Tropical storms appear headed for the Poles, peaking in ferocity at successively higher latitudes over the past three decades, according to a new study in the journal Nature. (Related: "Hurricanes 101.")
Climate scientists generally predict that tropical storms (called hurricanes, typhoons, or cyclones, depending on the ocean where they form) will increase in power but decline in frequency in coming decades due to global warming.
But the storms also appear to be on the move—driven by warmer oceans and wind-shear changes in the upper atmosphere—according to the Nature study, led by James Kossin of the NOAA National Climatic Data Center. "The poleward trends are evident in the global historical data," says the study.
Looking at satellite observations from 1982 to 2009—averaged across eight ocean basins—the researchers located the peak intensity of tropical cyclones, which they determined was occurring farther away from the equator.
In the Northern Hemisphere, the storms have moved an average of 33 miles (53 kilometers) north; and in the Southern Hemisphere 37 miles (60 kilometers) south. Despite fears raised by 2012's Superstorm Sandy, however, Atlantic hurricanes appear to have bucked the global migration by staying put. (Related: "Hurricane Sandy Report Warns of Rising Sea, More Storms.")
Mapping seasonal intensity
This map shows the seasonal intensity of hurricanes, typhoons, and tropical cyclones—all three names refer to the same phenomenon—since 1851 as recorded in NOAA's public archives. Storms in the Atlantic have been recorded for a much longer period, and therefore appear denser. Only in recent decades has activity in the more tumultuous Pacific been reliably monitored.
Charting seasonal hurricanes
This chart shows summaries of historical hurricane seasons, adding up recorded length in days of each storm and where storms rate on the Saffir-Simpson scale throughout their lifetimes, for a sense of overall activity.
JOHN NELSON, IDV SOLUTIONS; MATTHEW TWOMBLEY, NGM STAFF. SOURCE: NOAA INTERNATIONAL BEST TRACK ARCHIVE FOR CLIMATE STEWARDSHIP
Global warming, which both heats the ocean waters that power the storms and strengthens the winds that spin them up, appears to be fueling the overall migration, says climate scientist Hamish Ramsay of Australia's Monash University, in a commentary accompanying the study.
It's unclear why Atlantic storms seem unaffected by this trend, but Ramsay suggests that it could be linked to the impact of the El Niño and La Niña weather cycles on hurricanes.
Ramsay says that whether the migrations lead to a larger or smaller number of intense tropical storms in the future, or to more storms striking coasts, are the big questions raised by the storm-migration findings.
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