WP4 Existing metrics
 

Task 4.1 Review of available metrics

Objectives

The objective of this task is


Metodology and scientific achievements related to Task including contribution from partners

Based on an extensive literature review and our own research in this field we are assessing the various existing metrics of climate change. The main focus is on radiative forcing (RF) and GWP since these form the basis for present climate policy. But GWPs and their application in policy making have been debated, and several other alternative concepts have been suggested by both natural and social scientists. There has been relatively little discussion of which purpose and functions alternative metrics serve, and which purpose and functions metrics of climate change should serve. We address the question of which functions metrics of climate change can serve, and which trade-offs that may be associated with alternative metrics. Our work gives an overview of how cost issues are dealt with, the climate impact (end point) against which gases are weighted, and the extent to which and how temporality is included, both with regard to emission control and with regard to climate impact. A list of criteria and "check points" is also developed. The question of purpose and function of the metrics is discussed in order to evaluate the metrics according to this. The results of the literature review are synthesized in Fuglestvedt et al. (2002).

We evaluated how sensitive climate policy is to use of various metrics. This is done with Norway as a case (Godal and Fuglestvedt, 2002): The comprehensive approach adopted in the Kyoto Protocol relies on the use of 100-year Global Warming Potentials (GWPs) to convert emissions of various gases to "carbon dioxide (CO2) equivalents". This particular set of weights, or metric, has a limited capacity to handle the large variations in atmospheric adjustment times, and emissions of various gases that are equal in terms of "CO2 equivalents" will not result in equal climatic effects. In this study, the 100-year GWP metric is assessed in the context of implementing the Kyoto Protocol. Using data from Norway, we explore how abatement policy formulated on the basis of 100-year GWPs compares to policies based on other metrics in terms of compliance costs and abatement profile, that is, the composition of the basket of gases reduced. We found that the costs for Norway change significantly when other metrics are used, but changes in the composition of the basket of gases are moderate. However, since compliance costs can be controlled through other mechanisms for post-Kyoto Protocols, the use of 100-year GWPs versus other metrics has little impact on the general formulation of Norwegian climate policy.

We tested how GWPs can be used in economic analyses of damages of climate change and the degree of equivalence that is obtained when damages of climate change are taken into consideration (Sygna et al., 2002). We look at the capacity of Global Warming Potentials (GWPs) to act as indicators of equivalence for temperature development and damage costs. We look at two abatement scenarios that are equivalent when using a 100-year GWP metric: one scenario reduces short-lived gases, mainly methane; the other scenario reduces CO2. Model calculations show that, despite their equivalence in terms of CO2 equivalents, the scenarios do not result in equal rates or levels of temperature change. The disparities become more prominent the further we move down the chain of consequences towards damage costs, measured either in respect to rate of climate change or level of climate change. Compared to the methane mitigation scenario, the CO2 mitigation scenario showed present-value costs 1.3 and 1.4 times higher for level- and rate-dependent damage costs, respectively. This implies that the adequacy of using 100-year GWP as an index to reflect equivalent climate effects and damage costs from emissions is questionable.
 

Socio-economic relevance and policy implication

The results from our studies are relevant for the assessment of the application of GWPs and other metrics in the formulation of climate policy and also in economic analyses of climate change. A commentary article about IPCC's structure and work on GWPs and the need for a multi-disciplinary approach to this issue was submitted (Godal, 2002).
 

Discussion and conclusion

We have gained a good overview of existing metrics of climate change and useful insight to the problems related to the various metrics; both in terms of scientific limitations and shortcomings, the problems related to their application and the formulation of metrics in light of what function and purpose they should serve. Our multidisciplinary approach (political science, economics, natural science) enables us to understand the different aspects of the various alternative metrics and how they may function in policy-making and in the development of climate regimes.
 

Plan and objectives for next period

D4.1 and M4.1. are delayed. The paper Fuglestvetd et al. (2002) will be submitted by the end of 2001.
 
 
 
 

Task 4.2 Calculation of metrics
 

Objectives

The objective of Task 4.2 is

Methodology and scientific achievements related to Task including contribution from partners

We completed a FORTRAN program for routine calculation of GWPs for 88 gases for any chosen time horizon, and a set of GWPs was calculated.

No detailed documentation of the GWP values given by the IPCC in The Second Assessment Report (SAR) is, to our knowledge, available. This is remarkable since these GWP values form the basis for the implementation of the Kyoto Protocol. In Godal and Fuglestvedt (2002) we have given a quite detailed documentation of how these GWPs are calculated and which parameter values that are chosen (lifetimes, forcing parameters, concentrations, etc).

We also developed a method for relating GWPs for various time horizons (H) to metrics based on damage functions and discounting of future damages. These "backward calculations" give us insight to what the use of GWPs for the different gases and different time horizons means in terms of the nature and shape of the damage function and the rate for discounting future damages climate change.
 

Socio-economic relevance and policy implication

It is important that it is possible to understand how the GWP values given by the IPCC are calculated and to reproduce these calculations. Thus, a clear and detailed documentation is required. This is not given by the IPCC, but the appendix in Godal and Fuglestvedt (2002) gives an outline of how the GWPs can be calculated in order to reproduce the values given by the IPCC. It also allows the calculation of GWPs for other time horizons or other choices of parameters or for updating the GWPs.

Our work on this WP has also formed the basis for several comments and input to the Third Assessment Report from the IPCC during the review process (Expert review and Government review).
 

Discussion and conclusion

M4.2 is delayed.
 

Plan and objectives for next period

We plan to use input from WPs 2 and 3 to calculate a set of metrics. We have the tools ready to start the work in this WP as soon as the input is available.
 
 
 
 

Task 4.3 Scientific evaluation of metrics
 

Objectives

The objective of this task is

Methodology and scientific achievements related to Task including contribution from partners

In this WP we have discussed for which climate parameter equivalence can be and should be expected (RF, integrated RF, dT, integrated temperature change, dSL, Damage (Euro), etc.).

A test was performed: The temperature effect (dT) of CO2 equivalent reductions in emissions (15 years), implemented for CO2 and methane using GWPs for time horizons of 20, 100 and 500 years has been calculated (Figure 4.1). Obviously there is no equivalence in dT, which is no surprise to scientists. but probably to policy makers and users from other disciplines. This may be a matter of communication about expectations.

Figure 4.1: Temperature responses to changes in emissions of CO2 and CH4 in terms of CO2 equivalents for various time horizons.


 

Equivalence further down the cause-effect chain has been tested (Sygna, et al., 2002). We use scenarios (from Fuglestvedt et al., 20002) that are equivalent based on 100-year GWPs:

and The calculation show large differences in rates and levels of temperature change between the scenarios (i.e., no equivalence). Damage costs are calculated based on level of temperature change or rate of temperature change. Large disparities between the scenarios in terms of development of damage costs over time are found. But in terms of present value (PV) costs the scenarios did not show very large differences.
 
 
 
Discount rates 
Ratio of PV costs between scenarios (S1/S2) 1 % 2 % 3 % 7 % 10 %
Level dependence 0.81 1.05 1.26 1.76 1.74
Rate dependence 0.77 1.10 1.37 1.64 1.50

 

Socio-economic relevance and policy implication

The fact that emissions may be equivalent in terms of GWP but not in terms of other metric like temperature change, rate of temperature change or damage costs, might have an impact on design and choice of metrics in a follow-up treaty to the Kyoto Protocol.
 

Discussion and conclusion

Our calculations illustrate that emissions that are equal in terms of CO2 equivalents will not produce equivalent climatic effects. The results from our work also imply that the adequacy of using GWP100 as an index to reflect equivalent climate effects and damage costs from emissions is questionable. On the other hand, the limitations and inaccuracies in the GWP metric have to be weighted against the advantage of having transparent and simple tools.

Regarding possible refinements of metrics: Several different metrics with various key parameters (dT, dT/dt, dSL, etc.) can be constructed. But although a climate convention is established and a protocol for reductions of GHGs has been negotiated, there is so far no common conception or agreement regarding what aspects of climate change are most important. According to Article 2 of the UNFCCC, "the ultimate objective of the convention is to achieve stabilization of GHG concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system." A reasonable interpretation given the comprehensive approach principle in the Convention is that radiative forcing is to be stabilized at a level that prevents a dangerous interference with the climate system and that a suite of GHGs can be reduced according to the comprehensive approach to meet the forcing target. But since "dangerous" can be interpreted in several ways, this goal formulation does not provide any guide to evaluation criteria for existing metrics or for a new metric concept.
 

Plan and objectives for next period

We plan to evaluate the metric calculated for the runs performed in WPs 2 and 3.