Possible North Atlantic extratropical cyclone activity in a warmer climate

The impact of greenhouse gas (GHG)-induced global warming on the North Atlantic storm climate is investigated by using dynamically downscaled outputs from Canadian Regional Climate Model (CRCM). The downscaling simulations were performed with CRCM, driven by estimates from simulations of the third Generation Coupled Global Climate Model (CGCM3.1) following the Intergovernmental Panel on Climate Change (IPCC) 20th Century (20C3M) (1970-1999) and SRES A1B Scenario emissions (2040-2069) simulations. We show that CRCM can capture the general characteristics of the storm tracks and wind fields suggested by the reanalysis data for the current climate over the North Atlantic area. Compared with CGCM3's results, CRCM gives improved estimates of the distribution of storm tracks with respect to reanalysis data, although it still tends to underestimate the track density over the Northwest Atlantic area. For the high-CO2 A1B climate change scenario, both CRCM and CGCM3 show that there is a small reduction in the total number of cyclones, but an increase in the most intense ones. Similar to previous studies, we show that for future climate estimates, simulations also show that the dominant North Atlantic storm tracks shift northward, especially over the northern Northeast Atlantic, where the occurrence of the most intense cyclones (with minimum mean sea level pressure below 970hPa or maximum winds > 27 m/s) increases. However, over the North Atlantic mid-latitudes, the storm density decreases, and the occurrence of the most intense cyclones also slightly decreases, during 2040-2069. The storm density changes are connected with changes in the mean upper level steering atmospheric flow. In terms of storm structure, composite analysis of the most intense cyclones show that they tend to become larger and more intense in the climate change scenario considered here (A1B).