El Niño-Southern Oscillation-induced variability in terrestrial carbon cycling
We examined the response of terrestrial carbon fluxes to climate variability induced by the El Niño–Southern Oscillation (ENSO). We estimated global net primary production (NPP) from 1982 to 1999 using a light use efficiency model driven by satellite-derived canopy parameters from the Advanced Very High Resolution Radiometer and climate data from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis project. We estimated a summed heterotrophic respiration and fire carbon flux as the residual between NPP and the terrestrial net carbon flux inferred from an atmospheric inversion model, excluding the impacts of land use change. We propose that for global applications this approach may be more robust than traditional, biophysically based approaches of simulating heterotrophic respiration. NPP interannual variability was significantly related to ENSO, particularly at lower latitudes (22.5°N–22.5°S) but was weakly related to global temperature. Global heterotrophic respiration and fire carbon fluxes were strongly correlated with global temperature (7.9 pgC/°C). Our results confirm the dependence of global heterotrophic respiration and fire carbon fluxes on interannual temperature variability and strongly suggest that ENSO-mediated NPP variability influences the atmospheric CO2 growth rate.