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Uncertainties in implementation of common metrics
Jolene Cook, 3 April 2012, Bonn
With thanks to: Chris Huntingford (CEH), Laila Gohar (Met Office Hadley Centre), Nick Howarth (Oxford Univ.), Myles Allen (Oxford Univ.), Alex Lorenz (Oxford Univ.), Keith Shine (Reading Univ.), Bill Collins (Met Office Hadley Centre), Jason Lowe (Met Office Hadley Centre), David Lee (Tau Scientific)
Uncertainties in current knowledge and use of metrics
• Physical- e.g. climate sensitivity, radiative impact
• Structural- e.g. impact of different lifetimes, choice of time horizon, relationship with
end impact
• Economic- e.g. choice of discount rate, potential for perverse incentives
• Political- e.g. winners and losers, ease of communication, stability
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Value choices affect metrics
• Policy goals, e.g. 2°C, emission trading, reporting and monitoring
• What’s included in the basket of gases
• Revisions due to new evidence, e.g. SAR to AR4.
• Choice of metric, e.g. GWP, GTP or other?
• Choice of time horizon
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Value choices affect metrics
• Policy goals, e.g. 2°C, emission trading
• What’s included in the basket of gases
• Revisions due to new evidence, e.g. SAR to AR4
• Choice of metric, e.g. GWP, GTP or other?
• Choice of time horizon
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Value choices affect metrics
• Policy goals, e.g. 2°C, emission trading
• What’s included in the basket of gases
• Revisions due to new evidence, e.g. SAR to AR4
• Choice of metric, e.g. GWP, GTP or other?
• Choice of time horizon
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Impact of new evidence:updating GWP values
IPCC SAR IPCC AR4
CO2 1 1
CH4 21 25
N2O 310 298
HFC23 11,700 14,800
SF6 23,900 22,800
Other HFCs 140 – 9,200 124 – 9,810
Source: IPCC 2007;
0
10
20
30
40
50
60
1990 2008 1990 2008 1990 2008 1990 2008
High
N2O
CH4
CO2
SAR AR4
26.4% 26.2%
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Impact of new evidence
Global total CO2e emissions per year
(GWP100)
Impact of new evidence
0
2
4
6
8
10
12
1990 2008 1990 2008 1990 2008 1990 2008 1990 2008 1990 2008 1990 2008 1990 2008
High F gases
N2O
CH4
CO2
160% 155%
8.6% 8.6%
8.2% 8.5%
7.9% 6.5%
No change
Smaller increase
No significant effect
Smaller decrease
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
China EU-27USA BrazilSAR AR4 SAR AR4 SAR AR4 SAR AR4
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Value choices affect metrics
• Policy goals, e.g. 2°C, emission trading
• What’s included in the basket of gases
• Revisions due to new evidence, e.g. SAR to AR4
• Choice of metric, e.g. GWP, GTP or other?
• Choice of time horizon
Impact of choice of metric
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
GWP100 GTP100
CO2 1 1
CH4 25 4
N2O 298 265
HFC23 14,800 16,000
SF6 22,800 28,000
Other HFCs 124 – 12,200 18 – 15,100
Source: IPCC 2007; Fuglestvedt et al. 2010
0
10
20
30
40
50
60
1990 2008 1990 2008 1990 2008 1990 2008
High F Gases
N2O
CH4
CO226% 27%
Global total CO2e emissions per year
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Impact of choice of metric
GWP100 GTP100
0
2
4
6
8
10
12
1990 2008 1990 2008 1990 2008 1990 2008 1990 2008 1990 2008 1990 2008 1990 2008
High F gasesN2OCH4 CO2
8.2% 7.2%
160% 193%
8.5% 7.8 %
Larger increase
Smaller increase
Smaller decrease
Stronger decrease7.9% 16%
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
China USA EU27 Brazil
GWP GTP GWP GTP GWP GTP GWP GTP
Impact of choice of metric
Value choices affect metrics
• Policy goals, e.g. 2°C, emission trading
• What’s included in the basket of gases
• Revisions due to new evidence, e.g. SAR to AR4
• Choice of metric, e.g. GWP, GTP or other?
• Choice of time horizon
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
0
10
20
30
40
50
60
70
80
0 100 200 300 400 500
Time Horizon (years)
Met
ric v
alue
GWP
GTP
Impact of choice of time horizon:e.g. methane
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
Data source: IPCC, 2007; Fuglestvedt, et al. 2010
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
0
10
20
30
40
50
60
70
20 years 100 years 20 years 100 years
High F gasesN2O
CH4
CO2
Impact of choice of time horizon
GWP GTP
Conclusions
• Both GWP and GTP require value choices.
• Large sensitivity to choice of time horizon.
• Important to consult IPCC Fifth Assessment Report related to status of scientific findings related to metrics
• Next step: consider economic implications.
• Any value in changing metric when impact on other areas unknown?
3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS
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