1. Metrics and stabilization of the global average surface temperature
UNFCCC workshop on common metrics
Bonn, Germany,
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 climate target should be met at lowest possible abatement cost.
Based on optimizing Integrated Assessment Models (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 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 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 stabilisation year,
-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
Surface Air Temperature Change
DOECLIM (Kriegler, 2005)
Emissions of greenhouse gases & related agents
CH4 & N2O
SF6 & 29 Halocarbons
Tropos-/Stratospheric O3
Sulfate/Carbonaceous Aerosols (direct/indirect)
Stratospheric H2O
OH, NOx, CO, VOC
Atmospheric Chemistry
Total Radiative Forcing
Carbon Cycle
Hooss et al. (2001)
IRF 4-Box Model
Atmosphere
Joos et al. (1996)
Ocean Uptake
Land Uptake
Parameterization
Climate
Parameterization (Joos et al., 2001)
Temperature feedback
Max 2ºC above pre-industrial level
Minimizing NPV abatement cost
Tanaka et al., 2007, MPI Report;
Tanaka et al., 2009, GRL
Tanaka et al., 2009, Climatic Change

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. N2O 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. Importance of discount rate CH4
Johansson, 2011, Economics- and physical-based metrics for comparing greenhouse gases, Climatic Change.

20. Importance of discount rate N2O

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