IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Chapter 3Changes in Climate Extremes and their Impacts on the Natural Physical Environment100Alaska100Central North America100Canada and Greenland100North Europe100North Asia40201054020105402010540201054020105ALLANTALLANTALLANTALLANTALLANT100Western North America100South Europe100China402010540201054020105ALLANTALLANTALLANT1004020105Eastern North America1004020105South Asia1004020105Central AsiaALLANTALLANTALLANTCentral America and Mexico100100Southern South America100Southern Africa100Australia100Global Land40201054020105402010540201054020105ALLANTALLANTALLANTALLANTALLANTFigure 3-2 | Estimated return periods (years) and their 5 and 95% uncertainty limits for 1960s 20-year return values of annual extreme daily temperatures in the 1990s climate(see text for more details). ANT refers to model simulated responses with only anthropogenic forcing and ALL is both natural and anthropogenic forcing. Error bars are for annualminimum daily minimum temperature (red: TNn), annual minimum daily maximum temperature (green: TXn), annual maximum daily minimum temperature (blue: TNx), and annualmaximum daily maximum temperature (pink: TXx), respectively. Grey areas have insufficient data. Source: Zwiers et al., (2011).studies. Kuglitsch et al. (2009, 2010) homogenized and analyzed over250 daily maximum and minimum temperature series in theMediterranean region since 1960, and found that after homogenizationthe positive trends in the frequency of hot days and heat waves in theEastern Mediterranean region were higher than reported in earlier studies.This was due to the correction of many warm-biased temperature datain the region during the 1960s and 1970s.In summary, regional and global analyses of temperature extremes onland generally show recent changes consistent with a warming climateat the global scale, in agreement with the previous assessment in AR4.Only a few regions show changes in temperature extremes consistentwith cooling, most notably for some extremes in central North America,the eastern United States, and also parts of South America. Based on theavailable evidence we conclude that it is very likely that there has beenan overall decrease in the number of cold days and nights and very likelythat there has been an overall increase in the number of warm days andnights in most regions, that is, for land areas with data (correspondingto about 70 to 80% of all land areas; see Table 3-2). It is likely that thisstatement applies at the continental scale in North America, Europe,and Australia (Table 3-2). However, some subregions on these continentshave had warming trends in temperature extremes that were small or notstatistically significant (e.g., southeastern Europe), and a few subregionshave had cooling trends in some temperature extremes (e.g., central NorthAmerica and eastern United States). Asia also shows trends consistentwith warming in most of the continent, but which are assessed here tobe of medium confidence because of lack of literature for several regionsapart from the global study from Alexander et al. (2006). Most of Africais insufficiently well sampled to allow an overall likelihood statement tobe made at the continental scale, although most of the regions on thiscontinent for which data are available have exhibited warming intemperature extremes (Table 3-2). In South America, both lack of dataand some inconsistencies in the reported trends imply low confidence inthe overall trends at the continental scale (Table 3-2). In many (but notall) regions with sufficient data there is medium confidence that thenumber of warm spells or heat waves has increased since the middle ofthe 20th century (Table 3-2).Causes of Observed ChangesThe AR4 (Hegerl et al., 2007) concluded that surface temperatureextremes have likely been affected by anthropogenic forcing. Thisassessment was based on multiple lines of evidence of temperature135