Metrics and stabilization of the global average surface temperature

1. Metrics and stabilization of the global average surface temperature UNFCCC workshop on common metrics Bonn, Germany, 2012-04-03 Daniel J.A. Johansson Division of Physical Resource Theory, Department of Energy and Environment Chalmers University of Technology Gothenburg, Sweden.

2. Outline • Emissions profiles • Global Cost Potential (GCP) • Global Temperature change Potential (GTP) • Cost-Effective Temperature Potential (CETP)

3. Stabilizing below 2ºC cost-effectively CO2 equivalent emissions using GWP-100 GWP was not designed to facilitate the basket approach in a cost effective stabilization regime. UNEP, 2010, The Emissions Gap Report

4. Global Cost Potential (GCP). • Based on that a climatetargetshould be met at lowestpossibleabatementcost. • Based on optimizingIntegratedAssessmentModels (IAMs).

5. Optimizing Integrated Assessment Model Economy & Energy module Emissions Climate module: Calculates concentrations, radiative forcing and subsequent temperature response

6. Optimizing Integrated Assessment Model • Objective: • Minimize total NPV abatement costs to stabilize the temperature at 2°C above the pre-industrial level • Cost optimal emissions profiles compatible with this target • Cost optimal emissions prices (taxes) needed to induce abatement Economy & Energy module Emissions Climate module: Calculates concentrations, radiative forcing and subsequent temperature response

7. Global Cost Potential (GCP) • Based on that a climatetargetshould be met at lowestpossibleabatementcost. • Based on optimizingIntegratedAssessmentModels (IAMs). • The metric is the ratioof the cost-optimal price (tax) on emissions of a gas X to the cost-optimal tax on emissions of CO2.

8. Global Cost Potential (GCP) 2100 2200 2000 2000 Manne & Richels, 2001, An alternative approach to establishing trade-offs among greenhouse gases, Nature

9. GCP - Transparency and numerical models • Optimizing IAMs are complex and far from transparent for most climate scientist, policy advisors and policy makers. • Include a range of very uncertain parameters and uncertain structural relationships.

10. Global Temperature change Potential (GTP) GTP for year t GTP initially developed in: Shine K.P., Fuglestvedt J.S., Hailemariam K., Stuber N. , 2005, Alternatives to the Global Warming Potential for Comparing Climate Impacts of Emissions of Greenhouse Gases, Climatic Change

11. Comparison GCP and GTP for CH4 Results from runs with the MiMiC model (Azar, Johansson & Persson) Relationship between GTP and GCP originally formulated in : Shine K.P., Berntsen T.K., Fuglestvedt J.S., Bieltvedt Skeie R., Stuber N., 2007, Comparing the climate effect of emissions of short- and long-lived climate agents, Philosophical Transactions of The Royal Society A

12. Cost-Effective Temperature Potential (CETP) An approximation of GCP. Includes: -physical information, -an estimate of stabilisationyear, -discount rate. Johansson, 2011, Johansson, 2011, Economics- and physical-based metrics for comparing greenhouse gases, Climatic Change.

13. CETP The time integrated discounted temperature pulse beyond the target time year. e-rτ=Discount factor r-discount rate τ -time CETP for year t Integrate and discount

14. Simple Carbon Cycle and Climate model ACC2 Climate Carbon Cycle Temperature feedback Max 2ºC above pre-industrial level Minimizing NPV abatement cost Atmosphere Joos et al. (1996) IRF 4-Box Model Hooss et al. (2001) IRF 4-Box Model Land Uptake Ocean Uptake Total Radiative Forcing Surface Air Temperature Change Parameterization Atmospheric Chemistry DOECLIM (Kriegler, 2005) Emissions of greenhouse gases & related agents CH4 & N2O SF6 & 29 Halocarbons Tropos-/Stratospheric O3 Parameterization (Joos et al., 2001) Sulfate/Carbonaceous Aerosols (direct/indirect) Tanaka et al., 2007, MPI Report; Tanaka et al., 2009, GRL Tanaka et al., 2009, Climatic Change Stratospheric H2O OH, NOx, CO, VOC

15. CH4 metric value in 2°C stabilization scenario Tanaka K., Berntsen T.K., Fuglestvedt J.S., Johansson D.J.A., O’Neill B., 2012, [working title:] Evaluation of emission metrics under climate stabilization targets, Ongoing work.

16. CH4 metric value in 2°C stabilization scenario Tanaka K., Berntsen T.K., Fuglestvedt J.S., Johansson D.J.A., O’Neill B., 2012, [working title:] Evaluation of emission metrics under climate stabilization targets, Ongoing work.

17. CH4 metric value in 2°C stabilization scenario Tanaka K., Berntsen T.K., Fuglestvedt J.S., Johansson D.J.A., O’Neill B., 2012, [working title:] Evaluation of emission metrics under climate stabilization targets, Ongoing work.

18. N2Ometric value in 2°C stabilization scenario Tanaka K., Berntsen T.K., Fuglestvedt J.S., Johansson D.J.A., O’Neill B., 2012, [working title:] Evaluation of emission metrics under climate stabilization targets, Ongoing work.

19. Importance of discount rateCH4 Johansson, 2011, Economics- and physical-based metrics for comparing greenhouse gases, Climatic Change.

20. Importance of discount rateN2O

21. Conclusion • GWP was not constructed to facilitate the implementation of cost-effective climate stabilization regime… • … although it has enabled the implementation of the basket approach. • Using cost effective trade-off ratios (Global Cost Potential - GCP) instead of GWP could enhance the cost-effectiveness of a stabilization regime… • … but one would then depend on complex and uncertain optimizing IAMs. • CETP approximate GCP well under a range of assumptions. • Neither GTP, CETP and GCP take into account climate effects in the short term. • CETP and GCP do to take into account climate effects in the long-term, beyond stabilization, while GTP does not.

22. THANK YOU! Questions, comments?

23. Additional cost of meeting the 2°C limit when using GWP-100 as compared to GCP • The use of GWP-100 would set a too high price on CH4 (short lived gases) years far from when stabilization occur, while the opposite hold for years close to when stabilization occur. • The cost of of using GWP-100 is very approximately about 5% of Net Present Value (NPV) abatement cost. Based on: Johansson, Persson & Azar, 2006, The cost using Global Warming Potentials, Climatic Change