Search

Plastics show the strongest production growth of all bulk materials and are already responsible for 4.5% of global greenhouse gas emissions 1,2. If no new policies are implemented, we project a doubling of global plastic demand by 2050 and more than a tripling by 2100, with an almost equivalent increase in CO 2 emissions. Here we analyse three alternative CO 2 emission-mitigation pathways for the global plastics sector until 2100, covering the entire life cycle from production to waste management. Our results show that, through bio-based carbon sequestration in plastic products, a combination of biomass use and landfilling can achieve negative emissions in the long term; however, this involves continued reliance on primary feedstock. A circular economy approach without an additional bioeconomy push reduces resource consumption by 30% and achieves 10% greater emission reductions before 2050 while reducing the potential of negative emissions in the long term. A circular bioeconomy approach combining recycling with higher biomass use could ultimately turn the sector into a net carbon sink, while at the same time phasing out landfilling and reducing resource consumption. Our work improves the representation of material flows and the circular economy in global energy and emission models, and provides insight into long-term dynamics in the plastics sector.

Adaptation is a key societal response to reduce the impacts of climate change, yet it is poorly represented in current modelling frameworks. We identify key research gaps and suggest entry points for adaptation in quantitative assessments of climate change to enhance policy guidance.

More than 100 countries have communicated or adopted new Nationally Determined Contributions (NDCs) and net-zero target pledges. We investigate the impact on global, national, sectoral, and individual greenhouse gas emissions projections under different scenarios based on the announced NDCs and net-zero pledges using the IMAGE integrated assessment model. Our results show that while the net-zero pledges, if implemented, could be an important step forward, they are still not enough to achieve the Paris Agreement goals of well below 2°C and preferably 1.5°C by the end of the century. Still, our net-zero scenarios project significant all-sector decarbonization, in particular, electricity; however, certain sectors like industry and transport prove hard to completely abate.

This chapter provides an overview of the multi-faceted landscape of methods used to study the steering effects of the Sustainable Development Goals. After a discussion of the political use of science and the complex relations between science and politics, the chapter showcases a selection of different methods that are employed to trace the steering effects of the Sustainable Development Goals. Selecting the most suitable method for a particular research question requires understanding their main characteristics, strengths and weaknesses. The chapter highlights that all methods and tools need to be combined to comprehensively assess the political impact of the goals, the progress towards their achievement, and their overall transformative potential. As data gaps and unequal geographical coverage still hamper a broader understanding of the political impact of the globalgoals, we need to build bridges across language communities, disciplines and methodological camps, which still work very much in isolation.

This chapter provides an overview of the multi-faceted landscape of methods used to study the steering effects of the Sustainable Development Goals. After a discussion of the political use of science and the complex relations between science and politics, the chapter showcases a selection of different methods that are employed to trace the steering effects of the Sustainable Development Goals. Selecting the most suitable method for a particular research question requires understanding their main characteristics, strengths and weaknesses. The chapter highlights that all methods and tools need to be combined to comprehensively assess the political impact of the goals, the progress towards their achievement, and their overall transformative potential. As data gaps and unequal geographical coverage still hamper a broader understanding of the political impact of the globalgoals, we need to build bridges across language communities, disciplines and methodological camps, which still work very much in isolation.

Adaptation is a key societal response to reduce the impacts of climate change, yet it is poorly represented in current modelling frameworks. We identify key research gaps and suggest entry points for adaptation in quantitative assessments of climate change to enhance policy guidance.

The use of solar photovoltaic has strongly increased in the last decade. A significant part of this growth comes from home owners installing rooftop photovoltaic. Despite this key role, most long-term model-based scenarios do not consider decentralized supply of rooftop photovoltaic but concentrate on utility-scale photovoltaic instead. In this paper, we implement rooftop photovoltaic in the Integrated Assessment Model IMAGE to study its possible role in energy and climate scenarios. We first calculated the global technical and economic potential to derive regional cost-supply curves for rooftop photovoltaic. Next, we have added a new decision in the IMAGE model allowing household investment in rooftop photovoltaic based on the comparison of the whole-sale electricity price with the price of rooftop photovoltaic. The global suitable roof surface area was assessed at 36 billion m2, or 4.7 m2 capita−1, leading to a potential for rooftop photovoltaic of 8.3 PWh y−1, roughly 1.5 times the 2015 global residential electricity demand. In the baseline scenario, adding rooftop photovoltaic could lead to a 80–280% increased share of photovoltaic electricity production in 2050 (i.e. from 6% to 17% in total power production). This increase depends on regional characteristics that are essential to the deployment of rooftop photovoltaic: differences in social-economic and policy factors (capital costs, household income, and electricity prices) are considerably more important than physical factors, such as solar irradiance.

The steel industry is responsible for a large share of the industrial energy consumption and greenhouse gas emissions and several long-term energy models have some representation of this sub-sector. It is found that models, commonly use a flow-based approach for projecting steel demand neglecting that in-use steel stocks serve as a better demand indicator than steel consumption. A stock-based method that uses the historical steel stock results from detailed material flow analysis is developed for making steel demand projections and implemented in the IMAGE Integrated Assessment Model. Large differences between the two approaches arise. For the first half of the 21st century, global steel demand increases with both approaches and at a similar rate to reach 2300 Mt/yr by 2050. For the second half of the 21st century, however, the developments differ drastically. With the stock-based approach, global steel demand decreases by 0.8%/a to reach 1600 Mt/yr, while with the flow-based approach it increases by 0.3%/a to reach 2600 Mt/yr in 2100. Given that steel production levels have a profound contribution to greenhouse gas emissions, using the right approach is crucial. This means that long-term energy models may currently overestimate the industrial emissions in the last half of the century.

Mitigation scenario ensembles are becoming an important tool to bring new and robust insights into the transition to net zero. This Perspective unpacks their potential and identifies key steps for better use of scenario ensembles and to foster good practices. As they gain new users, climate change mitigation scenarios are playing an increasing role in transitions to net zero. One promising practice is the analysis of scenario ensembles. Here we argue that this practice has the potential to bring new and more robust insights compared with the use of single scenarios. However, several important aspects have to be addressed. We identify key methodological challenges and the existing methods and applications that have been or can be used to address these challenges within a three-step approach: (1) pre-processing the ensemble; (2) selecting a few scenarios or analysing the full ensemble; and (3) providing users with efficient access to the information.

Biomass is often seen as a key component of future energy systems as it can be used for heat and electricity production, as a transport fuel, and a feedstock for chemicals. Furthermore, it can be used in combination with carbon capture and storage to provide so-called "negative emissions". At the same time, however, its production will require land, possibly impacting food security, land-based carbon stocks, and other environmental services. Thus, the strategies adopted in the supply, conversion, and use of biomass have a significant impact on its effectiveness as a climate change mitigation measure. We use the IMAGE 3.0 integrated assessment model to project three different global, long term scenarios spanning different socioeconomic futures with varying rates of population growth, economic growth, and technological change, and investigate the role of biomass in meeting strict climate targets. Using these scenarios we highlight different possibilities for biomass supply and demand, and provide insights on the requirements and challenges for the effective use of this resource as a climate change mitigation measure. The results show that in scenarios meeting the 1.5 degrees C target, biomass could exceed 20% of final energy consumption, or 115-180 EJ(Prim)/yr in 2050. Such a supply of bioenergy can only be achieved without extreme levels land use change if agricultural yields improve significantly and effective land zoning is implemented. Furthermore, the results highlight that strict mitigation targets are contingent on the availability of advanced technologies such as lignocellulosic fuels and carbon capture and storage.

Given the increasing interest in keeping global warming below 1.5°C, a key question is what this would mean for China's emission pathway, energy restructuring, and decarbonization. By conducting a multimodel study, we find that the 1.5°C-consistent goal would require China to reduce its carbon emissions and energy consumption by more than 90 and 39%, respectively, compared with the "no policy" case. Negative emission technologies play an important role in achieving near-zero emissions, with captured carbon accounting on average for 20% of the total reductions in 2050. Our multimodel comparisons reveal large differences in necessary emission reductions across sectors, whereas what is consistent is that the power sector is required to achieve full decarbonization by 2050. The cross-model averages indicate that China's accumulated policy costs may amount to 2.8 to 5.7% of its gross domestic product by 2050, given the 1.5°C warming limit.

Correction to: Nature Climate Change https://doi-org.proxy.library.uu.nl/10.1038/s41558-020-00952-0, published online 25 November 2020.

Correction to: Nature Climate Change https://doi-org.proxy.library.uu.nl/10.1038/s41558-020-00952-0, published online 25 November 2020.

Current emissions scenarios include pathways that overshoot the temperature goals set out in the Paris Agreement and rely on future net negative emissions. Limiting overshoot would require near-term investment but would result in longer-term economic benefit. Global emissions scenarios play a critical role in the assessment of strategies to mitigate climate change. The current scenarios, however, are criticized because they feature strategies with pronounced overshoot of the global temperature goal, requiring a long-term repair phase to draw temperatures down again through net-negative emissions. Some impacts might not be reversible. Hence, we explore a new set of net-zero CO2 emissions scenarios with limited overshoot. We show that upfront investments are needed in the near term for limiting temperature overshoot but that these would bring long-term economic gains. Our study further identifies alternative configurations of net-zero CO2 emissions systems and the roles of different sectors and regions for balancing sources and sinks. Even without net-negative emissions, CO2 removal is important for accelerating near-term reductions and for providing an anthropogenic sink that can offset the residual emissions in sectors that are hard to abate.

Long-term emissions scenarios have served as the primary basis for assessing future climate change and response strategies. Therefore, it is important to regularly reassess the relevance of emissions scenarios in light of changing global circumstances and compare them with long-term developments to determine if they are still plausible, considering the newest insights. Four scenario series, SA90, IS92, SRES, and RCP/SSP, were central in the scenario-based literature informing the five Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC) and the sixth assessment cycle. Here we analyze the historical trends of carbon dioxide (CO2) emissions from fossil fuel combustion and industry and emissions drivers between 1960 and 2017. We then compare the emission scenario series with historical trends for the period 1990–2017/2018. The results show that historical trends are quite consistent with medium scenarios in each series. As a result, they can be regarded as valid inputs for past and future analyses of climate change and impacts. Global CO2 emissions 1960–2018 (and 1990–2018) comprised six (and three) overall subperiods of emissions growth significantly higher and lower than average. Historically, CO2 emissions (in absolute numbers and growth rate) are tightly coupled with primary energy and indirectly with GDP. Global emissions generally followed a medium-high pathway, captured by “middle-of-the-road” scenario narratives in the earlier series, and by combinations of “global-sustainability” and “middle-of-the-road” narratives in the most recent series (SRES and SSP-baselines). Historical non-OECD trends were best captured by “rapid-growth” and “regional-competition” scenarios, while OECD trends were close to regional-sustainability and global-sustainability scenarios. Areas where the emissions scenarios captured the historical trends less well, are renewable and nuclear primary energy supply. The fact that the actual historical development is consistent with rapid-growth narratives in the non-OECD regions might have important implications for future greenhouse gas emissions and associated climatic change.

We present an overview of results from 11 integrated assessment models (IAMs) that participated in the 33rd study of the Stanford Energy Modeling Forum (EMF-33) on the viability of large-scale deployment of bioenergy for achieving long-run climate goals. The study explores future bioenergy use across models under harmonized scenarios for future climate policies, availability of bioenergy technologies, and constraints on biomass supply. This paper provides a more transparent description of IAMs that span a broad range of assumptions regarding model structures, energy sectors, and bioenergy conversion chains. Without emission constraints, we find vastly different CO2 emission and bioenergy deployment patterns across models due to differences in competition with fossil fuels, the possibility to produce large-scale bio-liquids, and the flexibility of energy systems. Imposing increasingly stringent carbon budgets mostly increases bioenergy use. A diverse set of available bioenergy technology portfolios provides flexibility to allocate bioenergy to supply different final energy as well as remove carbon dioxide from the atmosphere by combining bioenergy with carbon capture and sequestration (BECCS). Sector and regional bioenergy allocation varies dramatically across models mainly due to bioenergy technology availability and costs, final energy patterns, and availability of alternative decarbonization options. Although much bioenergy is used in combination with CCS, BECCS is not necessarily the driver of bioenergy use. We find that the flexibility to use biomass feedstocks in different energy sub-sectors makes large-scale bioenergy deployment a robust strategy in mitigation scenarios that is surprisingly insensitive with respect to reduced technology availability. However, the achievability of stringent carbon budgets and associated carbon prices is sensitive. Constraints on biomass feedstock supply increase the carbon price less significantly than excluding BECCS because carbon removals are still realized and valued. Incremental sensitivity tests find that delayed readiness of bioenergy technologies until 2050 is more important than potentially higher investment costs.

One key aspect of the Paris Agreement is the goal to limit the global average temperature increase to well below 2 °C by the end of the century. To achieve the Paris Agreement goals, countries need to submit, and periodically update, their Nationally Determined Contributions (NDCs). Recent studies show that NDCs and currently implemented national policies are not sufficient to cover the ambition level of the temperature limit agreed upon in the Paris Agreement, meaning that we need to collectively increase climate action to stabilize global warming at levels considered safe. This paper explores the generalization of previously adopted good practice policies (GPPs) to bridge the emissions gap between current policies, NDCs ambitions and a well below 2 °C world, facilitating the creation of a bridge trajectory in key major-emitting countries. These GPPs are implemented in eleven well-established national Integrated Assessment Models (IAMs) for Australia, Brazil, Canada, China, European Union (EU), India, Indonesia, Japan, Russia, South Korea, and the United States, that provide least-cost, low-carbon scenarios up to 2050. Results show that GPPs can play an important role in each region, with energy supply policies appearing as one of the biggest contributors to the reduction of carbon emissions. However, GPPs by themselves are not enough to close the emission gap, and as such more will be needed in these economies to collectively increase climate action to stabilize global warming at levels considered safe.

Sub-Saharan Africa faces several challenges that hamper the effort to provide universal electricity access. The challenges are not the result of lack of energy resources but rather the result of governance and institutional problems as well as lack of capital to meet the high investment requirement. This study aims to provide relevant policy recommendations to facilitate the path towards universal electricity access in Sub-Saharan Africa. We do this by identifying the barriers for electricity access and the relevant actors, institutions, and regulations using desk research, stakeholder interviews and expert workshops. The results show that the absence of overall plans and approaches and lack of clarity in policies are the main challenges for the sector. Setting standards for electricity products, such as solar panels, could help to reduce the problem of counterfeit poor quality products. A broader participation of non-governmental actors is needed to increase the speed of electrification. This requires innovative revenue schemes, financial and fiscal incentives and elimination of market distortions. More generally, we conclude that stable and consistent policy frameworks and improved coordination between actors, are crucial to accelerate electrification in the region.

This paper presents an introduction to and overview of the papers in this Special Issue of Technological Forecasting & Social Change on ‘Transition Pathways’ is presented. Each of these papers are an output of the PATHWAYS project (EC FP7-funded, 2013–2017) which looked into ways to integrate alternative approaches for analysing sustainability transitions. Methods to bridge across scenario-modelling, socio-technical transition, and practice-based action research approaches (Turnheim et al. 2015; Geels et al., 2016) were implemented in eight empirical and modelling studies reported here. A variety of approaches to bridging emerged in practice, with differing methodological strategies employed, analysing transitions processes across different sectors, at a range of scales, and separately, comparatively or in a fully integrated way. This paper suggests a framework for understanding different approaches to bridging and shows how policy- and decision-making can be enriched by theoretically- and empirically-informed bridging approaches to transitions analysis.

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 planetary boundaries (PBs) framework proposes global quantitative precautionary limits for human perturbation of nine critical Earth system processes. Together they define a global safe operating space for human development. Translating the global limits to the national level increases their policy relevance. Such translation essentially divides up the global safe operating space. What is considered fair distribution is a political decision and there is no globally agreed principle that can be applied. Here, we analyse the distributional consequences of alternative perspectives on distributive fairness. We scale the global limits of selected PBs to resource budgets for the EU, US, China and India, using three allocation approaches from the climate change literature. Furthermore, we compare the allocated budgets to 2010 environmental footprints of the four economies, to assess their performance with respect to the selected PBs. The allocation approaches are based on (1) current shares of global environmental pressure (‘grandfathering’); (2) ‘equal per capita’ shares, and (3) ‘ability to pay’ to reduce environmental pressure. The results show that the four economies are not living within the global safe operating space. Their 2010 environmental footprints are larger than the allocated budgets for all approaches and parameterisations analysed for the PBs for climate change and biogeochemical flows, and, except for India, also for the PB for biosphere integrity. Grandfathering was found to be most favourable for the EU and US for all PBs, and ability to pay as least favourable. For climate change and biogeochemical flows, ability to pay even resulted in negative resource budgets for the two economies. In contrast, for China and India, equal per capita allocation and ability to pay were most favourable. Results were sensitive to the parameterisation. Accounting for future population growth in the equal per capita approach benefits India, with lower budgets for the EU, US and China, while accounting for future economic growth in ability to pay benefits the EU and US, with lower budgets for China and India. Our results underline the need for all four economies to act, while hinting at diverging preferences for specific allocation approaches. The methodology and results may help countries to define policy targets in line with global ambitions, such as those defined by the Sustainable Development Goals (SDGs), accounting for differences in countries’ circumstances and capacities. Further attention is required for PB-specific allocation approaches and integration of biophysical and socioeconomic considerations in the allocation.

The steel industry is responsible for a large share of the industrial energy consumption and greenhouse gas emissions and several long-term energy models have some representation of this sub-sector. It is found that models, commonly use a flow-based approach for projecting steel demand neglecting that in-use steel stocks serve as a better demand indicator than steel consumption. A stock-based method that uses the historical steel stock results from detailed material flow analysis is developed for making steel demand projections and implemented in the IMAGE Integrated Assessment Model. Large differences between the two approaches arise. For the first half of the 21st century, global steel demand increases with both approaches and at a similar rate to reach 2300 Mt/yr by 2050. For the second half of the 21st century, however, the developments differ drastically. With the stock-based approach, global steel demand decreases by 0.8%/a to reach 1600 Mt/yr, while with the flow-based approach it increases by 0.3%/a to reach 2600 Mt/yr in 2100. Given that steel production levels have a profound contribution to greenhouse gas emissions, using the right approach is crucial. This means that long-term energy models may currently overestimate the industrial emissions in the last half of the century.

The future environmental impacts of battery electric vehicles (EVs) are very important given their expected dominance in future transport systems. Previous studies have shown these impacts to be highly uncertain, though a detailed treatment of this uncertainty is still lacking. We help to fill this gap by using Monte Carlo and global sensitivity analysis to quantify parametric uncertainty and also consider two additional factors that have not yet been addressed in the field. First, we include changes to driving patterns due to the introduction of autonomous and connected vehicles. Second, we deeply integrate scenario results from the IMAGE integrated assessment model into our life cycle database to include the impacts of changes to the electricity sector on the environmental burdens of producing and recharging future EVs. Future EVs are expected to have 45-78% lower climate change impacts than current EVs. Electricity used for charging is the largest source of variability in results, though vehicle size, lifetime, driving patterns, and battery size also strongly contribute to variability. We also show that it is imperative to consider changes to the electricity sector when calculating upstream impacts of EVs, as without this, results could be overestimated by up to 75%.

International shipping accounts for around 2 % of global CO2 emissions. The International Maritime Organization (IMO) has set the ambition to halve shipping GHG emissions by 2050 to help mitigate climate change. As shipping connects countries and sectors, its future development is highly dependent on regional and sectoral trends. So far, the literature on the decarbonization of shipping has focused on sectoral analyses while integrated assessment models (IAMs) have paid little attention to this matter. In this study, the IMAGE model is used to assess different futures of energy, agricultural and industry impacting the effort required to meet IMO's target for 2050. To that end, long-term seaborne trade projections are created from outputs of the IMAGE model. The results show that varying pathways of socio-economic development strongly affect the size of the sector. The mass shipped globally ranges from 17 to 35 Gt/yr in 2050. This corresponds to an energy demand between 9 and 25 EJ in the same year, which would require significant amounts of low-carbon fuels. Interestingly, in a climate policy scenario, the avoided trade of fossil energy, although partially compensated by an increase of biofuel trade, lowers the international shipping mitigation effort.

Mitigation pathways allowing for temperature overshoot often ignore the related climate and macroeconomic impacts. Net-zero pathways with limited overshoot could reduce low-probability high-consequence risks and economic loss. Mitigation pathways exploring end-of-century temperature targets often entail temperature overshoot. Little is known about the additional climate risks generated by overshooting temperature. Here we assessed the benefits of limiting overshoot. We computed the probabilistic impacts for different warming targets and overshoot levels on the basis of an ensemble of integrated assessment models. We explored both physical and macroeconomic impacts, including persistent and non-persistent climate impacts. We found that temperature overshooting affects the likelihood of many critical physical impacts, such as those associated with heat extremes. Limiting overshoot reduces risk in the right tail of the distribution, in particular for low-temperature targets where larger overshoots arise as a way to lower short-term mitigation costs. We also showed how, after mid-century, overshoot leads to both higher mitigation costs and economic losses from the additional impacts. The study highlights the need to include climate risk analysis in low-carbon pathways.

Long-term scenarios play an important role in research on global environmental change. The climate change research community is developing new scenarios integrating future changes in climate and society to investigate climate impacts as well as options for mitigation and adaptation. One component of these new scenarios is a set of alternative futures of societal development known as the shared socioeconomic pathways (SSPs). The conceptual framework for the design and use of the SSPs calls for the development of global pathways describing the future evolution of key aspects of society that would together imply a range of challenges for mitigating and adapting to climate change. Here we present one component of these pathways: the SSP narratives, a set of five qualitative descriptions of future changes in demographics, human development, economy and lifestyle, policies and institutions, technology, and environment and natural resources. We describe the methods used to develop the narratives as well as how these pathways are hypothesized to produce particular combinations of challenges to mitigation and adaptation. Development of the narratives drew on expert opinion to (1) identify key determinants of these challenges that were essential to incorporate in the narratives and (2) combine these elements in the narratives in a manner consistent with scholarship on their inter-relationships. The narratives are intended as a description of plausible future conditions at the level of large world regions that can serve as a basis for integrated scenarios of emissions and land use, as well as climate impact, adaptation and vulnerability analyses.

International audience; Although the cement industry emits around 6% of global CO2 emissions, most global Integrated Assessment Models (IAMs) barely represent this industrial subsector or do not cover all important processes. This study, describes the state-of-the-art of cement modelling in IAMs, suggests possible improvements and discusses the impacts of these on energy and greenhouse gas emissions (GHG) in the IMAGE global IAM.It is found that two cement-sector specific GHG mitigation measures are often not explicitly accounted for in IAMs, namely: (i) retrofitting and (ii) reducing the clinker to cement ratio. For retrofitting, many measures are identified as cost-effective and when incorporating these in the IMAGE model overall energy use reduces between 2010 and 2035 by 9.8 and 11 EJ (4% and 5%) under the baseline and GHG mitigation scenarios, respectively. When incorporating the clinker to cement ratio by linking material availability to the activities in the steel industry and coal-fired power plants, the 2050 energy use reduces by 15% under the baseline scenario and increases by 9% under the GHG mitigation scenario as fewer coal-fired power plants are in operation. This is even more prominent in the long term. The 2100 energy use is 14% higher in the GHG mitigation scenario as even fewer coal-fired power plants are used drastically limiting the potential for clinker substitution with fly ash. These results highlight the importance of capturing cross-sectoral relationships between industries and of including sector specific mitigation measures in long-term energy models.

Correction for “Limiting global-mean temperature increase to 1.5–2 °C could reduce the incidence and spatial spread of dengue fever in Latin America,” by Felipe J. Colón-González, Ian Harris, Timothy J. Osborn, Christine Steiner São Bernardo, Carlos A. Peres, Paul R. Hunter, and Iain R. Lake, which was first published May 29, 2018; 10.1073/pnas.1718945115 (Proc. Natl. Acad. Sci. U.S.A. 115, 6243–6248). The authors note that Rachel Warren and Detlef van Vuuren should be added to the author list. Rachel Warren should appear as the seventh author, following Paul R. Hunter. Detlef van Vuuren should appear as the eighth author, following Rachel Warren and preceding Iain R. Lake. Rachel Warren should be credited with designing research. Detlef van Vuuren should be credited with contributing data. The corrected author line, affiliation line, and author contributions appear below. The online version has been corrected. The authors also note that the following statement should be added to the Acknowledgments: “R.W. and D.v.V. also received funding from the United Kingdom government, Department for Business, Energy, and Industrial Strategy, as part of the ‘Implications of Global Warming of 1.5 °C and 2.0 °C Project.’”

An estimated 26% of current global child deaths can be attributed to various and modifiable environmental factors, which are addressed under multiple Sustainable Development Goals (SDGs). This study assesses future reductions in child mortality in relation to the achievement of environment-related SDG targets. It uses projections of health risk factors from the IMAGE 3.0 Integrated Assessment Model, based on the Shared Socioeconomic Pathways (SSPs), linked to a standard multi-state health model (GISMO), distinguishing risk factors, disease occurrence and cause-specific death. The study concludes that, on a global level, the SDG target on child mortality will not be achieved in any of the three SSP scenarios analysed, mainly due to persistent high mortality rates in Sub-Saharan Africa and South Asia. By 2030, environmental health risk factors – including childhood undernutrition, no access to improved drinking water and sanitation, no access to modern fuels and exposure to malaria – will still be responsible for 14% to 16% of total global child deaths (8% to 10% when excluding nutrition-related mortality). Under the middle-of-the-road SSP2 baseline scenario, achievement of the SDG targets on hunger, drinking water and sanitation and modern energy services, would avoid 433 thousand child deaths by 2030. If, in addition, also higher standards would be achieved for access to water and energy, as well as universal secondary female education and advanced malaria control, a total of 733 thousand child deaths is projected to be avoided by 2030 (444 thousand child deaths, when excluding nutrition-related mortality), which would reduce projected global child mortality by 13%. Overall, more than 25% of the child mortality reduction that is needed to achieve the SDG target in Sub-Saharan Africa can be achieved through SDG-related policies on food, water and energy. This requires integrated and intersectoral approaches to environmental health.

Global river flood risk is expected to increase substantially over coming decades due to both climate change and socioeconomic development. Model-based projections suggest that southeast Asia and Africa are at particular risk, highlighting the need to invest in adaptation measures. Understanding global future river flood risk is a prerequisite for the quantification of climate change impacts and planning effective adaptation strategies1. Existing global flood risk projections fail to integrate the combined dynamics of expected socio-economic development and climate change. We present the first global future river flood risk projections that separate the impacts of climate change and socio-economic development. The projections are based on an ensemble of climate model outputs2, socio-economic scenarios3, and a state-of-the-art hydrologic river flood model combined with socio-economic impact models4,5. Globally, absolute damage may increase by up to a factor of 20 by the end of the century without action. Countries in Southeast Asia face a severe increase in flood risk. Although climate change contributes significantly to the increase in risk in Southeast Asia6, we show that it is dwarfed by the effect of socio-economic growth, even after normalization for gross domestic product (GDP) growth. African countries face a strong increase in risk mainly due to socio-economic change. However, when normalized to GDP, climate change becomes by far the strongest driver. Both high- and low-income countries may benefit greatly from investing in adaptation measures, for which our analysis provides a basis.

In the version of ‘Supplementary Data 1’ originally published with this Article, the units for the ‘Capacity|Electricity|*’ variables in the ‘Non_Investment_Annual’ tab were incorrectly given as EJ/yr; they should have read GW. This has now been corrected. Also, some of the variables listed in the ‘Non_Investment_Variable_Defs’ were not required and have therefore been removed.

This article is part of the special issue “Assessing Large-scale Global Bioenergy Deployment for Managing Climate Change (EMF-33)” edited by Steven Rose, John Weyant, Nico Bauer, Shinichiro Fuminori, Petr Havlik, Alexander Popp, Detlef van Vuuren, and Marshall Wise.; International audience; We present an overview of results from 11 integrated assessment models (IAMs) that participated in the 33rd study of the Stanford Energy Modeling Forum (EMF-33) on the viability of large-scale deployment of bioenergy for achieving long-run climate goals. The study explores future bioenergy use across models under harmonized scenarios for future climate policies, availability of bioenergy technologies, and constraints on biomass supply. This paper provides a more transparent description of IAMs that span a broad range of assumptions regarding model structures, energy sectors, and bioenergy conversion chains. Without emission constraints, we find vastly different CO2 emission and bioenergy deployment patterns across models due to differences in competition with fossil fuels, the possibility to produce large-scale bio-liquids, and the flexibility of energy systems. Imposing increasingly stringent carbon budgets mostly increases bioenergy use. A diverse set of available bioenergy technology portfolios provides flexibility to allocate bioenergy to supply different final energy as well as remove carbon dioxide from the atmosphere by combining bioenergy with carbon capture and sequestration (BECCS). Sector and regional bioenergy allocation varies dramatically across models mainly due to bioenergy technology availability and costs, final energy patterns, and availability of alternative decarbonization options. Although much bioenergy is used in combination with CCS, BECCS is not necessarily the driver of bioenergy use. We find that the flexibility to use biomass feedstocks in different energy sub-sectors makes large-scale bioenergy deployment a robust strategy in mitigation scenarios that is surprisingly insensitive with respect to reduced technology availability. However, the achievability of stringent carbon budgets and associated carbon prices is sensitive. Constraints on biomass feedstock supply increase the carbon price less significantly than excluding BECCS because carbon removals are still realized and valued. Incremental sensitivity tests find that delayed readiness of bioenergy technologies until 2050 is more important than potentially higher investment costs.

Access to electricity services is fundamental to development, as it enables improvements to the quality of human life. At the same time, increasing electricity access can have notable consequences for global climate change. This paper analyses trade-offs and synergies between achieving universal electricity access and climate change mitigation in Sub-Saharan Africa, using the IMAGE-TIMER integrated assessment model. For this purpose, we analysed developments in a number of indicators that describe demand, production, and costs of the future power system under various scenarios with and without climate change mitigation policies. The results show that, achieving universal electricity access requires an annual investment of USD 27–33 billion until 2030 on top of baseline investment. There is a strong synergy in emissions reduction and investment savings, particularly driven by the regions’ efficiency improvements of household appliances (the purchase of efficient appliances and the efficient use of the appliances). On the other hand, climate mitigation policies are projected to increase the cost of electricity per kWh, depending on fossil fuel share in the mix. Therefore, we conclude that, climate policies will need to be combined with complementary policies- e.g. pro-poor tariffs, fuel subsidies, and cross subsidization- to protect the poor from increasing electricity prices.

In the Paris Agreement under the United Nations Framework Convention on Climate Change (UNFCCC), for the first time, non-state actors were addressed in the international negotiations and were explicitly invited to act on climate change. Indeed, there are many transnational emission reduction initiatives (TERIs) outside the UNFCCC, driven by non-state actors or national governments, which aim at reducing greenhouse gas (GHG) emissions. Using an Integrated Assessment Model (IAM), this study assessed the potential impact of a selection of large TERIs that existed before the Paris Agreement on global greenhouse gas emissions. TERIs could lead to significant emission reductions: the eleven selected initiatives included in the analysis here could – if fully implemented – deliver annual GHG emission reductions of 2.5 GtCO2eq by 2020 and of 5.0 GtCO2eq by 2030 from a no-policy-baseline emission level of 53.7 GtCO2 and 61.1 GtCO2eq, respectively. Although these reductions are of similar magnitude as those pledged by countries under the umbrella of the UNFCCC, these reductions may significantly overlap with those of pledges and Nationally Determined Contributions. The maximum estimate of overlap is around 70% by 2020 and 80% by 2030. This means that the combined impact on global GHG emissions of TERIs and NDCs, assuming a maximum overlap, would lead to emission levels between 53 and 55 GtCO2eq by 2030, compared to a level of 54 to 56 GtCO2eq resulting from NDCs alone.

This article shows the potential impact on global GHG emissions in 2030, if all countries were to implement sectoral climate policies similar to successful examples already implemented elsewhere. This assessment was represented in the IMAGE and GLOBIOM/G4M models by replicating the impact of successful national policies at the sector level in all world regions. The first step was to select successful policies in nine policy areas. In the second step, the impact on the energy and land-use systems or GHG emissions was identified and translated into model parameters, assuming that it would be possible to translate the impacts of the policies to other countries. As a result, projected annual GHG emission levels would be about 50 GtCO2e by 2030 (2% above 2010 levels), compared to the 60 GtCO2e in the ‘current policies’ scenario. Most reductions are achieved in the electricity sector through expanding renewable energy, followed by the reduction of fluorinated gases, reducing venting and flaring in oil and gas production, and improving industry efficiency. Materializing the calculated mitigation potential might not be as straightforward given different country priorities, policy preferences and circumstances. Key policy insightsConsiderable emissions reductions globally would be possible, if a selection of successful policies were replicated and implemented in all countries worldwide.This would significantly reduce, but not close, the emissions gap with a 2°C pathway.From the selection of successful policies evaluated in this study, those implemented in the sector ‘electricity supply’ have the highest impact on global emissions compared to the ‘current policies’ scenario.Replicating the impact of these policies worldwide could lead to emission and energy trends in the renewable electricity, passenger transport, industry (including fluorinated gases) and buildings sector, that are close to those in a 2°C scenario.Using successful policies and translating these to policy impact per sector is a more reality-based alternative to most mitigation pathways, which need to make theoretical assumptions on policy cost-effectiveness.

Although nearly all 2 °C scenarios use negative CO2 emission technologies, only relatively small investments are being made in them, and concerns are being raised regarding their large-scale use. If no explicit policy decisions are taken soon, however, their use will simply be forced on us to meet the Paris climate targets.

Although nearly all 2 °C scenarios use negative CO2 emission technologies, only relatively small investments are being made in them, and concerns are being raised regarding their large-scale use. If no explicit policy decisions are taken soon, however, their use will simply be forced on us to meet the Paris climate targets.

Targets for human development are increasingly connected with targets for nature, however, existing scenarios do not explicitly address this relationship. Here, we outline a strategy to generate scenarios centred on our relationship with nature to inform decision-making at multiple scales.

Targets for human development are increasingly connected with targets for nature, however, existing scenarios do not explicitly address this relationship. Here, we outline a strategy to generate scenarios centred on our relationship with nature to inform decision-making at multiple scales.

The authors regret that, as a reader informed us, the presented historic data for steel production from scrap did not match the available data sources for the USA and Western Europe. A close inspection of the model code revealed that for the historic period 1971–2010, the market share for scrap was erroneously allocated twice (once forced by the scrap availability and a second time as part of the historic data on production shares). As a result, our model indicated a too high production share of steel from scrap in the year 2010, which also influenced the results for 2020 due to slow turnover of the production stock. The results for 2050 were not influenced by this error because there is a full capital stock turnover between 2010 and 2050. Since this error only influenced the market allocation of steel production technologies, and not the total level of steel production, correcting this error only lead to minor changes in the composition of final energy use and CO2 emissions. The regions with the largest adjustments are those with high shares of steel recycling, such as Western Europe and the USA. We have corrected this error, reran all scenarios with the updated model, and present below a corrected version of the text and figures that were influenced by this error. The main changes are related to Section 4.1.1 in the original paper. Instead of electric arc furnace (EAF) accounting for 75% and 66% of steel production in 2010 in respectively the USA and Western Europe, this now only represents around 50% and 42%. Future projections for EAF to account for 60% and 50% by 2050 are similar, but indicate an increase of scrap share rather than a decrease (as mentioned in the original paper). For India and China the share of EAF in total steel production now increases respectively from 10% to 30% and 10% to 50% between 2010 and 2050 (originally the 2010 values were 13% and 18%, respectively). Globally, the share of scrap-EAF increases from 23% in 2010 to over 40% by 2050 (instead of remaining stable around 40% in the entire period). There are only minor changes in the results for energy intensity per tonne steel, carbon intensity per tonne steel and final energy for steel production. These changes do not influence any trends and numbers discussed in the text, but we have included the updated figures in this addendum. The emissions of carbon dioxide (CO2) from steel production have changed slightly as result of correcting the error with scrap EAF. Global CO2 emissions are now 3215 megatonnes (Mt) CO2 per year (yr) in 2010 (was 3250 MtCO2/yr) and 3525 MtCO2/yr by 2020 (was 3350 MtCO2/yr) but remain around 2500 MtCO2/yr in 2050. Emissions in the USA and Western Europe are still decreasing from 110 Mt (was 150 Mt) to around 100 MtCO2/yr by 2050 and from 170 Mt (was 180 Mt)1

Poverty and lack of access to electricity are highly correlated. In Sub-Saharan Africa, one of the poorest regions in the world, two in every three people have no access to electricity. This paper describes a purpose designed model to explore and project the development in the Sub-Saharan African electricity sector in Baseline and Universal access scenarios. The results provide insight into the role of different systems and technologies in providing access to electricity in the region and associated investment requirements. We project that Baseline developments do not lead to universal access to electricity, especially in Eastern Africa and the rural areas. The results show that central grid extension should be complemented with off-grid systems (mini-grid and stand-alone) to increase access in Sub-Saharan Africa. At the same time, the targeted level of consumption has large implications on the preferred electrification technology and associated investment requirements. For low levels of consumption, off-grid technologies are the most important technologies to increase access rate, while for high levels of consumption, extending the central grid is more economical. Total cumulative investment in the period 2010-2030 amount to 22 billion USD for low levels of consumption and exceed 2.5 trillion USD for high levels of consumption.

The European Union (EU) is committed to reducing its greenhouse gas (GHG) emission levels by 80%–95% in 2050 compared to 1990 levels. Various approaches have been developed to secure and evaluate the progress made towards this objective. To gain insights into how EU Member States are aligning to this collective long-term objective, we systematically compare the planning and ex-ante evaluation processes for five EU countries (respectively Denmark, France, Germany, the Netherlands and the United Kingdom). The comparative analysis consists of a qualitative comparison of (1) the governance of long-term policy planning and evaluation processes, (2) the national arrangement for quantitative (model-based) ex-ante policy evaluation and (3) the national arrangement for qualitative ex-ante policy evaluation (stakeholder participation). In a second step we conduct a quantitative comparison of national model-based ex-ante evaluation studies to assess the relative differences between the considered routes and the differences across the various countries. Although the five Member States plan policies along the same EU objective, we find a high diversity in how long-term commitments are established, governed and evaluated on the national level. Model-based scenario analyses are commonly used to explore and evaluate the possible national routes towards the EU 2050 objective. However, as these processes mostly concentrate on domestic action, they pay little attention to how domestic policies are affected by, or affecting, other international activities throughout Europe. Hence, current findings suggest that cross-border collaboration and stakeholder participation could further strengthen the analytical understanding of required transformative change in Europe and subsequently lead to a more durable long-term solution over time.

Long-term scenarios play an important role in research on global environmental change. The climate change research community is developing new scenarios integrating future changes in climate and society to investigate climate impacts as well as options for mitigation and adaptation. One component of these new scenarios is a set of alternative futures of societal development known as the shared socioeconomic pathways (SSPs). The conceptual framework for the design and use of the SSPs calls for the development of global pathways describing the future evolution of key aspects of society that would together imply a range of challenges for mitigating and adapting to climate change. Here we present one component of these pathways: the SSP narratives, a set of five qualitative descriptions of future changes in demographics, human development, economy and lifestyle, policies and institutions, technology, and environment and natural resources. We describe the methods used to develop the narratives as well as how these pathways are hypothesized to produce particular combinations of challenges to mitigation and adaptation. Development of the narratives drew on expert opinion to (1) identify key determinants of these challenges that were essential to incorporate in the narratives and (2) combine these elements in the narratives in a manner consistent with scholarship on their inter-relationships. The narratives are intended as a description of plausible future conditions at the level of large world regions that can serve as a basis for integrated scenarios of emissions and land use, as well as climate impact, adaptation and vulnerability analyses.

Climate researchers use carbon dioxide emission scenarios to explore alternative climate futures and potential impacts, as well as implications of mitigation and adaptation policies. Often, these scenarios are published without formal probabilistic interpretations, given the deep uncertainty related to future development. However, users often seek such information, a likely range or relative probabilities. Without further specifications, users sometimes pick a small subset of emission scenarios and/or assume that all scenarios are equally likely. Here, we present probabilistic judgments of experts assessing the distribution of 2100 emissions under a business-as-usual and a policy scenario. We obtain the judgments through a method that relies only on pairwise comparisons of various ranges of emissions. There is wide variability between individual experts, but they clearly do not assign equal probabilities for the total range of future emissions. We contrast these judgments with the emission projection ranges derived from the shared socio-economic pathways (SSPs) and a recent multi-model comparison producing probabilistic emission scenarios. Differences on long-term emission probabilities between expert estimates and model-based calculations may result from various factors including model restrictions, a coverage of a wider set of factors by experts, but also group think and inability to appreciate long-term processes.

Better water demand projections are needed in order to better assess water scarcity. The focus in this paper is on non-agricultural water demand, as this is the fastest-growing and least well-modelled demand component. We describe an end use-oriented model for future water demand in the electricity, industry and municipal sectors, with several new features. In the electricity sector, effects of thermal efficiency improvements on water demand are incorporated in our model. In the industry and municipal sectors, we separately estimate potential water efficiency improvements for withdrawal and consumption, so that consumption is no longer a simple fraction of withdrawal. We develop three scenarios for 26 regions and the period 1971-2100. The Medium and High scenarios project increasing global withdrawal (1930-2876km3/yr) and consumption (537-694km3/yr) in 2100, with especially dramatic increases in developing regions. Also, an alternative future is presented, with high standards of living and much lower water withdrawal (1010km3/yr) and consumption (236km3/yr). Aggressive efficiency measures can reduce baseline withdrawal and consumption in 2100 by 60% relative to zero efficiency gains.

Most model studies focus on technical solutions in order to meet the 2°C climate target, such as renewable, carbon capture and energy efficiency technologies. Such studies show that it becomes increasingly more difficult to attain the 2°C target with carbon price driven technical solutions alone. This indicates the need to focus more on non-economic and non-technological drivers of energy system transformations, which are generally not explicitly included in long-term scenario studies. This study implements a set of lifestyle change measures for residential energy use, mobility and waste management in the integrated assessment model IMAGE. We analyze the implications of these lifestyle changes in a business-as-usual and 2°C climate mitigation reference case. We find that lifestyle change measures included in this study mostly affect the end-use sectors. By 2050, the measures reduce CO2 emissions in the residential sector by about 13% and in the transport sector by about 35% compared to baseline emissions. The indirect implications in the industry and energy supply sectors were found to be negligible. In mitigation scenarios the contribution of lifestyle measures is dampened in end-use sectors as they overlap with more technical measures. Yet, as they may create opportunities to mitigate in sectors without more radical changes in (1) the energy infrastructure and (2) on the short term, it leads to a more cost-efficient mitigation strategy. Further research in how behavior can be internalized into integrated assessment studies is recommendable.

Most modelling studies that explore long-term greenhouse gas mitigation scenarios focus on cost-efficient emission pathways towards a certain climate target, like the internationally agreed target to keep global temperature increase below 2 °C compared to pre-industrial levels (the 2 °C climate target). However, different timing of reductions lead to different transient temperature increase over the course of the century and subsequently to differences in the time profiles of not only the mitigation costs but also adaptation costs and residual climate change damage. This study adds to the existing literature by focussing on the implication of these differences for the evaluation of a set of three mitigation scenarios (early action, gradual action and delayed action), all three limiting global temperature increase below 2 °C above pre-industrial levels, using different discount rates. The study shows that the gradual mitigation pathway is, for these discount rates, preferred over early or delayed action in terms of total climate costs and net benefits. The relative costs and benefits of the early or delayed mitigation action scenarios, in contrast, do strongly depend on the discount rate applied. For specific discount rates, these pathways might therefore be preferred for other reasons, such as reducing long-term uncertainty in climate costs by early action.

Better water demand projections are needed in order to better assess water scarcity. The focus in this paper is on non-agricultural water demand, as this is the fastest-growing and least well-modelled demand component. We describe an end use-oriented model for future water demand in the electricity, industry and municipal sectors, with several new features. In the electricity sector, effects of thermal efficiency improvements on water demand are incorporated in our model. In the industry and municipal sectors, we separately estimate potential water efficiency improvements for withdrawal and consumption, so that consumption is no longer a simple fraction of withdrawal. We develop three scenarios for 26 regions and the period 1971-2100. The Medium and High scenarios project increasing global withdrawal (1930-2876km3/yr) and consumption (537-694km3/yr) in 2100, with especially dramatic increases in developing regions. Also, an alternative future is presented, with high standards of living and much lower water withdrawal (1010km3/yr) and consumption (236km3/yr). Aggressive efficiency measures can reduce baseline withdrawal and consumption in 2100 by 60% relative to zero efficiency gains.

The residential sector plays an important role in the energy system of developing countries. In this paper we introduce a bottom up simulation model for household energy use. The model describes energy demand for several end-use functions based on a set of physical drivers, such as floor space and heating degree days. The model also recognizes different population groups: i.e. urban and rural households, each distinguishing five income quintiles. The model is applied to analyze possible future developments of residential energy use in five developing world regions: India, China, South East Asia, South Africa and Brazil. We find that in each of these regions cooking is currently the main end-use function, but that other functions, such as space heating, cooling and appliances become more important. At the same time, energy consumption slowly shifts towards modern fuels. The model also shows that climate policy can reduce residential energy emissions, but could also slow down the energy transition away from traditional fuels in low income classes. (C) 2011 Elsevier Ltd. All rights reserved.

Corporate climate action is increasingly considered important in driving the transition towards a low-carbon economy. For this, it is critical to ensure translation of global goals to greenhouse-gas (GHG) emissions reduction targets at company level. At the moment, however, there is a lack of clear methods to derive consistent corporate target setting that keeps cumulative corporate GHG emissions within a specific carbon budget (for example, 550-1,300GtCO2 between 2011 and 2050 for the 2°C target). Here we propose a method for corporate emissions target setting that derives carbon intensity pathways for companies based on sectoral pathways from existing mitigation scenarios: the Sectoral Decarbonization Approach (SDA). These company targets take activity growth and initial performance into account. Next to target setting on company level, the SDA can be used by companies, policymakers, investors or other stakeholders as a benchmark for tracking corporate climate performance and actions, providing a mechanism for corporate accountability.