Observations show that the amplitude of the annual atmospheric carbon dioxide cycle has increased. Lagged correlations between carbon dioxide, temperature, and vegetation suggest a modulation by ecosystem response, but the mechanisms remain unclear. Hypotheses include an early season uptake increase and/or winter respiration increase related to climate warming, and increased cycling in cooler conditions caused by disturbances such as fire. The first hypotheses suggest a positive feedback to regional warming, whereas the last suggests a negative feedback. In order to test the likely contributions of climatic warming and disturbance (occurrence of fire) variations on ecosystem carbon dioxide uptake and gross primary production, a series of experiments was performed using the Arctic Region Climate System Model. Results showed that fire, as it influences species composition, can serve to enhance the increase in early season uptake but that a crucial determinant for the sign of the feedback is the impact of climate change on soil moisture.