TC detections in twelve of the twenty models reproduce observed TC formation numbers and geographic distributions reasonably well, with annual numbers within ±50% of observed. TC detections in seven models were particularly low in number, ranging from 10% to 28% of global observed TC numbers, and detections in the remaining model were approximately double that observed. All but one of the twelve models with a reasonable TC climatology project decreases in global and Southern Hemisphere frequency varying between 7 and 28%. In the Northern Hemisphere, where there are larger inter-model variations, projections range from a 13% increase to a 25% decrease in TCs.
While these results are consistent with results from previous generations of climate models, they are at odds with two recent publications by Emanuel (2013) and Camargo (2013), which showed respectively a dominant increasing trend in TC frequency, and a mix of increasing and decreasing TC frequency. It is of concern that three independent studies of TC projection frequency in the same set of models could have such widely diverse findings. Given the level of public interest in this subject it is imperative that the differences in results be investigated further. It is now more important than ever to understand exactly what it is that the TC detectors detect, and to understand what is changing in the models that leads to the differences in detections between the future and historical scenarios.
In this presentation we will first attempt to reassure the audience that the OWZP TC detector does indeed detect TCs, and that projections made from using this technique are not particularly sensitive to the choice of thresholds, before summarizing the projection results discussed above. We anticipate that an investigation into differences in seasonal parameters (known to impact TC formation) and differences in TC precursor behavior between the historical and rcp85 scenarios will begin in the near future. Preliminary results from that study will also be presented.
Camargo, S. J., 2013: Global and regional aspects of tropical cyclone activity in the CMIP5 models. J. Clim. In press.
Emanuel, K. A., 2013: Downscaling CMIP5 climate models shows increased tropical cyclone activity over the 21st century. PNAS Early Edition. www.pnas.org/cgi/doi/10.1073/pnas.1301293110
Tory, K. J., S. S. Chand, J. L. McBride, H. Ye and R. A. Dare, 2013: Projected Changes in Late-twenty-First-Century Tropical Cyclone Frequency in 13 Coupled Climate Models from Phase 5 of the Coupled Model Intercomparison Project. J. Clim., 26, 99469959.