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Understanding future emissions from low-carbon power systems by integration of life-cycle assessment and integrated energy modelling

DOI:10.1038/s41560-017-0032-9
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Michaja Pehl at Potsdam Institute for Climate Impact Research
Michaja Pehl
Anders Arvesen
Anders Arvesen
Anders Arvesen
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Florian Humpenöder at Potsdam Institute for Climate Impact Research
Florian Humpenöder
Alexander Popp at Potsdam Institute for Climate Impact Research
Alexander Popp
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Abstract and Figures

Both fossil-fuel and non-fossil-fuel power technologies induce life-cycle greenhouse gas emissions, mainly due to their embodied energy requirements for construction and operation, and upstream CH4 emissions. Here, we integrate prospective life-cycle assessment with global integrated energy-economy-land-use-climate modelling to explore life-cycle emissions of future low-carbon power supply systems and implications for technology choice. Future per-unit life-cycle emissions differ substantially across technologies. For a climate protection scenario, we project life-cycle emissions from fossil fuel carbon capture and sequestration plants of 78-110 gCO2eq kWh⁻¹, compared with 3.5-12 gCO2eq kWh⁻¹ for nuclear, wind and solar power for 2050. Life-cycle emissions from hydropower and bioenergy are substantial (~100 gCO2eq kWh⁻¹), but highly uncertain. We find that cumulative emissions attributable to upscaling low-carbon power other than hydropower are small compared with direct sectoral fossil fuel emissions and the total carbon budget. Fully considering life-cycle greenhouse gas emissions has only modest effects on the scale and structure of power production in cost-optimal mitigation scenarios.
| Embodied energy use of electricity production as a percentage of lifetime electricity production. Global average values are shown by secondary energy carrier (coloured bars) for capacities built in 2050. Combined model variations over both regions and technology variants (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) are shown as grey boxplots. See also Supplementary Table 1.
| Embodied energy use of electricity production as a percentage of lifetime electricity production. Global average values are shown by secondary energy carrier (coloured bars) for capacities built in 2050. Combined model variations over both regions and technology variants (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) are shown as grey boxplots. See also Supplementary Table 1.
… 
| Specific direct and indirect GHG emissions. Global 2050 average of lifetime emissions over lifetime electricity production (solid coloured bars), for capacities built in 2050 in a 2 °C-consistent mitigation scenario. Model variations (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) across both regions and technology variants are shown as boxplots. Ranges of specific emissions from AR5, from section 7.8.1, Fig 7.6 in ref. 4 are shown as light blue ranges. BECCS is not assessed there. The (median) 2050 CO 2 intensity of electricity production for AR5 scenarios without CCS (technology category T3) reaching 430-480 ppm CO 2 eq (climate category 1) is shown in red as a proxy for the level of specific net emissions (without negative emissions from BECCS) in line with the 2 °C target. See also Supplementary Table 2.
| Specific direct and indirect GHG emissions. Global 2050 average of lifetime emissions over lifetime electricity production (solid coloured bars), for capacities built in 2050 in a 2 °C-consistent mitigation scenario. Model variations (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) across both regions and technology variants are shown as boxplots. Ranges of specific emissions from AR5, from section 7.8.1, Fig 7.6 in ref. 4 are shown as light blue ranges. BECCS is not assessed there. The (median) 2050 CO 2 intensity of electricity production for AR5 scenarios without CCS (technology category T3) reaching 430-480 ppm CO 2 eq (climate category 1) is shown in red as a proxy for the level of specific net emissions (without negative emissions from BECCS) in line with the 2 °C target. See also Supplementary Table 2.
… 
Total global 2050 emissions Both direct and indirect emissions from global power production in 2050 for the Baseline (no climate policy) and the Policy (2 °C-compatible) scenario. Direct fossil fuel CO2 (non-CCS) emissions derive from non-CCS fossil fuel plants, while direct fossil fuel CO2 (imperfect CCS capture) from fossil fuel plants with CCS. See also Supplementary Table 3.
Total global 2050 emissions Both direct and indirect emissions from global power production in 2050 for the Baseline (no climate policy) and the Policy (2 °C-compatible) scenario. Direct fossil fuel CO2 (non-CCS) emissions derive from non-CCS fossil fuel plants, while direct fossil fuel CO2 (imperfect CCS capture) from fossil fuel plants with CCS. See also Supplementary Table 3.
… 
Differences between global indirect emissions a,b, Differences between the Policy (2 °C-compatible) and Baseline (no climate policy) scenarios over time (a) and cumulated from 2010 to 2050 (b). Indirect emissions include those from construction, operation (except fuel burning), LULUC, and upstream and biogenic CH4 emissions. See also Supplementary Table 4.
Differences between global indirect emissions a,b, Differences between the Policy (2 °C-compatible) and Baseline (no climate policy) scenarios over time (a) and cumulated from 2010 to 2050 (b). Indirect emissions include those from construction, operation (except fuel burning), LULUC, and upstream and biogenic CH4 emissions. See also Supplementary Table 4.
… 
Impact on optimal technology choice a,b, Electricity production by technology for two variants of the Policy (2 °C-compatible) scenario, accounting only for direct emissions or all indirect emissions (a) and differences between the two variants in 2050 (b). Accounting for the effect of indirect emissions (upstream and biogenic CH4, LULUC and life-cycle CO2 emissions) reduces electricity production by about 3 EJ yr⁻¹ in 2050 (a). Technologies with comparatively high specific indirect emissions (gas, hydropower and bioenergy) produce significantly less electricity, which is largely offset by increased production from technologies with lower specific indirect emissions (wind, nuclear and CSP) (b). See also Supplementary Table 6.
Impact on optimal technology choice a,b, Electricity production by technology for two variants of the Policy (2 °C-compatible) scenario, accounting only for direct emissions or all indirect emissions (a) and differences between the two variants in 2050 (b). Accounting for the effect of indirect emissions (upstream and biogenic CH4, LULUC and life-cycle CO2 emissions) reduces electricity production by about 3 EJ yr⁻¹ in 2050 (a). Technologies with comparatively high specific indirect emissions (gas, hydropower and bioenergy) produce significantly less electricity, which is largely offset by increased production from technologies with lower specific indirect emissions (wind, nuclear and CSP) (b). See also Supplementary Table 6.
… 
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Articles
https://doi.org/10.1038/s41560-017-0032-9
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
1Potsdam Institute of Climate Impact Research, PO Box 60 12 03 Potsdam, Germany, . 2Industrial Ecology Programme and Department of Energy and
Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. 3Center for Industrial Ecology, Yale School for Forestry
and Environmental Studies, New Haven, CT, USA. *e-mail: michaja.pehl@pik-potsdam.de; gunnar.luderer@pik-potsdam.de
The Paris Agreement of COP21 confirmed the goal of limiting
global temperature increase well below 2 °C and acknowledged
the need to achieve net greenhouse gas neutrality during the
second half of the century1. Previous research based on integrated
energy–economy–climate models has shown that achieving these
targets cost-effectively requires a rapid, almost full-scale decarbon-
ization of the electricity system by mid-century2,3. In electricity pro-
duction, ample low-carbon alternatives are available4 and electricity
is a potential substitute for fossil-based fuels in all economic sectors,
which leads to final energy electricity shares of 25–45% in stringent
mitigation scenarios2.
The life-cycle assessment (LCA) literature illustrates that all
energy transformation technologies are associated with upstream
energy demands and corresponding indirect (that is, not caused by
fuel-burning on site) greenhouse gas (GHG) emissions4–7. Concerns
have been voiced that these can impair the emission reduction
potential of low-carbon technologies6,8,9. However, LCA studies of
electricity mostly focus on impacts on a per-kilowatt-hour basis
in static settings, typically neglecting technology improvements in
electricity generation technologies, as well as the effects of concur-
rent decarbonization measures in other sectors of the energy system
and the economy6,10,11.
Integrated energy–economy–climate modelling approaches
estimate cost-optimal long-term strategies to meet the emissions
constraints implied by climate targets3. Whereas direct combustion
emissions as well as CH4 from fossil fuel extraction and indirect
land-use change emissions are accounted for by many state-of-the-
art modelling systems, other indirect emissions, in particular those
related to energy required for the construction of power plants
and the production and transportation of fuels and other inputs
(defined here as embodied energy use, EEU), are not considered in
the optimization. We investigate to what extent this omission leads
to incomplete internalization of externalities.
A previous study by Hertwich et al.5 used prospective LCA to
compare similar scenarios in terms of environmental impacts,
but relied on exogenous scenarios for technology deployment,
and focused on non-climate environmental impacts to assess co-
benefits and trade-offs of climate change mitigation. Daly et al.9 and
Scott et al.12 investigated the influence of national climate policy on
domestic and non-domestic indirect GHG emissions and found
them to have a large potential for carbon leakage, as the ratio of
emissions caused domestically and overseas shifts to the latter due
to imports of goods and services. However, their analysis consid-
ered only the United Kingdom, based carbon intensities on aggre-
gate input–output relationships rather than process detail, and did
not account for policy-induced non-domestic emission reductions
in the context of coordinated international climate change mitiga-
tion efforts. Portugal-Pereira et al.13 included LCA emission coef-
ficients in an integrated assessment model (IAM) and studied the
effect of taxing indirect emissions on the electricity mix. However,
they considered only the Brazilian electricity system and used static
LCA coefficients.
In this study, we present consistent and detailed modelling of
EEU and indirect GHG emissions for global scenarios of future
electricity systems. By linking an IAM with EEU coefficients from a
prospective LCA model, we can provide a holistic and detailed per-
spective on future life-cycle greenhouse gas emissions of low-carbon
technologies and power systems in the context of a universal climate
change mitigation regime, thus closing an important research gap14–16
by quantifying these emissions and their effect on the choice of low-
carbon technologies in mitigation scenarios. This study combines
results from the REMIND model17,18, which details energy use and
Understanding future emissions from low-carbon
power systems by integration of life-cycle
assessment and integrated energy modelling
Michaja Pehl 1*, Anders Arvesen 2, Florian Humpenöder1, Alexander Popp1, Edgar G. Hertwich 3
and Gunnar Luderer1*
Both fossil-fuel and non-fossil-fuel power technologies induce life-cycle greenhouse gas emissions, mainly due to their embod-
ied energy requirements for construction and operation, and upstream CH4 emissions. Here, we integrate prospective life-
cycle assessment with global integrated energy–economy–land-use–climate modelling to explore life-cycle emissions of future
low-carbon power supply systems and implications for technology choice. Future per-unit life-cycle emissions differ substan-
tially across technologies. For a climate protection scenario, we project life-cycle emissions from fossil fuel carbon capture and
sequestration plants of 78–110gCO2eq kWh−1, compared with 3.5–12gCO2eq kWh−1 for nuclear, wind and solar power for 2050.
Life-cycle emissions from hydropower and bioenergy are substantial (∼ 100gCO2eq kWh−1), but highly uncertain. We find
that cumulative emissions attributable to upscaling low-carbon power other than hydropower are small compared with direct
sectoral fossil fuel emissions and the total carbon budget. Fully considering life-cycle greenhouse gas emissions has only
modest effects on the scale and structure of power production in cost-optimal mitigation scenarios.
NATURE ENERGY | VOL 2 | DECEMBER 2017 | 939–945 | www.nature.com/natureenergy 939
The Nature trademark is a registered trademark of Springer Nature Limited.
... demand changes, is considered in the foreground systems and the supply chains involved in supplying those products and services are considered in the background systems. Studies applying a prospective lifecycle assessment framework generally either mapp integrated assessment modeling results for future decarbonization scenarios to lifecycle inventory databases 22,23 , or combine results from integrated assessment models (IAMs) with lifecycle inventories and additional analytical tools to understand the deployment of new technologies, such as Morfeldt et al. 24 for electric cars or Pehl et al. 25 for power systems. ...
... Adjustments have been made to account for transmission and distribution losses. Upstream emissions from maintenance in power generation plants and fuel production are estimated for each technology based on global averages for each of the two global decarbonization pathways 25 . ...
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In this paper we study the impact of alternative metrics on short- and long-term multi-gas emission reduction strategies and the associated global and regional economic costs and emissions budgets. We compare global warming potentials with three different time horizons (20, 100, 500 years), global temperature change potential and global cost potentials with and without temperature overshoot. We find that the choice of metric has a relatively small impact on the CO 2 budget compatible with the 2° target and therefore on global costs. However it substantially influences mid-term emission levels of CH 4 , which may either rise or decline in the next decades as compared to today’s levels. Though CO 2 budgets are not affected much, we find changes in CO 2 prices which substantially affect regional costs. Lower CO 2 prices lead to more fossil fuel use and therefore higher resource prices on the global market. This increases profits of fossil-fuel exporters. Due to the different weights of non-CO 2 emissions associated with different metrics, there are large differences in nominal CO 2 equivalent budgets, which do not necessarily imply large differences in the budgets of the single gases. This may induce large shifts in emission permit trade, especially in regions where agriculture with its high associated CH 4 emissions plays an important role. Furthermore it makes it important to determine CO 2 equivalence budgets with respect to the chosen metric. Our results suggest that for limiting warming to 2 °C in 2100, the currently used GWP100 performs well in terms of global mitigation costs despite its conceptual simplicity. Copyright Springer Science+Business Media Dordrecht 2014
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Effects of exemplar scenarios on public preferences for energy futures using the my2050 scenario-building tool
Article
Understanding which energy future configurations provide publicly acceptable levels of energy security, affordability, and environmental protection is critical for institutional decision-making. However, little is known about how scenarios influence energy preferences. Here we present nationally representative UK data on public preferences for energy futures using the my2050 scenario-building tool that encourages engagement with the holistic complexities of system change. Engagement with the tool strengthened existing preferences for renewable energy and intentions to take personal action. Importantly, patterns of energy preferences were influenced by exemplar scenarios, which served as reference points that anchored choices. Carbon capture and storage, nuclear power, biofuels, and changes to heating and travel were particularly impacted by scenarios indicating uncertainty and ambivalence regarding these options. Scenarios (and scenario-building tools) are valuable for engaging citizens about future energy systems. However, care is required in their design and interpretation to reach robust conclusions about underlying preferences and acceptance.
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Industrial ecology in integrated assessment models
Article
  • Jan 2017
Technology-rich integrated assessment models (IAMs) address possible technology mixes and future costs of climate change mitigation by generating scenarios for the future industrial system. Industrial ecology (IE) focuses on the empirical analysis of this system. We conduct an in-depth review of five major IAMs from an IE perspective and reveal differences between the two fields regarding the modelling of linkages in the industrial system, focussing on AIM/CGE, GCAM, IMAGE, MESSAGE, and REMIND. IAMs ignore material cycles and recycling, incoherently describe the life-cycle impacts of technology, and miss linkages regarding buildings and infrastructure. Adding IE system linkages to IAMs adds new constraints and allows for studying new mitigation options, both of which may lead to more robust and policy-relevant mitigation scenarios. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
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Overlooked impacts of electricity expansion optimisation modelling: The life cycle side of the story
Article
This work evaluates implications of incorporating LCA-GHG (life cycle assessment of GHG emissions) into the optimisation of the power generation mix of Brazil through 2050, under baseline and low-carbon scenarios. Furthermore, this work assesses the impacts of enacting a tax on LCA-GHG emissions as a strategy to mitigate climate change. To this end, a model that integrates regional life cycle data with optimised energy scenarios was developed using the MESSAGE-Brazil integrated model. Following a baseline trend, the power sector in Brazil would increasingly rely on conventional coal technologies. GHG emissions from the power sector in 2050 are expected to increase 15-fold. When enacting a tax on direct-carbon emissions, advanced coal and onshore wind technologies become competitive. GHG emissions peak at 2025 and decrease afterwards, reaching an emission level 40% lower in 2050 than that of 2010. However, if impacts were evaluated through the entire life cycle of power supply systems, LCA-GHG emissions would be 50% higher in 2050 than in 2010. This is due to loads associated with the construction of plant infrastructures and extraction and processing of fossil fuel resources. Thus, taxes might not be as effective in tackling GHG emissions as shown by past studies, if they are only applied to direct emissions.
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Land-use protection for climate change mitigation
Article
  • Nov 2014
Land-use change, mainly the conversion of tropical forests to agricultural land, is a massive source of carbon emissions and contributes substantially to global warming. Therefore, mechanisms that aim to reduce carbon emissions from deforestation are widely discussed. A central challenge is the avoidance of international carbon leakage if forest conservation is not implemented globally. Here, we show that forest conservation schemes, even if implemented globally, could lead to another type of carbon leakage by driving cropland expansion in non-forested areas that are not subject to forest conservation schemes (non-forest leakage). These areas have a smaller, but still considerable potential to store carbon. We show that a global forest policy could reduce carbon emissions by 77 Gt CO 2, but would still allow for decreases in carbon stocks of non-forest land by 96 Gt CO 2 until 2100 due to non-forest leakage effects. Furthermore, abandonment of agricultural land and associated carbon uptake through vegetation regrowth is hampered. Effective mitigation measures thus require financing structures and conservation investments that cover the full range of carbon-rich ecosystems. However, our analysis indicates that greater agricultural productivity increases would be needed to compensate for such restrictions on agricultural expansion.
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