Tropical cyclones and climate change Bob Tuleya (NOAA visiting scientist-CCPO/ODU) Collaborators: (GFDL/NOAA) Tom Knutson Morris Bender Hyeong-Seog Kim Joe Sirutis Gabriel Vecchi Steve Garner Isaac Held Hurricane Katrina, August 2005 Transatlantic Solutions to Sea Level Rise Adaptation: Moving Beyond the Threat Old Dominion University, Oct.30-31, 2013

Why are we concerned about changes to hurricanes??? Before Sandy!

Some Virginia Hurricanes 1896 ‘gale’1933 Chesapeake 1933 OBX Hurricane 1955 Connie 2003 Isabel 1944 Great Atlantic

El Chichón Pinatubo AgungPelée Source: Meehl et al., J. Climate, 2004 Climate change includes both natural and man-made causes Science is based on theory,observation and models

Summary Statement on Tropical Cyclones and Climate Change WMO International Workshop on Tropical Cyclones VI Tropical SSTs have increased o C in the past several decades. IPCC has concluded that the likely primary cause of the global mean temperature rise in the past 50 years is increased greenhouse gases. Climate change temperature signal can be observed… Some recent studies have reported a large increase in tropical cyclone energy, numbers, and wind speeds in some regions during the last few decades in association with warmer sea surface temperatures. Other studies report that changes in observational techniques and instrumentation are responsible for these changes. Effect of climate change on hurricanes not yet statistically verified; signal not emerged from natural climate noise. Background: Caveat: Effect of climate change on hurricanes still a rapidly evolving research area, with more relevant studies in review, etc…

The frequency of recorded storms (low-pass filtered) in the Atlantic basin is well-correlated with tropical Atlantic SSTs Source: Emanuel (2006); Mann and Emanuel (2006) Michaels et al (2006) The maximum intensity of hurricanes increases with tropical Atlantic SSTs Atlantic

Hurricanes should increase in intensity & frequency during global warming due to increased SST ?? Not obvious since hurricanes also depend on wind shear and atmospheric stability Some evidence indicates that wind shear and atmospheric stability counteract increased SST in global warming scenarios Observational issues and model defects make firm conclusions problematic

Warming climate signal added to reanalysis data downscaling using GFDL regional models (Knutson et al; 2007 Bender et al, 2010) 28% fewer storms fewer, more intense hurricanes Supported by other studies e.g. Knutson and Tuleya, 2004, OOuchi et al, 2006; Contrast with Emanuel, 2013

Hurricane damage threat: winds & flooding Summary Winds > storm intensity, size, gustiness & path Flooding (coastal surge and inland) ---> storm intensity, size, rainfall & path Hurricane impacts not just dependent on storm intensity Conclusions Changes in size and path..no firm results (recent?) Most evidence indicates reduced frequency Small increase in most intense storms Increase in rainfall expected Effects on Hurricanes dependent on climate models Hurricanes & storms will have larger future impact because of sea level rise