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Unformatted text preview: Atlantic hurricanes and natural variability in 2005 Kevin E. Trenberth 1 and Dennis J. Shea 1 Received 13 May 2006; accepted 24 May 2006; published 27 June 2006. [ 1 ] The 2005 North Atlantic hurricane season (1 June to 30 November) was the most active on record by several measures, surpassing the very active season of 2004 and causing an unprecedented level of damage. Sea surface temperatures (SSTs) in the tropical North Atlantic (TNA) region critical for hurricanes (10 to 20 N) were at record high levels in the extended summer (June to October) of 2005 at 0.9 C above the 190170 normal and were a major reason for the record hurricane season. Changes in TNA SSTs are associated with a pattern of natural variation known as the Atlantic Multi-decadal Oscillation (AMO). However, previous AMO indices are conflated with linear trends and a revised AMO index accounts for between 0 and 0.1 C of the 2005 SST anomaly. About 0.45 C of the SST anomaly is common to global SST and is thus linked to global warming and, based on regression, about 0.2 C stemmed from after-effects of the 200405 El Nin o. Citation: Trenberth, K. E., and D. J. Shea (2006), Atlantic hurricanes and natural variability in 2005, Geophys. Res. Lett. , 33 , L12704, doi:10.1029/2006GL026894. 1. Introduction [ 2 ] The record 2005 North Atlantic hurricane season featured the largest number of named storms (28) (sustained winds over 17 m s 1 ) and is the only time names have ventured into the Greek alphabet. In fact the season extended well beyond the official dates into December by Epsilon and Zeta (Dec. 30). It had the largest number of hurricanes (15) (sustained winds > 33 m s 1 ) recorded (note Cindy was belatedly upgraded to hurricane status), and is the only time there has been four category 5 storms (maximum sustained winds > 67 m s 1 ). These included the most intense Atlantic storm on record (Wilma, recorded surface pressure in the eye 882 hPa), the most intense storm in the Gulf of Mexico (Rita, 897 hPa), and the most damaging storm on record (Katrina), with over 1000 people killed and 1 million homeless in the United States. (See http://www.ncdc.noaa.gov/oa/climate/research/2005/ hurricanes05.html for details on these storms. Some esti- mates place total losses as high as $200B (http://www. whartonsp.com/articles/article.asp?p=416413&rl=1) and in- sured losses up to $60B http://www.rms.com/Publications/ KatrinaReport_LessonsandImplications.pdf.) Following on the heels of the very active 2004 hurricane season [ Trenberth , 2005], such statistics raise legitimate questions about whether global warming is playing a role in changing such storms or whether natural variability associated with the AMO dominates. Indeed, claims have been made that the AMO is the main source of the recent increase in hurricane activity since 1995 [ Mayfield , 2005] and that global warming has played little or no role [e.g., Pielke et al. , 2005; Landsea , 2005]. In this paper, we propose a new, 2005]....
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