Lakigigar
Legacy Member
More hurricanes to hit Western Europe due to global warming
Interessant.
Interessant.
They show that in the North Sea and Gulf of Biscay there is a clear increase in thefrequency of severe winds (Beaufort 11–12, >28.4 m s–1)during autumn (Figures 2a–2d).
Additionally, the season ofhighest occurrence shifts from winter to autumn in the North Sea and Gulf of Biscay regions. The maximum windspeed in early autumn increases substantially along thewestern European coast (Figure 2e), emphasizing the intensi-fication of extreme winds during that season.
The occurrence of extreme wind speeds can be attrib-uted to a few storms during the 30 year integration period(Figure 2f ). Summed over Norway, the North Sea, and theGulf of Biscay the number of hurricane force storms (Beaufort 12, >32.6 m s–1) in early autumn (August–October)increases from 2 to 13 over the 21st century. We have tracedback the origin of these events (see Model and Experimental set-up), showing that virtually all future west-Europeanhurricane-force storms originate as hurricanes or tropicalstorms in the tropics (Figure 3b). In contrast, the fewhurricane-force storms in the present climate have predominantly an extratropical origin (Figure 3a). This suggests that the climatological mechanisms driving western Europehurricane-force winds are likely to change dramatically overthe 21st century.
In the auxiliary material we show that tropical cyclones will increase the probability of present-day extreme events over the North Sea and the Gulf of Biscay with a factor of 5 and 25, respectively, with far reaching consequences especially for coastal safety
In the current climate, the main genesis region forhurricanes is confined to the western tropical Atlantic, whereSSTs are above the threshold (27C) required for tropical cy-clones to develop. (Note that the SST threshold for tropicalstorm development will be affected by changes in the stabil-ity characteristics of the atmosphere, with the projected tro-pospheric warming hampering tropical cyclone genesis.)Future tropical storms that reach western European coasts(and cause hurricane-force storms) predominantly originatefrom the eastern part of the tropical Atlantic (east of 50W;Figure 3b). This is because climate warming in the easterntropical Atlantic causes SSTs to rise well above the 27Cthreshold (Figure 3b). The occurrence of hurricane-forcewinds indeed shows that, notwithstanding the increasedatmospheric stability, the eastern boundary of the hurricanedevelopment region shifts about 10to the east in responseto the SST rise (Figures 3c and 3d). The present develop-ment region exhibits a decrease in hurricane frequency, which, inciden-tally, has significant implications for hurricanes reachingNorth America. This agrees with the finding that the numberof Atlantic hurricanes to make landfall in North America isreduced during years with an anomalous warm tropicalAtlantic and consequent eastward extension of the develop-ment region [Wang et al., 2011].
After their formation, tropical cyclones are pushedpoleward by the beta-effect [Rossby, 1948]. Combined withthe ambient prevailing westward trade winds, this causes theinitial path of Atlantic tropical cyclones to be in a northwest-erly direction. When they reach the midlatitudes they arecaught by the predominant westerly winds, thereby veeringtheir track in a northeasterly direction, with the possibilityof reaching western Europe. Geometrically, this likelihoodincreases if their genesis region in the tropical Atlantic isfurther to the east. In addition, the shorter travel distance inthe midlatitudes will enable the “tropical”characteristics ofhurricanes to be better preserved along their journey towestern Europe. Hence, the likelihood of these stormsmaintaining their strength when reaching western Europewill increase, because there is simply less time for them todissipate .
