Year to year, variations in the rate of atmospheric CO2 growth arise primarily from fluctuations in carbon uptake by ecosystems on land. Evidence for the dominant drivers of changes in the global land carbon sink is conflicted, however.
Using a mixture of modelling approaches, Martin Jung from the Max Planck Institute for Biogeochemistry, Germany, and co-workers investigate the roles of temperature and water availability in regulating gross primary productivity, terrestrial ecosystem respiration, and net ecosystem exchange at local and global scales.
They find that drivers are scale-dependant, with water availability the dominant driver at the local scale while at the global scale temperature fluctuations dominate. Two compensatory water effects explain this apparent paradox. These findings suggest that the spatial covariation of climate variables drives the global carbon-cycle response. Consequently if climate change alters these spatial covariations it could alter carbon-cycle sensitivities and the strength of climate–carbon cycle feedbacks.