Coupled model simulations of hurricanes in a CO2-warmed climate

This study explores how a CO2 warming-induced enhancement of hurricane intensity could be altered by the inclusion of hurricane/ocean coupling. Simulations are performed using a coupled version of the GFDL hurricane prediction system in an idealized setting with highly simplified background flow fields. The large-scale atmospheric boundary conditions for these high resolution experiments (atmospheric temperature and moisture profiles and SSTs) are derived from control and high CO2 climatologies obtained from a low resolution (R30) global coupled ocean-atmosphere climate model. The high CO2 conditions are obtained from years 71-120 of a transient +1%/yr CO2 increase experiment with the global model. The CO2-induced SST changes from the global climate model range from +2.2 to +2.7C in the six tropical storm basins studied. In the storm simulations, ocean coupling significantly reduces the intensity of simulated tropical cyclones, in accord with previous studies. However, the net impact of ocean coupling on the simulated CO2 warming-induced intensification of tropical cyclones is relatively minor. For both coupled and uncoupled simulations, the percentage increase in maximum surface wind speeds averages about 5-6% over the six basins and varies from about 3 to 10% across the different basins. Both coupled and uncoupled simulations also show strong increases of near storm precipitation under high CO2 climate conditions, relative to control (present day) conditions.