Discrete climatic events cause substantial damage. Heavy losses of human life, property damage, and other environmental damages were recorded during the El Niño-Southern Oscillation (ENSO) event of 1997-1998. Details are reported in the regional chapters on Africa, Asia, and the Americas, and Chapter 8 assesses the damages from a financial services perspective. For many policymakers and stakeholders, the impacts of climatic extremes and variability are a major concern (Downing et al., 1999b). The uneven impacts of climatic hazards raises humanitarian concerns for development and equity.

An increase in variability and frequency of extreme events could have greater impacts than changes in climate means (e.g., Katz and Brown, 1992; Mearns, 1995; Semenov and Porter, 1995; Wang and Erda, 1996). Extreme events are a major source of climate impactsunder the present climate, and changes in extreme events are expected to dominate impacts under a changing climate (see Section 12.1).

Methodological issues concerning extreme events in the context of climate change include developing climate scenarios, estimating impacts, evaluating responses, and looking at large-scale effects.

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