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 2012 UNCERTAINTIES 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 2012 UNCERTAINTIES 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 2012 UNCERTAINTIES 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 2012 UNCERTAINTIES IN IMPLEMENTATION OF METRICS Impact of new evidence: updating GWP values IPCC SARIPCC AR4 CO 2 11 CH N2ON2O HFC2311,70014,800 SF 6 23,90022,800 Other HFCs140 – 9, – 9,810 Source: IPCC 2007;

High N2ON2O CH 4 CO 2 SAR AR4 26.4%  26.2%  3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS Impact of new evidence Global total CO 2 e emissions per year (GWP100)

Impact of new evidence High F gases N2ON2O CH 4 CO 2 160%  155%  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 CO 2 e emissions per year (GWP100) ChinaEU-27USABrazil SARAR4SARAR4SARAR4SARAR4

3 APRIL 2012 UNCERTAINTIES 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 GWP100GTP100 CO 2 11 CH N2ON2O HFC2314,80016,000 SF 6 22,80028,000 Other HFCs124 – 12,20018 – 15,100 Source: IPCC 2007; Fuglestvedt et al. 2010

High FGases N2O CH4 CO2 26%  27%  Global total CO 2 e emissions per year 3 APRIL 2012 UNCERTAINTIES IN IMPLEMENTATION OF METRICS Impact of choice of metric GWP100GTP100

CO 2 e emissions per year High F gases N2ON2O CH 4 CO 2 8.2%  7.2%  160%  193%  8.5%  7.8 %  Larger increase Smaller increase Smaller decrease Stronger decrease 7.9%  16%  3 APRIL 2012UNCERTAINTIES IN IMPLEMENTATION OF METRICS ChinaUSAEU27Brazil GWPGTPGWPGTPGWPGTPGWPGTP 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

Time Horizon (years) Metric value 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 years100 years20 years100 years High F gases N2ON2O CH 4 CO 2 Impact of choice of time horizon Global emissions in 2008 (CO 2 e) GWPGTP

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