Too early to infer a global NPP decline since 2000

The global terrestrial carbon cycle plays a pivotal role in regulating the atmospheric composition of greenhouse gases. It has recently been suggested that the upward trend in net primary production (NPP) seen during the 1980's and 90's has been replaced by a negative trend since 2000 induced by severe droughts mainly on the southern hemisphere. Here we compare results from an individual-based global vegetation model to satellite-based estimates of NPP and top-down reconstructions of net biome production (NBP) based on inverse modelling of observed CO2 concentrations and CO2 growth rates. We find that simulated NBP exhibits considerable covariation on a global scale with interannual fluctuations in atmospheric CO2. Our simulations also suggest that droughts in the southern hemisphere may have been a major driver of NPP variations during the past decade. The results, however, do not support conjecture that global terrestrial NPP has entered a period of drought-induced decline.