A process-based biogeochemistry model is used with a set of fire databases to estimate the role of fires, within the context of multiple stresses (CO₂ fertilization, climate change, permafrost dynamics), on net carbon exchanges in boreal regions for the past several decades. Our model simulations show that the region is a net source of carbon to the atmosphere at rate of 0.25 Pg C yr^-1 during the 1990s, with fire accounting for 88 percent of these net carbon emissions. Our analyses suggest that the effects of fire disturbances need to be considered when estimating future net carbon exchanges in the boreal region. A high priority should be given to developing the capability to accurately predict the occurrence, size and intensities of future fires.