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Wildfires over permafrost put perennially frozen carbon at risk.
However, wildfire emissions from biomass burning over the diverse range of permafrost regions and their share in global wildfire emissions have not been revealed. The results showed a dramatic increase in wildfire carbon emissions from permafrost regions over the period 1997–2021. The share of permafrost in global wildfire CO2 emissions increased from 2.42% in 1997 to 20.86% in 2021.
Accelerating wildfire emissions from continuous permafrost region is the single largest contributor to increased emissions in northern permafrost regions. Fire-induced emissions from 2019–2021 alone accounted for approximately 40% of the 25-year total CO2 emissions from continuous permafrost regions.
The rise in wildfire emissions from continuous permafrost regions is explained by desiccation within a 5–10 cm soil depth, where wildfires combust belowground fuel. These findings highlight the acceleration of fire-induced carbon emissions from continuous permafrost regions, which disturb the organic carbon stock and accelerate the positive feedback between permafrost degradation and climate warming, thus stimulating permafrost towards a climatic tipping point.
Graphical abstract
Introduction
Permafrost covers nearly 25% of the Northern Hemisphere land area and the carbon stocks in the frozen soil account for about 50% of global soil organic carbon[1]. Approximately half of the global permafrost area is continuous permafrost, with a coverage of 90%–100%[2], which stores approximately 40% of permafrost soil carbon[3]. Continuous permafrost has the fastest growth rate of temperature[4] and highest soil organic storage[5] compared to other permafrost regions, making it vulnerable to permafrost thawing. The thawing of permafrost under climate warming promotes the decomposition of frozen organic matter, releasing more carbon dioxide (CO2) and methane (CH4) into the atmosphere[6].
The additional release of CO2 and CH4 from the thawed permafrost amplifies global warming and accelerates permafrost degradation[7]. Such positive permafrost carbon feedback (PCF) is likely to amplify anthropogenic warming[8]. PCF is irreversible on human timescales because under climate warming, the burial mechanisms of permafrost slow down or even cease and there is no way to convert CO2 into organic matter and freeze it back into the permafrost[9]. Therefore, greenhouse gases released from large frozen carbon pools into the atmosphere can alter the magnitude and path of future climate change.
Wildfires are a major ecosystem disturbance in permafrost zones[10]. Wildfires in Arctic and subarctic regions eliminate surface litter and topsoil organic matter that insulate permafrost[11], exposing the underlying permafrost to substantial warming, which induces rapid deepening of the active layer and thermokarst development in ice-rich permafrost regions[12]. This puts large amounts of ancient carbon stores at risk of being released into the atmosphere[13].
Moreover, the increasing number of overwinter fires smoldering belowground can release legacy carbon from environments that were previously believed to be fire-resistant[14], [15]. As the climate warms, Arctic wildfires are projected to increase by 130%–350% in the first half of the 21st century, releasing a growing quantity of carbon from permafrost[16]. By the end of the 21st century, wildfires are predicted to enhance carbon emissions from permafrost soil by 30% compared with emissions from warming alone under a moderate emission scenario[17].
Wildfires can cause the abrupt thawing of permafrost, leading to rapid thermal, hydrological, and vegetation changes[8]. In addition to landscape instability, abrupt thaw after wildfires releases carbon into the atmosphere by exposing previously frozen carbon to enhanced microbial activities and altering hydrology, which is critical for CO2 and CH4 emissions [7]. Carbon losses due to abrupt thawing constitute approximately 40% of the mean net emissions from gradual thaw[18]. Fire-induced abrupt thawing and subsequent decomposition of previously frozen organic matter may become the dominant source of high-latitude carbon emissions in the near future[19].
The Arctic mean annual surface temperature has increased at over double the global average rate since the 1980s[20]. The temperatures over continuous permafrost zones are increasing faster than those over other permafrost zones[4]. In recent years, especially from 2014 to 2019, Arctic surface air temperatures have increased, exceeding all previous years in observational records from 1900[21]. Record-breaking heatwaves were reported across Siberia and Alaska in 2019[21], Siberia in 2020[19], and North America in 2021[22].
However, the influence of rapid Arctic warming on fuel availability, wildfire carbon emissions, and the role of wildfire emissions in the carbon budget of permafrost regions have not yet been determined. Therefore, this study investigated the spatial and temporal characteristics of wildfire carbon emissions in different types of northern permafrost regions and their contributions to global wildfire emissions and the regional carbon budget over 25 years (1997–2021) using wildfire carbon emissions derived from the Global Fire Emissions Database (GFED) and Global Fire Assimilation System (GFAS).
Study region
We focused on wildfire emissions in the permafrost zones in the Northern Hemisphere, excluding the Tibetan Plateau permafrost region, where wildfire occurrence is negligible compared to that at high latitudes. A permafrost map derived from an equilibrium-state model simulating temperatures at the top of the permafrost[2] was used to identify the extent of permafrost coverage. The permafrost was divided into four subregions according to the underlain permafrost coverage. Continuous,
Permafrost wildfire emissions
The total wildfire CO2 emission in permafrost zones from 1997–2021 was about 13.19 Pg, with approximately 36.61% (4.83 Pg) emitted from continuous permafrost, 13.42% (1.77 Pg) from discontinuous permafrost, 21.99% (2.90 Pg) from sporadic permafrost, and 27.98% (3.69 Pg) from isolated permafrost. Wildfire-induced mean annual CO2 emissions in the entire permafrost region accounted for approximately 7.30% of annual global CO2 emissions from 1997–2021, with the ratio significantly increasing from
Discussion
Although the global burned area has been continuously decreasing during the 21st century, largely because of human fire suppression activities[36], [37], our study showed that wildfire emissions have increased over permafrost regions during the last two decades, accounting for a significantly higher contribution to global fire-induced emissions (Table S2 online). This increase is attributed to the striking rise in wildfire emissions from the continuous permafrost. This result corroborates the
Conclusion
We observed an increase in wildfire carbon emissions from biomass burning in permafrost regions from 1997–2021. The share of permafrost in global wildfire CO2 emissions increased from 2.42% in 1997 to 20.86% in 2021, whereas the share of permafrost in global wildfire CH4 emissions increased from 2.73% in 1997 to 38.39% in 2021. The accelerated increase in wildfire-induced carbon emissions from continuous permafrost was the single largest contributor to increased permafrost wildfire emissions.
Conflict of interest
The authors declare no conflicts of interest.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was supported by the National Key R&D Program of China (2022YFF0801904). The wildfire data obtained from the GFAS were generated using the Copernicus Atmosphere Monitoring Service Information and neither the European Commission nor the ECMWF is responsible for any use that may be made of the information it contains.
Author contributions
Xiyan Xu and Gensuo Jia conceived and designed this study. Xingru Zhu performed data analysis. All the authors wrote the manuscript and contributed to the discussion of
XingruZhu is a PhD at the Institute of Atmospheric Physics, Chinese Academy of Sciences. Her research interest focuses on permafrost wildfires and their carbon emissions in high-latitude ecosystems.
This job has navigated right into my heart.
Fresh work you have here.
We need to address this issue together and work towards finding sustainable solutions. Let’s all do our part to protect our planet for future generations!