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Inter-Agency Climate Change Forum
Meeting Date: December 19 2007
Paper: IACCF 2007 Dec/5 Stabilisation wedges – a discussion paper for
the UK nature conservation agencies
This paper provides a critique of the “7 wedges” approach previously presented to
the forum. It concludes that the size of the wedges is highly dependent upon the
selection of an appropriate emissions reduction scenario. The deployment of the
technologies required to deliver deep cuts in emissions has the potential to give rise
to adverse biodiversity impacts. Further work is required to assess the size and
potential impacts of the wedges necessary to deliver deep reductions in UK
emissions. Given the level of expertise required it is likely that such work would need
to be commissioned from outside of the nature conservation agencies.
Action by IACCF:

That the forum considers the appropriateness of various stabilisation scenarios
with the aim of endorsing the adoption by the UK of a minimum emissions
reduction target of 80%

That the forum considers whether work should be commissioned to assess the
energy mix required to deliver such reductions by 2050, thereby assessing the
size of the UK wedges. It is suggested that a first step would be to commission
an analysis of the WWF/RSPB/IPPR “80% Challenge” document.

That the forum considers whether further work is required to assess the impact of
UK-based wedges on domestic and overseas biodiversity.
Documents:
IACCF 2007 Dec-5 Discussion paper
IACCF 2007 Dec-6 PDF of WWF/IPPR/RSPB “80% Challenge” publication
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Inter-Agency Climate Change Forum
STABILISATION WEDGES
A DISCUSSION PAPER FOR THE UK NATURE
CONSERVATION AGENCIES
1.
Summary
The concept of stabilisation wedges provides a useful solution-orientated approach
to illustrate how significant emissions reductions may be practically delivered on a
global level.
However, the original approach was not without its problems and, as proposed by
many advocates, contains weaknesses arising from an inappropriate choice of
stabilisation levels and resulting unrealistic pathways to emissions reductions. These
weaknesses have to some extent been addressed by other parties.
An initial analysis of the “seven wedges” approach to reducing global emissions
suggests that there may be significant adverse biodiversity impacts associated with
some of the proposed technologies, although many will have neutral or positive
effects on nature conservation interests. In particular the levels of production
associated with the size of bio-fuels wedges reinforces concerns about tropical
deforestation and domestic land use changes arising from fuel crops.
There are a number of problems associated with translating the wedges approach to
a national (United Kingdom) level because it currently focuses on displacing
emissions growth globally to 2050 whereas UK policy is to reduce overall national
emissions by a significant amount well before that date. A UK wedges based
scenario would, therefore, be based on selecting a portfolio of technologies to deliver
emissions reductions and displace existing technologies rather than displacing
growth (which in any event on a UK-wide basis will be extremely low compared to
global “business as usual” growth predictions). Further analysis on behalf of the
nature conservation agencies may be required to assess the size and impact of
these wedges, particularly if an 80% emissions reduction target is favoured over the
60% reduction currently proposed in the Climate Change Bill.
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Inter-Agency Climate Change Forum
2. Introduction
The body of evidence in respect of climate change, together with growing
assessment of risk levels, is now sufficient1 to give clear and strong guidance to
policy makers to shape a response to the challenge posed by human release of
greenhouse gases into the atmosphere.
However there is confusion concerning options for mitigation with some
commentators claiming that emissions reductions can be delivered within the scope
of existing technologies while others have claimed that radical new technology is
required to deliver a low-carbon economy.
Two Princeton researchers, Stephen Pacala and Robert Scolow, published a paper
in Science in 20042 advocating an approach which identifies options to “solve the
climate problem for the next-half century”. This approach identifies “stabilization
wedges”, essentially bundles of existing low- or zero-carbon technologies, capable of
delivering emissions reductions. Each wedge increases in size over time, displacing
the growth in carbon emissions arising from increased demand for energy. They
advocate that the fifteen technologies, grouped into seven main wedges (forming a
“stabilization triangle”), could be scaled up to provide stabilisation of atmospheric
CO2 at the level of 500ppm.
3. Critique of the wedges approach - key issues
The approach proposed by Pacala and Scolow is attractive because it is solutionorientated; offering a positive message that climate change can be addressed with
existing technologies. As a result the approach has been endorsed by a number of
organisations; both within the corporate and NGO sectors.
The wedges approach is of particular value in testing stakeholder opinion on the
deployment of the various technologies and has spawned a number of web-based
tools which can be used to explore the effect of various mixtures of technology on
carbon emissions. However, as a tool for policy makers to set targets for deployment
of low or zero-carbon technology, the use of the “wedges” approach is problematic
unless the assumptions underlying the methodology are questioned. Pacala and
Scolow acknowledge that the approach is an “idealization”3, however the following
issues should be considered:
3.1 Choice of stabilisation level
Pacala and Scolow’s approach focuses on limiting atmospheric CO 2 to 500 ± 50
ppm. However, since 2004 (when the paper was published) many commentators
have revised their opinion as to what an appropriate stabilisation level should be.
Stern Review – “The Science of Climate Change: Scale of the Environment Challenge”, page 2
Pacala, S & Socolow, R (2004), Stabilization Wedges: Solving the Climate Problem for the Next 50
Years with Current Technologies, Science, 305, p968-972
3 Presentation to the Scientific Symposium on the Stabilisation of Greenhouse Gases, Exeter 2005 http://www.stabilisation2005.com/day3/Socolow.pdf
1
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Much of this commentary has focussed on minimising the risk of exceeding a 2ºC
increase in global temperature above pre-industrial levels. This 2ºC approach was
adopted by The International Symposium on Greenhouse Gas Concentrations and
Avoiding Dangerous Climate Change (ADCC)4 in Exeter in 2005 and in the Stern
Review5. For the purposes of this paper it has been assumed that this approach is
appropriate although it should be noted that some commentators suggest that even
a 1ºC change would constitute “dangerous climate change”6.
Generally, while there is some disagreement about what emissions stabilisation level
would lead to global temperature change remaining below 2ºC, there is general
consensus that it would be considerably lower than the 500ppm CO2 level (around
600ppm CO2 equivalent7) adopted by Pacala and Scolow.
Box 1 – Measurements of greenhouse gas levels - CO2 equivalent (CO2e)
Carbon dioxide equivalent, CO2eq or CO2e, is used to provide a broader measure of total greenhouse gas
contributions than solely that arising from atmospheric carbon dioxide. It expresses the global warming potential
of all greenhouse gases in terms of the amount of atmospheric carbon dioxide that would have the same global
warming potential. The carbon dioxide equivalent for a gas is derived by multiplying the mass of that gas by the
associated Global Warming Potential (“GWP”). For example, the GWP for methane is 21. This means that
emissions of 1 million metric tonnes of methane are equivalent to emissions of 21 metric tonnes of carbon dioxide.
For the purposes of this paper references will be made to CO2e, which will be used from this point onwards
Table 1 (below) provides a summary of global mean temperature increases above
pre-industrial levels predicted by the IPCC to occur for given atmospheric
greenhouse gas levels.
It can be seen from the table that the emissions stabilisation scenario utilised by
Pacala and Scolow (WRE500) would probably lead to a temperature increase above
pre-industrial levels of around 3.5ºC. It would, therefore be appropriate to consider
other emission stabilisation scenarios when assessing the size of stabilisation
wedges.
Table 1
Co2 concentrations and emissions
4
CO2
concentration
(ppm)
CO2 – equivalent
concentration
(ppm)
Global mean
temperature
increase above preindustrial level at
equilibrium (ºC)
Peaking year
for CO2
emissions
Global change in
CO2 emissions in
2050 (% of 2000
emissions)
350-400
400-440
440-485
485-570
445-490
490-535
535-590
590-710
2.0 – 2.4
2.4 – 2.8
2.8 – 3.2
3.2 – 4.0
2000-2015
2000-2020
2010-2030
2020-2060
-50 to -85
-30 to -60
+5 to 30
+10 to +60
Schnellnhuber, H.J (ed)(2006), Avoiding Dangerous Climate Change, Cambridge 2006
5http://www.hm-
treasury.gov.uk/independent_reviews/stern_review_economics_climate_change/stern_review_report.
cfm
6 e.g. http://pubs.giss.nasa.gov/docs/2006/2006_Hansen_etal_1.pdf
7 See Box 1
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570-660
660-790
710-855
855-1130
4.0 – 4.9
4.9 – 6.1
2050-2080
2060-2090
+25 to +85
+90 to +140
From WEO 20078, based on IPCC 20079
3.2 Scenarios for stabilisation below WRE500 (approx 600ppm
CO2e)
For the purposes of this paper two emissions stabilisation scenarios are discussed,
both published by the International Energy Agency in its World Energy Outlook
(WEO) in November 2007. These scenarios have been chosen because they
combine the robustness of IPCC climate change scenarios (which include the
potential impact of differing atmospheric greenhouse gas concentrations on global
mean temperature) with current market-based predictions of emission levels
(including those arising from recent increases in economic growth in India and
China). The selection of these scenarios is for the purpose of discussing the
assessment of wedge size only, rather than representing the endorsement of any
particular climate change prediction.
The first of these scenarios, the “Alternative Policy Scenario”, is based on a 550ppm
CO2e stabilisation level. While this level is lower than that utilised by Pacala and
Scolow, such a level would still correspond to an increase in average temperature of
around 3ºC above pre-industrial levels10.
The second scenario published by the IEA is the “450 Stabilisation Case”.
Stabilisation at 450 ppm CO2e offers an even chance of staying below the 2ºC
level11. However, as Table 1 highlights, such a scenario requires emissions to peak
in the very near future and for large scale cuts in emissions to be delivered by 2050.
When it is remembered that Pacala and Scolow propose no requirement for cuts in
emissions before 2050 it becomes apparent that, if a 450ppm CO 2e target is
desirable, the shape of the “stabilisation triangle” (and the wedges which form it) are
likely to be very different than that advocated in their 2004 paper.
It should be noted that adoption of a 450ppm CO 2e target would not guarantee that
global warming was constrained to below 2ºC. Indeed both Stern and the IPCC
express the possibility of limiting increases to 2ºC at not much better than 50% under
a 450ppm CO2e target. For this reason many commentators have advocated more
ambitious targets. For example WWF International has adopted a 400ppm CO 2e
target as the basis for its wedged-based analysis.12
International Energy Agency, World Energy Outlook 2007, Chapter 5 “Global Environmental
Repercussions”
9 Intergovernmental Panel on Climate Change, Climate Change 2007: Fourth Assessment Report,
IPCC, Geneva
10 WEO 2007, page 207
11 ADCC 2006, page 265
12 WWF International (2007) http://assets.panda.org/downloads/climatesolutionweb.pdf
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3.3 Choice of stabilisation scenario determines the size of the
wedges
Figure 1 at the rear of this paper illustrates how the stabilisation triangle and wedges
vary according to which stabilisation target is selected.
Figure 1(a) illustrates the triangle selected under the WRE500 scenario chosen by
Pacala and Scolow. In this case reductions in carbon emissions below current levels
would not be required until after 2050. The resulting triangle (and wedges) therefore
focuses only on displacing “business as usual” predictions of emissions growth.
The WEO Alternative Policy Scenario, introduced above, would produce a
stabilisation triangle similar to that shown in Figure 1(b). Under this 550ppm CO2e
stabilisation scenario emissions stabilise in the mid-2020s and fall thereafter to
around 30% of 2000 emissions by 205013 with further decreases thereafter (see also
Table 1).
The WEO 450 Stabilisation Case gives rise to a significantly larger triangle than that
proposed by Pacala and Scolow; see Figure 1(c). Under this scenario global energy
related CO2 emissions peak in 2012 at around 30Gt and decline to 23 Gt in 2030
with further decreases thereafter to between 50-85% of 2000 emissions by 205014.
3.4
Other factors may affect the size of the wedges
The shape of the stabilisation triangle is also affected by the selection of “Business
as Usual” (BAU) scenario. The World Energy Outlook 2007 Reference Scenario
provides a very recent forecast of emission levels. While Pacala and Scolow utilise
an average growth rate of 1.5% per year, the WEO work suggests an average
growth of 1.8%, giving rise to a 57% increase in world emissions between 2005 and
203015. In particular, the report stresses the importance of the contribution of recent
strong economic growth in India and China towards these increases in emissions.
Again, this suggests that the real size of the stabilisation triangle and component
wedges will be significantly higher if such growth is to be displaced by zero-carbon or
carbon-neutral technologies at the same time as delivering cuts in emissions.
The shape of the wedges may also be affected by other issues. Valuing the
contribution of wedges may be problematic (particularly in respect of sinks and the
contribution of deforestation to atmospheric CO2 levels). Additionally, technical
constraints may not allow the wedges to develop uniformly. Supply chain bottlenecks
(as already experienced in the wind energy industry), shortage of capital, regulatory
barriers and environmental constraints may all restrict the full potential of all the
wedges from being developed16.
13
WEO 2007, Chapter 5
ibid
15 WEO 2007, page 192
16 Wellington et al “Scaling Up: Global Technology Deployment to Stabilize Emissions”, World
Resources Institute. http://pdf.wri.org/scalingup.pdf
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3.5
Reassessment of the size of the global wedges
It is clear from the above that a re-assessment of the size of the wedges from those
proposed in the 2004 paper is required. The gap between the WEO Reference
Scenario (i.e. BAU) and the 450 Stabilisation Case amounts to 19 Gt in 2030,
compared to the 7 Gt “gap” in 2054 (approximately 3.3Gt in 2030) envisaged by
Pacala and Scolow.
The World Energy Outlook 2007 suggests that the 450 Stabilisation Case is
realisable with existing technology but that “exceptionally strong and immediate”
policy action would be essential for this to happen and the associated costs would be
“very high” (partly because existing plant would need to be replaced immediately
rather than at the end of its lifespan). Figure 2 (to rear of this paper), taken from
WEO2007, illustrate how such reductions might be delivered. It should be noted that
Figure 2 details the “wedges” required to deliver the reduction difference between
the Alternative Policy Scenario (550ppm CO2e) and the 450 Stabilisation Case, not
the entire portfolio of wedges required to deliver to 450ppm CO 2e target. Additionally
the WEO work does not focus on issues such as sinks, deforestation or agricultural
practices, rather it focuses solely on energy use.
WWF International has calculated climate solution wedges based on a 400ppm
CO2e target17 (see Figure ). Such an approach (which is likely to be desirable from a
nature conservation viewpoint) stresses the key themes of energy efficiency,
deforestation, carbon capture and storage and renewables discussed by Pacala and
Scolow. However, as the paper acknowledges, the difficulties with delivering such a
programme are exceptional, resulting in an “ominous” outlook. For that reason this
paper has discussed the more “realistic” (although still challenging) 450ppm CO 2e
scenario. Additionally it should be noted that the WWF International model does not
adopt an economic approach – rather it considers wedge-size based on carbon
reduction capacity.
4. Biodiversity impacts of the global wedges
Pacala and Socolow identify 15 wedges (grouped into 7 larger wedges), each
contributing towards reducing carbon emissions from 2004 to 2054 by 25 GtC. The
increased deployment of novel technologies may have adverse impacts on
biodiversity. An assessment of the potential impact of each of the 15 wedges is set
out at Table 2 (at the rear of this paper).
Of the 15 wedges, the majority would probably not give rise to adverse biodiversity
impacts, particularly as many focus on energy efficiency. However one wedge,
relating to biofuels, has the potential to give rise to adverse biodiversity impacts.
Such impacts may occur domestically (for example from changes in agricultural
17
http://assets.panda.org/downloads/climatesolutionweb.pdf
- this paper also provides in the technical appendices a useful analysis of the problems associated
with calculating wedge sizes
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Inter-Agency Climate Change Forum
cropping) or overseas. The current risks are summarised in the JNCC position
statement on transport biofuels and biodiversity18.
A further five wedges (shaded yellow in Table 2) could give rise to adverse impacts
depending on how they were implemented. This may be of particular concern if, as
appears likely, extremely large cuts in emissions are required over a relatively short
timescale leading to rapid deployment of technologies.
Two wedges (reforestation and conservation tillage) could give rise to positive
biodiversity effects.
It is unlikely, therefore, that a wedges based approach would significantly alter the
nature conservation agencies’ current policy advice on the potential adverse effects
of emissions reduction technology, namely:




Robust certification of biofuels
Reduction of deforestation
Careful siting of development by utilising Strategic Environmental Assessment
and Environmental Impact Assessment
Continued stress on the importance of energy efficiency
Larger wedges which, as discussed above, will be necessitated by the requirement
for urgent cuts in emissions, could give rise to increased biodiversity impacts,
particularly in respect of inappropriately sited development. It is not currently
possible to assess the impacts of such larger wedges although some work has been
carried out in individual sectors. For example, WWF International have estimated
that biomass with an energy content of between 110 and 250 exajoules could be
achieved from sustainable production by 205019. This level of production, which it is
calculated, can be delivered without prejudicing nature conservation interests or food
production, would amount to between 9 and 21% of global energy demand in 2050.
5. Identification of “threat wedges”
The concept of threat wedges was introduced in a World Resources Institute Paper
in April 200720. Threat wedges relate to technologies which increase global carbon
emissions. The WRI identify three technologies which, driven by energy security
concerns (particularly in North America), could contribute to growing emissions. BAU
scenarios could be increased by production of synthetic liquid fuels from coal (CTL),
heavy oil production from tar sands and production of oil from shale rock-types.
To be available from www.jncc.gov.uk – also attached to this paper
http://assets.panda.org/downloads/climatesolutionweb.pdf
20 Wellington et al “Scaling Up: Global Technology Deployment to Stabilize Emissions”, World
Resources Institute. http://pdf.wri.org/scalingup.pdf
18
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6. Developing a UK based wedges approach
The wedges approach could be applied to UK emissions reductions targets to
provide an illustration of how those targets could be delivered. A UK-based wedged
approach would have a different shaped stabilisation triangle than that applying to
the global scenarios described above.
UK greenhouse gas emissions under a business as usual scenario are predicted to
be relatively flat, falling to the mid 2020s and then rising thereafter 21. The UK
government has already committed to a 60% reduction in emissions from 1990
levels by 2050 in the draft Climate Change Bill. The shape of the stabilisation triangle
required to deliver this level of reduction is shown at Figure 4(a).
However, many commentators have suggested that a 60% emissions reduction
target would be incompatible with a goal of stabilisation at 450ppm CO 2e. For
example, Höhne et al (2007)22 suggest that the UK should be aiming to reduce
greenhouse gas emissions from 1990 levels by 35-45% by 2020 and by 80-95% by
2050. Calls for an 80% reduction target for the UK has been supported by a number
of NGOs including WWF, RPSB and the IPPR in the publication “80% Challenge –
Delivering a low-carbon UK”23. An 80% reduction target would give rise to a
significantly larger stabilisation triangle, as illustrated at Figure 4(b).
Calculation of the size of the UK stabilisation triangle (and its component wedges)
would need to take account of the following issues.
6.1 Mix of UK wedges is likely to be different from global
counterparts
The wedges of technology making up the UK stabilisation triangle are likely to be
different from those making up the global stabilisation triangle. The selection of
technologies for the UK wedges will therefore need to take account of the nature of
the UK economy and environment. For example, the UK’s wind, wave and tidal
resources are high compared to the global average, whereas capacity for
photovoltaic (solar) energy is probably more limited. The legacy of North Sea oil
extraction suggests that there may be more potential for carbon capture and
sequestration (CCS).
In 2000 the Royal Commission on Environmental Pollution (RCEP) published an
assessment of how a 60% reduction in emissions might be delivered 24. The work
provides four scenarios for achieving a 60% reduction from 1997 levels by 2050.
Details of these scenarios are attached at Tables 3 and 4. Table 3 details four
21
UK CO2 Emissions Projections, Annex C, The Energy Challenge, Department of Trade and Industry
(2006)
22 Höhne, N. Phylipsen, D. and Moltmann, S (2007) Factors underpinning future action – 2007 update.
Report for DEFRA http://unfccc.int/resource/docs/2007/smsn/ngo/026c.pdf
23 http://www.ippr.org/publicationsandreports/publication.asp?id=573
24 The Royal Commission On Environmental Pollution's 22 nd Report, 2000
http://www.rcep.org.uk/newenergy.htm
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Inter-Agency Climate Change Forum
reduction scenarios and Table 4 details how the resulting energy mix could be
delivered.
Scenarios for 80% scenarios are less well developed. The “80% challenge”
document referred to above provides some limited scenarios based on two models,
suggesting that such a target is achievable within the scope of existing technologies
and without recourse to nuclear power (the same case as adopted in the 2 nd and 4th
RCEP scenarios). Figure 5 shows a potential energy mix under one of the 80%
challenge scenarios. However, it should be noted that many of the assumptions, for
example those relating to large market penetration of wind power or the use of
carbon capture and storage (CCS), rely upon technologies only at a very early stage
of development. Furthermore the work’s reliance on market demand based models
does not take into account potential barriers to deployment such as the planning
system, grid constraint or potential conflicts with other land- and sea- users (for
example protected areas, housing and agriculture).
Two particularly contentious issues would need to be addressed as part of the
selection of appropriate wedges; the role of nuclear power and the contribution of
aviation to CO2 levels.
The role of nuclear power is problematic, partly because the environmental safety
issues associated with long term waste storage have not been solved.
In the context of large emission cuts in other sectors the projected rapid growth in
aviation related greenhouse gas emissions could be seen as anomalous. Indeed
modelling carried out by the Tyndall Centre for Climate Change Research 25 has
suggested that at an annual growth rate of only half of that experienced by UK
aviation in 2004, the UK’s aviation sector would account for 50% of permissible
emissions under a 550ppm scenario and would consume the entire UK carbon
budget under the 450ppm model.
6.2
Assessing the biodiversity impacts of the UK wedges
It would be essential to assess the biodiversity impact of the UK stabilisation triangle.
Such an assessment should also assess the overseas impact of UK energy
consumption, particularly in respect of bio-fuel production and hydrocarbon
extraction. The “80% challenge” document constrains the amount of bio-fuel use and
wind generation within the UK to provide environmental safeguards to limit
biodiversity impacts26.
Three of the four RCEP scenarios detailed in Table 4 incorporate the use of tidal
barrage technologies. Such projects could give rise to significant adverse impacts on
biodiversity
25
Bows et al (2006), Contraction & Convergence: UK carbon emissions and the implications for UK
air traffic, Tyndall Centre Technical Report No.40
26 http://www.ippr.org/publicationsandreports/publication.asp?id=573 – page 12
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6.3
Delivery of wedges on a country basis – sharing the burden
It would also be important to assess the impact of each of the UK wedges on the
constituent countries of the United Kingdom. For example, the vast majority of
wind power is situated in Wales and Scotland rather than England. Scottish
waters would provide most of the UK’s tidal and wave power resource. The
delivery of UK based wedges could therefore have greater implications for
individual country agencies than for the national environment as a whole.
It should also be noted that the Scottish Government has is about to start
consultation on a climate change bill which would include provisions to reduce
Scottish emissions by 80% by 205027.
7. Conclusions and recommendations
As discussed above the wedges approach to stabilisation is a useful tool to explore
how emissions reductions will be delivered. However, further work may be required
to assess the sizes of the wedges necessary to deliver lower stabilisation levels of
atmospheric greenhouse gases than those assumed under the WRE500 scenario
adopted in the 2004 paper. In particular it may be useful to commission an
independent assessment of the scenarios adopted for the UK under the “80%
Challenge” document which, while providing robust evidence for delivery in the
power and transport sectors, does not fully take into account supply constraints.
Should such work be commissioned, agreement would first be required between the
country agencies on the following issues:





Selection of appropriate stabilisation for temperature (e.g. 2ºC)
Selection of appropriate emissions stabilisation scenario to meet this
target (e.g. 450ppm CO2e). This will need to take into account the risks
associated with overshoot and the probabilities of achieving the target.
Selection of appropriate “business as usual” scenario (e.g. WEO 2007)
Agreement on appropriate UK-wide emissions reduction target (e.g. 80%),
noting that Scotland is already likely to adopt an 80% target.
Discussion of status of various technologies, most notably nuclear power
Further work would probably be required to assess the potential biodiversity impacts
of the technologies involved although it may be possible to rely upon a precautionary
approach similar to that adopted in the 80% Challenge document. Any analysis of
potential biodiversity impacts would need to consider both the domestic and
overseas footprint of the resulting technical solutions including, most notably, the use
of bio-fuels.
Andrew Prior
Renewable Energy Advisor
Joint Nature Conservation Committee
5th December, 2007
27http://www.scotland.gov.uk/Topics/Environment/Climate-Change/16327/Climate-Change-
Bill/Proposals-Timescales
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Figures & tables
Figure 1
The shape and size of the stabilisation wedges is highly dependent upon the choice
of stabilisation level. In scenarios (b) and (c) wedges must deliver emissions
reductions rather than solely displacing growth as is the case with Pacala &
Socolow’s proposals. Within scenario (c) reductions might be delivered within the
scope of the technologies reviewed by Pacala & Socolow, but delivery will be
extremely challenging.
(a) Pacala & Socolow stabilisation triangle based on WRE500 scenario
BAU
2000
Reductions
only after
2054
2050
(b) Stabilisation “triangle” based on a 550ppm CO2 equivalence stabilisation
scenario28
Reductions required
before 2054
(c) Stabilisation “triangle” based on a 450ppm CO2 equivalence stabilisation
scenario29
28
29
WEO 2007 – Alternative Policy Scenario
WEO 2007 – 450 Stabilisation Case
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Inter-Agency Climate Change Forum
Substantial
reductions required
before 2054
Note: above figures are illustrative only, not to scale. The choice of scenarios is indicative only and does not
endorse a particular approach
Figure 2
From WEO (2007)
CO2 emissions in the 450 Stabilisation Case
Reduction in emissions from Alternative Policy Scenario to 450 Stabilisation Case by 2030 delivered
by:
Carbon capture and storage (industry and power)
Renewables in power sector
Nuclear Generation
Second generation bio-fuels in transport
Fossil fuel efficiency (buildings and industry)
Lower electricity use from energy efficient buildings
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21%
19%
16%
4%
27%
13%
Inter-Agency Climate Change Forum
Figure 3
From WWF International (2007)
Energy wedges in 2050 under a 400 ppm CO2e stabilisation scenario
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Inter-Agency Climate Change Forum
Figure 4
Calculating the size of the UK wedges
UK business as usual30 and Climate Change Bill 2050 target (60%)
(a)
1990 level
2000
2050
`
(b)
UK business as usual and increased Climate Change Bill 2050 target
(80%)
Note: above figures are illustrative only, not to scale.
30
UK CO2 Emissions Projections, Annex C, The Energy Challenge, Department of Trade and
Industry (2006)
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Inter-Agency Climate Change Forum
Table 2
Pacala & Socolow’s Stablisation Wedges and their potential impacts on biodiversity
Option
Effort required
Potential biodiversity
impact
1
Efficient vehicles
Increase fuel economy for 2 billion cars from 30 to 60
mpg
Neutral
2.
Reduced use of vehicles
Decrease car travel for 2 billion 30-mpg cars from
10,000 to 5,000 miles per year
Neutral / positive (assuming
reduced road-building etc)
3.
Efficient buildings
Cut carbon emissions by one-fourth in buildings and
appliances projected for 2054
Neutral
4.
Efficient baseload coal plants
Produce twice today’s coal power output at 60%
instead of 40% efficiency (compared with 32% today)
Neutral
5.
Gas baseload power for coal
baseload power
Replace 1400 GW 50%-efficient coal plants with gas
plants (four times the current production of gas-based
power)
Neutral (assuming based on
existing sites)
6.
Capture CO2 at baseload power
plant
Introduce CCS at 800 GW coal or 1600 GW natural
gas (compared with 1060 GW coal in 1999)
See below
7
Capture CO2 at H2 plant
Introduce CCS at plants producing 250 MtH2/year
from coal or 500 MtH2/year from natural gas
(compared with 40 MtH2/ year today from all sources)
See below
8.
Capture CO2 at coal-to-synfuels
plant
Introduce CCS at synfuels plants producing 30 million
barrels a day from coal (200 times Sasol), if half of
feedstock carbon is available for capture
See below
Geologic storage
Create 3500 Sleipners
Potentially negative
(infrastructure development,
particularly in marine
environment)
9.
Nuclear power for coal power
Add 700 GW (twice current capacity)
Potentially negative – longterm storage solutions remain
unresolved
10.
Wind power for coal power
Add 2 million 1-MW-peak windmills (50 times the
current capacity) “occupying” 30x106 ha, on land or
offshore
Neutral if appropriate siting
(avoiding sensitive habitats,
migratory routes etc).
Offshore capacity limited by
water depth
11.
PV power for coal power
Add 2,000 GW-peak PV (700 times the current
capacity) on 2x106 ha
Neutral if assume much is
sited on existing structures or
can be appropriately sited
elsewhere
12.
Wind H2 in fuel-cell car for
gasoline in hybrid car
Add 4 million 1-MW-peak windmills (100 times the
current capacity)
Neutral but see above in
respect of siting of wind
turbines
13.
Biomass fuel for fossil fuel
Add 100 times the current Brazil or U.S. ethanol
production, with the use of 250x106 ha (one-sixth of
world cropland)
Current rates of deforestation
to provide biofuels etc
suggest that this could only
be delivered at expense of
biodiversity
14.
Reduced deforestation, plus
reforestation, afforestation, and
new plantations
Decrease tropical deforestation to zero instead of 0.5
GtC/year, and establish 300 Mha of new tree
plantations (twice the current rate)
Positive
15.
Conservation tillage
Apply to all cropland (10 times the current usage)
Neutral (although may be
mildly positive)
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Inter-Agency Climate Change Forum
Table 3
RCEP scenarios for reducing UK CO2 emissions by 60% by 2050
From RCEP (2000)31
Four scenarios were constructed to illustrate the options available for balancing
demand and supply for energy in the middle of the 21st century if the UK has to
reduce carbon dioxide emissions from the burning of fossil fuels by 60%:
scenario 1: no increase on 1998 demand, combination of renewables and either
nuclear power stations or large fossil fuel power stations at which carbon dioxide is
recovered and disposed of
scenario 2: demand reductions, renewables (no nuclear power stations or routine
use of large
fossil fuel power stations)
scenario 3: demand reductions, combination of renewables and either nuclear
power stations or large fossil fuel power stations at which carbon dioxide is
recovered and disposed of
scenario 4: very large demand reductions, renewables (no nuclear power stations or
routine use of large fossil fuel power stations).
The key parameters for these four scenarios are as follows:
31
RCEP(2000), Chapter 9 – “Possible UK Energy Balances in 2050”, page 173
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Inter-Agency Climate Change Forum
Table 4
Number of generating plants required under RCEP scenarios to deliver 60%
target
From RCEP(2000)32
Figure 5
Electricity generation mix to 2050 under MARKAL-MACRO model
From “80% Challenge – delivering a low-carbon UK”33
32
33
RCEP(2000), Appendix E – “Illustrative Energy Balances for the UK in 2050”, page 225
http://www.ippr.org/publicationsandreports/publication.asp?id=573 – page 16
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