Enhanced seasonal exchange of CO2 by northern ecosystems since 1960

Downs and Ups Every spring, the concentration of CO 2 in the atmosphere of the Northern Hemisphere decreases as terrestrial vegetation grows, and every fall, CO 2 rises as vegetation dies and rots. Climate change has destabilized the seasonal cycle of atmospheric CO 2 such that Graven et al. (p. 1085 , published online 8 August; see the Perspective by Fung ) have found that the amplitude of the seasonal cycle has exceeded 50% at some latitudes. The only way to explain this increase is if extratropical land ecosystems are growing and shrinking more than they did half a century ago, as a result of changes in the structure and composition of northern ecosystems.