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.

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

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

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

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

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

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

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

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 3 APRIL 2012

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

Impact of choice of metric 10 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 UNCERTAINTIES IN IMPLEMENTATION OF METRICS 3 APRIL 2012

Impact of choice of metric 2 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

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

Impact of choice of time horizon: e.g. methane 10 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 3 APRIL 2012

Impact of choice of time horizon 10 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

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