Climate scientists have been warning for a while that as the planet heats up, storms will become fewer but stronger. This trend has been seen in a variety of historical data tracking wind speed, rain and snow over the past century or so. Now a team of researchers has figured out why, and the explanation is firmly rooted in atmospheric thermodynamics. Global warming is intensifying the world’s water cycle, and that drains energy from the air circulation that drives stormy weather, say Frederic Laliberté of the University of Toronto and his colleagues.
The researchers “have offered a thermodynamic explanation for what the models have been doing all along,” says Olivier Pauluis of New York University, who wrote an accompanying perspective article on the study.
Earth's atmosphere acts like a gigantic heat engine, working on many of the same principles as your car’s engine. Fuel—in this case, energy from the sun—is used to do work. Because more sunlight hits the tropics than higher latitudes, the planet constantly redistributes heat via air motions. Those air motions are the engine’s work. They also help produce the rainstorms and snowstorms that can ruin your day. The engine isn't 100-percent efficient, though. Some heat is lost to space. And much of the remaining energy is expended in the planet’s water cycle, used in the evaporation and precipitation of water.
In their new study, appearing today in Science, Laliberté and his colleagues wanted to see how climate change is affecting this engine's performance. They compared climate records from 1981 to 2012 with climate simulations that model how Earth will behave from 1982 to 2098. They calculated that about a third of the atmospheric energy budget goes to the water cycle. But due to climate change, more energy is going into that cycle—overall, there’s more evaporation and more precipitation—leaving less energy for atmospheric circulation. The atmosphere still needs to get rid of all that precipitation, but it has to do it in fewer storms, which is why the storms get more intense.
“In a warming climate, there will be more water vapor lying around and therefore more fuel for such a storm, making it deepen even more and dump even more precipitation,” Laliberté says. This week’s big snowstorm in the Northeast “was a prime example of the type of atmospheric motions we describe in this paper. It was large-scale, it contained a lot of water vapor [and] it deepened quickly as it encountered a very cold air mass coming down from Canada.”
But while this week’s storm may be an example of what to expect, the paper does not say whether storms in any one part of the world should become more intense than others. “It remains to be understood how do [these findings] translate in terms of specific systems,” Pauluis says. “For example, should we expect the same reduction across the globe, or should tropical systems be affected more strongly?”
“This study says very little about regional climate change,” Laliberté admits. However, he says, “statements for different regions using the same perspective are in the works.”