When Hurricane Sandy hit land near New York City nearly a decade ago, bringing with it huge storm surges and 7 inches of rain that caused widespread flooding and power outages, the superstorm was considered an extremely rare occurrence. While such storms are common in equatorial regions, including the Caribbean and along the Gulf Coast, such storms rarely hit the northeastern United States directly
However, a new study suggests that as the planet warms, the storms will become more common in mid-latitude regions – between the 30th and 60th parallel in both hemispheres – including New York City and Boston, as well as Beijing, Tokyo and other major cities in East Asia and Australia.
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“Places like New York that aren’t in the deep tropics have always had hurricanes, but rarely,” said Joshua Studholme, climate physicist at Yale University and lead author of the study, published last month in Nature Geoscience. “Climatology is changing and that will likely be a shock.”
A growing range of hurricanes means more people, as well as homes and businesses in coastal areas, could be at risk, said Jim Kossin, a former National Oceanic and Atmospheric Administration scientist who was not involved in the new research.
The equatorial region that leads to tropical cyclones – known as hurricanes in the Atlantic and typhoons in the western Pacific – is likely to expand towards both poles as meteorological conditions that favor tropical cyclones become more common there.
“Even a small shift in average latitude toward the pole where tropical cyclones travel can cause very large changes in exposure at higher latitudes,” said Dr. Kossin, who now works for The Climate Service, a climate risk analysis company.
Hurricanes typically develop in regions where the prevailing winds are weak and the sea surface temperature is over 80 degrees Fahrenheit. Such conditions are common in tropical regions, but were less far from the equator and closer to the poles. However, as global temperatures rise, the jet streams – western bands of fast winds that orbit up to 14 kilometers above the earth – weaken and shift in regions in the mid-latitudes. This allows hurricanes and typhoons to form over a larger area.
In the past 170 years, the average global temperature has risen by two degrees Fahrenheit, according to a report released by the Intergovernmental Panel on Climate Change in August. According to the report, temperatures would continue to rise by at least 0.7 degrees through 2100, due to greenhouse gas emissions “clearly caused by human activity,” including fossil fuel burning.
The last time hurricanes formed at higher latitudes was during the Pliocene, a period between 5.3 million and 2.6 million years ago that was characterized by high temperatures and high levels of atmospheric carbon dioxide, according to the study.
“The tropical cyclones of the 21st century will most likely occupy a greater latitude than ever before in the past three million years,” said Dr. Studholme.
His group based the research on satellite observations of current weather as well as simulations of Earth’s past and projections of future weather. Such simulations have limitations, in part because they rely on incomplete data describing how the climate has behaved in the past to project future patterns.
“Because of the uncertainty in the observations, it is very difficult to verify a climate model specifically for long-term, multi-decadal changes in global tropical cyclones,” said Hiroyuki Murakami, a project scientist at NOAA’s Geophysical Fluid Dynamics Laboratory who was not involved in the project Education. But, he added, it was “reasonable to infer the possible future polar shift in tropical latitudes,” based on the study.
Given the potential threat, some cities are not waiting for precise information.
Last year, New York City Emergency Management updated the city’s coastal storm plan using new data to define the areas most at risk from hurricane flooding and changing the boundaries of the city’s six hurricane evacuation zones accordingly.
The agency “continues to educate New Yorkers and prepare them for the potential impact of hurricanes as climate change has increased their frequency and intensity,” it said in a statement.
Boston is expanding its efforts to prepare for a potentially wet and stormy future, in part by redesigning riverside parks with riparian bumps and flood walls to better cope with rising water, and building a new riverside park to withstand hurricanes and catastrophic floods, so Rev. Mariama White-Hammond, city chief for the environment, energy and open space.
“In the case of hurricanes, we don’t know how and when, but we already know where our low-lying areas are,” she said. “We know enough to act.”
Write to Aylin Woodward at [email protected]
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