply-push incentives. If unreformed, the existing policy mix will most likely lead to substantial public expenditure on BECCS research, development, and demonstration without leading to any substantial deployment and diffusion.

Optimal combination of bioenergy and solar photovoltaic for renewable energy production on abandoned cropland

Ambitious climate change mitigation scenarios require large-scale deployment of bioenergy and solar photovoltaics. Utilizing recently abandoned cropland for renewable energy production is a promising option for energy supply while reducing competition for land and food security. However, the magnitude of abandoned cropland and its potential for renewable energy production is still unclear. Here, we mapped recently abandoned croplands at a global level and assessed the site-specific primary energy potentials for bioenergy and solar photovoltaics considering local climatic conditions, energy yields, and socio-economic feasibility constraints to identify optimal land use for renewable energy production. Of the 83 Mha of the identified abandoned cropland between 1992 and 2015, 68% of the area presented higher development potentials for the establishment of solar photovoltaic compared to dedicated bioenergy crops. In total, 125 EJ/year of primary energy can be produced with this optimal land management, of which 114 EJ/year is from solar photovoltaic and 11 EJ/year is from bioenergy. This figure corresponds to 33–50% of the projected median renewable energy demand in 2050 across the 1.5 °C stabilization scenarios. Mapping the suitability of renewable energy sources across different local, environmental, and socio-economic constraints will help identify the best implementation options for future energy systems transformation.

Future health impacts of long-term exposure to fine particulate matter under climate change, demographic change and urbanisation in India

Background: Rapid socio-economic development in India has been accompanied by gains in life expectancy and improvements in a range of health outcomes. However, it is uncertain how the fast pace of urbanisation, the aging of the population, and climate change will alter this trend in the future. This study estimates dynamically over time the health co-benefits from projected changes in exposure to ambient fine particulate matter (PM2.5) in India up to 2050 under alternative climate change mitigation and air pollution abatement scenarios, considering future demographic change, urbanisation trends and changes in disease burdens. Methods: We use outputs from an integrated assessment model and a multi-dimensional cohort-component projection model to explore dynamically over time the range of potential health impacts across urban and rural areas in all states of India. Results: We show that pursuit of the aspirational climate change mitigation targets can bring clear co-benefits from cleaner air by averting up to 7.9 million deaths and adding up to 0.8 years to average life expectancy at birth in 2050 compared to business-as-usual. Combining these targets with policy measures that target air pollution explicitly can double human health benefits. Across the population, the largest health gains from PM2.5 reduction will occur for those living in rural areas, as well as for males and the elderly. Future health co-benefits differ substantially between states, with the highest potential gains observed in the regions around the Indo-Gangetic Plain, where high population density and low baseline life expectancy coincide with high PM2.5 levels. Conclusions: Our analysis helps reduce one of the main uncertainties in future health impact assessments (changes in the size, structure, disease burden, and distribution of the population), demonstrates the impact of different PM2.5 pathways on survival and highlights the important synergies between climate change mitigation and air quality control.

Implications of climate change mitigation strategies on international bioenergy trade

Most climate change mitigation scenarios rely on increased use of bioenergy to decarbonize the energy system. Here we use results from the 33rd Energy Modeling Forum study (EMF-33) to investigate projected international bioenergy trade for different integrated assessment models across several climate change mitigation scenarios. Results show that in scenarios with no climate policy, international bioenergy trade is likely to increase over time, and becomes even more important when climate targets are set. More stringent climate targets, however, do not necessarily imply greater bioenergy trade compared to weaker targets, as final energy demand may be reduced. However, the scaling up of bioenergy trade happens sooner and at a faster rate with increasing climate target stringency. Across models, for a scenario likely to achieve a 2 °C target, 10–45 EJ/year out of a total global bioenergy consumption of 72–214 EJ/year are expected to be traded across nine world regions by 2050. While this projection is greater than the present trade volumes of coal or natural gas, it remains below the present trade of crude oil. This growth in bioenergy trade largely replaces the trade in fossil fuels (especially oil) which is projected to decrease significantly over the twenty-first century. As climate change mitigation scenarios often show diversified energy systems, in which numerous world regions can act as bioenergy suppliers, the projections do not necessarily lead to energy security concerns. Nonetheless, rapid growth in the trade of bioenergy is projected in strict climate mitigation scenarios, raising questions about infrastructure, logistics, financing options, and global standards for bioenergy production and trade.

Combining Climate Change Mitigation Scenarios with Current Forest Owner Behavior: A Scenario Study from a Region in Southern Sweden

This study investigates the need for change of current forest management approaches in a southern Swedish region within the context of future climate change mitigation through empirically derived projections, rather than forest management according to silvicultural guidelines. Scenarios indicate that climate change mitigation will increase global wood demand. This might call for adjustments of well-established management approaches. This study investigates to what extent increasing wood demands in three climate change mitigation scenarios can be satisfied with current forest management approaches of different intensities in a southern Swedish region. Forest management practices in Kronoberg County were mapped through interviews, statistics, and desk research and were translated into five different management strategies with different intensities regulating management at the property level. The consequences of current practices, as well as their intensification, were analyzed with the Heureka Planwise forest planning system in combination with a specially developed forest owner decision simulator. Projections were done over a 100-year period under three climate change mitigation scenarios developed with the Global Biosphere Management Model (GLOBIUM). Current management practices could meet scenario demands during the first 20 years. This was followed by a shortage of wood during two periods in all scenarios unless rotations were reduced. In a longer timeframe, the wood demands were projected to be easily satisfied in the less ambitious climate change mitigation scenarios. In contrast, the demand in the ambitious mitigation scenario could not be met with current management practices, not even if all owners managed their production forests at the intensive extreme of current management approaches. The climate change mitigation scenarios provide very different trajectories with respect to future drivers of forest management. Our results indicate that with less ambitious mitigation efforts, the relatively intensive practices in the study region can be softened while ambitious mitigation might push for further intensification.

On the feasibility of cropland and forest area expansions required to achieve long-term temperature targets

Biomass-based negative emission technologies (NETs) such as bioenergy with carbon capture and storage (BECCS) and afforestation/reforestation (AR) are regarded as important options to achieve the 2 °C and 1.5 °C targets stipulated in the Paris agreement, but the feasibility of their large-scale deployments remains very uncertain. This study focused on the speed of expansions of land-use area related to the biomass-based NETs and assessed the feasibility of climate change mitigation scenarios to achieve the temperature targets. Our model analysis shows that expansions at unprecedented speeds are required for total cropland area (including energy cropland) in Sub-Saharan Africa and for planted forest area for carbon sink in many regions in the next decades, under the assumption of global least-cost measures for CO2 emission reduction. On the other hand, when the speed of the land-use expansions is limited as observed in the real world, the CO2 emission reduction costs become unrealistically high around the middle of this century, particularly in scenarios for the 1.5 °C target; relatively low-cost measures such as BECCS in Sub-Saharan Africa and AR in many regions are limited in deployment due to the limited speed of the land-use expansion, and yet energy systems must be transformed to nearly net-zero/negative CO2 emissions for the 2 °C/1.5 °C target, which necessitates using other mitigation technologies of much higher costs. These results may cause concern over the feasibility of achieving the temperature targets, especially for the 1.5 °C target, and point to technical and scenario design aspects that will need further research for biomass-based NETs and their allowable expansion speed.

The role of transport electrification in global climate change mitigation scenarios

Electrification is widely considered an attractive solution for reducing the oil dependency and environmental impact of road transportation. Many countries have been establishing increasingly stringent and ambitious targets in support of transport electrification. We conducted scenario simulations to depict the role of transport electrification in climate change mitigation and how the transport sector would interact with the energy-supply sector. The results showed that transport electrification without the replacement of fossil-fuel power plants leads to the unfortunate result of increasing emissions instead of achieving a low-carbon transition. While transport electrification alone would not contribute to climate change mitigation, it is interesting to note that switching to electrified road transport under the sustainable shared socioeconomic pathways permitted an optimistic outlook for a low-carbon transition, even in the absence of a decarbonized power sector. Another interesting finding was that the stringent penetration of electric vehicles can reduce the mitigation cost generated by the 2 °C climate stabilization target, implying a positive impact for transport policies on the economic system. With technological innovations such as electrified road transport, climate change mitigation does not have to occur at the expense of economic growth. Because a transport electrification policy closely interacts with energy and economic systems, transport planners, economists, and energy policymakers need to work together to propose policy schemes that consider a cross-sectoral balance for a green sustainable future.