Source: China News Network
Text | China Science News reporter Shen Chunlei Gao Yali
According to the Canadian Forest Fire Centre, there have been nearly 3500 forest fires in the country this year. As of July 5, 88,000 square kilometers of Canadian forests have been burned in a record-breaking area, and 670 fires are still burning across Canada, more than half of which are out of control.
"Our team estimates that Canadian forest fires have emitted more than 724 million tonnes of CO2 this year as of July 5, compared to 546 million tonnes of energy-related CO2 emissions in Canada for all of 2021." Liu Zhihua, a researcher at the Shenyang Institute of Applied Ecology of the Chinese Academy of Sciences (hereinafter referred to as the Shenyang Institute of Ecology), told China Science News.
Liu Zhihua, who mainly works on forest fires, believes that due to the abnormal climate brought by El Niño, Canada is expected to continue the current high temperature, drought and other extreme weather in July, and if there is no stronger fire fighting measures, Canada's forest fire area is likely to continue to grow, and carbon dioxide release will continue to rise.
Canada's forests are "on fire"
Since May this year, forest fires in Canada have continued to spread, causing widespread concern in the international community.
On July 6, Natural Resources Canada predicted that forest fires would continue throughout the summer due to high temperatures and drought. Currently, all Canadian provinces are experiencing drought, and drought is increasing in some areas. The Canadian Aboriginal Services Agency also issued a message on the same day that the country's forest fire season this year is more serious and destructive than before, and a total of 45 aboriginal communities across the country have been affected.
According to Canadian domestic media reports, more than 155,000 people have been evacuated from forest fires in Canada this year, a record record.
Liu Zhihua introduced that May ~ October every year is the active period of Canadian forest fires. Global climate change has led to continuous high temperatures in North America this year, among which the temperature in some provinces in Canada in spring is 10~15 degrees Celsius higher than the same period of previous years; Coupled with the excessive accumulation of combustible materials in Canada's boreal forests, the unusually hot and dry climate increases the frequency and intensity of forest fires.
"By mid-June, smoke from the Canadian bushfires had spread along the coast of Europe with atmospheric circulation, even reaching Spain, about 7,000 kilometers away." Liu Zhihua said that smoke from forest fires has caused severe air pollution in North America and Europe.
"A large number of pollutants emitted by Canadian bushfires, including black carbon, nitrates, etc., can be transmitted far away by wind direction, and the whole of North America will be affected, and these pollutants can also directly affect Europe through the Atlantic westerly wind belt." Wang Zhifang, a researcher at the Institute of Atmospheric Physics of the Chinese Academy of Sciences, explained to China Science News that he mainly works on Earth system models.
Carbon emissions from forest fires are "exceeding"
According to the existing research, the methods for calculating carbon emissions from forest fires mainly include emission factor method, remote sensing observation method, model simulation method and monitoring inversion method.
Wang spontaneously introduced that the emission factor method needs to be calculated according to the area of fire, regional vegetation density, forest structure, burning ratio, and carbon content of different forest components. The monitoring inversion method needs to calculate how much carbon dioxide is emitted based on the monitoring data, and then deduce how far it has spread according to the difference in the surrounding data.
"Although these methods have their own advantages, the proportion of over-fire area and the density of vegetation in over-fire areas are not yet accurately grasped, and the forest structure and burning ratio are also different." Wang spontaneously said that there are some differences in the use of different methods to estimate.
To this end, the Chinese Academy of Sciences organized experts to conduct comprehensive discussion and judgment, and finally selected the estimation method of "model simulation + remote sensing observation" developed by the Shenyang Institute of Ecology.
Cumulative map of the burned area in Canada. Photo courtesy of Liu Zhihua
"The basic principle of this method is to calculate the carbon emission intensity of forest fires based on data such as the burning area observed by remote sensing day by day, and simulate the cumulative carbon emissions of forest fires, which takes into account timeliness and accuracy." Liu Zhihua told reporters.
"Using this methodology, we estimate that Canada's carbon dioxide emissions from forest fires this year have exceeded 724 million tonnes as of July 5, which is about 7% higher than the Copernicus Atmospheric Monitoring Service, an international authority." Liu Zhihua said.
According to data released by the Global Carbon Plan in 2022, Canada's and Germany's energy-related CO2 emissions in 2021 were 546 million tons and 674 million tons, respectively, with Germany ranking seventh in the world.
"For a long time, the impact of forest fires on forest ecosystems has been relatively stable." Liu explained that because ecosystem fires can be restored within a certain period of time, the carbon impact of forest fires can be reabsorbed over a period of time.
Why are Canadian bushfires in the spotlight this year? "In the context of a warming climate, the global forest fire situation is serious, forest fires are frequent, and the carbon impact of spreading forest fires in Canada may take longer to recover." Liu Zhihua said that forest fires have become a source of carbon emissions that cannot be ignored.
According to relevant studies, in 2021, high-latitude forest fires in North America and Eurasia released nearly 1.76 billion tons of carbon dioxide into the atmosphere. This figure is 1.5 times higher than the average annual carbon dioxide emissions of forest fires in the same area in 2000~2020. Liu Zhihua predicts that 2023 is likely to reach a new high. In addition, forest fires at high latitudes will accelerate the concentrated release of carbon from permafrost, further accelerating global warming.
How can forest fires be prevented
Historical data show that since the 21st century, with the intensification of climate warming and the impact of human activities, the scale and frequency of forest fires have expanded.
In recent years, extreme forest fires have occurred frequently, including the 2019 Amazon forest fire, the 2019~2020 Australian forest fire, the 2022 Siberian forest fire, and this year's Canadian forest fire.
"How can forest fires be effectively controlled?" In response to reporters' questions, Liu Zhihua said, "The main control means is early detection and early extinguishing of fires, once the fire spreads, it is difficult to control when it is transformed into a canopy fire." ”
Liu Zhihua introduced that forest fires can usually be divided into three categories: surface fires, canopy fires and underground fires. Among them, surface fires burn dead branches and leaves and weeds and shrubs on the surface of the woodland, which is a low-intensity fire. Super destructive canopy fires, usually high-intensity, can burn forests, most or all of their plants, animals, and microorganisms.
"Although forest fires are difficult to control, effective measures can be taken to prevent them." Zhu Jiaojun, director of the Shenyang Institute of Ecology, who has long been engaged in forest ecology research, told China Science News, "If the combustible materials in the forest are reduced to a certain extent, or the water content is high enough, it will be difficult for forest fires to ignite." Therefore, in areas with high incidence of forest fires, it is necessary to actively control the combustible materials in the forest, such as removing the combustible materials that may cause forest fires in time, so as to produce biochar that is not easy to decompose, which can not only reduce fires, but also increase carbon sinks. ”
Zhu Jiaojun believes that different tree species have different possibilities for resistance or initiation of forest fires. Therefore, it is necessary to consider adjusting the tree species composition of the forest to form a forest belt that is resistant to forest fires and build a natural "green fire escape".
Despite the severe challenges of superimposed natural and social factors, with the joint efforts of many parties, the fire prevention work of mainland forests and grasslands has made great progress, and the comprehensive fire prevention and control capacity has been significantly improved. Zhang Yongli, director of the Office of the National Forest and Grassland Fire Prevention and Extinguishing Command and deputy director of the State Forestry and Grassland Administration, took forest fires as an example to introduce that the number of fires and the area of affected forests remained at a historic low for two consecutive years in 2021 and 2022.
Recently, the General Office of the CPC Central Committee and the General Office of the State Council issued the "Opinions on Comprehensively Strengthening the Prevention and Extinguishing of Forest and Grassland Fires under the New Situation", which clearly put forward "prevention first, prevention and rescue combined", reflecting the determination of the Party Central Committee and the State Council to resolve major forest and grassland fire risks and make every effort to safeguard the safety of people's lives and property and ecological security.
Zhu Jiaojun suggested that in view of the worldwide problems of extreme forest fire prediction and prevention and control, scientific researchers should be organized to further study and build a technical system for identification, early warning prediction and prevention and control of forest fire risks in mainland China, and strengthen the research on carbon emissions in the forest fire process, and establish a more scientific, comprehensive, independent and controllable carbon accounting system.
(China Science News WeChat public account)
Source: China Science News WeChat public account
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