Canada is currently experiencing its worst fire season on record. According to the Canadian Interagency Forest Fire Centre (CIFFC), as of July 26 local time, a total of 4,774 fires had occurred across the country so far this year, with a cumulative burned area of over 121,000 square kilometers. This figure has surpassed the land area of South Korea (about 103,000 square kilometers) and is 7.5 times the cumulative area affected by forest fires in China from 2000 to 2021.
On July 27, Beijing time, scientists from the Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences estimated that the carbon dioxide emissions from forest fires in Canada this year had reached 1 billion tons. According to Dr. LIU Zhihua, a forest fire expert from IAE, "The greenhouse gases emitted from these fires, such as carbon dioxide, methane, and nitrous oxide, have an undeniable impact on global climate warming, which has become a global environmental event."
Remote sensing technology is an effective method for estimating carbon emissions from large-scale wildfires. Based on the carbon emission intensity and the burned area observed by remote sensing, a rapid assessment of carbon emissions from forest fires can be accomplished. The scientists from IAE estimated that as of July 26 local time (Canada), the greenhouse effect of methane and nitrous oxide emitted by the wildfires in Canada this year is equivalent to about 110 million tons of carbon dioxide.
Combined with the direct emission of 1 billion tons of carbon dioxide, the greenhouse gas emissions from these fires are equivalent to about 1.11 billion tons of carbon dioxide equivalent. Additionally, about 1/8 of these wildfires occurred in permafrost areas, promoting the release of methane stored in the permafrost.
Apart from contributing to climate change through the emission of greenhouse gases, wildfires also release air pollutants such as PM2.5, PM10, organic aerosols, and black carbon, which have adverse effects on the environment and pose risks to human health. To date, wildfires in Canada have caused four notable instances of transboundary transport, which occurred during the periods of May 17-26, June 6-19, June 23-30, and July 15-20.
These episodes significantly degraded air quality in the United States, with particulate matter levels exceeding 50 μg/m3, resulting in flight cancellations, school closures, and severe disruptions to production and daily life. For example, the second instance of transboundary transport led to the worst air pollution in New York City since 1960, while the third led to Chicago's air quality index exceeding the standard by 5.6 times on June 27.
These air pollutants are also transported over long distances worldwide via westerly circulation, affecting areas in Europe, North Africa, and Asia. During the atmospheric transport process from June 27-30, PM2.5 contributed more than 5 μg/m3 to the European region. This transport also affected North Africa and Asia, contributing about 1-2 μg/m3 to PM2.5 concentrations in the western region of China.
Wildfires also affect forest ecosystems. The rapid burning of wildfires results in extensive vegetation destruction and loss of biodiversity, depriving animals of habitat and food sources. In addition, wildfires can reduce vegetation cover and expose soil surfaces, increasing the occurrence of secondary disasters, such as soil erosion, sediment runoff, and landslides.
Such large-scale forest fires have exceeded the range of natural variation and become a destructive disaster. Frequent and severe forest fires not only rapidly deplete carbon reserves in vegetation and soil but also alter natural forest succession, resulting in ecosystem degradation towards shrubland or grassland. Consequently, the carbon sequestration capacity of the ecosystem is reduced. As a result, large-scale wildfires disrupt ecosystem equilibrium and are no longer viewed solely as traditional ecological disturbance processes.
In recent years, the intensification of climate change and human activity has repeatedly led to extreme wildfires. For example, fires in the Amazon Rainforest in 2019 burned over 90,000 square kilometers in 10 months, and the 2019-2020 bushfires in Australia burned over 243,000 square kilometers in one year. The wildfire season in Canada usually lasts until October, and the ongoing wildfires may continue to spread, raising concerns that the scale of the disaster could grow even larger, surpassing the country's historical records.
According to the "2022 China National Land Greening Report," China's forest area is about 2.31 million square kilometers, which is about two-thirds of Canada's forest area. Forests cover about 24.02% of China's land area. Such an extensive distribution of forested land poses considerable challenges to forest fire prevention. Over the years, the Chinese government has adhered to the policy of "Combining prevention and control, with prevention as the primary focus."
Through cooperative efforts involving all segments of society, China has gained valuable expertise in forest fire prevention and control. This concerted approach has successfully reduced the occurrence of forest fires and minimized disaster losses, resulting in a significant improvement in the nation's overall fire prevention and control capability.
It is estimated that carbon dioxide emissions from forest fires in China between 2000 and 2021 were about 15 million tons per year, approximately 0.2% of the carbon dioxide emissions from global wildfires.
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