Environmental Research Letters
LETTER • OPEN ACCESS
The role of large—scale BECCS in the pursuit of
the 1.5°C target: an Earth system model
perspective
To cite this article: Helene Muri 2018 Environ. Res. Lett. 13 044010
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Environ. Res. Lett. 13 (2018) 044010
https://doi.org/10.1088/1748-9326/aab324
LETTER
OPEN ACCESS
The role of large—scale BECCS in the pursuit of the 1.5◦C
target: an Earth system model perspective
RECEIVED
30 October 2017
Helene Muri1,2
REVISED
1
27 February 2018
2
Department of Geosciences, University of Oslo, Oslo, Norway
Now at: Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway
ACCEPTED FOR PUBLICATION
1 March 2018
PUBLISHED
26 March 2018
E-mail: helene.muri@ntnu.no
Keywords: BECCS, 1.5◦ C target, Earth system modelling, carbon cycle
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Abstract
The increasing awareness of the many damaging aspects of climate change has prompted research
into ways of reducing and reversing the anthropogenic increase in carbon concentrations in the
atmosphere. Most emission scenarios stabilizing climate at low levels, such as the 1.5 ◦ C target as
outlined by the Paris Agreement, require large-scale deployment of Bio-Energy with Carbon Capture
and Storage (BECCS). Here, the potential of large-scale BECCS deployment in contributing towards
the 1.5 ◦ C global warming target is evaluated using an Earth system model, as well as associated climate
responses and carbon cycle feedbacks. The geographical location of the bioenergy feedstock is shown
to be key to the success of such measures in the context of temperature targets. Although net negative
emissions were reached sooner, by ∼6 years, and scaled up, land use change emissions and reductions
in forest carbon sinks outweigh these effects in one scenario. Re-cultivating mid-latitudes was found
to be beneficial, on the other hand, contributing in the right direction towards the 1.5 ◦ C target, only
by −0.1 ◦ C and −54 Gt C in avoided emissions, however. Obstacles remain related to competition for
land from nature preservation and food security, as well as the technological availability of CCS.
1. Introduction
The temperature targets of the Paris Agreement are
associated with small and rapidly declining carbon
budgets (Millar et al 2017, Rogelj et al 2015), and
indicates a need for carbon dioxide removal (CDR) to
compensate from lack of mitigation commitments by
nations, cf current National Determined Contributions
(NDCs) (Minx et al 2017). Of the 400 Intergovernmental Panel on Climate Change (IPCC) climate scenarios
that have a 50% or better chance of less than 2 ◦ C
warming, 344 assume the successful and large-scale
uptake of negative emission technologies such as BioEnergy with Carbon Capture and Storage (BECCS).
The 56 scenarios that do not include negative emissions technologies are deemed unrealistic, as the global
emissions peak in around year 2010, which is not supported by available emission data (Anderson 2015).
Hence negative emissions technologies like BECCS
seem necessary in order to reach 2 ◦ C, and more
certainly for 1.5 ◦ C. BECCS involves growing biofuel
© 2018 The Author(s). Published by IOP Publishing Ltd
crops that absorb CO2 from the atmosphere through
photosynthesis and the biomass can be burned in
a power plant or converted in another form of
energy, producing e.g. electricity. Any CO2 produced by such biomass conversion is subsequently
captured and sequestered for long-term purposes in
geological reservoirs (e.g. Smith et al 2016, Kemper
2015). The process hence results in net negative emissions and is considered a form of CDR (Shepherd
et al 2009). For the purpose of BECCS, managed woody and herbaceous bioenergy agricultural
estates could be regularly harvested and with coupling to storage of the extracted carbon in geological
reservoirs (Lenton 2010, Fuss et al 2014).
There are uncertainties around the size of the carbon budget compatible with a warming of 1.5 ◦ C.
Rogelj et al (2015) found that scenarios corresponding to a 1.5 ◦ C warming have an atmospheric CO2 e
concentration of 420–440 ppmv by the end of the
century. These scenarios have accumulated carbon
emissions over 2011–2100 of 200–415 GtCO2 , with an
Environ. Res. Lett. 13 (2018) 044010
active net removal of CO2 during the second half of
the century, whilst IPCC found 90–310 GtCO2 accumulated emissions permissible for a 1.5 ◦ C warming
(Edenhofer et al 2014). Millar et al (2017) report a
somewhat more optimistic cumulative post-2015 carbon budget of 250–540 GtC (or 918–1982 GtCO2 ).
Nonetheless, considering current emission rates of
about 9.9 Gt yr−1 (Le Quéré et al 2016), allowable
budgets are running out fast. Notably, all scenarios
aligning with the most ambitious temperature target depend on BECCS, primarily, as the negative
emissions driver.
Land availability for biofeedstock is limited by
the competition from food production, nature conservation and furthermore, with regards to climate
change mitigation, avoiding potentially unfavourable
surface albedo reductions. BECCS competition with
food security and local livelihoods are all contextdependent, and the specific negative effects depend
on the project, location, land use history, and societal needs (Smith and Torn 2013). Anthropogenic land
use change can have large impacts on the climate not
only through changes to the carbon cycle (Canadell
et al 2007, Bonan 2008), but also changes in biogeophysical processes and alterations to surface energy and
moisture fluxes (Betts 2001, Bala et al 2007, Lawrence
and Chase 2010). Fertilizer use in growing biocrop
cultivation is another concern that should be taken
into account when considering the total impacts of
BECCS. Nitrous oxide is a bi-product of nitrogen fertilizer use, with a global warming effect of 296 times
that of CO2 (Crutzen et al 2008). Popp et al (2014) and
Kato and Yamagata (2014) estimate emissions from
fertilizing biocrops to be of 3–24 GtCO2-equivalent
and 5.1 Pg C-equivalent (18.7 GtCO2 -equivalent),
respectively, during the 21st century for ∼2 ◦ C global
warming scenarios. Fertilizer availability may prove
to become a constraint, as well as water scarcity.
Biocrop production requires energy inputs for machinery used for soil preparation and seed sowing,
cultivation, irrigation infrastructure, harvest, and transportation to the processing plant (Qin et al 2006).
Fertilizer, pesticides, and herbicides may result in
additional carbon costs through its manufacture, transportation and application procedure. Furthermore,
energy inputs in the conversion, capture, and storage processes increase the resources required reducing
the net negative potential of BECCS (Rhodes and
Keith 2005, Qin et al 2006). Current biodiversity losses
are tied to land use changes (MEA 2005). BECCS
could hence be a threat to biodiversity, depending
on deployment scale, native ecosystem type, land
use history, biocrop specie, and spatial distribution
of habitats. Primary forests tend to have higher
plant and animal diversity than secondary or plantation forest (Zurita et al 2006, Barlow et al 2007).
Restored grasslands or forests often have lower biodiversity than nearby native ecosystems (Camill et al
2004). Such factors need to be taken into account
2
in the total evaluation of approaches to limit climate
change.
Boysen et al (2017) used a global vegetation model
to assess the climate effects of different land use
scenarios, prioritizing either food production, nature
conservation or terrestrial CDR, not coupled to CCS.
It was found that the most effective terrestrial CDR
pathway would be to change dietary habits or recultivation of abandoned and marginal land. The
land use and land cover change impacts on climate
in RCP2.6 (representative concentration pathway) in
the CMIP5 (Coupled Model Intercomparison Project
phase 5) ensemble were assessed by Brovkin et al
(2013). It was found that biogeophysical effects were
not significant on the global scale, though with some
regional effects where the land use change exceeded
10%. Cai et al (2016) used a regional model centred over
North America to assess land use change impacts of
biocrops. They found that, through non-linear albedo
effects and radiative processes, there was a spatially heterogeneous response to land conversions to the same
biocrop. The results are suggestive of highly variable
albedo effects from land use change depending on geographical locations and native vegetation. BECCS has
furthermore been much discussed as a policy option
in the integrated assessment modelling (IAM) literature (e.g. Fuss et al 2014, Azar et al 2013, Smith
et al 2016, Klein et al 2014, Tavoni et al 2017). Vaughan
and Gough (2016) found, however, that assumptions concerning the availability of BECCS in future
IAM scenarios are too optimistic according to expert
judgment, and this could indeed lead to overshoot
of temperature targets with a substantial bearing on
near-term mitigation options. With this, a closer evaluation of BECCS seems necessary, as also pointed out
by Anderson (2015).
There is a lack of Earth system modelling assessment of this approach. To get a more complete picture
of the climatic effects of BECCS, fully coupled models
are needed, accounting for carbon cycling and biogeochemical cycles. Here, this gap in the literature
is abridged with an innovative approach to implementing interactive BECCS code in a state-of-the-art
Earth system model. Improving our understanding
the relationship between land use for BECCS along
with trade-offs and side effects for the climate and
environment is essential in determining the potential of such mitigation pathways. This paper assesses
the potential of BECCS deployment in contributing towards the ambitious 1.5 ◦ C target by the use
of Earth system model simulations, in the first ESM
study with interactive CCS, as described in section
2.2. The climate response to two different large-scale
BECCS deployment scenarios is evaluated and the carbon cycle—climate feedbacks are assessed. The supply
side of bioenergy feedstock is considered, including the
climatic drivers, as well as the negative emissions potential from the two different deployment scenarios, also
accounting for the net effects by including for carbon
Environ. Res. Lett. 13 (2018) 044010
lost by change in land use. This paper describes the
model and method, including the CCS approach, in
section 2, and the results are presented in section 3,
with the investigation of the temperature response, in
particular, to the land use change and the CCS coupling,
before conclusions are drawn in section 4.
2. Model and method
2.1. The Norwegian Earth System Model
The Norwegian Earth System Model with interactive carbon cycle and fully coupled biogeochemistry
(NorESM1-ME) is used (Tjiputra et al 2013) and
run in emission drive mode. This model contributed
to CMIP5 and the AR5 (5th Assessment Report)
of the IPCC. The horizontal resolution is of 1.9◦
latitude × 2.5◦ longitude both for the atmospheric and
land modules. The atmosphere model is CAM4-Oslo
(Bentsen et al 2012), the ocean model is MICOM, coupled to the HAMMOCC ocean carbon cycle module,
and CICE4 is the sea ice component.
The land model, Community Land Model version
4 (CLM4) (Lawrence et al 2012a, 2012b), includes
ecosystem cycling and the land surface is represented
in a sub-grid cell hierarchy of multiple land units,
columns, and plant functional types (PFTs). The land
unit describes the large-scale shapes of the landscape
including vegetated areas, wetlands, lakes, glaciers, and
urban spaces. The potential variability in the soil and
snow state variables within a land unit is represented at
the column level. The PFT level declares exchanges
between the land surface and atmosphere. Furthermore, vegetation state variables and treatment of bare
ground are computed at the PFT level. Soil are represented down to 50 m, with the upper 3.8 m being
hydrologically active (top 10 levels), whilst five bedrock
layers below 3.8 m act as thermal reservoirs. The
carbon-nitrogen cycle model represents the biogeochemistry of carbon and nitrogen in vegetation, litter
and soil-organic matter (Thornton et al 2007). The
assimilated carbon is estimated from photosynthesis.
The nitrogen availability for plants comes from nitrogen uptake in soils and retranslocation from senescing
plant tissues, and affects the gross primary production (GPP). The vegetated land unit is divided into a
mosaic of PFTs (Oleson et al 2010). Land use transitions are based on four classes of primary vegetation
(undisturbed natural vegetation), secondary vegetation
(regrowth vegetation following human disturbance, or
a period of alternative land use), crop, and pasture
(Hurtt et al 2011). The spatial distribution of PFTs is
prescribed annually.
2.2. Experiment design
The land cover change scenarios of CMIP5 include
details on the land cover transformations and wood
harvest based on natural land cover distributions,
anthropogenic land cover and land use conversions,
3
and account for the carbon releases associated with
such changes. The data provides historical land cover
and wood harvest changes on an annual basis from
1850–2005 (Hurtt et al 2006, 2011), as well as future
representative concentration pathways from 2006–
2100 (van Vuuren et al 2011). The RCP2.6 scenario
is used as baseline in this study. RCP2.6 is chosen
as the background scenario out of the CMIP scenarios available for use in Earth system models, as it is
deemed the scenario most in line to reach the Paris
Agreement target of 1.5 ◦ C. It would be even more
challenging to reach such a target with extra BECCS
alone in the higher GHG emissions scenarios; RCP4.5,
RCP6 and RCP8.5. RCP2.6 already contains some
level of deployment of BECCS, at levels for net fossil fuel emissions to become negative towards the end
of the century (figure 2(b)). RCP2.6 has a decrease
in forested areas and a substantial increase in crops.
This is accompanied by a small decrease in pasture,
and the use of some crop areas for biofuels, scaled
up to around 0.5 Gha in year 2100–∼one quarter of
the area used for food crops (van Vuuren et al 2011).
The main drivers of the RCP2.6 scenario emissions
include improvement of energy efficiency, replacement
of fossil fuel use by combined fossil fuel use with
CCS, nuclear and renewable energy, in addition to
BECCS, as already mentioned (van Vuuren et al 2007,
2011). BECCS in the standard RCP2.6 CMIP5 scenario uses input data as prepared for the MIP, based
on output from integrated assessment model IMAGE,
including land properties and emissions accounting
for the deployment of BECCS.
Two different land use change scenarios were
implemented in the model on the background of the
RCP2.6 scenario. In these land use scenarios, increasing areas are used for biofuel harvest expansion start in
year 2020 of RCP2.6, increasing until year 2100. In the
first scenario, Aban, cropland that becomes abandoned,
and marginal land is here used for increased harvesting for BECCS (figure 1(a)) (Thomson et al 2010,
2011). This means a gradual expansion into areas previously used for agriculture mostly, and since abandoned.
This includes in particular land areas across Eurasia,
mid-latitudinal North America, Central America, and
southern Brazil, covering ∼4% of the non-glaciated
land surface by year 2100. In a second BECCS deployment scenario, Defor, (figure 1(b)), fertilized croplands
are taking over from woodlands (A2r case in Riahi
et al 2007, 2011). This is largely in tropical and extratropical areas, including Africa, east Australia and
South America, covering ∼5% of the non-glaciated
land surface by 2100. Land that was cleared for grazing
and agriculture for food in scenario A2r in Riahi et al
(2007) is here instead assumed cleared for the purpose
of bioenergy (figure 1(b)). These areas of additional
biofeedstock are added to the land already dedicated
to BECCS in the RCP2.6 land use scenario. In this
way the new land use scenarios with increasing areas of
biofeedstock were developed to assess the potential for
Environ. Res. Lett. 13 (2018) 044010
a)
b)
90N
90N
60N
60N
30N
30N
EQ
EQ
30S
30S
60S
180
120W
0
0.05
60W
0.1
0
0.2
0.3
60E
0.4
120E
0.5
180
0.6
60S
180
120W
0
0.05
60W
0.1
0
0.2
0.3
60E
0.4
120E
0.5
180
0.6
c)
90N
60N
30N
EQ
30S
60S
180
120W
0.1
0.2
60W
0.3
0.4
0
0.5
0.6
60E
0.7
0.8
120E
0.9
180
1
Figure 1. The fractional gridbox cover increase in bioenergy feedstock in year 2100 compared to year 2005 in (a) the Aban and
AbanCCS scenarios, and (b) the Defor and DeforCCS scenarios. (c) The fractional grid box cover of crop and pasture areas reserved
for food production in year 2005, which was kept constant throughout the BECCS simulations.
Table 1. Description of the scenarios used in this study.
Scenario
Description
Pre-industrial
RCP2.6
Aban
Pre-industrial CMIP5 simulation.
Emission driven CMIP5 RCP2.6.
As RCP2.6, but land-use changed to re-cultivate
abandoned and marginal land over years
2020–2100.
As Aban, coupled to interactive CCS code.
As RCP2.6, but with land use change deforesting
tropics and extra-tropics in favour of biocrops
over years 2020–2100.
As Defor, coupled to interactive CCS code.
AbanCCS
Defor
DeforCCS
negative emissions. And these two different land-use
scenarios were coupled to CCS in one set of simulations (AbanCCS and DeforCCS), whilst they were also
run without CCS to assess the land—use change feedbacks on climate. With the inclusion of an interactive
carbon cycle, carbon emissions from land use change
are taken into account and calculated prognostically.
See table 1 for an overview of simulations.
BECCS in RCP2.6 in Earth system models in
CMIP5 is done in an implicit manner and is prescribed
by the input data from IAMs. This includes prescription of properties within the land model; such as plant
functional types and associate biogeophysical properties, with the corresponding changes in the terrestrial
carbon uptake due to the use of BECCS. In addition,
4
the fossil fuel emissions from industry and transport
changes with the use of BECCS. Hence, through the
use of the fossil fuel emission profile developed by the
IAMs, with the associated changes to the land model,
BECCS can be simulated by the ESMs. Though this is
not done in the interactive way presented in this paper;
the AbanCCS and DeforCCS cases. These two cases
have some implicit BECCS as per the CMIP5 method,
with additional explicit BECCS, as developed here and
described above.
With regards to agricultural land available for food
production and grazing, this was preserved at the same
level throughout the Aban, AbanCCS, Defor and DeforCCS scenarios (figure 1(c)) and kept at the observed
2005 levels (FAO 2005), which amounts to about 30%
of the global land area. PFTs C3 non-Arctic grass, C4
grass and C3 crops were used for this purpose. Agricultural intensification and optimization of current
agricultural practices on given land, as well as a reduction in meat consumption, is hence implied, given the
population increase to 9 billion by the end of the century in the RCP2.6 baseline scenario. An increase in
agricultural intensity has been observed over the past
few decades, a trend which is expected to continue to
increase (Rudel et al 2009).
The carbon removal capacity of the biocrops was
calculated as following: the net primary production
(NPP) in the areas used for bio-harvest is used,
Environ. Res. Lett. 13 (2018) 044010
2.5
a)
TAS: Near surface air temperature
10
b)
8
2.0
C: Fossil fuels emissions
RCP2.6
AbanCCS
DeforCCS
[K]
[Gtc / yr]
6
1.5
RCP2.6
Aban
AbanCCS
Defor
DeforCCS
1.0
4
2
0
–2
2020 2030 2040 2050 2060 2070 2080 2090 2100
Year
d)
ΔC: Fossil fuels emissions
0.0
2020 2030 2040 2050 2060 2070 2080 2090 2100
Year
c)
Atmospheric CO2 concentrations
540
AbanCCS
DeforCCS
520
–0.2
480
[Gtc / yr]
[ppmv]
500
460
440
420
400
RCP2.6
Aban
AbanCCS
Defor
DeforCCS
–0.4
–0.6
–0.8
–1.0
380
2020 2030 2040 2050 2060 2070 2080 2090 2100
Year
2020 2030 2040 2050 2060 2070 2080 2090 2100
Year
Figure 2. (a) Global four-year running mean near surface air temperature difference from the pre-industrial simulation. The grey
shading indicates the 1.5 and 2 ◦ C temperature targets of the Paris Agreement. (b) Fossil fuel and cement emissions in the three
scenarios. (c) Atmospheric CO2 concentrations. (d) The difference in carbon emissions from RCP2.6 (GtC yr−1 ). Green solid line:
RCP2.6, pink solid: AbanCCS, pink dashed: Aban, purple solid: DeforCCS, and purple dashed line: Defor.
with the assumption of a harvesting efficiency of 48%,
following Haberl et al (2007), considering not all of
the NPP can be completely harvested. This estimate
is on the conservative side and one could assume
that this efficiency would increase with time. Furthermore, the value is representative of the global mean,
and regional variation might be expected, though not
taken into account here. A CCS efficiency of 85% was
assumed in the biofuel production phase, following
Sanchez et al (2015) and IPCC (2005). This is at the
low end of the range cited in IPCC (2005). Considering industrial—scale BECCS is not yet in place,
these estimates must be considered to be uncertain. If
less conservative efficiencies were used in this study,
with improved negative emissions potential, atmospheric CO2 concentrations could possibly go down
faster though there might be compensating feedbacks
from reduced carbon fertilization of the vegetation.
The harvesting of the biocrops and implicit production of biofuels then result in a reduction in fossil
fuel emissions the following year after harvest (figure
2(b)), as it is assumed that fossil fuel consumption
is replaced, based on the new availability of biofuels.
The CCS code runs interactively with the model in
its emission driven mode. There is no actual geological
carbon storage in the model and we are hence assuming
this part of the technology works, as well as infrastructure being in place. The effectiveness of the BECCS
5
rollout is dependent on further factors that are
accounted for in the model, including any soil—and
vegetation carbon losses when converting forest into
cropland, biogeophysical changes such as albedo and
roughness length, as well as any impacts on large-scale
sinks and the oceanic biogeochemical cycle.
3. Results
RCP2.6 gives a temperature change of 1.79 ◦ C during
the last decade of this century compared to the preindustrial simulation (figure 2(a)), i.e. 0.29 ◦ C off the
most ambitious goal of the Paris Agreement (UNFCCC
2015). RCP2.6 exceeds 1.5 ◦ C for the first time in the
late 2020s and is consistently above from year 2035
onwards. The 1.5 ◦ C target is exceeded by 0.26 ◦ C on
average over 2035–2100 in RCP2.6 (table 2). Increasing the biofuel harvesting and coupling to CCS in the
AbanCCS case, lowers the temperatures closer to the
1.5 ◦ C target, and remains on average 0.17 ◦ C above
1.5 ◦ C over the 2035–2100 period when RCP2.6 is
overshooting this target. Aban is 0.21 ◦ C above 1.5 ◦ C
during this time. The CCS hence enhances the cooling
by 0.02 ◦ C. For the Defor scenario, a warming is seen
compared to the RCP2.6 scenario, both with and without the CCS coupling. DeforCCS is 0.43 ◦ C above the
1.5 ◦ C target during the 2035–2100 period, and even
Environ. Res. Lett. 13 (2018) 044010
Table 2. Global annual means of key variables. ΔTas: temperature difference from RCP2.6 over years 2035–2100. ΔTas—1.5 ◦ C: temperature
difference from the 1.5 ◦ C target over years 2035–2100. ΔPr: global mean precipitation rate difference from RCP2.6 (2020–2100) (mm yr−1 ).
CO2 peak: maximum atmospheric CO2 concentrations (ppmv). ΔQVEGT: canopy transpiration difference from RCP2.6 (2020–2100)
(mm yr−1 ). ΔTOTVEGC: total vegetation C difference from RCP2.6 (PgC). ΔSoil C Loss difference from RCP2.6 (PgC yr−1 ) (2020–2100).
ΔAR: autotrophic respiration difference from RCP2.6 (PgC yr−1 ) (2020–2100). ΔNEP: net ecosystem production difference from RCP2.6,
excl. fire flux; positive for sink (PgC yr−1 ) (2020–2100). ΔGPP: gross primary production difference from RCP2.6 (PgC yr−1 ) (2020–2100).
ΔTas
ΔTas—1.5 ◦ C
ΔPr
CO2 peak
ΔQVEGT
ΔTOTVEGC
ΔSoil C Loss
ΔAR
ΔNEP
ΔGPP
RCP2.6
AbanCCS
Aban
DeforCCS
Defor
−
0.26
−
485
−
−
−
−
−
−
−0.095
0.17
0.703
465
2.057
37.82
−0.412
−0.743
0.764
−0.732
−0.047
0.21
0.988
470
1.642
37.51
−0.396
−0.317
0.811
−0.227
0.167
0.43
5.711
523
−4.360
−127.24
0.317
0.422
1.026
1.799
0.201
0.46
6.856
527
−4.934
−126.41
0.368
0.670
1.038
2.156
exceeds 2 ◦ C during the last five years of this century.
Defor overshoots the 2 ◦ C target several years during
the last part of the century. The temperature change
from the land use change is larger than the CCS cooling effect in both land use change scenarios, which is
linked to the carbon cycle, as discussed below.
The emissions from fossil fuels and industry
become net negative 6 years earlier than RCP2.6 in the
two large-scale BECCS scenarios; year 2066 compared
to 2072 (figure 2(b)). AbanCCS increases the net negative emissions by −0.81 Gt C yr−1 by the end of this
century, whilst DeforCCS furthers this to −1.04 Gt C
per year (figure 2). Despite the larger net negative
emissions, a larger fraction of CO2 remains in the
atmosphere from the land use change emissions, and
the reduction in carbon sink from loss of tropical
forest in particular, in the DeforCCS scenario. The
atmospheric CO2 concentrations peak at 485 ppmv
in RCP2.6, 465 ppmv in AbanCCS, and 523 ppmv
in DeforCCS (figure 2(c), and table 2), i.e. above
the 1.5 ◦ C scenarios of Rogelj et al (2015). These
changes to the carbon cycle indicate that the geographical location of the bioenergy feedstock is key
to the success of such measures in the context of climate targets. Though net negative emissions can be
reached sooner and scaled up, the land use change
emissions firstly and reductions in forest carbon sinks
secondly may outweigh these effects. The coupling to
CCS reduces the CO2 fertilization effect. The accumulated carbon emissions from fossil fuels and industry in
RCP2.6 is of 197.5 GtC over years 2020–2100. 53.8 and
54.6 GtC of these anthropogenic emissions are avoided
in the AbanCCS and DeforCCS scenarios, respectively,
not accounting for land use change emissions. Emissions from land use change and changes to carbon
sinks amount to −39.0 GtC in the Aban scenario and
130.6 Gt C in Defor. The reduction in atmospheric CO2
concentration in Aban is from a higher uptake by
vegetation, with a lesser amount being taken up by
soils (table 2, figures S1 and S2 available at stacks.iop.
org/ERL/13/044010/mmedia).
As the biogeochemical effects in the Aban scenario
lead to reductions in atmospheric CO2 concentrations,
6
this is indeed accompanied by cooling. The biogeophysical effects, however, can be a cooling or a warming.
The spatial pattern of annual mean temperature differences from RCP2.6 over the years when RCP2.6
overshoots the 1.5 ◦ C target, i.e. from 2035 onwards
(figure 3) are cooler over land, with −0.5 to −1 ◦ C
over Eurasia, and parts of the ocean in the Aban scenario (figure 3(a)). Any regions with a warming, e.g.
North American land, are mostly not statistically significant as per Student’s t-test. The biogeochemical
effects of the land use change are hence largely dominating. This has previously been found by Pongratz
et al (2010). Coupling to CCS (figure 3(c)), amplifies the cooling pattern. For the Defor scenario (figure
3(b)), there is a statistically significant warming over
land, peaking at 1 ◦ C–2 ◦ C over the North Siberian
Lowlands, and Laptev Sea, across the Arctic and also
a small warming over the ocean. The warming pattern
exhibits typical polar amplification signs, as seen in
the CMIP5 ensemble (Collins et al 2013). The increase
in the atmospheric CO2 concentrations from the land
use change is driving this global warming. When coupling Defor to CCS, the warming is reduced everywhere
(figure 3(d)). Cooling is seen over southern Brazil,
which could be related to increased evapotranspiration from the vegetation changes, with intensified water
cycling and precipitation rates (figure S3).
With these warmer temperatures, the precipitation
rates are increased, by 5.7 and 6.9 mm yr−1 in DeforCCS
and Defor respectively (table 2, and figure S3. Global
means of further key variables can be seen in table 2).
Cultivating abandoned and marginal land as per the
other land use change scenario, only increases the precipitation negligibly, by less than 1 mm yr−1 in both
AbanCCS and Aban. The warmer and wetter climate
in DeforCCS and Defor increases the soil carbon losses
somewhat (0.3 PgC yr−1 ). The total vegetation carbon
is reduced quite substantially in DeforCCS and Defor,
from the loss of forest in particular, as also relected
in the reductions in canopy transpiration (table S1).
The losses are of −126 and −127 PgC in DeforCCS
and Defor, respectively (table 2). On the other hand,
re-cultivating land in Aban and AbanCCS increases
Environ. Res. Lett. 13 (2018) 044010
a)
180°
b)
120°W
–3
–2
–1
60°W
–0.5 –0.25 –0.1
0°
0
60°E
0.1 0.25 0.5
1
2
60°N
30°N
30°N
0°
0°
30°S
30°S
60°S
60°S
90°S
120°E
[K]
60°N
180°
3
–3
–1 –0.5 –0.25 –0.1
0°
0
60°E
0.1 0.25 0.5
90°S
120°E
1
[K]
2
3
(0.201)
d)
120°W
–3
–2
60°W
(–0.047)
c)
180°
120°W
–2
60°W
–1 –0.5 –0.25 –0.1
0°
0
60°E
0.1 0.25 0.5
[K]
2
60°N
30°N
30°N
0°
0°
30°S
30°S
60°S
60°S
90°S
120°E
1
60°N
3
(–0.095)
180°
120°W
–3
–2
60°W
–1 –0.5 –0.25 –0.1
0°
0
[K]
60°E
0.1 0.25 0.5
90°S
120°E
1
2
3
(0.167)
Figure 3. The annual mean temperature difference from RCP2.6 over years 2035–2100, i.e. the years when RCP2.6 is overshooting the
1.5 ◦ C target. (a) Aban, (b) Defor, (c) AbanCCS, and (d) DeforCCS. The global annual mean values are shown in purple. Non-stippling
indicates a confidence level higher than 90% following student’s t-test.
the total vegetation carbon by 37 PgC. At the same
time, the autotropic respiration is reduced, as the climate is cooler. The global mean land albedo over land
is reduced somewhat in all cases (table S1), and the
small changes in downwelling shortwave radiation at
the land surface (table S1) indicates that biogeophysical
feedbacks play a smaller role. There are, however, some
local impacts, where shortwave radiation is increased at
the surface in deforested regions of around +2 Wm−2 ,
where the local water recycling and cloudiness
has been reduced (not shown).
4. Discussion and conclusions
BECCS is an essential technology in the future scenarios that aim at stabilizing climate warming at low
levels (Fuss et al 2014). The potential contribution
from large-scale BECCS deployment in reaching the
1.5 ◦ C target of the Paris Agreement was assessed using
an Earth system model. In these fully coupled simulations with an interactive carbon cycle and including
the effects of climate on yields, it was found that making use of mid-latitudinal land, a slight cooling was
achieved of about −0.1 ◦ C. On the other hand, replacing tropical forest with biocrops reduced the carbon
sink, increased land use change emissions, and warmed
the climate by +0.17 ◦ C. The most ambitious target was
hence overshot by 0.17 ◦ C and 0.43 ◦ C (in AbanCCS
and DeforCCS respectively). A higher fraction of CO2
remained in atmosphere in the deforestation scenarios (Defor and DeforCCS), hence what land areas are
7
geographically prioritized to bioenergy is key to the net
climate effect it will have.
Some regional cooling from the biocrops was
found, but also warming, from biogeophysical feedbacks. The overall climate warming or cooling,
however, is dominated by the atmospheric CO2
concentrations—the biogeochemical effect. The atmospheric CO2 concentrations are dependent on the net
reduction in fossil fuel emissions resulting from NPP
harvesting, combined with resulting emission of carbon to the atmosphere from the land use changes.
The emissions became net negative 6 years earlier
in the BECCS cases, with potentials of −0.81 and
−1.04 GtC yr−1 by the end of this century, and accumulated avoided fossil fuel emissions of ∼54–55 Gt C
over years 2020–2100. Land use change emission and
changes to carbon sinks came to −39 GtC in Aban scenario, and as much as +130 GtC in the Defor scenario.
Aban is indicative of substantial mitigation potentials
from managing land areas. Defor, on the other hand,
results in a need for increased simultaneous efforts like
mitigation to achieve the climate targets of COP21 (21st
Conference of the Parties). Land use change emissions and available land areas are leading constraints
and uncertainties when it comes to the net negative potentials of BECCS. Possibilities of meaningful
contributions towards the climate targets are possible,
if such constraints are taken into consideration.
Rosenzweig et al (2014) suggest that regionally,
crops may be sensitive to changes in climatic conditions such as heat stress and water availability and
CO2 fertilization effects. Further studies of the climate
Environ. Res. Lett. 13 (2018) 044010
effects of agricultural production, including biocrops,
and regional crop model studies are needed to assess
the viability of bioenergy plantations under future scenarios, such as those stabilizing at the Paris Agreement
targets. This will help inform mitigation strategies and
planning.
Deploying BECCS at a large enough scale to significantly contribute towards the 1.5 ◦ C target within
the surrounding constraints may be highly challenging. The results presented here indeed suggest that
due to geophysical limitations, substantial strengthening of the NDCs are needed in 2020 to protect against
dangerous climate change and the social, economic,
technological and political restrictions of the unprecedented scale-up of options such as BECCS.
Acknowledgments
This work was funded by Research Council of Norway project 1.5C-BECCSy (grant no. 261862/E10). The
simulations were performed on resources provided by
UNINETT Sigma2—the National Infrastructure for
High Performance Computing and Data Storage in
Norway; accounts nn9083k, NS9083K. Thanks to Andy
Wiltshire (UK Met Office Hadley Centre) for useful input and to Asbjørn Torvanger and Glen Peters
(CICERO) for interesting discussions around BECCS.
ORCID iDs
Helene Muri
493X
https://orcid.org/0000-0003-4738-
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