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

Changes in the climate systemlong-term observations of key components of theclimate system (in particular from the oceans). Someof these sources of uncertainty can be reduced byfurther research and data collection but they willnever be fully eliminated. Assessments of climateimpacts on human communities and ecosystems arefurther complicated by the need to consider relevantchanges in economic, demographic, technical,institutional and cultural factors. Finally, the climatesystem exhibits substantial natural variability, inparticular on the regional level.In general, uncertainties about future climatechange are smaller for changes in temperaturethan for precipitation and other climate variables,for changes at global and continental scales thanat regional scale, and for changes in mean climatethan for extreme events. The importance of differentsources of climate uncertainty also varies over time.Natural climate variability and model uncertaintyis the dominating factor in the short term. On timescales of 50 years and longer, scenario uncertaintybecomes the main source of the uncertainty abouttemperature change whereas model uncertaintyremains the main source of uncertainty forprecipitation (Cox and Stephenson, 2007; Hawkinsand Sutton, 2009; 2011).Providing the best available scientific informationto decision-makers, including a characterisation ofuncertainties, helps narrowing the range of possiblefuture conditions that policies need to address. Forexample, Figure 2.4 depicts key aspects of futureclimate change in northern and southern Europefor two future periods (see Section 2.2 for furtherinformation on observed and projected climatechange in Europe). Key uncertainties are depictedby showing the results for two different emissionsscenarios and for several climate models separately.One robust conclusion is that both regions areexpected to warm further, whereby the detailsdepend on the region, emissions scenario, climatemodel and time horizon. Furthermore, (almost)all climate models agree that northern Europe willbecome substantially wetter annually averagedand in particular in winter (see Section 2.2). Allmodels agree that southern Europe will becomedrier towards the end of the 21st century undera business-as-usual precipitation scenarioannually averaged and in particular in summer(see Section 2.2). Projected precipitation changes inthe first half of the 21st century and for a mitigationscenario are less certain. Finally, differences betweenemissions scenarios increase over time.2.2 Key climate variables2.2.1 OverviewRelevanceAnthropogenic emissions of GHGs are thedominating cause of the observed rapid increasesin global average temperature over recent decades.Natural factors like volcanoes and solar activitycan explain a large portion of the temperaturevariability up to the middle of the 20th century butcan only explain a small part of the warming trendover the past 50 years. Changes in precipitationand storminess have been more varied than thetemperature trend but they can also exert majorimpacts on natural and social systems.Key messages: 2.2 Key climate variables• Three independent records show long-term warming trends of global and European average annualtemperature since the end of the 19th century, with most rapid increases in recent decades. Thelast decade (2002–2011) was the warmest on record globally and in Europe. Heat waves have alsoincreased in frequency and length. All these changes are projected to continue at an increased pacethroughout the 21st century.• Precipitation changes across Europe show more spatial and temporal variability than temperature.Since the mid-20th century, annual precipitation has been generally increasing across most of northernEurope, most notably in winter, but decreasing in parts of southern Europe. In western Europe intenseprecipitation events have provided a significant contribution to the increase. Most climate modelprojections show continued precipitation increases in northern Europe (most notably during winter)and decreases in southern Europe (most notably during summer). The number of days with highprecipitation is projected to increase.• Observations of storm location, frequency and intensity show considerable variability across Europeduring the 20th century. Storm frequency shows a general increasing trend from the 1960s to 1990s,followed by a decrease to the present. Available climate change projections show no clear consensus ineither the direction of movement or the intensity of storm activity.54 Climate change, impacts and vulnerability in Europe 2012