We present an analysis of soil CO₂ emissions in boreal and tundra regions during the non-growing season. We show that when the soil is completely frozen, soil temperature is the main control on CO₂ emissions. When the soil is around the freezing point, with a mix of liquid water and ice, the liquid water content is the main control on CO₂ emissions. This study highlights that the vegetation–snow–soil interactions must be considered to understand soil CO₂ emissions during the non-growing season.