IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Changes in Impacts of Climate Extremes: Human Systems and EcosystemsChapter 4Venton, 2004; UNFCCC, 2007; Mechler, 2008). Because the chance ofoccurrence of a disaster event can be expressed as a probability, itfollows that the benefits of reducing the impact of that event can beexpressed in probabilistic terms. Costs and benefits should be calculatedby multiplying probability by consequences; this leads to risk estimatesthat account for hazard intensity and frequency, vulnerability, andexposure (Smyth et al., 2004; Ghesquiere et al., 2006).National-level studies of adaptation effectiveness in the EuropeanUnion, the United Kingdom, Finland, and The Netherlands, as well as ina larger number of developing countries using the National AdaptationProgramme of Action approach, have been conducted or are underway(Ministry of Agriculture and Forestry, 2005; DEFRA, 2006; Lemmen et al.,2008; de Bruin et al., 2009; Parry et al., 2009). Yet the evidence base onthe economic aspects including economic efficiency of adaptationremains limited and fragmented (Adger et al., 2007; Moench et al.,2007; Agrawala and Fankhauser, 2008; Parry et al., 2009). As noted atthe start of Section 4.5.3.2, many adaptation studies focus on gradualchange, especially for agriculture. Those studies considering extremeevents, and finding or reporting net benefits over a number of keyoptions (Agrawala and Fankhauser, 2008; Parry et al., 2009), do so bytreating extreme events similarly to gradual onset phenomena andusing deterministic impact metrics, which is problematic for disasterrisk. A recent, risk-focused study (ECA, 2009) concentrating on nationaland sub-national levels went so far as to suggest an adaptation costcurve, which organizes relevant adaptation options around their costbenefitratios. However, given available data including future projectionsof risk and the effectiveness of options, this is probably at most heuristicrather than a basis for policy.There are several complexities and uncertainties inherent in the estimatesrequired for a CBA of DRR. As these are compounded by climate change,CBA’s utility in evaluating adaptation may be reduced. These includedifficulties in handling intangibles and, as is particularly important forextremes, in the discounting of future impacts; CBA does not accountfor the distribution of costs and benefits or the associated equity issues.Moench et al. (2007) argue that CBA is most useful as a decision supporttool that helps the policymaker categorize, organize, assess, and presentinformation on the costs and benefits of a potential project, rather thangive a definite answer. Overall, the applicability of rigorous CBAs forevaluations of adaptation is thus limited based on limited evidence andmedium agreement.4.5.3.3. Attribution of Impacts to Climate Change:Observations and LimitationsAttribution of the impacts of climate change can be defined and used in away that parallels the well-developed applications for the physical climatesystem (IPCC, 2010). Detection is the process of demonstrating that asystem affected by climate has changed in some defined statisticalsense, without providing a reason for that change. Attribution isthe process of establishing the most probable causes, natural oranthropogenic, for the detected change with some defined level ofconfidence.The IPCC Working Group II Fourth Assessment Report found, with veryhigh confidence, that observational evidence shows that biologicalsystems on all continents and in most oceans are already being affectedby recent climate changes, particularly regional temperature increases(Rosenzweig et al., 2007).Attribution of changes in individual weather and climate events toanthropogenic forcing is complicated because any such event mighthave occurred by chance in an unmodified climate as a result of naturalclimate variability (see FAQ 3.2). An approach that addresses this problemis to look at the likelihood of such an event occurring, rather than theoccurrence of the event itself (Stone and Allen, 2005). For example,human-induced changes in mean temperature have been shown toincrease the likelihood of extreme heat waves (Meehl and Tebaldi, 2004;Stott et al., 2004). For a large region of continental Europe, Stott et al.(2004) showed that anthropogenic climate change very likely doubledthe probability of surpassing a mean summer temperature not exceededsince advent of the instrumental record in 1851, but which was by the2003 event in Europe. More recent work provides further support forsuch a linkage (Barriopedro et al., 2011; see Section 3.3.1).Most published studies on the attribution of impacts of extremes tonatural and anthropogenic climate change have focused on long-termrecords of disaster losses, or examine the likelihood of the event occurring.Most published effort has gone into the analysis of long-term disasterloss records.There is high confidence, based on high agreement and mediumevidence, that economic losses from weather- and climate-relateddisasters have increased (Cutter and Emrich, 2005; Peduzzi et al., 2009,2011; UNISDR, 2009; Mechler and Kundzewicz, 2010; Swiss Re 2010;Munich Re, 2011). A key question concerns whether trends in suchlosses, or losses from specific events, can be attributed to climatechange. In this context, changes in losses over time need to becontrolled for exposure and vulnerability. Most studies of long-termdisaster loss records attribute these increases in losses to increasingexposure of people and assets in at-risk areas (Miller et al., 2008;Bouwer, 2011), and to underlying societal trends – demographic,economic, political, and social – that shape vulnerability to impacts(Pielke Jr. et al., 2005; Bouwer et al., 2007). Some authors suggest thata (natural or anthropogenic) climate change signal can be found in therecords of disaster losses (e.g., Mills, 2005; Höppe and Grimm, 2009),but their work is in the nature of reviews and commentary rather thanempirical research. Attempts have been made to normalize loss recordsfor changes in exposure and wealth. There is medium evidence and highagreement that long-term trends in normalized losses have not beenattributed to natural or anthropogenic climate change (Choi and Fisher,2003; Crompton and McAneney, 2008; Miller et al., 2008; Neumayerand Barthel, 2011). The evidence is medium because of the issues setout toward the end of this section.268