(CNN)As extreme weather wreaked havoc across the globe in 2021, a stunning change was happening in the far northern Arctic, largely out of sight but detectable by a network of sensors. Lightning increased significantly in the region around the North Pole, which scientists say is a clear sign of how the climate crisis is altering global weather.
Another sign things are getting weird: Lightning around the North Pole increased dramatically in 2021
Vaisala, an environmental monitoring company that tracks lightning around the world, reported 7,278 lightning strokes occurred last year north of 80 degrees latitude, nearly twice as many as the previous nine years combined.
Arctic lightning is rare -- even more so at such far northern latitudes -- and scientists use it as a key indicator of the climate crisis, since the phenomena signals warming temperatures in the predominantly frozen region. Lightning occurs in energetic storms associated with an unstable atmosphere, requiring relatively warm and moist air, which is why they primarily occur in tropical latitudes and elsewhere during summer months.
The annual number of lightning strokes in the Arctic -- the region north of around 65 degrees latitude -- has remained consistent over the past decade, but it is now surging significantly in the extreme north. Chris Vagasky, meteorologist and lightning applications manager at Vaisala, said a warming planet is charging up the Arctic's environment for more lightning to occur.
"What we've been seeing is that lightning and thunderstorms are developing over Siberia, and then moving out over the Arctic Ocean and continuing very far north," Vagasky told CNN, underscoring "the warm, humid air from all continents are now going out over the Arctic Ocean and they're persisting over the Arctic Ocean, so that you get storms that are developing there."
Jose Martinez-Claros, a researcher at the University of California, San Diego's Center for Western Weather and Water Extremes, who is not involved with the report, said the findings were "concerning."
"It seems to suggest in the drying and warming climate, these types of storms now reach latitudes that are very much higher than they used to be and closer to the Arctic," he said.
A 2021 study also found Arctic lightning had increased between 2010 and 2020 and the trend was strongly linked to global warming, which is caused by fossil fuel emissions.
"We know that the Arctic is changing faster than the rest of the Earth with respect to its climate," Vagasky said. "And so monitoring these trends in thunderstorms and lightning in this very remote area helps us detect where these warm, moist air intrusions are occurring in this region."
Lightning in the US also increased in 2021, according to the Vaisala report, where more than 194 million lightning strokes occurred -- 24 million more than what was observed in 2020.
More than 1 million of those occurred in December, in concert with several unprecedented winter time severe weather outbreaks that ravaged the Central and Southern US. It was the highest number of strokes researchers have seen in December since 2015, Vagasky said, noting now "even the December time period, you might be getting spring- or summer-type conditions," he added.
In the US, Texas recorded the most lightning last year, primarily due to its large area and warm, storm-prone location, Vaisala reports. Florida saw the highest lightning density than any other state, with 223 lightning events per square mile, followed by Louisiana and Texas.