Transcript Mitigating Greenhouse Gas Emissions

Cost-effectiveness and
implications of GWPs and GTPs
under alternative policy goals
Andy Reisinger1 Keywan Riahi2 Oscar van Vliet2
1 New
Zealand Agricultural Greenhouse Gas Research Centre
2 International Institute for Applied Systems Analysis (IIASA)
Manuscript submitted to Climatic Change
Work funded by NZ Ministry of Agriculture and various EU-FP7 programs
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In a nutshell
100-year GWPs are not a cost-effective way of comparing GHGs if
the main policy goal is to limit long-term climate change.
Few studies have explored the cost and climate policy implications
if other physically-based metrics were to replace GWPs.
1.Determine the global cost-effectiveness of different metrics
for the main policy goal of limiting radiative forcing in 2100 to
450 or 550ppm CO2-equivalent
2.Evaluate influence of metrics on additional policy goals
(realised warming, GDP, timing of CO2 emissions peak)
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Evaluated alternative metrics:
GWPs, fixed and time-dependent GTPs
CH4
N2O
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Sensitivity tests: technology/policy assumptions
•
Assumed policy goal is to limit radiative forcing in 2100:


450 ppm CO2-eq (~2.7 Wm-2)
550 ppm CO2-eq (~3.8 Wm-2)
•
Rate of improvement of agricultural mitigation potential
 No improvement / rapid improvement
 Additional technology from 2030 or 2070 to
mitigate CH4 from enteric fermentation
• Policy treatment of agricultural GHG emissions
 Fully included in global mitigation efforts /
fully excluded / excluded until 2050
Use integrated assessment model MESSAGE to determine
cost-minimising abatement pathways over 21st century
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Radiative forcing paths – all metrics/assumptions
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CO2 and CH4 emissions – all metrics/assumptions
Global agricultural marginal
abatement costs from Beach et al. (2008)
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CH4 emissions – detailed examples
fixed 100-year GTPs:
less CH4 mitigation
time-dependent GTPs:
less CH4 mitigation initially,
more CH4 mitigation by 2100
Global agricultural marginal
abatement costs from Beach et al. (2008)
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Global
net costsresults
MESSAGE
450ppm
CH4 mitigation determines ‘atmospheric space’ for CO2 emissions
and hence total mitigation costs
550ppm
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Global agricultural CH4 emission pathways
8
rapid improvement in
agricultural mitigation
potential
no improvement in
agricultural mitigation
potential
rapid improvement in
agricultural mitigation
potential
250
200
150
NPV mitigation cost (US$ 2005 billion)
4000
100
50
3000
0
agriculture
CH4 2010 - 2050
2000
1000
0
Global discounted net
present value mitigation
costs (2010-2100)
Example for 550ppm
CO2-eq stabilisation
N2O 2010 - 2050
CH4 2050 - 2100
N2O 2050 - 2100
agriculture
industry
waste
forestry
energy
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GTP GTP
GWP CH
GTP GTP
GlobalGWPagricultural
emission pathways
(fixed) (time-dep.)
(fixed) 4
(time-dep.)
9
NPV mitigation cost (US$ 2005 billion)
5000
no improvement in
agricultural mitigation
potential
Global cost-effectiveness of metrics
• Fixed GTPs result in higher CO2 prices and higher total
mitigation costs than GWPs, but lower prices/costs on CH4
• Time-dependent GTPs (focusing on year 2100) result in lower
CO2 prices and lower total mitigation costs than GWPs; prices
and costs for CH4 are lower initially but (much) higher later
• Assumptions about agriculture mitigation potential
have a larger effect on global costs than alternative metrics
• Different long-term stabilisation targets
have a much larger effect than alternative metrics
• Excluding agriculture globally is by far the most costly ‘metric’
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What about other relevant policy goals?
• Realised amount of warming and overshoot
• GDP impacts
• Timing of cost-effective CO2 emissions peak
• Regional implications
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Realised warming – rate and peak
Peak: 2-2.25°C
Rate (2020-2050):
0.2-0.26°C / decade
Most of the
differences are due
to alternative
assumptions, not
alternative metrics
Global agricultural marginal
abatement costs from Beach et al. (2008)
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GDP impacts
Time-dependent GTPs result in
lower aggregate costs, but
greater GDP losses relative to
BAU towards 2100 than GWPs
Global agricultural marginal
abatement costs from Beach et al. (2008)
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Timing of cost-effective CO2 emissions peak
Different metrics and assumptions
allow the CO2 emissions peak to
be delayed by almost 15 years
But most of the delay comes from
different assumptions; metrics
have a smaller influence
All pathways shown result in radiative forcing of 450ppm CO2-eq in 2100,
but the timing of CO2 mitigation differs due to metrics and other assumptions
Global agricultural marginal
abatement costs from Beach et al. (2008)
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Conclusions
GWPs are not the most cost-effective metric to compare GHGs
IF the main goal is to limit long-term radiative forcing in 2100,
and to do so via cost-minimising global abatement pathways
Fixed 100-year GTPs are even less cost-effective (+ 5 to 10%)
time-dependent GTPs would be more cost-effective (- 4 to 5%)
Cost implications of alternative metrics: smaller than alternative
assumptions about future agricultural mitigation potential, and much
smaller than choices of long-term target
Other policy goals: different equivalent metrics do not result in
equivalent other environmental outcomes – but differences are again
smaller than those arising from other assumptions
Regional implications: regional effect of metrics on production
systems and land-use change – see second presentation please!
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Questions to the policy community

How important is it for the policy process to have a metric
that is optimal for a particular policy goal but, almost by
definition, will do a poorer job for other policy goals?

How sustainable is the implementation of a metric that
implies escalating cost of CH4 emissions globally?

What are the social/policy benefits and costs of continuously
updating a metric to achieve optimality (however defined)?

Are tests of metrics useful that assume full global and
sectoral participation at full price levels?

What are the implications of different metrics for
regional and sectoral engagement to climate change?
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