Simulated Changes in Tropical Cyclone Size, Accumulated Cyclone Energy and Power Dissipation Index in a Warmer Climate
Detection, attribution, and projection of changes in tropical cyclone intensity statistics are made difficult from the potentially decreasing overall storm frequency combined with increases in the peak winds of the most intense storms as the climate warms. Multi-decadal simulations of stabilized climate scenarios from a high-resolution tropical cyclone permitting atmospheric general circulation model are used to examine simulated global changes from warmer temperatures, if any, in estimates of tropical cyclone size, accumulated cyclonic energy, and power dissipation index. Changes in these metrics are found to be complicated functions of storm categorization and global averages of them are unlikely to easily reveal the impact of climate change on future tropical cyclone intensity statistics.
While importance has been ascribed to observed increases in hurricane accumulated cyclonic energy (ACE) in the Atlantic Ocean, this work suggests that such changes are not necessarily to be expected at the global scale. While ACE and power dissipation index (PDI) of the strongest tropical cyclones are expected to increase, the possibility of decreases in overall tropical storm frequency counteracts resulting in little change in either global metric as simulated by the high-resolution CAM5. Hence, despite the robustness of global average ACE and PDI, neither serves as a good candidate for a detection and attribution metric. We must then turn to less robust metrics such as the exceedance of these metrics over a high threshold complicating the prognosis for any climate change signal to emerge in the near future. Likewise, Atlantic (or other regional) ACE or PDI may exhibit future changes but also suffer from data size limitations due to the lower tropical storm count.
I conclude that global average ACE and PDI are unsuitable climate change detection and attribution metrics and that focus should be directed to changes in their extremes.