Leading Partners in Science Cost-effectiveness and implications of GWPs and GTPs under alternative policy goals Andy Reisinger 1 Keywan Riahi 2 Oscar van

Leading Partners in Science

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 Centre2 International Institute for Applied Systems Analysis (IIASA)

Manuscript submitted to Climatic ChangeWork funded by NZ Ministry of Agriculture and various EU-FP7 programs

Copyright © 2010 New Zealand Agricultural Greenhouse Gas Research Centre April 20, 2023 | 1


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)




Evaluated alternative metrics:GWPs, fixed and time-dependent GTPs

CH4 N2O


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




Radiative forcing paths – all metrics/assumptions



Global agricultural marginal abatement costs from Beach et al. (2008)

CO2 and CH4 emissions – all metrics/assumptions



fixed 100-year GTPs:less CH4 mitigation

time-dependent GTPs: less CH4 mitigation initially,

more CH4 mitigation by 2100


CH4 emissions – detailed examples


Global agricultural CH4 emission pathways8

MESSAGE results

450ppm

550ppm

Global net costs

CH4 mitigation determines ‘atmospheric space’ for CO2 emissionsand hence total mitigation costs


Global agricultural CH4 emission pathways9

0

1000

2000

3000

4000

5000

NP

Vm

itiga

tion

cost

(US

$20

05

bill

ion)

agricultureindustrywasteforestryenergy

GWP GTP GTP(fixed) (time-dep.)

0

50

100

150

200

250

NP

Vm

itiga

tion

cost

(US

$20

05

billi

on

)

agriculture

CH4 2010 - 2050

N2O 2010 - 2050

CH4 2050 - 2100

N2O 2050 - 2100

no improvement inagricultural mitigation

potential

rapid improvement inagricultural mitigation

potential

no improvement inagricultural mitigation

potential

rapid improvement inagricultural mitigation

potential

GWP GTP GTP(fixed) (time-dep.)

Global discounted net present value mitigation

costs (2010-2100)

Example for 550ppmCO2-eq stabilisation


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 potentialhave 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’



What about other relevant policy goals?

• Realised amount of warming and overshoot

• GDP impacts

• Timing of cost-effective CO2 emissions peak

• Regional implications





Realised warming – rate and peak

Peak: 2-2.25°CRate (2020-2050): 0.2-0.26°C / decade

Most of the differences are due to alternative assumptions, not alternative metrics

Peak: 2-2.25°CRate (2020-2050): 0.2-0.26°C / decade

Most of the differences are due to alternative assumptions, not alternative metrics




GDP impacts

Time-dependent GTPs result in lower aggregate costs, butgreater GDP losses relative to BAU towards 2100 than GWPs

Time-dependent GTPs result in lower aggregate costs, butgreater GDP losses relative to BAU towards 2100 than GWPs




Timing of cost-effective CO2 emissions peak

Different metrics and assumptionsallow the CO2 emissions peak tobe delayed by almost 15 years

But most of the delay comes fromdifferent assumptions; metricshave a smaller influence

Different metrics and assumptionsallow the CO2 emissions peak tobe delayed by almost 15 years

But most of the delay comes fromdifferent assumptions; metricshave 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



Conclusions

GWPs are not the most cost-effective metric to compare GHGsIF 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!



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?

Documents

Leading Partners in Science Cost-effectiveness and implications of GWPs and GTPs under alternative policy goals Andy Reisinger 1 Keywan Riahi 2 Oscar van