The Impact of Climate Change on Northwest Atlantic Extratropical Hurricanes and Winter Storms

Following studies by Knutson, Tuleya, Walsh and colleagues, we explore possible climate change scenarios for midlatitude extratropical transitioning hurricanes (ETs), experiencing significant intensification as they propagate from their genesis areas in the North Atlantic topical basin into the midlatitute Northwest Atlantic. Two approaches were adopted. For summer-autumn extratropical cyclones, simulations were performed with the Canadian mesoscale compressible community (MC2) model, driven by control and high-CO2 climate estimates from the global coupled atmosphere-ocean climate model, the Canadian Climate Centre CGCM2 model. For winter storms, simulations were performed with the Canadian Regional Climate Model (CRCM), again driven by control and high-CO2 climate estimates from CGCM2. The control condition, representing present climate, consists of years 1975 to 1994. The high- CO2 climate change conditions were obtained from years 2040-2059 of a transient +1% yr-1 CO2 increase experiment with CGCM2, following IPCC IS92a, which gives a nearly doubling of CO2 concentrations by 2050, compared to the 1980s. Compared with the current climate, the storm tracks in the climate change scenario more nearer the coastal area of North Atlantic, become less tightly distributed in space and tend to propagate slightly faster (~10%). A very slight increase in storm intensity is suggested in simulations, and composite storm structure does show change. Averaged winds around the storm center become stronger, and although the maximum low-level tropospheric winds are weaker, higher-level tropospheric winds show notable strengthening (~5%). In storm simulations, the net impact of the climate change scenario is to cause a slight tendency for increase in number of severe storms (~5%). An ensemble approach was also used, and produced consistent results.