Climate Change and Tropical Cyclone Forward Speed

26 01 2020

Dale C.S. Destin|

Many have made tropical cyclones (hurricanes, tropical storms and tropical depressions) the posterchild for climate change with respect to how they are or may be responding to a warming climate. It is a hot topic of debate that researchers are continuously investigating for answers. One of the many questions been asked is, “Are global tropical cyclones moving slower in a warning climate?”  

The track of Hurricane Irma – 2017

A recent research letter, in the Institute of Physics (IOP) Publishing, by Kelvin T.F. Chan, of the School of Atmospheric Sciences, and Guangdong Province Key Laboratory for Climate and Natural Disaster Studies, Sun Yat-sen University, Zhuhai, People’s Republic of China, weighed in, quite forcefully and persuasively, on the above question.

Time series of annual-mean global tropical-cyclone translation speed and their linear trends in periods 1949–2016 (blue) and 1970–2016 (orange).

According to Chan, the short answer to the question is no. Chan successfully show that, with the use of reliable data from 1970 to 2016, there is no significant change in the forward speed of tropical cyclones, notwithstanding the pronounced warning of the globe seen over the last half-century.

Chan’s finding virtually contradicts a 2018 paper present by James P. Kossin of the NOAA National Centers for Environmental Information, Center for Weather and Climate, Madison, WI, USA. Kossin found that there was a 10% slowdown in global tropical-cyclone translation (forward) speed over the past 68 years – 1949 to 2016. His implication was that this was related to anthropogenic climate change.

The IOP letter, by Chan, successfully shows that the findings of Kossin was based on the use of widely accepted spurious data obtained prior to the satellite era – pre 1966. Unanimously accepted, more accurate data since the satellite era – 1970 to 2016, show no significant slowdown of tropical cyclones. Understandably, prior to weather satellites in 1966, accurately tracking tropical cyclones was very difficult to impossible; hence, translation speed data before then are highly unreliable.

This finding of Chan is consistent with the findings of Knutson et al, in a very comprehensive study on the entire subject of climate change and tropical cyclones. According to Knutson, the results for the models “indicate no significant changes, and only 2 of the 10 individual… model projections show a significant change (increase).” He concluded that there was no clear consistent trend in the forward speed of tropical cyclones.

The question of how climate change is or may impact the forward speed of tropical cyclones is very important from a adoptation standpoint. A slower moving tropical cyclone has the potential for more destruction and vice versa. Naturally, the longer a tropical cyclone hangs around a particular populated area, the more the destruction is likely to be via wind, flooding rainfall and storm-surge.

Intuitively, it would be consistent to think that since a warning climate is slowing down the circulation of the tropics, it is also slowing down tropical cyclones, embedded its circulation. However, this is clearly not happening, certainly not based on the data since 1970 to 2016.

Tropical cyclones may be the posterchild for climate change; however, there is no evidence to support any changes in tropical cyclones forward speed, due to the changing climate being forced by humans.  

More broadly, there exist no evidence that there have been any changes in tropical cyclones, due to anthropogenic climate change. However, that is not to say that climate change won’t have an impact on tropical cyclones in the future.  

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