Tropical Storms and Cyclones Moving Poleward
For years we have known that the tropics are expanding towards the poles. However, there is something decidedly destructive accompanying that shifting warm weather: tropical cyclones.
In a recent study led by Dr. James Kossin from the NOAA National Climatic Data Center, researchers discovered that cyclones are reaching their maximum intensity farther towards the poles than before. On average, these storm systems have been peaking in intensity towards the north and south poles at a rate of 53 and 62 kilometres (33 and 39 miles) per decade respectively.
The researchers unexpectedly came upon this while they were studying something else: the upper-atmosphere temperatures above tropical cyclones.
“The poleward migration of the tropical cyclones was something we stumbled on…” Kosin said. “We kept seeing a trend that we couldn’t explain unless the storms themselves were migrating away from the deep tropics. This did surprise us at first, but after looking at how the environment has been changing over the past few decades, it makes good physical sense.”
Part of this environmental change has to do with the deep tropics becoming increasingly hostile to cyclone formation, while its expanding edges turn into benign grounds for them.
Two of the factors that determine cyclone generation are vertical wind shear and potential intensity. Essentially, vertical wind shear disrupts the formation of storm clouds, while potential intensity describes the maximum strength a storm can reach in a specific area. In the deep tropics vertical wind shear has become more pronounced while potential intensity has dropped, with the opposite happening in the subtropics.
The causes for these are still unknown. However, they are linked to climate change, which the scientists tentatively connect with human activities such as stratospheric ozone depletion, increasing greenhouse gases, and particulate pollution.
Disruption on a global scale?
And what of the effects of this trend? Although whether it is good or bad depends on whom you ask (and where), it does not bode well for the majority of Earth’s inhabitants.
Regions close to the equator could see a decreased risk in cyclones while areas farther away need to prepare themselves for more powerful storms. That being said, parts of the world that traditionally rely on cyclone rainfall to renew freshwater sources may come to experience water shortages. Overall, Kossin noted that the status quo cannot be maintained, and that this will be typically disruptive to societies.
So what is next? According to Kossin we should view this as strong evidence that humans can and do impact the behavior of extreme weather events, which can dramatically affect mortality and risk.
From a scientific point of view, he and his colleagues are already trying to decipher the underlying causes and effects of this weather phenomenon.
“Given the motivation and relevance to society, we hope others will do the same,” Kossin said, highlighting the need for more research to understand this global trend.
- Kossin, J. P., Emanuel, K. A., & Vecchi, G. A. (2014). The poleward migration of the location of tropical cyclone maximum intensity. Nature, 509(7500), 349-352.