BEIJING, April 7 (Xinhua) -- There has been a significant increase in carbon dioxide emissions from forest wildfires in the world's northern part over the past two decades, with the year 2021 hitting a record high, Chinese scientists and their overseas counterparts have found.

The increase was partly caused by the extreme drought events, which led to more frequent wildfires, in the mid-high latitudes of the northern hemisphere, according to the findings recently published in the journal Science.

Wildfires, which are fires that occur in wildlands such as forests and grasslands, play an important role in the global carbon cycle. Extreme wildfires pose a threat to human health and the global climate by damaging ecosystems and releasing harmful pollutants and greenhouse gases.

According to the paper, wildfires in boreal forests had received less attention in the past than those in tropical forests.

Researchers from Tsinghua University, along with their counterparts from home and abroad, developed a satellite-based atmospheric inversion system to monitor fire emissions in boreal forests between 2000 and 2021, noticing a rise in carbon dioxide emissions throughout this period.

The researchers found that boreal wildfires contributed 23 percent of global fire carbon dioxide emissions in 2021, while the proportion was typically only 10 percent 20 years ago.

As soil water deficit increased, wildfire events began to invade high-latitude boreal forests that had previously been less prone to fires, said Zheng Bo, one of the team leaders from the Tsinghua Shenzhen International Graduate School.

He noted that the fires occurred particularly in areas with high forest coverage between 60 and 70 degrees north latitude, where wildfire carbon emissions in 2021 have more than tripled compared to the average from 2000 to 2020, while the increase in areas near 50 degrees north latitude was 70 percent.

"The soil in boreal forests is rich in organic carbon. The burning vegetation and organic soil release a large amount of carbon, seriously threatening the carbon sink function of this area," the researcher said.

Zheng's team had focused on global climate research and studied carbon emissions from wildfires for years. The carbon dioxide monitoring system developed by them is unlike the conventional ones. It innovatively inverts wildfire carbon emissions through carbon monoxide concentration based on satellite remote sensing data, instead of monitoring carbon dioxide directly.

The atmospheric carbon dioxide has a relatively high background concentration due to its long-term accumulation, making it difficult to accurately monitor wildfire events based on carbon dioxide emissions, Zheng said.

By contrast, the carbon monoxide from wildfires is more active and has a lower background concentration. Satellites can monitor it more clearly, he noted.

The team noticed a great decline in the burning area of global wildfires over the past years. However, the carbon emissions from burning remained almost unchanged. They published their findings in the journal Science Advances in 2021 and explained the reason.

The decline in burning areas mainly occurred in grassland, while in forests, which constitute larger carbon dioxide sources per unit than grassland, the burning area tended to increase, according to the paper.

"So we tried to figure out in which forests the burning areas are increasing, and this is where our latest research findings come from," Zheng said.

Editor: Guo Lili