Significance Dramatic warming in northern high latitudes has led to increased photosynthetic carbon uptake during the short, intense growing season; however, microbial decomposition of soil carbon and increased emissions during the long cold season may offset summer uptake and impart a positive feedback on the global climate system. We show that current airborne and satellite measurements of atmospheric CO ₂ can accurately quantify summer uptake but are insufficient to detect regional changes in cold season emissions. As the potential for Arctic carbon budgets to become impacted by permafrost thaw and cold season emissions increases, strategies focused on year-round vertical profiles and improved spatial sampling will be needed to track carbon balance changes.