This weekend, something peculiar visited the Arctic, a mere 300 miles from the north pole: lightning. Peculiar because thunderstorms are typically a warm-weather phenomenon, in which the sun heats air, which rises and condenses into water droplets. At the same time, cooler air pulls downward in the “deep convective cloud,” and all that moving air builds electrical charges that eventually blast down to Earth as lightning.
The Arctic is supposed to be cold, of course, making thunderstorms—much less the dozens, perhaps hundreds of strikes that materialized near the north pole over the weekend—a rarity. But no longer. The region is warming twice as fast as the rest of the planet, and this summer in particular has brought record-breaking heat. A lack of sea ice means more water is exposed to the sun, which means more moisture rises, forming thunderstorms. “The probability of this kind of event occurring would increase as the sea ice extent retreats farther and farther north in the summertime,” says Alex Young, a meteorologist with the National Weather Service in Fairbanks, Alaska.
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Weirder still, on top of there typically being not enough heat to form deep convective clouds in the Arctic, there’s also a limit to how high these things can build up into the atmosphere. Around the equator, the tropopause—a sort of boundary between the troposphere and the stratosphere—sits on average about 10 miles up, while near the poles it’s on average half that high. “It’s this stable layer in the atmosphere that acts essentially as a lid on these convective clouds,” says UCLA climate scientist Daniel Swain. One of these convective clouds needs to rise at minimum 15,000 feet if it’s going to produce a thunderstorm, and the tropopause makes that harder to do in the Arctic than at the equator.
Ratcheting up the weirdness of these Arctic thunderstorms, satellite imagery shows that the lightning was sometimes striking over sea ice. “That’s pretty amazing, because the preconditions that are necessary, to the extent that they’re unusual in the Arctic, they are vanishingly unusual over the sea ice in the Arctic ocean itself,” says Swain. Sea ice provides less heat and moisture to feed a deep convective cloud as it rises ever higher. But this time, a storm still managed to brew.
This summer, the drier, warmer Arctic has been burning to an unprecedented degree, which raises the question of whether more frequent thunderstorms might spark more wildfires, releasing still more carbon into the atmosphere… making for yet more warming. Swain says the phenomenon is too new to say for sure.