TROPICAL CYCLONES IN A WARMER WORLD Dr Mark Saunders Benfield Hazard Research Centre Department of Space and Climate Physics University College London Workshop for Under 35s Reinsurance Group 14th October 2004 Regional Occurrence NATURAL HAZARDS IN A WARMER WORLD Slide 2 Workshop for Under 35s Reinsurance Group 1
Tropical Cyclones in a Warmer World 14th October, 2004 Relevance for (Re)Insurers l U.S. and Caribbean. Caribbean. Rank as the region region s costliest natural disaster. disaster. l Asia. Asia. Rank as the most costly and deadly natural disaster affecting much of Japan, South Korea, Taiwan, the Philippines, and coastal areas in other SE Asian countries. l Australia and SW Pacific. Pacific. Rank as a significant cause of natural disaster loss. NATURAL HAZARDS IN A WARMER WORLD Slide 3 Losses Isabel l l U.S. Hurricane annual damage bill 1950-2003 is estimated as US $ 5.1 bn (economic), US $ 2.6 (insured) at 2004 $. US East Coast - 2003 Asia. Typhoon annual damage bill (1990-2001) is US $3.5 bn (economic) at 2004 $. Taiwan - 2000 NATURAL HAZARDS IN A WARMER WORLD Workshop for Under 35s Reinsurance Group Slide 4 2
U.S. Damaging Storms 2004 Courtesy of NOAA and UW-CIMSS NATURAL HAZARDS IN A WARMER WORLD Slide 5 Where Does 2004 Rank? North Atlantic ACE (Accumulated Cyclone Energy) index: 3rd highest (after 1950 and 1995) since 1950. U.S. ACE index: 2nd highest (after 1964) since 1950. U.S. hurricane total insured loss: 2nd highest (after 1992) since 1950. Tropical storm strikes on Japan: Equal 1st for most (records since 1970). NATURAL HAZARDS IN A WARMER WORLD Slide 6 Workshop for Under 35s Reinsurance Group 3
Return Periods - 2004 U.S. hurricane strikes (4 or more): 17 years. U.S. ACE index (7.5 x 10 4 kts 2 ): 40 years. U.S. hurricane total insured loss (US $ 22bn): 37 years (see opposite). Hilti,, Saunders and Lloyd-Hughes (2004) NATURAL HAZARDS IN A WARMER WORLD Slide 7 How has Tropical Cyclone Activity Varied in the Past? NATURAL HAZARDS IN A WARMER WORLD Slide 8 Workshop for Under 35s Reinsurance Group 4
250 North Atlantic ACE index 1950-2003 200 150 100 50 0 1950 1960 1970 1980 1990 2000 NATURAL HAZARDS IN A WARMER WORLD Slide 9 NE Pacific ACE index 1966-2003 NE Pacific ACE Index 350 300 250 200 150 100 50 0 1966 1971 1976 1981 1986 1991 1996 2001 NATURAL HAZARDS IN A WARMER WORLD Slide 10 Workshop for Under 35s Reinsurance Group 5
600 NW Pacific ACE index 1965-2003 500 400 300 200 100 0 1965 1970 1975 1980 1985 1990 1995 2000 NATURAL HAZARDS IN A WARMER WORLD Slide 11 10 9 8 7 6 5 4 3 2 1 0 U.S. ACE index 1900-2003 US ACE Index 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 NATURAL HAZARDS IN A WARMER WORLD Slide 12 Workshop for Under 35s Reinsurance Group 6
Florida ACE index 1900-2003 6 5 4 3 2 1 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 NATURAL HAZARDS IN A WARMER WORLD Slide 13 Japan ACE index 1959-2003 Japan ACE Index 6 5 4 3 2 1 0 1959 1969 1979 1989 1999 NATURAL HAZARDS IN A WARMER WORLD Slide 14 Workshop for Under 35s Reinsurance Group 7
12 Australian ACE index 1970/1-2003/4 10 8 6 4 2 0 1970 1975 1980 1985 1990 1995 2000 NATURAL HAZARDS IN A WARMER WORLD Slide 15 Significant Trend or Change in Variance? l No significant change in ACE index or ACE index variance is observed anywhere,, either over the full period or, for the U.S., using the recent 1978-2003 period compared to prior 26-year periods. l The change in ACE index due to natural climate variability is everywhere an order of magnitude greater than that which may be attributable to trend in the historical record. NATURAL HAZARDS IN A WARMER WORLD Slide 16 Workshop for Under 35s Reinsurance Group 8
Conclusions 1. Global warming has, at present, had little or no increasing impact on northern hemisphere tropical cyclone activity. 2. Observed changes in activity are due predominantly to natural climate variability. NATURAL HAZARDS IN A WARMER WORLD Slide 17 Multi-Decadal Variability (Goldenberg et al., Science, 2001) Leading mode of Atlantic non-enso SST variability 1870-2000. Temporal reconstruction of SST mode-related variability for hurricane main development region. NATURAL HAZARDS IN A WARMER WORLD Slide 18 Workshop for Under 35s Reinsurance Group 9
What is our Current Understanding of How Tropical Cyclone Activity Will Vary in the Future? NATURAL HAZARDS IN A WARMER WORLD Slide 19 Atlantic Hurricane Predictors Trade Wind Predictor SST Predictor NATURAL HAZARDS IN A WARMER WORLD Slide 20 Workshop for Under 35s Reinsurance Group 10
Hurricane Numbers 1950-2004 Tropical Atlantic, Caribbean Sea and Gulf Perfect Predictors R 2 = 0.67 NATURAL HAZARDS IN A WARMER WORLD Slide 21 Future Projections for Tropical Atlantic, Caribbean and Gulf Hurricane Numbers NATURAL HAZARDS IN A WARMER WORLD Slide 22 Workshop for Under 35s Reinsurance Group 11
Future Projections for Tropical Atlantic, Caribbean and Gulf Intense Hurricane Nos NATURAL HAZARDS IN A WARMER WORLD Slide 23 Future Projections for Tropical Atlantic SST NATURAL HAZARDS IN A WARMER WORLD Slide 24 Workshop for Under 35s Reinsurance Group 12
Hurricane Intensity Knutson and Tuleya (2004) in a detailed GCM modeling study predict: 1. 6% increase in hurricane maximum intensity with an 80% increase in CO 2. This is line with theoretical estimates by Emanuel. 2. 18% increase in mean precipitation rate within 100km of the storm centre. These changes may not be detectable for a few decades. NATURAL HAZARDS IN A WARMER WORLD Slide 25 Conclusions 1. The number of North Atlantic, U.S. and Caribbean hurricanes may rise slowly due to global warming. 2. However, the increase in the number of hurricanes and in hurricane maximum intensity over the next 100 years is thought to be about 10% and thus is small compared to the range of natural year-to-year variability. NATURAL HAZARDS IN A WARMER WORLD Slide 26 Workshop for Under 35s Reinsurance Group 13
The historical record shows repeated quiet and active periods for U.S. hurricanes. Since 1999, U.S. hurricane strikes have been running 50% below average and U.S. hurricane insured losses 80% below norm. 2004 In Context 2004 has seen the recent hurricane dry spell corrected. NATURAL HAZARDS IN A WARMER WORLD Slide 27 Future Risk to (Re)Insurers? Although uncertainties remain, the vast majority of future hurricane losses in the U.S. and Caribbean are thought to continue to result from natural interannual and decadal climate variability and not from global warming. Since traditional insurance policies are set for the year ahead (or at most out to five years) the impact of global warming on risk over this timescale will be small or negligible. NATURAL HAZARDS IN A WARMER WORLD Slide 28 Workshop for Under 35s Reinsurance Group 14