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The above discussion identifies a number of reasons why the establishment of a baseline case is very difficult and uncertain. There are some additional reasons why this is so. The difficulty in predicting the evolution of development patterns over the long term stems, in part, from a lack of knowledge about the dynamic linkages between technical choices and consumption patterns and, in turn, how these interact with economic signals and policies. Technology and consumption patterns are endogenous, their direction being determined at least partly by political decisions. There are also many general uncertainties that impact on the establishment of a baseline case, for example political and social changes.
The above considerations further emphasize the need for work on the basis of several alternative baseline scenarios characterized by different assumptions regarding development patterns and innovation. This allows the mitigation or adaptation assessments to create an estimate range for the costs associated with very different development paths. Indeed, the range of emission levels associated with alternative baseline scenarios could well be greater than the difference between a certain baseline and the corresponding active policy case.
In reality, this can only provide a partial insight into the costs of climate change. Despite the large disparities in cost estimates likely to arise through the use of multiple baselines, they do allow the future to be framed within a much wider analytical perspective. Using a number of different development patterns is of particular importance to developing countries. Since the major part of their infrastructure and energy systems is yet to be built, the spectrum for future development is wider than in industrialized countries. A baseline scenario approach that assumes current development trends to continue is therefore not very useful in these countries (IPCC, 1996a, Chapter 8).
The scenarios of the IPCC Special Report on Emissions Scenarios (IPCC, 2000a) show that alternative combinations of driving-force scenario variables can lead to similar levels and structure of energy use and land-use patterns. Hence for a given scenario outcome, for example in terms of GHG emissions, alternative pathways can lead to that outcome. The conclusion is therefore that one and only one development path does not exist and studies preferably should include multiple baseline scenarios that facilitate a sensitivity analysis of the key scenario variables and assess the consequence of different development patterns.
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