Winter CO2 emissions from northern ecosystems are crucial for understanding the carbon cycle. A study analyzed data from 57 sites and found that deciduous forests have the highest winter CO2 release, while arctic wetlands have the lowest. Temperature, especially air and soil temperature, is the main factor influencing winter CO2 emissions. The amount of recent carbon available for respiration in winter also plays a role, but to a lesser extent. The sensitivity of winter CO2 emissions to temperature differences across locations is higher than over time. This means that future warming may have a greater impact on winter CO2 emissions than previously thought.