Permafrost soils store vast amounts of organic carbon, which could amplify global warming through increased respiration as temperatures rise. A study using a terrestrial ecosystem model that includes permafrost carbon dynamics, inhibition of respiration in frozen soils, vertical mixing of soil carbon, and methane emissions from flooded areas shows that terrestrial ecosystems north of 60°N could shift from carbon sinks to sources by the end of the 21st century under a high-emission scenario. The model predicts a shift from a carbon sink of 68 Pg to a source of 4–18 Pg by 2100, depending on processes and parameters. Methane emissions from high-latitude regions are expected to increase from 34 Tg CH4/y to 41–70 Tg CH4/y, influenced by CO2 fertilization, permafrost thaw, and warming-induced methane flux densities, partially offset by reduced wetland extent. The study highlights the importance of permafrost carbon in the global carbon cycle, with estimates of the total northern carbon pool at 495 Pg for the top meter of soils, 1,024 Pg to 3 m, and an additional 648 Pg for deeper carbon stored in yedoma and alluvial deposits. These carbon stocks, formed during the Pleistocene and Holocene, are currently not cycling but may become available for respiration if frozen soils thaw. The study also shows that current models underestimate initial carbon stocks due to the lack of peatland and organic soil buildup modeling. The study used the ORCHIDEE model to simulate the effects of permafrost processes on carbon and methane balances. The model shows that warming leads to significant warming at high latitudes, with a 8°C increase in surface soil temperature by 2100 and a 30% reduction in permafrost extent. The inclusion of permafrost processes leads to a larger cumulative carbon source, with the permafrost experiment showing a 62±6 Pg CO2 source and the heating experiment showing an 85±16 Pg CO2 source. Methane emissions from wetlands and deep permafrost are also significant, with emissions increasing from 34 Tg CH4/y to 71–74 Tg CH4/y under CO2 fertilization. The study emphasizes the need for improved models that account for carbon-nitrogen interactions and soil hydrology to reduce biases. It also highlights the uncertainty in future high-latitude carbon-climate feedbacks due to incomplete understanding of biogeochemical and physical processes. The study concludes that including permafrost carbon in models leads to a qualitative change in results, showing high latitudes as future CO2 and CH4 sources, leaving mid-latitudes as potential climate regulators. The study underscores the importance of considering permafrost carbon in climate models to accurately predict future climate change.Permafrost soils store vast amounts of organic carbon, which could amplify global warming through increased respiration as temperatures rise. A study using a terrestrial ecosystem model that includes permafrost carbon dynamics, inhibition of respiration in frozen soils, vertical mixing of soil carbon, and methane emissions from flooded areas shows that terrestrial ecosystems north of 60°N could shift from carbon sinks to sources by the end of the 21st century under a high-emission scenario. The model predicts a shift from a carbon sink of 68 Pg to a source of 4–18 Pg by 2100, depending on processes and parameters. Methane emissions from high-latitude regions are expected to increase from 34 Tg CH4/y to 41–70 Tg CH4/y, influenced by CO2 fertilization, permafrost thaw, and warming-induced methane flux densities, partially offset by reduced wetland extent. The study highlights the importance of permafrost carbon in the global carbon cycle, with estimates of the total northern carbon pool at 495 Pg for the top meter of soils, 1,024 Pg to 3 m, and an additional 648 Pg for deeper carbon stored in yedoma and alluvial deposits. These carbon stocks, formed during the Pleistocene and Holocene, are currently not cycling but may become available for respiration if frozen soils thaw. The study also shows that current models underestimate initial carbon stocks due to the lack of peatland and organic soil buildup modeling. The study used the ORCHIDEE model to simulate the effects of permafrost processes on carbon and methane balances. The model shows that warming leads to significant warming at high latitudes, with a 8°C increase in surface soil temperature by 2100 and a 30% reduction in permafrost extent. The inclusion of permafrost processes leads to a larger cumulative carbon source, with the permafrost experiment showing a 62±6 Pg CO2 source and the heating experiment showing an 85±16 Pg CO2 source. Methane emissions from wetlands and deep permafrost are also significant, with emissions increasing from 34 Tg CH4/y to 71–74 Tg CH4/y under CO2 fertilization. The study emphasizes the need for improved models that account for carbon-nitrogen interactions and soil hydrology to reduce biases. It also highlights the uncertainty in future high-latitude carbon-climate feedbacks due to incomplete understanding of biogeochemical and physical processes. The study concludes that including permafrost carbon in models leads to a qualitative change in results, showing high latitudes as future CO2 and CH4 sources, leaving mid-latitudes as potential climate regulators. The study underscores the importance of considering permafrost carbon in climate models to accurately predict future climate change.