Climate change could both boost the power of thunderstorms and bring more stretches of hot, still days, in the mid-latitudes of the Northern Hemisphere, including North America, a new MIT study suggests.
With temperatures rising globally, and particularly in the Arctic, the energy in the atmosphere is being redistributed. The result is that more energy will be available to fuel thunderstorms, while less energy will go toward summertime extratropical cyclones, researchers said in a statement.
Extratropical cyclones are larger, milder weather systems that are usually associated with winds and fronts that generate rain, researchers said.
“Extratropical cyclones ventilate air and air pollution, so with weaker extratropical cyclones in the summer, you’re looking at the potential for more poor air-quality days in urban areas,” study author Charles Gertler, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences, said in a statement.
He said the changes also meant “the potential for more destructive thunderstorms and more stagnant days with perhaps longer-lasting heat waves.”
Extratropical cyclones, which generally occur outside the tropics, in the mid-latitudes, are usually less violent than tropical cyclones, which are also known as hurricanes or typhoons. Forecasters often refer to extratropical cyclones as “lows” or “depressions.”
Gertler and his co-author, Associate Professor Paul O’Gorman, are publishing their results in the Proceedings of the National Academy of Sciences.
The researchers said extratropical cyclones feed off the differences in average temperatures between northern and southern latitudes. But in recent decades, the Arctic has warmed faster than the rest of the Earth, effectively shrinking the difference.
The researchers found that since 1979 the energy available for large-scale extratropical cyclones has decreased by 6 percent, whereas the energy that could fuel smaller, more local thunderstorms has gone up by 13 percent.
The results jibe with other recent evidence that in the Northern Hemisphere summer winds associated with extratropical cyclones have decreased with global warming and, in some areas, there has been more convective rainfall (rain caused by heating of the Earth’s surface, leading to rising warm air that cools and evaporates), including from thunderstorms, researchers said.
“Researchers are finding these trends in winds and rainfall that are probably related to climate change,” Gertler said in the statement. “But this is the first time anyone has robustly connected the average change in the atmosphere to these subdaily-timescale events. So we’re presenting a unified framework that connects climate change to this changing weather that we’re seeing.”
The researchers said their study estimated the average impact of global warming on summertime energy in the atmosphere over the Northern Hemisphere. Going forward, they hope to fill in more details.
“We’d like to work out what’s happening to the available energy in the atmosphere, and put the trends on a map to see if it’s, say, going up in North America, versus Asia and oceanic regions,” O’Gorman said in the statement. “That’s something that needs to be studied more.”
While the MIT study was not detailed, another researcher has used climate models to predict steamy summers in the future of Boston and other cities. That study predicted that Boston in 2080 would have weather similar to Baltimore’s.