Climate Change 2001:
Working Group III: Mitigation
Other reports in this collection Precautionary Considerations

In decision making, the precautionary principle is considered when possibly dangerous, irreversible, or catastrophic effects are identified, but scientific evaluation of the potential damage is not sufficiently certain, and actions to prevent these potential adverse effects need to be justified (Jonas, 1985; O’Riordan and Cameron, 1994; CEC, 2000). The precautionary principle implies an emphasis on the need to prevent such adverse effects. It thus acknowledges societal risk preferences, which are, plausibly, that humankind would rather be risk averse than risk neutral or risk seeking if one considers, for instance, future climate-induced loss of GNP (Pearce, 1994; Jaeger et al., 1998). Hence, attitudes towards risk play a key role in decision making under uncertainty. However, one might also favour prevention to cure even where one is certain about the damage.

With the precautionary principle, uncertainty about the damage to be incurred does not serve as an argument to delay action. In the face of great uncertainty, a precautionary approach might even result in a more stringent emission-reductions target and/or adaptational response (Cantor and Yohe, 1998).

The evaluation of uncertainty and the necessary precaution is plagued with complex pitfalls. These include the global scale, long time lags between forcing and response, the impossibility to test experimentally before the facts arise, and the low frequency variability with the periods involved being longer than the length of most records (Moss and Schneider, 2000). Some of these uncertainty aspects may be irreducible in principle, and hence decision makers will have to continue to take action under significant uncertainty, so the problem of climate change evolves as a subject of risk management in which strategies are formulated as new knowledge arises (Jaeger et al., 1998).

Aspects of uncertainty are associated with each link of the causal chain of climate change, beginning with GHG emissions, covering damage caused by climate change, followed by a set of mitigation and adaptation measures (Jepma and Munasinghe, 1998). In particular, damage-function estimates are prone to low confidence as they involve uncertainty in both natural and socioeconomic systems. To quantify the impact of climate change on flora and fauna needs consideration of many effects because of the complexity of the biological and ecological systems. Similarly, the manner in which humans adapt to climate change is not well known, socioeconomic modules are still at a stage of low disaggregation, and damage as a function of vulnerability, adaptation and time-dependency is poorly understood (Tol et al., 1998; Tol, 1999a, 1999b).

However, following the precautionary principle, uncertainty is not an argument for delaying action, as the UNFCCC acknowledges in Article 3.3: parties should “take precautionary measures to anticipate, prevent or minimize the causes of climate change and mitigate its adverse effects. Where there are threats of serious or irreversible damage, lack of full scientific certainty should not be used as a reason for postponing such measures...” (UNFCCC, 1993). Pursuing this principle, mitigation and adaptation measures are to be implemented before full information is available and uncertainties regarding the scope and timing of climate change are resolved. Yet, the question of timing and extent of mitigation and/or adaptation policies remains unquantified by the precautionary principle (Portney, 1998).

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