Tropical storms are migrating out of the tropics, reaching their peak intensity in higher latitudes, where larger populations are concentrated, a new NOAA-led study published in the journal Nature says.
Each decade for the past 30 years, tropical cyclones — which include hurricanes and typhoons — have become strongest on average about 30 to 40 miles farther north or south of the equator, the study says.
In a statement on the National Oceanic and Atmospheric Administration's website, the agency says:
"As tropical cyclones move into higher latitudes, some regions closer to the equator may experience reduced risk, while coastal populations and infrastructure pole-ward of the tropics may experience increased risk. With their devastating winds and flooding, tropical cyclones can especially endanger coastal cities not adequately prepared for them."
While intensity estimates for tropical storms have proven difficult to pin down, "the location where a tropical cyclone reaches its maximum intensity is a more reliable value and less likely to be influenced by data discrepancies or uncertainties," says Jim Kossin, a scientist with NOAA's National Climatic Data Center, who is the paper's lead author.
As the BBC points out, the study underscores previous research indicating that the extent of the tropics had expanded by 1 to 3 degrees of latitude (about 70-100 miles) in the Northern and Southern hemispheres since 1979.
"The rate at which tropical cyclones are moving toward the poles is consistent with the observed rates of tropical expansion," says Kossin. "The expansion of the tropics appears to be influencing the environmental factors that control tropical cyclone formation and intensification, which is apparently driving their migration toward the poles."
Nature World News writes: "In order to track these storms' paths over recent years, researchers used international data from 1982 to 2012. They then marked the peak intensity of each of the storms in order to see whether the hurricanes were traveling further afield."
"The absolute value of the latitudes at which these storms reach their maximum intensity seems to be increasing over time, in most places," study co-author Kerry Emanuel, an MIT professor, said in a news release. "The trend is statistically significant at a pretty high level."
The release from MIT News says that "while the scientists who conducted the study are still investigating the atmospheric mechanisms behind this change, the trend seems consistent with a warming climate."
In the Southern Hemisphere, tropical cyclones in the Pacific and Indian oceans show a strong movement toward the South Pole. In the Northern Hemisphere, the marked trend is in the western Pacific, while tropical storms forming in the Atlantic and North Pacific are moving toward the poles more slowly, the study's authors say.
"This is an important, very well researched paper that uncovers something that was unknown previously," said hurricane researcher Chris Landsea, science officer at the National Hurricane Center, according to The Associated Press.