MADISON, Wis., May 15 (UPI) -- According to a new study, tropical cyclone intensity continues to shift closer and closer to Earth's poles each year.
In analyzing tropical cyclone data collected over the last 30 years, NOAA researchers working at the University of Wisconsin-Madison showed that the latitude at which tropical cyclones climax has shifted poleward 33 to 39 miles per decade.
The research looks at tropical cyclones generally, meaning the findings are both derived from and applicable to the hurricanes of the Atlantic and eastern Pacific oceans and the typhoons of the western Pacific.
The new study was published in the journal Nature this week. Jim Kossin, lead author and scientist at NOOA's National Climatic Data Center, says the findings suggest new coastal cities may be at greater and greater risk of storm damages. The shift may also mean that tropical regions, often reliant on the heavy rains of cyclone season for farming, will see less and less precipitation.
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But though Kossin says the evidence of the shift is rather definitive, the broader picture -- the why and the how -- isn't exactly crystal clear.
"What we can't be sure of yet is exactly what's causing the trend," Kossin told BBC News. "There is compelling evidence that the expansion of the tropics is attributable to a combination of human activities, but we don't know which is the primary factor."
"If ozone depletion is mainly to blame, then the situation is likely to stabilize by the middle of the century after ozone-depleting chemicals are phased out," he added. "But if climate change is the main factor then there's no end in sight to this phenomenon."
Kossin theorizes that the cause is a little bit of everything: "greenhouse gases, stratospheric ozone depletion, and particulate pollution, all by-products of human activity."
