Boreal ecosystems sequestered more carbon in warmer years

A 13‐year (1990–1996, 1999–2004), hourly air CO 2 record measured on a 40 m tower in northern Canada is analyzed against interpolated marine boundary layer CO 2 data representing the free troposphere above the tower. In warmer years, the planetary boundary layer was more depleted with CO 2 , suggesting that the land area (10 3 –10 4 km 2 ) upwind of the tower sequestered more carbon. After using a novel approach to derive the photosynthetic flux from the air CO 2 diurnal variation pattern, it is confirmed that boreal ecosystem photosynthesis increased more than ecosystem respiration in warmer years.