1. 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)
Much of the analysis contained in this presentation is the initial findings from a project currently underway by a number of UK research institutes including Oxford and Reading Universities, the MOHC and Tau Scientific.

2. 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
As Jan has mentioned, the closer you get to a more relevant metric, the larger the uncertainties become.
Physical
Subject to uncertainties in our scientific knowledge
Highlight impact of uncertainties on the use of metrics.
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

3. 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
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

4. 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
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

5. 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
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

6. Impact of new evidence: updating GWP values
IPCC SAR
IPCC AR4
CO2 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;
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

7. Global total CO2e emissions per year (GWP100)
Impact of new evidence 10 20 30 40 50 60
1990
2008
High
N2O
CH4
CO2
SAR
AR4
26.4% 
26.2% 
Global total CO2e emissions per year (GWP100) .
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

8. CO2e emissions per year (GWP100)
Impact of new evidence 2 4 6 8 10 12
1990
2008
High F gases
N2O
CH4
CO2
160% 
155% 
8.6% 
8.2% 
8.5% 
7.9% 
6.5% 
No change
Smaller increase
No significant effect
Smaller decrease
CO2e emissions per year (GWP100)
SAR
AR4
SAR
AR4
SAR
AR4
SAR
AR4
China
USA
EU-27
Brazil
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

9. 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
Because GTP has been raised, interested in implications. Not considering a move from GWP as the full range of impacts (including economics and political) have to been explored.
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
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10. Impact of choice of metric
GWP100
GTP100
CO2 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
Impact of time horizon/lifetime
Source: IPCC 2007; Fuglestvedt et al. 2010
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

11. Impact of choice of metric10 20 30 40 50 60
1990
2008
High F
Gases
N2O
CH4
CO2
26% 
27% 
Global total CO2e emissions per year
The absolute level of emissions falls in terms of CO2e but the baseline also falls (GTP100 leads to 15% decrease in baseline for global total).
However, relative changes could lead to improvements or deteriorations in CO2e performance relative to 1990.
GWP100
GTP100
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12. Impact of choice of metric2 4 6 8 10 12
1990
2008
CO2e emissions per year
High F gases
N2O
CH4
CO2
8.2% 
7.2% 
160% 
193% 
8.5% 
7.8 % 
Larger increase
Smaller increase
Smaller decrease
Stronger decrease
7.9% 
16% 
Change from 1990 to 2008 emissions.
Note that emissions in CO2e is lower for all using GTP100 as a result of lower weighting for non-CO2 gases.
GWP
GTP
GWP
GTP
GWP
GTP
GWP
GTP
China
USA
EU27
Brazil
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

13. 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
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

14. Impact of choice of time horizon: e.g. methane10 20 30 40 50 60 70 80
100
200
300
400
500
Time Horizon (years)
Metric value
GWP
GTP
Data source: IPCC, 2007; Fuglestvedt, et al. 2010
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
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15. Impact of choice of time horizon10 20 30 40 50 60 70
20 years
100 years
High F gases
N2O
CH4
CO2
Global emissions in 2008 (CO2e)
GWP
GTP
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012

16. 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?
Economic implications and market.
Choice of time horizon has greater impact than choice of metric/update.
Unknown benefits and impacts. Final point is just a question for the audience. Not suggesting that we provide an answer!
UNCERTAINTIES IN IMPLEMENTATION OF METRICS
3 APRIL 2012