Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Changes in the climate system2.2.3 Temperature extremesRelevanceGlobal climate change is affecting the frequencyand intensity of extreme events. Extremes of bothwarm and cool temperature are important indicatorsas they can have strong impacts on natural as wellas human systems. Importantly, a temperaturethat is 'normal' for one region may be extreme foranother region that has not regularly experiencedthis temperature in the past. For example, mortalityhas been estimated to increase by between 1 and4 % for every 1 °C increase above a locationspecifictemperature threshold, with the elderly,disabled and socio‐economically deprived at mostrisk (Baccini et al., 2008; EEA, 2011a) (see alsoSection 4.4).Past trendsExtreme high temperatures, for example numberof warm days and nights and heat waves, havebecome more frequent in the past while extremelow temperatures, for example cool days and nights,cold spells and frost days, have become less frequent(Klein Tank and Wijngaard, 2002; IPCC, 2007b). Theaverage length of summer heat waves over westernEurope has doubled since 1880, and the frequencyof hot days has almost tripled (Della-Marta et al.,2007). All these observations are consistent with thegeneral warming trend observed across Europe.Since 1960, significant increases in the number ofwarm days and nights, and decreases in the numberof cool days and nights have been noted throughoutEurope (Map 2.3). Between 1960 and 2011, thenumber of warm days increased by between 4 and10 days per decade across Europe, and the numberof warm nights increased by between 5 and 11 perdecade (not shown). The number of cool nightsdecreased by between 1 and 6 per decade in thesame period. Western and central Europe haveshown the largest increases in warm days/nights,and the Iberian peninsula, north-western Europeand Scandinavia have shown the largest warmingin cool days/nights. Despite a clear long‐termwarming trend across Europe, it is normal toobserve considerable variability between and withinyears. Further information on recent heat extremes isprovided in Box 2.3.ProjectionsExtreme high temperatures across Europe areprojected to become more frequent and last longerduring this century (IPCC, 2007a; b; Haylock et al.,2008; Sillman and Roeckner, 2008; Seneviratne et al.,2012). These changes are consistent with projectionsof future average warming as well as observedtrends over recent decades.The number of days that combine a hot summer day(defined as having a temperature exceeding 35 °C)and a tropical night (defined as having a minimumtemperature higher than 20 °C) is a basic indicator ofhuman comfort due to heat stress. Model projectionsproject the number of such combined heat stress daysto double across most parts of southern Europe by2071 to 2100 (Map 2.4). The most severe increases, ofabout 25 days per year, are projected in low‐altituderiver basins and along the Mediterranean coastswhere many densely populated urban centres arelocated (Fischer and Schär, 2010).Key messages: 2.2.3 Temperature extremes• Extremes of cold have become less frequent in Europe while warm extremes have become morefrequent. Since 1880, the average length of summer heat waves over western Europe has doubled andthe frequency of hot days has almost tripled.• Recent cold winters in northern and western Europe do not contradict the general warming trend ondecadal time scales. Historic records show a clear long-term warming trend across Europe but it isnormal to observe considerable variability between and within years due to natural variability.• Extreme high temperatures are projected to become more frequent and last longer across Europe overthe 21st century.62 Climate change, impacts and vulnerability in Europe 2012