The Arctic is not usually a hotbed for lightning — the air is simply not warm enough for thunderstorms to usually occur. But as the Arctic warms at an alarming rate, that lightning frequency is changing as well.
事实上, Arctic lightning has tripled in just the last decade, according to a new 研究, published this week in the Geophysical Research Letters.
The University of Washington study used data collected by its network of lightning sensors, called the World Wide Lightning Location Network (WWLLN), which has been tracking lightning strokes globally since 2004. The data showed that above 65 degrees latitude the number of lightning strikes has increased significantly from 2010 至 2020.
While the study focused on areas inside the Arctic Circle — northern portions of Canada, 阿拉斯加州, 俄国, Greenland and the central Arctic Ocean — not all of those areas had equal results.
Lightning induced wildfires
In the Arctic Circle there was an even greater increase in lightning strikes in the Eastern Hemisphere, specifically over Siberia.
This is likely because lightning is more likely to occur over ice-free land than over oceans or over large ice sheets such as Greenland or even Antarctica, explains Robert H. Holzworth, one of the authors of the research letter and a professor of Earth and Space Sciences at the University of Washington.
“Thunderstorms occur when there is differential surface heating, so an updraft-downdraft convection can occur,” Holzworth says. “You need a warm moist updraft to get a thunderstorm started, and that is more likely to occur over ice free land than land covered with ice.”
This is concerning because an area in northern Russia has also seen an uptick in wildfires in recent years. 然而, just because the lightning count has increased doesn’t mean it will always trigger lightning induced wildfires.
Both northern Siberia and Canada are covered in a thick forest of trees, which are highly flammable. So the ingredients are already in place to induce lightning-triggered wildfires. However just because the lightning in the area has increased threefold does not mean that wildfires have increased at this same rate.
Conversely, there are also indirect impacts from the wildfires to consider. Wildfires emit carbon dioxide and other greenhouse gases that warm the planet.
“In Arctic and boreal forest ecosystems, fires burn organic carbon stored in the soils and hasten the melting of permafrost, which release methane, another greenhouse gas, when thawed,” according to NASA.
另外, wildfire smoke can travel hundreds of miles in the atmosphere. It contains a number of pollutants including carbon monoxide, nitrogen oxides, volatile organic compounds, and solid aerosol particles. So the potential for hazardous conditions is not just for local populations but also for those further away.
A warming climate likely to blame
The Arctic has been warming more than twice as fast as the rest of the planet. This warming in the Arctic tundra has led to more thunderstorm development which has produced more electrical discharge — lightning.
“The tundra in Siberia is melting, with mastodon tusks appearing, 等等, and this is indicative of the warming ground, giving new opportunities for differential heating to show up, and thunderstorms to grow over the Eastern Hemisphere Arctic more so than the Western Arctic,” Holzworth said.
在八月 2019, there was one particularly unique event in which nearly 30 strikes were registered less than about 60 miles from the North Pole. This was a “major convective event” and it was unique to have lightning that close to the North Pole, 根据研究.
The image above shows that the fraction of global lightning has increased by more than a factor of three during the summer. It demonstrates the strong similarity between the fraction of strikes and the three month average global summer temperature anomaly. So while global temperatures may not be the entire cause for the increased lightning strike count, there is certainly a connection.
It is important to note that during the 11-year period studied there was also an increase in the number of WWLLN data stations. While this would naturally cause an increase in the number of strikes observed, this alone could not fully explain the substantial increase in lightning strikes across the Arctic.
