Ecosystem memory affects atmospheric CO2 growth rate variations

Accurate prediction of the atmospheric CO2 mole fraction is a first order requirement for climate prediction. Feedbacks between the climate system, terrestrial ecosystems, and ocean processes will determine the trajectory of the atmospheric CO2 growth rate. We use models and observations to show that the atmospheric CO2 growth rate responds to climate variations on interannual timescales. Some of these responses occur on multi-year or lagged timescales, suggesting that memory within the carbon cycle governs the ultimate feedback strength. These findings also affect how observations must be used to evaluate and refine predictive models.