Are global tropical cyclones moving slower in a warming climate?

Abstract

The local tropical-cyclone-related rainfall totals largely depend on the rain rate near the center and the translation speed of a tropical cyclone. Understanding how they respond to a changing climate has been a hot topic. A recent astounding study reported a 10% slowdown in global tropical-cyclone translation speed over the past 68 years (1949-2016) and implicitly related this to the weakening of tropical circulation forced by the anthropogenic warming. It thereby suggested that it might result in more local rainfall totals in a warming climate. However, here this study shows that no robust and significant observational and modeling evidences reveal that they are. The data artefacts introduced by the changes in measurement practices, particularly the introduction of satellite capabilities since the 1970s, are likely the main source of heterogeneities leading to such disagreement. The global slowdown of tropical-cyclone translation speed becomes indeterminate and a significant global speedup trend is even found over land if the records in more reliable satellite sensing era period starting from 1970 are examined, where this period is also the most pronounced warming period in the last half-century. The relationship between the slowdown of tropical cyclones and anthropogenic warming is therefore not apparent and the relevant potential increase in local rainfall totals in the future warming climate is suspicious.