http://www.carbonbrief.org/analysis-how-much-is-the-uk-relying-on-negative-emissions-to-meet-its-climate-targets
Analysis: Is the UK relying on ‘negative emissions’ to meet its
climate targets?
The Paris Agreement on climate change pledges to keep warming “well
below 2C” and “pursue efforts” to limit the increase since preindustrial
times to no more than 1.5C.
But what rarely gets discussed is that the modelling by scientists
showing how this might be possible typically assumes that the world will
deploy “negative emissions” technologies (NETs) later on this century.
In a week-long series of articles, Carbon Brief has been looking at NETs
– the options, implications, history and feasibility. In the last part
of our series, we turn the spotlight on the UK to see if – and how – it
might resort to “sucking” CO2 from the atmosphere, in order to help meet
its climate targets in the future.
Carbon Brief's series on negative emissions
Explainer: 10 ways ‘negative emissions’ could slow climate change
In-depth: Experts assess the feasibility of ‘negative emissions’
Timeline: How BECCS became climate change’s ‘saviour’ technology
Guest post: Do we need BECCS to avoid dangerous climate change?
Analysis: Is the UK relying on ‘negative emissions’ to meet its
climate targets?
Does the UK need negative emissions?
A full seven years before the ink dried on the Paris Agreement, the UK
was enshrining in law its own national commitment to tackling climate
change.
In 2008, the UK’s parliament passed the Climate Change Act, which set a
legally binding target for reducing greenhouse gas emissions in 2050 by
80%, relative to 1990 levels.
In light of the Paris Agreement’s tightened temperature limit – it was
nudged from the older “below 2C compared to preindustrial levels”
commitment to “well below” 2C – the Committee on Climate Change (CCC),
the UK government’s independent advisory body, recently determined that
the UK’s fifth carbon budget for the 2028-2032 period should remain
unchanged. The government will formally respond to the CCC’s advice and
set out the policies to meet the target later this year.
5th Carbon Budget, CCC, 2015.
Source: The Fifth Carbon Budget – The next step towards a low-carbon
economy, Committee on Climate Change, 2015.
But, as far back as 2010, the UK’s Department for Energy and Climate
Change (DECC) recognised that “negative emissions” would likely need to
feature in the world’s effort to keeping the global temperature rise to
below 2C by the end of this century. A DECC-commissioned study into the
potential for negative emissions in the UK concluded:
“It seems increasingly likely that CO2 emissions will overshoot the
limit on the cumulative total needed to limit a global temperature rise
to below 2C above pre-industrial levels. It may therefore become
necessary to remove CO2 from the atmosphere.”
Recognising that the UK needed a “robust strategic plan” to uphold its
part of the bargain, the study examined potential approaches, concluding
that bioenergy with carbon capture and storage (BECCS) had “the most
immediate negative emissions potential” in the UK.
Similarly, a 2015 report by the CCC outlining the scientific context for
the UK’s fifth carbon budget described BECCS as a “sensible way to
maximise emissions reduction”.
How much could BECCS lower the UK’s emissions?
According to the 2010 DECC-commissioned study, carried out as part of
the AVOID2 project, a middle estimate for the negative emissions
potential of BECCS using only domestically-sourced biomass is just under
50m tonnes of carbon dioxide equivalent per year (MtCO2e) by 2030. This
is equivalent to about 10% of the UK’s current emissions. The authors
concluded:
“[T]his may provide significant flexibility in delivering long-term GHG
[greenhouse gas] reduction targets by offsetting emissions that are
difficult to capture (e.g. from agriculture and transportation point
sources).”
It would take about 11 years to scale-up BECCS to its full potential,
the study said. There is also a fair amount of uncertainty around the
figures, with estimates of negative emissions in the literature ranging
from 18-80 MtCO2e (or 3-16% of the UK’s emissions in 2015).
Glossary
CO2 equivalent: Greenhouse gases can be expressed in terms of carbon
dioxide equivalent, or CO2eq. For a given amount, different greenhouse
gases trap different amounts of heat in the atmosphere, a quantity known
as… Read More
The 10% figure assumes that all coal plants in the UK are replaced with
BECCS and that 90% of the CO2 released in combustion can be captured and
sequestered. It also assumes that biomass plants run at a similar
efficiency to coal power plants (around 40%).
Importing the bioenergy from elsewhere in the world would increase the
UK’s access to biomass, the study notes. By how much is uncertain,
however, since different forecasts of land availability and yields mean
estimates of global biomass potential vary by several orders of
magnitude. It is an open question how the accounting for these negative
emissions would work if the bioenergy is imported.
An alternative estimate for the potential for BECCS to achieve negative
emissions in the UK comes from the CCC’s advice to the government for
meeting the fifth carbon budget.
Although the figures have not yet been placed in the public domain, a
CCC spokesperson has confirmed to Carbon Brief that its central scenario
includes negative emissions from BECCS totalling 43 MtCO2 per year in
2050. The CCC tells Carbon Brief:
“Where BECCs is used (in certain CCC scenarios for 2050), this is not
because we need a contribution from negative emissions at this stage,
but because it makes the most of scarce bioenergy in reducing emissions
and therefore provides more room to accommodate difficult sectors in 2050.”
Decatur biofuel plant with operational CCS, Illinois. Credit: ADM
CCS has commenced at an existing biofuel plant in Decatur, Illinois.
Credit: ADM
At around 8.5% of current UK emissions, this is a similar contribution
to that discussed above, but achieved in 2050 rather than 2030. It also
assumes the UK has access to its “pro rata” share of internationally
traded biomass, as well as domestically-sourced supplies.
It’s worth noting, however, that to provide this level of abatement by
2050, BECCS begins to come online in the CCC’s central scenario from
2035 onwards. This, in turn, would require a successful programme of CCS
deployment during the 2020s.
This is a significant assumption. While some CCS pilot projects are in
operation around the world, the technology has yet to be demonstrated at
the commercial scale required for this level of BECCS. The UK government
has also recently pulled support for its £1bn CCS competition, for which
it has been widely criticised.
A February 2015 working paper on negative emissions by the University of
Oxford, as part of the Stranded Assets programme, concluded:
“Rollout of the CCS element, and integration of CCS with biomass
conversion technologies, appear likely to constrain BECCS more strongly
in 2050 than biomass availability.”
DECC’s “Carbon Plan”, published in 2011 to outline how the coalition
government intended to meet the UK’s long term carbon commitments,
offers a third perspective on how much negative emissions could come
from BECCS in the UK.
Of the four illustrative scenarios for what the UK’s energy mix might
look like in 2050, DECC’s “Higher CCS; more bioenergy” scenario sees
BECCS generating around 50 MtCO2e of negative emissions in 2050. This is
equivalent to about 10% of current UK emissions, slightly higher than
the CCC’s scenario.
UK primary bioenergy mix in 2050 (top) and sectoral use of bioenergy
(bottom) in 2010 and 2050 under the four Carbon Plan pathways
UK primary bioenergy mix in 2050 (top) and sectoral use of bioenergy
(bottom) in 2010 and 2050 under the four Carbon Plan pathways. The
“Higher CCS, more bioenergy” pathway is second from the right. Source:
Konadu et al., (2015)
What are the consequences of large-scale BECCS in the UK?
One implication of using domestically-grown bioenergy is that it would
displace other uses of land. A 2013 “horizon-scanning” report by DECC’s
Scientific Advisory Group – since disbanded – mentions food insecurity
as a potential “tradeoff” of large-scale BECCS deployment.
Talking generally about a global 2C goal, rather than the UK
specifically, the report explains:
“BECCS, as currently envisaged, would require a significant increase in
land-area used to generate crops, potentially leading to large areas of
forest or agricultural land to be replaced by energy crops.”
To better get to grips with these “critically important” issues, the
report recommended a programme of research and development. This has
been largely achieved through the AVOID2 project, led by the Met Office
in partnership with Imperial College London, the Tyndall Centre and the
Walker Institute at Reading University, a DECC spokesperson tells Carbon
Brief.
In a guest article earlier this week, as part of Carbon Brief’s series
on negative emissions, the Met Office’s Dr Jason Lowe, chief scientist
of the AVOID2 project, discussed the feasibility of BECCS in meeting the
2C goal.
The availability of negative emissions technologies in the UK is
expected to be determined in a research programme later this year, led
by the Natural Environment Research Council (NERC), a DECC spokesperson
tells Carbon Brief. To kick things off, NERC will get together with a
number of other research councils, academics and policymakers at a
workshop in London later this month to discuss options for how best to
harness “negative emissions” technologies.
In the meantime, what can existing research tell us about the potential
impacts of large-scale BECCS in the UK?
A 2015 study by a group of Cambridge academics looked in detail at how
much extra land would be needed for bioenergy in each of the scenarios
outlined in DECC’s 2011 Carbon Plan.
The authors calculated that the “High-CCS, more bioenergy” pathway,
which sees BECCS generate negative emissions equivalent to 10% of the
UK’s current emissions (discussed above), requires that 28% of the land
currently used to grow food in the UK be given over to growing energy
crops by 2050.
Under a more optimistic scenario in which crop yields increase by 30% by
2050, the amount of farmland needing to be repurposed for BECCS drops to
12%.
But this is not very realistic once you consider the potential impact of
climate variability on factors that influence yields, such as soil
quality, precipitation and temperature, says Dr Dennis Konadu, lead
author on the study. He tells Carbon Brief.
“12-28% of UK agricultural land is huge…Appropriating this amount of
good quality land for bioenergy cropping is not feasible…Moreover,
current top UK land use priority is for food production, hence, this may
not get state backing. The antidote to this will be the use of marginal
lands, which will result in reduced yield levels (unless irrigation and
fertilisers are applied) and, thus, more land will be required to meet
feedstock targets.”
Although the Carbon Plan pathways “appear to deliver the 80% GHG
reduction target”, this belies a “fundamental mismatch” between energy
policy and the physical limits of natural resources that could undermine
the UK’s GHG emissions target, say the authors in the paper.
Would the successful deployment of BECCS guarantee lower emissions?
Even assuming access to enough bioenergy, the availability of
commercial-scale CCS and a fully functioning agricultural sector, BECCS
still isn’t a guaranteed way to achieve negative emissions.
For example, emissions resulting from changing land use need to be
factored into estimates of carbon savings and not all bioenergy crops
will reduce emissions relative to fossil fuels, which makes the
selection of energy crops critical. (See Carbon Brief’s investigation
last year into whether burning imported biomass at Drax – the UK’s
largest power station -helps to lower emissions. In short, it’s
complicated, depending on the type of biomass used and what would have
happened if the land had been used for other purposes.)
Soil emissions from repurposing land for bioenergy crops. Source:
Hillier, Smith et al (2009) from the CCC Bioenergy Review, 2011.
Soil emissions resulting from repurposing different types of land for
growing bioenergy crops. Source: Hillier, Smith et al (2009) from the
CCC Bioenergy Review, 2011.
A conversation overdue
Negative emissions technologies, typically BECCS, are now baked into the
majority of the scenarios modelled by scientists showing how the world
can avoid breaching the 2C limit. These models tend to assume a growing
amount of BECCS being deployed globally from the 2040s onwards.
The vision for the UK is no different. The CCC has confirmed to Carbon
Brief that its own recommended “central scenario” for the UK’s carbon
reduction pathway for the decades ahead also assumes a rising amount of
BECCS from 2035 onwards. And yet research and development – let alone
the commercial upscaling of a demonstration project – is still at a
tentative, early stage.
Given that there are still large uncertainties about the efficacy and
scalability of BECCS – for example, the land-use implications; the
choice of bioenergy crop; the safe, available storage of sequestered
carbon – it seems that a conversation about negative emissions among
scientists, policymakers and the public is overdue.
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