Probabilistic climate scenarios may misrepresent uncertainty and lead to bad adaptation decisions

✍ Scribed by Jim Hall

• Book ID: 102263227
• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 183 KB
• Volume: 21
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/hyp.6573

✦ Synopsis

Development of climate scenarios at global and regional scales is set upon a course towards probabilistic representations of uncertainty. The motive for this probabilistic approach is clear. The presentation of scenarios without quantification of relative likelihood, as typified by the Intergovernmental Panel on Climate Change's (IPPC) Third Assessment Report (TAR) (Houghton et al., 2001), has been criticized as providing policy makers with insufficient information upon which to base decisions (Pittock et al., 2001;Schneider, 2001Schneider, , 2002)). If probabilities are not provided then, it is argued, decisions will be made with implied assessments of relative likelihood that depart, perhaps significantly, from experts' best judgement. A rational approach to dealing with climate risks will, it is argued, weigh up probabilities and consequences. This applies to adaptation decisions, e.g. in relation to water resource management, as much as it applies to the question of mitigation policy, where it has been most actively discussed.

Considerable progress has been made since the TAR in exploring the parameter space of general circulation models (GCMs) of the global climate and in conditioning model outputs with climate observations and paleoclimate data. It is therefore argued that the climate community is ready to provide probabilistic climate projections, which will be much more informative than the results published in the TAR. The UK Climate Impacts Programme (UKCIP) is committed to publishing probabilistic distributions in its next climate scenarios for the United Kingdom, which will supersede the four (Low, Medium Low, Medium High, High) scenarios published by UKCIP in 2002 (Hulme et al., 2002). As with global probabilistic scenarios, these forthcoming UKCIP scenarios will contain a great deal more information than the previous four discrete projections, which were presented without any indication of their relative likelihood, and were based upon only one GCM. But are these probabilistic scenarios in danger of providing more information than is actually warranted by the available evidence? While the motive for probabilistic scenarios is clear, there are several concerns that accompany their use for impact assessments and adaptation studies.