By alejandra Borunda.
Once upon a time, lightning in the Arctic was very rare, and people had never seen lightning in their lives. But this area is warming rapidly, and lightning is becoming more and more common, which may even affect places outside the Arctic.
A recent study predicts that the lightning frequency in the Arctic may double by the end of this century. Another study shows that the number of lightning in the Arctic has tripled in the past decade alone, but some researchers are skeptical about this result.
Scientists say that with the acceleration of climate change, the increase of lightning is worrying; They are also worried about the future: more lightning may cause a series of ecological changes, releasing a lot of carbon stored in the Arctic into the atmosphere, further accelerating climate warming.
Yang Chen, a researcher at the University of California, Irvine, said: "In the past, the number was small, but the climate impact was great." He is the first author of a study published in the journal Natural Climate Change.
Fires caused by lightning are increasing.
In 2002, the researchers interviewed the indigenous elderly in the Arctic community in northwest Canada. In their memory, they have never seen several thunderstorms in their lives. An elder recalled that she had only seen a storm once in the 1930s, when she was only five years old.
At that time, scientists didn't think there would be lightning in the Arctic: this phenomenon is so rare that even researchers who have worked in the Arctic for dozens of summers may have never seen lightning.
Uma Bart, a meteorologist at the University of Alaska at fairbanks, said, "When I first came to fairbanks, I was surprised to see thunderstorms. She has lived in Alaska for 22 years and has been studying lightning in the Arctic.
In 20 14 and 20 15, the biggest fires on record swept through a large area of Alaska and northwest Canada. Like more than 90% fires in the Arctic, these fires are all caused by lightning.
As the Arctic climate becomes warmer and drier, plants become more and more flammable. But after 20 14 and 20 15, Sander Veravebeke, a climate scientist at the Free University of Amsterdam and co-author of a recent paper, is thinking about another factor: Is lightning that causes fires becoming more and more common?
"I checked the lightning data for many years and found that it was not a coincidence," Veravebeke said. "The increase of lightning almost directly led to the increase of fire."
In the paper of 20 17, he and his colleagues found that since 1975, the number of fires caused by lightning has more than doubled in Alaska and northwest China. In the disastrous seasons of 20 14 and 20 15, the number of fires in both places broke records.
More lightning?
But is lightning really more frequent throughout the Arctic? This is a difficult question to answer because there is no continuous lightning record in the Arctic.
A satellite launched by 1995 recorded polar lightning, but it was retired in 2000. The new lightning sensing satellite can only observe the distant north and south poles and mid-latitude areas, but can't directly observe the polar regions.
Sensors used in the ground network can detect radio waves generated by lightning, and now they can record lightning almost all over the world. Bhatt found that lightning increased from 1986 to 20 15 by using Alaska's regional network.
However, climate scientists say that less than 20 years of records in the Arctic are not enough to prove that this is a stable development trend.
Recently, a research team from the University of Washington studied the data of the global lightning location network. This is a ground sensor network, which has been in operation since 2004. They found that the number of lightning recorded at 65 degrees north latitude increased from less than 50,000 in 20 10 to about 250,000 in 2020. Researchers say this is partly due to the increase in the number of sensors, but it is estimated that the number of lightning in this area has tripled in the past 10 years.
However, another global lightning detection network operated by Visala failed to capture this sharp increase. In 20 12, the global lightning database 360(GLD360) started to run, so compared with the Washington team, their recording time was shorter, but this network was more sensitive and recorded more and weaker lightning.
Ryan Saeed, a research engineer at Visala, said that from 20 12 to 2020, they did not record a significant increase in lightning activity; But this does not mean that there is no such trend, but scientists need more time to observe and find out the changes in weather patterns.
"This is just the beginning," he said.
In recent years, the lightning network in Visala has detected some unusual activities. In the summer of 20 19 and 2020, GLD360 recorded more than 100 lightning strikes at 85 degrees north latitude, including a series of lightning strikes less than 555 kilometers from the North Pole, which is extremely rare.
There will be more lightning in the future.
Yang Chen said that whether these changes happen or not, it is almost certain that climate change will mean more lightning in the Arctic.
The formation of lightning requires special factors, which are rare in the far north, but climate change may make them more common.
First of all, the air on the ground must be warm, full of moisture and able to float quickly. The air temperature above must be low enough. When warm air rises rapidly, water condenses into small ice particles. The whole system is very turbulent, the air rotates and the ice particles roll violently in it, which makes the electrons collide with each other and the ice particles are charged. Finally, large-scale discharge occurs inside clouds, or between clouds and the ground.
Historically, the cold and relatively stable atmosphere in the Arctic is not suitable for thunderstorms. But in the past 30 years, the temperature here has risen by 1 to 2 degrees, faster than all other places on the earth.
Yang Chen and his colleagues, including Vera Verbeke, want to know how much lightning will be triggered by these changes in climate conditions by the end of this century. They compared the Arctic lightning data recorded by satellites in the 1990s with the weather data of the same period, looking for which atmospheric conditions best matched the rare lightning.
The climate model predicts the favorable conditions of lightning. By extending the lightning (slightly different from the overall possibility of thunderstorm), it is found that the lightning frequency in the tundra area will be about 1.5 times of the original, and the northern forest area will almost double. The probability of lightning in the continental United States is expected to increase by 50%, in contrast, the number in the Arctic is much larger. Some studies show that by 2 100, the global lightning activity will decrease, partly because the tropical areas with frequent lightning may heat up and reduce the frequency of ice crystal formation.
The satellite data used by Yang Chen and his colleagues to estimate lightning cannot match the ground network used to detect recent lightning activity, so the two results cannot be directly compared or integrated. But they all stressed that "lightning in the Arctic is becoming more and more important," Veravebeke said.
But the most worrying thing is not the lightning itself, but the possible impact of lightning. Wildfires anywhere in the world will release carbon stored in forests and soil. For example, in 2020, wildfires in Australia released more than 800 million tons of carbon dioxide, nearly 1.5 times of the country's total annual emissions.
Wildfires don't just burn wood on the ground. "Combustion is three-dimensional," explained Michelle Mack, an ecologist and Arctic expert in northern arizona university. Under the surface flame, the organic matter in the soil is also burned. Compared with the soil in other parts of the world, the carbon content in the Arctic soil is much higher. The carbon accumulated in decades is often more than ten centimeters. Veravebeke said that the Arctic fire that devoured the topsoil released at least twice as much carbon as the California fire.
This study shows that by the end of this century, due to more lightning and more fires, the burning area and carbon emissions in the Arctic will increase by more than 150% compared with the annual emissions caused by fires (about 3.4 million tons).
But it could be worse. The fire changed the ecosystem, opened up new growth space for forests and shrubs, and urged them to migrate northward. This in turn will increase the possibility of fire, because trees are more likely to catch fire than tundra.
Forests will also get warmer and catch fire more easily than tundra, because they are darker and absorb more sunlight. Yang Chen and his colleagues found that if fires caused by lightning increase and forests move northward, carbon emissions will increase by 570%, and about 23 million tons of carbon dioxide will be released into the atmosphere every year, equivalent to one-fifth of the fires in California in 2020.
In this regard, the research team only made an overview, but did not make a detailed calculation: the permafrost area in the Arctic is 6.5438+0.3 million square kilometers, and the fire caused by lightning will also endanger the carbon-rich permafrost, accelerate melting, and release a large amount of carbon stored in permafrost. In other words, carbon emissions will increase by 570%. "This is just the lower limit of our estimate," Yang Chen said.
(Translator: Sky4)