Key Points

• Thawing permafrost is acting less like a sealed carbon store and more like a pathway for gas escape as ground structure softens near the freezing point.
• Laboratory work indicates permeability can rise sharply during thaw, creating a clearer physical mechanism for greenhouse-gas release.
• Field studies in Arctic peatlands show plant communities are shifting as thaw alters drainage, with grasses and mosses replacing frozen-ground vegetation in some places.
• Seasonal carbon balance is changing as early photosynthetic uptake is overtaken later by methane and carbon dioxide emissions.
• Microbial activity remains a major driver because warmer, wetter, or more oxygen-limited thawed soils can speed decomposition and carbon cycling.
• The main uncertainty is spatial variability: real permafrost differs widely in ice content, soil structure, nutrients, and hydrology, which affects how strong the feedback will be.
• Monitoring and projection remain incomplete because polar datasets are uneven and many studies emphasize the need for broader field coverage.