Weather extremes are already having significant impacts upon human and natural systems. Human activity has led to the increased temperature. It is likely that heat waves are more frequent - the chances of a repeat of the devastating 2003 European heat wave event has quadrupled due to climate change (Stott et al, 2004; Gutowski et al, 2008). Indeed, by the 2040s, more than half of European summers will be hotter than the summer of 2003, and by the end of this century, a summer as hot as that of 2003 will be considered 'mild' (Stott et al, 2004).
Increases in heavy rainfall events have been observed since 1950, with some increase in flooding irrespective of increases or decreases in total precipitation. It is also likely that there has been an increase in very rare extreme precipitation events. According to Laurens Bouwer of the Dutch Institute for Environmental Studies, Jakarta faces a potential doubling of economic losses until 2015, and in Bangladesh the amount of people potentially affected by flooding will increase by 35 per cent over the same period (Bouwer et al, 2007).
By definition, extreme events are rare, local and may be short lived, and observational data are limited. Therefore, trends are difficult to detect. Projecting the future frequency and severity of extreme events is also one of the more difficult aspects of climate research. Extreme events are, however, crucially important for understanding the likely damages and costs of climate change. The costs tend to have a non-linear response to severe weather events -relatively small changes in the frequency and severity of weather events usually cause disproportionately larger damages. And as cyclone Katrina in the US, the 2003 European heat waves and Australia's recent massive bushfires and extensive droughts have demonstrated, even resilient and wealthy nations with the capacity to adapt and respond are highly vulnerable to increases in extreme events.
The IPCC (2007b) concluded that more frequent extreme heat events and heat waves, more intense and prolonged (although not more frequent) tropical cyclones, and heavier precipitation and flooding can be expected in many regions.
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