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Abstract

Large interannual variations in the measured growth rate of atmospheric carbon dioxide (CO2) originate primarily from
fluctuations in carbon uptake by land ecosystems1–3. It remains
uncertain, however, to what extent temperature and water
availability control the carbon balance of land ecosystems across
spatial and temporal scales3–14. Here we use empirical models
based on eddy covariance data15 and process-based models16,17 to
investigate the effect of changes in temperature and water availability
on gross primary productivity (GPP), terrestrial ecosystem
respiration (TER) and net ecosystem exchange (NEE) at local
and global scales. We find that water availability is the dominant
driver of the local interannual variability in GPP and TER. To a
lesser extent this is true also for NEE at the local scale, but when
integrated globally, temporal NEE variability is mostly driven by
temperature fluctuations. We suggest that this apparent paradox can
be explained by two compensatory water effects. Temporal waterdriven
GPP and TER variations compensate locally, dampening
water-driven NEE variability. Spatial water availability anomalies
also compensate, leaving a dominant temperature signal in the yearto-
year fluctuations of the land carbon sink. These findings help to
reconcile seemingly contradictory reports regarding the importance
of temperature and water in controlling the interannual variability
of the terrestrial carbon balance3–6,9,11,12,14. Our study indicates that spatial climate covariation drives the global carbon cycle response.