The coastal Northeast — from Maine to Delaware — is heating faster than most areas of the United States due to dramatic shifts in the ocean and atmospheric conditions over the North Atlantic, according to a new study.
The study, published in Nature Climate Change on Thursday, showed that not only are Northeastern winters getting warmer, as the authors expected, but there is also rapid summer warming occurring along the Atlantic coast. In many parts of this region, which includes the highly populated cities of New York and Boston, the researchers found that warming over the past century exceeded 2 degrees Celsius — the overall global figure that countries have committed to avoiding in the 2015 Paris Climate Agreement.
That coastal warming is nothing less than “exceptional,” lead author Ambarish Karmalkar, a professor at the University of Massachusetts-Amherst said in a press statement that accompanied the research.
“Some of the biggest [population] centers in the U.S. are suffering the greatest degree of warming,” said Karmalkar, who conducted the study with Columbia University climate scientist, Radley Horton.
The authors surveyed several previous studies and reanalyzed existing datasets to explore the connection between sea surface temperature rise and a slowdown of the Atlantic Ocean’s system of currents — called the Atlantic Meridional Overturning Circulation (AMOC), according to the study.
Describing AMOC “as a conveyor belt that transports warm, salty water from the tropics north toward Greenland, where it cools and sinks,” the authors explained that this cooled water then flows south in deep-water currents. However, because the climate is warming, and Greenland’s glaciers are melting, that conveyor belt is slowing down.
“One consequence of this conveyor belt slowdown is more heating of the ocean off the Northeastern coast, which helps to explain the spike in ocean temperatures in the Mid-Atlantic Bight and Gulf of Maine regions,” Karmalkar said.
AMOC is also connected to rising temperatures in the Northeast’s coastal cities, due to a weather phenomenon called the North Atlantic Oscillation (NAO), which guides the winds that blow over the Atlantic Ocean from the U.S. to Europe, according to the researchers.
The NAO has settled into a pattern over the past few decades that has strengthened the impact of ocean air on the eastern seaboard, the authors explained. Coupled with the AMOC slowdown, this results in warmer ocean air blowing over the Northeast and accelerating land-based warming trends.
Although northeastern coastal cities may have already experienced 2 degrees Celsius of warming, Karmalkar said he does not see a direct link between this area-specific temperature rise and overall global heating, which sits at about 1.2 degrees Celsius thus far.
“To stay below 2 degrees Celsius of warming globally, we will need a global effort to reduce greenhouse gas emissions,” he told The Hill. “This certainly involves strong mitigation in states along the Northeast coast, but that alone will not help with meeting the 2-degree Celsius global warming target set in Paris.”
As far as the Northeast coast is concerned, however, the authors said that a fundamental dilemma as to whether AMOC’s current — which is at its slowest in the past millennium — has occurred due to human influences or internal variability.
Researchers, acknowledging the limit of their study, said the next step should involve more specialized models that delve into daily weather conditions, as the non-linear impacts of effects temperatures may be obscured by seasonal averages.
But what is evident from the study, they concluded, is that the “social and environmental vulnerability” of the highly populated Northeast coast warrants “more nuanced climate assessments” than were available in the past.
And without integrating improved high-resolution data into regional climate assessments, scientists and policymakers “may underemphasize warming in this populous region,” Karmalkar said in the press statement.
Fortunately, he told The Hill, these capabilities are readily available to scientists, who now have access to high-resolution observational datasets that show temperature and humidity changes at local scales.
“But in terms of understanding future projections, we need to better understand the ability of our current generation of climate models to capture these highly localized trends,” Karmalkar said.
Horton, the study’s co-author, stressed that recent extreme weather events, such as the Pacific Northwest heatwave and flooding in the Northeast, have “exceeded climate model projections and led to outsized impacts for vulnerable urban populations.”
“When considering how to reduce vulnerability, we can't limit our vision of the possible to the relatively narrow band of outcomes suggested by climate models,” Horton told The Hill. “And we need to realize that impacts may cascade in complex ways that our sectoral models simply cannot envision.”