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

2. Chalmers University of Technology Outline Emissions profiles Global Cost Potential (GCP) Global Temperature change Potential (GTP) Cost-Effective Temperature Potential (CETP)

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

4. Chalmers University of Technology Global Cost Potential (GCP). Based on that a climate target should be met at lowest possible abatement cost. Based on optimizing Integrated Assessment Models (IAMs).

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

6. Chalmers University of Technology Optimizing Integrated Assessment Model Economy & Energy module Emissions Climate module: Calculates concentrations, radiative forcing and subsequent temperature response 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

7. Chalmers University of Technology Global Cost Potential (GCP) Based on that a climate target should be met at lowest possible abatement cost. Based on optimizing Integrated Assessment Models (IAMs). The metric is the ratio of the cost-optimal price (tax) on emissions of a gas X to the cost-optimal tax on emissions of CO 2.

8. Chalmers University of Technology Global Cost Potential (GCP) Manne & Richels, 2001, An alternative approach to establishing trade-offs among greenhouse gases, Nature 2000 22002000 2100

9. Chalmers University of Technology 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. Chalmers University of Technology 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. Chalmers University of Technology Comparison GCP and GTP for CH 4 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. Chalmers University of Technology Cost-Effective Temperature Potential (CETP) An approximation of GCP. Includes: -physical information, -an estimate of stabilisation year, -discount rate. Johansson, 2011, Johansson, 2011, Economics- and physical-based metrics for comparing greenhouse gases, Climatic Change.

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

14. Chalmers University of Technology Simple Carbon Cycle and Climate model ACC2 Tanaka et al., 2007, MPI Report; Tanaka et al., 2009, GRL Tanaka et al., 2009, Climatic Change Surface Air Temperature Change DOECLIM (Kriegler, 2005) Emissions of greenhouse gases & related agents CH 4 & N 2 O SF 6 & 29 Halocarbons Tropos-/Stratospheric O 3 Sulfate/Carbonaceous Aerosols (direct/indirect) Stratospheric H 2 O OH, NO x, CO, VOC Atmospheric Chemistry Total Radiative Forcing Carbon Cycle Hooss et al. (2001) IRF 4-Box Model Atmosphere Joos et al. (1996) IRF 4-Box Model Ocean Uptake Land Uptake Parameterization Climate Parameterization (Joos et al., 2001) Temperature feedback Max 2ºC above pre-industrial level Minimizing NPV abatement cost

15. Chalmers University of Technology CH 4 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. Chalmers University of Technology CH 4 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. Chalmers University of Technology CH 4 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. Chalmers University of Technology N 2 O 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.

19. Chalmers University of Technology Importance of discount rate CH 4 Johansson, 2011, Economics- and physical-based metrics for comparing greenhouse gases, Climatic Change.

20. Chalmers University of Technology Importance of discount rate N 2 O

21. Chalmers University of Technology 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. Chalmers University of Technology THANK YOU! Questions, comments?

23. Chalmers University of Technology Additional cost of meeting the 2°C limit when using GWP-100 as compared to GCP Based on: Johansson, Persson & Azar, 2006, The cost using Global Warming Potentials, Climatic Change The use of GWP-100 would set a too high price on CH 4 (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.