Tropical cyclones develop over warm seas, generating strong winds and rain. At their most severe, these low-pressure, rotating storm systems are classified as hurricanes or typhoons. Because tropical cyclones can wreak havoc on coastal communities and offshore economic activity, it is important to investigate how climate change can affect their formation.

Since the mid-1990s, most models of climate change have predicted that a warming climate would result in fewer tropical cyclones around the world. However, these models also predict greater storm intensity. Now Sugi et al. have shown that the converse is also true: A cooler climate would give rise to more tropical cyclones with lower intensity.

The authors used an established atmospheric global climate model (MRI-AGCM3.2) to predict how cooler temperatures would affect tropical cyclone formation. First, they ran the model with sea surface temperatures from 1979 to 2003 to simulate tropical cyclone formation in today’s climate. Then, they ran the model twice more: once with sea surface temperatures uniformly decreased by 4°C and once with temperatures increased by 4°C.

As the researchers expected, the results showed that more tropical cyclones would form in a cooler future climate. These storms would be less intense than today’s cyclones but would form in similar locations. The results were also consistent with two competing hypotheses for the physical mechanism, the upward mass flux hypothesis and the saturation deficit hypothesis, by which a warmer climate might reduce the number of tropical cyclones.

Intriguingly, the results showed tropical cyclone formation at sea surface temperatures well below 26°C, which is thought to be the minimum required temperature for these storms. The researchers point out that some Arctic and Antarctic storms resemble tropical cyclones, so it may be that tropical cyclones can form with much lower sea surface temperatures than expected. Further studies will reveal whether these results are consistent across other climate models. (Geophysical Research Letters, doi:10.1002/2015GL064929, 2015)

—Sarah Stanley, Freelance Writer

Citation: Stanley, S. (2015), A cooler climate would trigger more tropical cyclones, Eos, 96, doi:10.1029/2015EO037847. Published on 22 October 2015.