Feedbacks from the carbon cycle in boreal and arctic ecosystems can significantly affect climate change, but the effects of climate change on the high-latitude carbon cycle during the dormant period remain uncertain. By analyzing the long-term atmospheric CO2 concentration record from Point Barrow in Alaska, we show that warming significantly boosts net CO2 release in autumn over the period 1974-2014. But this warming-stimulated effect has been attenuated since 1997. This deceleration of net CO2 release with warming is ascribed to the attenuation in respiration response to temperature rather than changing relationship between temperature and productivity or changes in atmospheric transport, fossil fuel emissions, or air-sea CO2 exchanges. The attenuated respiration response is likely due to decoupling between temperature and plant-derived carbon inputs to soil for decomposition. Contrary to previous suggestions, warming no longer results in a higher autumn net CO2 release.