Estimating the Effects of Climate Change on Tropical Cyclone Activity

The effects of our changing climate on tropical cyclones (TCs) remain an important yet controversial scientific issue. Here we present results using a global atmospheric model to examine changes in regional and global TC activity using prescribed CCSM4 climatological sea surface temperatures (SSTs) from the two extreme CMIP5 RCP scenarios, RCP2.6 and RCP8.5. In addition, two other experiments were performed. The first uses climatological SSTs derived from the CCSM4 CMIP5 historical simulation. The second uses the HadISST climatological SSTs (control experiment). For all four experiments, 14 years of simulations were conducted to derive TC statistics. The global atmospheric model used is the FSU/COAPS model (T126L27 resolution). Using an objective detection/tracking algorithm, the FSU/COAPS model has already been shown to have high skill in reproducing interannual TC activity in the North Atlantic given observed SSTs or bias corrected SSTs from the CFSv1 model. Additionally, the model also reproduces the roughly 90 global tropical cyclones observed annually. Global and regional changes in SSTs, tropical cyclone: counts, intensities, annual cycles, genesis and track densities are examined. Strengths and weaknesses of the model are also considered, and a comparison of its current climate TC estimates was made to the IBTrACS dataset. The model estimates a small global increase in TC frequency for RCP2.6 (the lower extreme of warming climate scenarios) and a small global decrease in TC frequency for RCP8.5 (the upper extreme of warming climate scenarios) when compared to its estimate of current climate using the climatological HadISST data. A closer look at the North Atlantic Basin also reveals an increase in tropical cyclone frequency for RCP2.6 and a decrease in tropical cyclone frequency for RCP8.5. The model estimates a global (and North Atlantic) increase in hurricane strength storms going from current climate SSTs all the way to RCP8.5 SSTs indicating an increase in the frequency of the most intense storms as SSTs increase.