Large Contribution of Sea Surface Warming to Recent Increase in Atlantic Hurricane Activity

Atlantic hurricane activity has increased significantly since 1995 but the underlying cause of this increase remains uncertain. It is widely thought that rising Atlantic sea surface temperatures have played a role, but the contribution of sea surface warming remains unknown. Here we quantify this contribution for storms that formed in the tropical North Atlantic, Caribbean Sea and Gulf of Mexico - regions that together account for most of the hurricanes that make landfall in the United States. We show that a statistical model based on two environmental variables – local sea surface temperature and an atmospheric wind field - can replicate a large proportion of the variance in tropical Atlantic hurricane frequency and activity between 1965 and 2005. We then remove the influence of the atmospheric wind field to assess the contribution of sea surface temperature. Our results indicate that the sensitivity of tropical Atlantic hurricane activity to August-September sea surface temperature over the period we consider is such that a 0.5 °C increase in sea surface temperature is associated with a ~40 per cent increase in hurricane frequency and activity. The results also indicate that local sea surface warming was responsible for ~40 per cent of the increase in hurricane activity relative to the 1950-2000 average between 1996 and 2005. Our analysis does not identify whether greenhouse gas induced warming contributed to the increase in hurricane activity, but the ability of climate models to reproduce the observed relationship between hurricanes and sea surface temperatures will serve as a useful means of assessing whether they are likely to provide reliable projections of future changes in Atlantic hurricane activity.