Cumulative impacts of disturbances on peatland carbon must be understood to predict future soil carbon stocks, yet the vulnerability and response of peatlands to disturbance have been neglected. We provide the first regional-scale assessment of peatland carbon storage across 1.7 million km2 of western boreal land. We estimate that disturbances, mainly fire, release approximately 6460 ¿ 930 GgCyr-1 to the atmosphere. Concurrently, disturbances reduce carbon uptake in continental peatlands by 85% compared to a no-disturbance scenario. A 17% increase in the area of peatland burned annually and the intensity of organic matter combustion would convert these peatlands into a regional net source of carbon to the atmosphere. Peatlands widely are considered to represent a northern carbon sink, however, we suggest reevaluation of this paradigm for continental boreal regions.