From a Central American cave comes research that holds a dire warning for the Northeastern U.S.: global warming may be sending more hurricanes your way.
New research shows a long-term northward shift of hurricanes in the Atlantic Ocean. By studying rainfall history derived from a stalagmite in a cave in Belize, scientists concluded that storms that once would have crashed ashore in Central America, the Gulf Coast or Florida are curving northward, a trend that puts major cities in the Northeast U.S. in the path of destructive storms.
Superstorm Sandy in 2012 and Hurricane Irene in 2011 are examples of the types of damage in store for the region more often, as increasing greenhouse gas levels affect the major air currents that steer tropical storms. A team of climate scientists reported this conclusion recently in the journal Scientific Reports.
"It's important to try and protect vulnerable areas and the financial centers in the Northeast from the impacts of similar storms which could occur more often in the future," said author Lisa Baldini, an American climate researcher at Durham University in England.
The chemical signature of rainfall derived from the stalagmite helped show the shift was mainly caused by manmade greenhouse gas emissions since the late 19th century. If the buildup of heat-trapping pollution continues, it could result in more frequent and powerful storms for the region, she said.
Given the potential for catastrophic damage, projecting how global warming will affect hurricanes has been a big goal of climate researchers. This study adds important information, said climate scientist Yang Hu, of the Alfred Wegener Institute for Polar and Marine Research in Germany, who was not involved in the study.
"I think the basic conclusion is in agreement with our research showing that the climate system is expanding toward the poles," said Yu, who has studied how shifts in key ocean currents are affecting storm tracks off the coasts of Africa, Asia and North America. He said the new findings also support the latest Intergovernmental Panel on Climate Change global assessment, which suggests that tropical storm tracks will shift northward.
How many storms will form and whether they maintain strength near the Northeast coast is a different question, he said, because one of his recent studies suggests that cooling of the North Atlantic from melting Arctic ice could reduce the frequency of storms in that region.
Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, said the researchers may have underestimated the influence of the El Niño-La Niña cycle, which can shift tropical storm activity. He said the research is inconclusive when it comes to storm tracks.
"There are no robust expectations for changes in tracks and the observational studies are very mixed in conclusions (as they should be) and depend on the dataset and period and parameters(s) analyzed," he said via email.
According to Suzana Camargo, an ocean and climate physics researcher with Columbia University's Lamont-Doherty Earth Observatory, there is scientific consensus on the global trend toward an increase in the number of the most intense storms, but fewer storms overall. Other studies documented a robust poleward shift of tropical storm tracks in the western North Pacific and South Pacific.
The signal is not as clear in the Atlantic, but Baldini and her co-researchers aimed to strengthen those projections by studying carbon and oxygen isotopes in the annual layers of the Belize stalagmite, which can tell a climate story like tree rings. Rainfall from hurricanes has a unique chemical fingerprint. The rainfall record preserved in the stalagmite is exceptionally clear going back 450 years.
"What we saw was a peak in tropical cyclone activity in Belize around 1650, then a gradual decrease to the present day," she said. "There are two possible explanations, either a decrease in number, or the storms are moving away from our site."
Other data has shown no overall decrease in the number of Atlantic hurricanes and the researchers found records of more hurricanes landing in places further north, like Jamaica, Florida and Bermuda.
The study concluded natural warming over the centuries has had some effect on hurricane tracks, but a sharp decrease in hurricane activity in the western Caribbean in the late 19th century coincided with increasing carbon dioxide and sulphate aerosol emissions to the atmosphere.
Co-author Dr Amy Frappier, of the Geosciences department at Skidmore College, said the findings illustrate how Atlantic hurricanes respond to warming.
Based on what's known from global climate models, the initial cooling of the Northern Hemisphere from heat-reflection aerosol pollution like sulfur dioxide from coal burning should have pushed the hurricane tracks southward. But that effect was overpowered by rising CO2, which is expanding the world's tropical belts and pushing hurricanes farther north, according to Frappier.
The northward shift of the hurricane track doesn't mean the Caribbean will be spared Warmer ocean temperatures in the western Caribbean could promote more hurricane development in that region, according to the researchers.
The 2016 Atlantic hurricane season started with a very unusual January storm in the mid-Atlantic and ended last week with another unusual storm, Hurricane Otto. That was the southernmost storm on record to hit Central America.