Northern boreal forests are sensitive to many effects of global change. This is of particular concern due to the proportionally greater climate change projected for the area in which these forests occur. One of the sensitive areas is the Far North of Ontario (FNO), consisting of one of the world's largest remaining tracts of unmanaged boreal forest, the world's third largest area of wetland, and the most southerly area of tundra. We studied past, present, and potential future carbon (C) balance of FNO forests using the Integrated Terrestrial Ecosystem Carbon Model and the Canadian Regional Climate Model with stand-replacing fire disturbance. The forced simulations of past (1901–2004) C balances indicated that vegetation C stock remained stable, while soil C stock gradually declined (−0.07 t C ha−1 yr−1, p < 0.001), resulting in an overall significant decrease in total ecosystem C balance (−0.07 t C ha−1 yr−1, p < 0.001). Two Representative Concentration Pathways (RCPs), RCP8.5 and RCP4.5, simulations of future (2007–2100) C balances indicated that the carbon dioxide fertilization and climate growth-enhancing effects of global change will outweigh C loss through increased ecosystem respiration, disturbance, and changes in forest age class structure resulting in an increase in total FNO ecosystem C stock by mid-21st century. However, the projected simulations also indicated that the relative sizes of forest C stocks will change, with relatively less in the soil and more in vegetation, increasing fuel loads and making the entire ecosystem susceptible to forest fire and insect disturbances.