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Alternative pathways to the 1.5 °C target reduce the need for negative emission technologies

DOI:10.1038/s41558-018-0119-8
Authors:
Detlef P. van Vuuren at Utrecht University
Detlef P. van Vuuren
E. Stehfest at PBL Netherlands Environmental Assessment Agency
E. Stehfest
David E.H.J. Gernaat at PBL Netherlands Environmental Assessment Agency
David E.H.J. Gernaat
Maarten Van den Berg at PBL Netherlands Environmental Assessment Agency
Maarten Van den Berg
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Abstract and Figures

Mitigation scenarios that achieve the ambitious targets included in the Paris Agreement typically rely on greenhouse gas emission reductions combined with net carbon dioxide removal (CDR) from the atmosphere, mostly accomplished through large-scale application of bioenergy with carbon capture and storage, and afforestation. However, CDR strategies face several difficulties such as reliance on underground CO2 storage and competition for land with food production and biodiversity protection. The question arises whether alternative deep mitigation pathways exist. Here, using an integrated assessment model, we explore the impact of alternative pathways that include lifestyle change, additional reduction of non-CO2 greenhouse gases and more rapid electrification of energy demand based on renewable energy. Although these alternatives also face specific difficulties, they are found to significantly reduce the need for CDR, but not fully eliminate it. The alternatives offer a means to diversify transition pathways to meet the Paris Agreement targets, while simultaneously benefiting other sustainability goals.
GHG emission for the baseline and mitigation scenarios a, Total emissions. b,c, Emissions for each emission category for the baseline (b) and mitigation scenarios (c). Emission categories include CO2 emissions from energy (black) and from land-use change (green), CH4 emissions (orange), N2O emissions (purple) and halogenated gases (yellow). The background shading in b and c refers to the colour of the scenario category in a (baseline, 2.6 and 1.9 W m⁻²).
GHG emission for the baseline and mitigation scenarios a, Total emissions. b,c, Emissions for each emission category for the baseline (b) and mitigation scenarios (c). Emission categories include CO2 emissions from energy (black) and from land-use change (green), CH4 emissions (orange), N2O emissions (purple) and halogenated gases (yellow). The background shading in b and c refers to the colour of the scenario category in a (baseline, 2.6 and 1.9 W m⁻²).
… 
CO2 emissions for the baseline and mitigation scenarios a, CO2 fluxes for the default 1.9 W m⁻² scenario. The plot shows the sum of all categories (yellow line), positive fossil fuel emissions (black), negative emissions from BECCS (dark blue for net negative emissions, light blue for other BECCS) and land-use-change emissions (dark green for positive emissions, light green for negative emissions). b,c, The same flows in terms of the cumulative emissions for the 2010–2100 period, for baseline cases (b) and mitigation scenarios (c). The yellow marker represents the net emissions. The shading in b and c refers to the colour of the scenario category in Fig. 1a (baseline, 2.6 and 1.9 W m⁻²).
CO2 emissions for the baseline and mitigation scenarios a, CO2 fluxes for the default 1.9 W m⁻² scenario. The plot shows the sum of all categories (yellow line), positive fossil fuel emissions (black), negative emissions from BECCS (dark blue for net negative emissions, light blue for other BECCS) and land-use-change emissions (dark green for positive emissions, light green for negative emissions). b,c, The same flows in terms of the cumulative emissions for the 2010–2100 period, for baseline cases (b) and mitigation scenarios (c). The yellow marker represents the net emissions. The shading in b and c refers to the colour of the scenario category in Fig. 1a (baseline, 2.6 and 1.9 W m⁻²).
… 
Transformations in land use/cover and energy use a,b, Land cover for agriculture crops, pasture, energy crops and total forest area (natural and managed) by category (a) (remaining natural land cover types are not included) and the evolution of agricultural land use (the sum of crop, pasture and bioenergy area in a) over time (b). c,d, Primary energy use per energy carrier (c) and the share of low-carbon technology in total primary energy (d). Low-carbon technology is defined as solar, wind, nuclear power, bioenergy (traditional and modern), hydropower and fossil fuels (coal, oil, natural gas) with CCS.
Transformations in land use/cover and energy use a,b, Land cover for agriculture crops, pasture, energy crops and total forest area (natural and managed) by category (a) (remaining natural land cover types are not included) and the evolution of agricultural land use (the sum of crop, pasture and bioenergy area in a) over time (b). c,d, Primary energy use per energy carrier (c) and the share of low-carbon technology in total primary energy (d). Low-carbon technology is defined as solar, wind, nuclear power, bioenergy (traditional and modern), hydropower and fossil fuels (coal, oil, natural gas) with CCS.
… 
The use of BECCS in mitigation scenarios a, The use of BECCS over time (that is, the bottom category of the energy bar chart in Fig. 3). b, The cumulative net CDR from energy (BECCS) as a function of radiative forcing target. Shown are the scenarios described in this paper (dots), and also the literature range (green area: 10–90th percentile for SSP2; grey line: average; dotted lines: range for all SSP scenarios). The dark lines in a and the black dots in b refer to the default 2.6 and 1.9 W m⁻² scenarios.
The use of BECCS in mitigation scenarios a, The use of BECCS over time (that is, the bottom category of the energy bar chart in Fig. 3). b, The cumulative net CDR from energy (BECCS) as a function of radiative forcing target. Shown are the scenarios described in this paper (dots), and also the literature range (green area: 10–90th percentile for SSP2; grey line: average; dotted lines: range for all SSP scenarios). The dark lines in a and the black dots in b refer to the default 2.6 and 1.9 W m⁻² scenarios.
… 
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Articles
https://doi.org/10.1038/s41558-018-0119-8
1PBL Netherlands Environmental Assessment Agency, The Hague, the Netherlands. 2Copernicus Institute for Sustainable Development, Utrecht University,
Utrecht, the Netherlands. *e-mail: Detlef.vanvuuren@pbl.nl
The Paris Agreement on climate change aims at ‘holding the
increase in the global average temperature to well below 2 °C’,
and ‘to pursue efforts to limit the temperature increase to
1.5 °C’1. However, the knowledge of how to achieve these ‘Paris
goals’ is still limited. The Intergovernmental Panel on Climate
Change (IPCC) Fifth Assessment Report examined a considerable
amount of literature on scenarios leading to a radiative forcing at
around 2.6 W m−2 above pre-industrial levels by 2100, correspond-
ing to a likely change (that is, > 66%) of not exceeding the 2 °C goal2.
The IPCC report hardly discussed the question of how to keep
warming below 1.5 °C (corresponding to a forcing level of around
1.9–2.0 W m−2) due to lack of existing literature (with some excep-
tions3,4). New scenarios for this goal are currently being developed
in response to the policy interest, and the IPCC will publish a spe-
cial report on this topic5.
Mitigation scenarios developed using integrated assessment
models (IAMs) can provide insight into strategies that drasti-
cally reduce greenhouse gas (GHG) emissions2,6,7. This is typically
achieved by finding a cost-optimal combination of technologies,
given model rules on system behaviour and a set of technology and
policy assumptions (for example, delay in participation)2,8. Scenarios
consistent with the Paris goals reduce GHG emissions by switch-
ing to zero- and low-carbon energy options, increasing energy effi-
ciency, using carbon capture and storage (CCS), reducing non-CO2
GHG emissions, eliminating emissions related to land-use change
and stimulating afforestation2,7. Cost-optimal scenarios, without
delays or constraints in technology deployment, project GHG emis-
sions to peak around 2020, followed by rapid emission reductions,
carbon neutrality sometime in the second half of the century and
eventually net CO2 removal (CDR) from the atmosphere2,7,9. This
can be referred to as the default strategy. Of the 114 scenarios
assessed by the IPCC leading to forcing values of around 2.6 W m−2
(likely probability for 2 °C), 104 show net CDR in the second half
of the century, mostly achieved by bioenergy with CCS (BECCS),
sometimes complemented by reforestation2. The total CDR in these
scenarios is substantial—that is, typically around 10 GtCO2 per
year in 2100 or 200–400 GtCO2 over the course of the century10,11.
Moreover, the same literature suggests considerable cost increases,
or even infeasibilities, if CDR is not available2. The relatively few
1.5 °C scenarios published to date show pathways similar to the 2 °C
scenarios, but with deeper reductions occurring earlier in time3.
Several publications question whether it is possible to achieve
the IAM-based scenarios and, especially, the proposed scale of
CDR11,12. Their concerns relate to the possible impacts of land-use-
based CDR options, such as bioenergy and reforestation, on food
production, biodiversity, GHG emissions and albedo11. Moreover,
while geological storage capacity estimates exceed several thou-
sand gigatonnes of CO2, questions remain about whether the full
capacity is available13,14. Finally, CCS has currently little societal sup-
port as demonstrated by the difficulty in implementing real-world
experiments13,15. As several key CDR options share these concerns,
they cannot readily substitute one another if future performance is
poorer or more difficult than projected. Since it will soon be impos-
sible to achieve ambitious climate goals without implementing CDR
to compensate overshoot of the carbon budget (that is, cumulative
CO2 emissions corresponding to a climate target)2, an assessment of
their use or alternative options will have to be made now, even if the
situation of net CDR will not occur before 205016.
As IAMs select technologies on the basis of relative costs, they
normally concentrate on reduction measures for which reason-
able estimates of future performance and costs can be made. This
implies that some possible response strategies receive less attention,
as their future performance is more speculative or their introduc-
tion would be based on drivers other than cost, such as lifestyle
change or more rapid electrification17,18. Moreover, existing studies
hardly look into more aggressive implementation of options such
as rapid implementation of the best available technologies or deep
reduction of non-CO2 GHGs (with some exceptions, for example,
Alternative pathways to the 1.5°C target reduce
the need for negative emission technologies
Detlef P. van Vuuren 1,2*, Elke Stehfest1, David E. H. J. Gernaat1,2, Maarten van den Berg1, David L. Bijl2,
Harmen Sytze de Boer1,2, Vassilis Daioglou 1,2, Jonathan C. Doelman1, Oreane Y. Edelenbosch1,2,
Mathijs Harmsen1,2, Andries F. Hof 1,2 and Mariësse A. E. van Sluisveld1,2
Mitigation scenarios that achieve the ambitious targets included in the Paris Agreement typically rely on greenhouse gas
emission reductions combined with net carbon dioxide removal (CDR) from the atmosphere, mostly accomplished through
large-scale application of bioenergy with carbon capture and storage, and afforestation. However, CDR strategies face several
difficulties such as reliance on underground CO2 storage and competition for land with food production and biodiversity protec-
tion. The question arises whether alternative deep mitigation pathways exist. Here, using an integrated assessment model,
we explore the impact of alternative pathways that include lifestyle change, additional reduction of non-CO2 greenhouse gases
and more rapid electrification of energy demand based on renewable energy. Although these alternatives also face specific
difficulties, they are found to significantly reduce the need for CDR, but not fully eliminate it. The alternatives offer a means to
diversify transition pathways to meet the Paris Agreement targets, while simultaneously benefiting other sustainability goals.
© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
NATURE CLIMATE CHANGE | VOL 8 | MAY 2018 | 391–397 | www.nature.com/natureclimatechange 391
The Nature trademark is a registered trademark of Springer Nature Limited.
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  • Jan 2015
p>In the future, the land system will be facing new intersecting challenges. While food demand, especially for resource-intensive livestock based commodities, is expected to increase, the terrestrial system has large potentials for climate change mitigation through improved agricultural management, providing biomass for bioenergy, and conserving or even enhancing carbon stocks of ecosystems. However, uncertainties in future socio-economic land use drivers may result in very different land-use dynamics and consequences for land-based ecosystem services. This is the first study with a systematic interpretation of the Shared Socio-Economic Pathways (SSPs) in terms of possible land-use changes and their consequences for the agricultural system, food provision and prices as well as greenhouse gas emissions. Therefore, five alternative Integrated Assessment Models with distinctive land-use modules have been used for the translation of the SSP narratives into quantitative projections. The model results reflect the general storylines of the SSPs and indicate a broad range of potential land-use futures with global agricultural land of 4900 mio ha in 2005 decreasing by 810 mio ha until 2100 at the lower (SSP1) and increasing by 1080 mio ha (SSP3) at the upper end. Greenhouse gas emissions from land use and land use change, as a direct outcome of these diverse land-use dynamics, and agricultural production systems differ strongly across SSPs (e.g. cumulative land use change emissions between 2005 and 2100 range from -54 to 402 Gt CO<sub>2</sub>). The inclusion of land-based mitigation efforts, particularly those in the most ambitious mitigation scenarios, further broadens the range of potential land futures and can strongly affect greenhouse gas dynamics and food prices. In general, it can be concluded that low demand for agricultural commodities, rapid growth in agricultural productivity and globalized trade, all most pronounced in a SSP1 world, have the potential to enhance the extent of natural ecosystems, lead to lowest greenhouse gas emissions from the land system and decrease food prices over time. The SSP-based land use pathways presented in this paper aim at supporting future climate research and provide the basis for further regional integrated assessments, biodiversity research and climate impact analysis.</p
Bottom-up simulations of methane and ethane emissions from global oil and gas systems 1980 to 2012
Article
Full-text available
Existing bottom-up emission inventories of methane from global oil and gas systems do not well explain year-on-year variation in atmospheric methane estimated by top-down models. Using a novel bottom-up approach this study quantifies and attributes methane and ethane emissions from global oil and gas production from 1980 to 2012. Country-specific information on associated gas flows from published sources are combined with inter-annual variations in observed flaring of associated gas from satellite images from 1994 to 2010, to arrive at country-specific annual estimates of methane and ethane emissions from flows of associated gas. Results confirm trends from top-down models and indicate considerably higher methane and ethane emissions from oil production than previously shown in bottom-up inventories for this time period.
Exploring SSP land-use dynamics using the IMAGE model: Regional and gridded scenarios of land-use change and land-based climate change mitigation
Article
Projected increases in population, income and consumption rates are expected to lead to rising pressure on the land system. Ambitions to limit global warming to 2 °C or even 1.5 °C could also lead to additional pressures from land-based mitigation measures such as bioenergy production and afforestation. To investigate these dynamics, this paper describes five elaborations of the Shared Socio-economic Pathways (SSP) using the IMAGE 3.0 integrated assessment model framework to produce regional and gridded scenarios up to the year 2100. Additionally, land-based climate change mitigation is modelled aiming for long-term mitigation targets including 1.5 °C. Results show diverging global trends in agricultural land in the baseline scenarios ranging from an expansion of nearly 826 Mha in SSP3 to a decrease of more than 305 Mha in SSP1 for the period 2010–2050. Key drivers are population growth, changes in food consumption, and agricultural efficiency. The largest changes take place in Sub-Saharan Africa in SSP3 and SSP4, predominantly due to high population growth. With low increases in agricultural efficiency this leads to expansion of agricultural land and reduced food security. Land use also plays a crucial role in ambitious mitigation scenarios. First, agricultural emissions could form a substantial component of emissions that cannot be fully mitigated. Second, bioenergy and reforestation are crucial to create net negative emissions reducing emissions in SSP2 in 2050 by 8.7 Gt CO2/yr and 1.9 Gt CO2/yr, respectively (1.5 °C scenario compared to baseline). This is achieved by expansion of bioenergy area (516 Mha in 2050) and reforestation. Expansion of agriculture for food production is reduced due to REDD policy (290 Mha in 2050) affecting food security especially in Sub-Saharan Africa indicating an important trade-off of land-based mitigation. This set of SSP land-use scenarios provides a comprehensive quantification of interacting trends in the land system, both socio-economic and biophysical. By providing high resolution data, the scenario output can improve interactions between climate research and impact studies.
Open discussion of negative emissions is urgently needed
Article
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.
A physically-based model of long-term food demand
Article
Reducing hunger while staying within planetary boundaries of pollution, land use and fresh water use is one of the most urgent sustainable development goals. It is imperative to understand future food demand, the agricultural system, and the interactions with other natural and human systems. Studying such interactions in the long-term future is often done with Integrated Assessment Modelling. In this paper we develop a new food demand model to make projections several decades ahead, having 46 detailed food categories and population segmented by income and urban vs rural. The core of our model is a set of relationships between income and dietary patterns, with differences between regions and income inequalities within a region. Hereby we take a different, more long-term-oriented approach than elasticity-based macro-economic models (Computable General Equilibrium (CGE) and Partial Equilibrium (PE) models). The physical and detailed nature of our model allows for fine-grained scenario exploration. We first apply the model to the newly developed Shared Socio-economic Pathways (SSP) scenarios, and then to additional sustainable development scenarios of food waste reduction and dietary change. We conclude that total demand for crops and grass could increase roughly 35–165% between 2010 and 2100, that this future demand growth can be tempered more effectively by replacing animal products than by reducing food waste, and that income-based consumption inequality persists and is a contributing factor to our estimate that 270 million people could still be undernourished in 2050.
Assessment of wind and solar power in global low-carbon energy scenarios: An introduction
Article
This preface introduces the special section on the assessment of wind and solar in global low-carbon energy scenarios. The special section documents the results of a coordinated research effort to improve the representation of variable renewable energies (VRE), including wind and solar power, in Integrated Assessment Models (IAM) and presents an overview of the results obtained in the underlying coordinated model inter-comparison exercise.
Designing the Ideal Offshore Platform Methane Mitigation Strategy
Conference Paper
  • Apr 2010
Sensitivity of projected long-term CO2 emissions across the Shared Socioeconomic Pathways
Article
  • Jan 2017
Scenarios showing future greenhouse gas emissions are needed to estimate climate impacts and the mitigation efforts required for climate stabilization. Recently, the Shared Socioeconomic Pathways (SSPs) have been introduced to describe alternative social, economic and technical narratives, spanning a wide range of plausible futures in terms of challenges to mitigation and adaptation. Thus far the key drivers of the uncertainty in emissions projections have not been robustly disentangled. Here we assess the sensitivities of future CO 2 emissions to key drivers characterizing the SSPs. We use six state-of-the-art integrated assessment models with different structural characteristics, and study the impact of five families of parameters, related to population, income, energy efficiency, fossil fuel availability, and low-carbon energy technology development. A recently developed sensitivity analysis algorithm allows us to parsimoniously compute both the direct and interaction effects of each of these drivers on cumulative emissions. The study reveals that the SSP assumptions about energy intensity and economic growth are the most important determinants of future CO 2 emissions from energy combustion, both with and without a climate policy. Interaction terms between parameters are shown to be important determinants of the total sensitivities. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.