7. Summary and Conclusions
7.5. Policy analysis
The policy messages that can be derived from current integrated assessments seem t o converge toward a common understanding - consensus would proba- bly be too strong a word here. This is related t o the stringency and urgency of abatement actions. The present review portrayed independent modeling studies that investigate the impacts of a ten-year delay in action and come roughly t o the same conclusion: it may not be optimal but the costs of delay are relatively modest. The only exception is the case when action today would lead t o avoiding a catastrophic climate change and ten years later would be too late. The question is how t o formulate this risk-benefit case in a meaningful, quantitative way?
A related concern is the cost of control. An often heard anxiety is that the longer we wait the more expensive will be the abatement. Independent modeling results show that this is not the case and that the cost difference issue is not the important part anyway. Rather, the crucial question is the resolution of uncertainties. The Lempert et al. study, for example, explicitly points out that the cost difference between the ambitious and less ambitious abatement policies will not change much if we learn later that the climate sensitivity is higher (say 4OC rather than 2.5' C).
These results seem t o be robust even if we consider the possibility of abrupt climate change. Here, the implicit assumption is t h a t the conditional probability of more rapid climate change increases. T h a t is, we face a higher conditional probability of a catastrophic climate change beyond an unknown threshold. Yet, this does not seem t o affect the choice of near-term policies a t t h e global level. However, we need t o consider the local and regional climate change as well. Here it is really important t o assess impacts. Historical case studies may be a useful starting point: t h e case of t h e Caspian Sea level presented by Golitsyn (this volume), or Lake Victoria where a 2-meter lake level change occurred in a two-year period, or the classic example of t h e Sahel region where abrupt change in precipitation on the order of 30-40% occurred during t h e 1960s and the region belongs t o a much drier regime now. Social and economic impacts of these abrupt local changes are more tangible and more significant than those derived from slow and gradual climate change scenarios.
Perhaps the most common misunderstanding in the "delay or not delay action" debate stems from the false interpretation of t h e underlying mod- els. Delaying action by ten years in intertemporal energy economy models does not mean business-as-usual continued for ten years. Non-myopic mod- els will anticipate t h e imposition of a carbon constraint in t h e future and start adding new technologies t h a t are necessary for an optimal preparation for t h e carbon constraint t o be imposed. Therefore, it is important t o dis- tinguish between instantaneous adaptation t o the carbon constraint today and planning for a possibly fast adjustment in 10, 20, or 30 years.
A more general aspect of the same misunderstanding is t h a t results of integrated assessments, especially those looking for an efficient control path in an optimization framework, are interpreted as projections of future paths for 50-200 years. This is simply not correct. T h e decision problem is about the action today and not about action over the next 100 years. However, a practical concern should also be addressed more thoroughly in the context of this debate. Namely, industrial development and technology deployment will not wait. Large quantities of industrial capacities and infrastructure will be deployed in t h e LDCs and in the E T s where deep structural changes over t h e next decade fashion energy-economy relationships for t h e long term.
Despite the numerous open issues in both the contributing scientific disciplines and in t h e techniques of synthesis, integrated assessments provide useful insights in the complex issue of global climate change. Considering t h e impressive development in a short period and the large number of current efforts underway, one might expect t h a t the emerging results will be more
relevant and more reliable for policy makers involved in various national and international processes of managing the climate change problem.
References
Dowlatabadi, H. and Morgan, M.G., 1993, A Model Framework for Integrated Stud- ies of the Climate Problem, Energy Policy 21(3):209-221.
Hammit, J.K., Lempert, R.J., and Schlesinger, M.E., 1992, A Sequential Decision Strategy for Abating Climate Change, Nature 357:315-318.
Kaya, Y . , NakiCenoviC, N., Nordhaus, W.D., Toth, F.L., eds., 1993, Costs, Impacts, and Benefits of COz Mitigation, CP-93-2, International Institute for Applied Systems Analysis, Laxenburg, Austria.
Lind, R.C., 1982, A Primer on the Major Issues Relating to the Discount Rate for Evaluating National Energy Options, pp. 21-94 in R.C. Lind, K.L. Arrow, G.R. Corey, eds., Discounting for Time and Risk in Energy Policy, The Johns Hopkins University Press, Baltimore, MD, USA.
Maier-Reimer, E. and Hasselmann, K., 1987, Transport and Storage of Carbon Dioxide in the Ocean: An Inorganic Ocean Circulation Carbon Cycle Model, Climate Dynamics 2:63-90.
Manne, A.S. and Richels, R.G., 1992, Buying Greenhouse Insurance: The Economic Costs of C 0 2 Emission Limits, MIT Press, Cambridge, MA, USA.
Nordhaus, W.D., 1994, Managing the Global Commons: The Economics of Climate Change, MIT Press, Cambridge, MA, USA.
Rosenzweig, C. and Parry, M.L., 1994, Potential Impact of Climate Change on World Food Supply, Nature 367:133-138.
Peck, S.C. and Teisberg, T.J., 1994, Global Warming Uncertainties and the Value of Information: An Analysis Using CETA, Resources and Energy, forthcoming.
Rotmans, J . , 1990, IMAGE: An Integrated Model to Assess the Greenhouse Effect, Kluwer, Dordrecht, Netherlands.
The Economist, 1989, (25 February), Stratospheres, p. 79.