A 2025 study reveals wildfires are weakening the Arctic–Boreal carbon sink, pushing parts of the region toward becoming a net CO₂ source.
The Arctic–Boreal Zone (ABZ) has long been considered a crucial carbon sink, helping to offset global emissions. However, this study reveals that wildfires are significantly weakening this role, with parts of the ABZ already becoming net CO₂ sources. By integrating terrestrial CO₂ flux data, remote sensing, and machine learning models, the research provides the most comprehensive assessment of the Arctic carbon balance to date.
Key Findings: Carbon Dynamics in the Arctic–Boreal Zone
Increasing CO₂ Uptake—But with Major Variability
From 2001 to 2020, the ABZ acted as a net terrestrial CO₂ sink, with an average net ecosystem exchange (NEE) of -548 ± 140 Tg C/yr.
However, more than 30% of the region functioned as a CO₂ source, indicating substantial spatial variability.
Tundra ecosystems may have already shifted to net carbon emitters, challenging previous assumptions of their long-term stability.
The Disruptive Role of Wildfires
When fire emissions are included in the carbon balance, the overall Arctic–Boreal sink is no longer statistically significant.
The CO₂ budget shrinks from -548 Tg C/yr to -319 Tg C/yr, and the permafrost region becomes nearly CO₂ neutral (-24 Tg C/yr).
Fires contribute ~237 Tg C/yr, equivalent to 43% of the region’s net CO₂ uptake, demonstrating their dominant role in shifting the carbon balance.
Regional and Seasonal Carbon Flux Trends
Spatial Variability: Boreal vs. Tundra Ecosystems
Boreal forests remain a significant CO₂ sink (-593 ± 101 Tg C/yr without fires), largely due to strong summer carbon uptake.
Tundra regions are now close to net CO₂ neutral (45 ± 53 Tg C/yr), with rising emissions during non-summer seasons.
Seasonal Carbon Trends: The Growing Impact of Non-Summer Emissions
During summer (June–August), vegetation absorbs CO₂ efficiently, leading to strong net carbon uptake.
However, increasing autumn and winter respiration (September–May) is offsetting these gains, particularly in the tundra.
Implications for Climate Feedbacks and Permafrost Stability
Threat to Permafrost Carbon Stocks
The ABZ holds nearly half of the world’s soil organic carbon. As permafrost thaws, carbon stored for millennia is being released as CO₂.
The study suggests that permafrost areas are now close to CO₂ neutral, raising concerns about future tipping points.
Fire–Carbon Cycle Interactions
As wildfire frequency and intensity increase, they release stored carbon, reducing the net CO₂ sink strength.
Burned areas take decades to recover and often return as lower-biomass ecosystems, further weakening carbon sequestration.
A Shift in the Arctic Carbon Budget?
Historically, the Arctic acted as a long-term carbon sink, but these findings suggest it is now on the edge of becoming a net source.
With continued warming and intensifying wildfires, this shift could accelerate, turning the ABZ from a carbon sink into a climate amplifier.
Policy and Research Recommendations
Wildfire Management in Boreal Forests: Fire suppression strategies and better land management practices are crucial to maintaining carbon storage.
Improved Monitoring of Arctic Carbon Fluxes: Current carbon cycle models underestimate the role of fires and non-summer emissions. More field stations and high-resolution remote sensing are needed.
Urgent Climate Mitigation Efforts:
If Arctic and boreal ecosystems become a consistent carbon source, it will make achieving global climate targets far more difficult.
Limiting warming below 1.5°C is critical to preventing further carbon feedback loops.
A New Understanding of the Arctic Carbon Balance
This study provides the most detailed picture yet of the Arctic–Boreal CO₂ budget. While the ABZ has historically acted as a carbon sink, wildfires and shifting seasonal carbon dynamics are significantly weakening this role. The findings reinforce the urgency of mitigating climate change, protecting boreal forests, and improving fire management strategies.
If current trends continue, the Arctic could soon transition from a carbon sink to a net source, amplifying global warming and further accelerating permafrost loss. This underscores the importance of immediate action to curb emissions and enhance ecosystem resilience.
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