Evidence that hurricanes are getting stronger
Kerry Emanuel
Abstract
On average, over the past 50 y, tropical cyclones have killed 10,000 people and incurred damages of $15 billion annually around the globe, while, over this interval, the population exposed to tropical cyclone hazards tripled, owing to migration into coastal areas (1). Theoretical work published more than 30 y ago predicted that greenhouse gas-induced climate change would increase the thermodynamic upper bound on tropical cyclone winds and thereby lead to a higher frequency of intense storms. The high toll of tropical cyclones and the human migration to coastal regions make it vital to find out whether the predicted increase of intense cyclones is actually occurring. But the paucity of intense storms, coupled with poor data quality, has made it difficult to detect theoretically predicted trends in the tropical cyclone record. In PNAS, Kossin et al. (2) attack this problem by analyzing satellite imagery over the period 1979–2017 and show a statistically significant upward trend in the global proportion of intense tropical cyclones. Tropical cyclone intensity is limited by the rate at which heat can be extracted from the ocean, the rate at which the energy of the winds is dissipated, and the thermodynamic efficiency of the process, which depends on difference of temperature across the troposphere (3). The limiting surface wind speed is referred to as the potential intensity, and increasing greenhouse gases lead to an increase in this limit (4). It is straightforward to calculate the potential intensity from … [↵][1]1Email: emanuel{at}mit.edu. [1]: #xref-corresp-1-1