Changepoint Analyses Confirms Global Tropical Cyclone Frequency Decline

Changes in tropical cyclone frequencies as the climate warms is a topic of significant current debate [1, 2]. There is no accepted theory of how tropical cyclogenesis might respond to a warmer ocean-atmosphere system as multiple controlling factors exist [3–7]. Anthropogenic warming of surface ocean temperatures due to increased greenhouse gas concentrations [8] increases the potential for tropical cyclogenesis [9–11]; however, realized cyclogenesis also requires an initial local disturbance [12–16] to develop. Most multi-decadal tropical cyclone permitting climate models (i.e. resolutions of 15-50km) exhibit frequency decreases in warmer climates, despite the increase in tropical cyclogenesis potential [17–25]. In this paper, we analyze the International Best Track Archive for Climate Stewardship, IBTrACS, [26] and the HURSAT-B1 [27] observed tropical storm data with mean shift changepoint and regression methods. Summarizing all of our analyses, we find that the global frequency of tropical cyclones with lifetime maximum sustained winds of 63km/hour or greater having a duration of more than two days (over all storm strengths) has at least very likely decreased. From the IBTrACS dataset, we also find at the global scale that it is extremely likely that the proportion of tropical cyclones that reach Category 3+ on the Saffir-Simpson Hurricane Wind Scale has increased and that it is virtually certain that both the proportion and frequency of Category 4+ storms has increased.