Impacts of climate variability and extremes on global net primary production in the first decade of the 21st century

A wide variety of studies have estimated the magnitude of global terrestrial net primary production (NPP), but its variations, both spatially and temporally, still remain uncertain. By using an improved process-based terrestrial ecosystem model (DLEM, Dynamic Land Ecosystem Model), we provide an estimate of global terrestrial NPP induced by multiple environmental factors and examine the response of terrestrial NPP to climate variability at biome and global levels and along latitudes throughout the first decade of the 21st century. The model simulation estimates an average global terrestrial NPP of 54.6 Pg C yr^–1 during 2000–2009, varying from 52.8 Pg C yr^–1 in the dry year of 2002 to 56.4 Pg C yr^–1 in the wet year of 2008. In wet years, a large increase in terrestrial NPP compared to the decadal mean was prevalent in Amazonia, Africa and Australia. In dry years, however, we found a 3.2% reduction in global terrestrial NPP compared to the decadal mean, primarily due to limited moisture supply in tropical regions. At a global level, precipitation explained approximately 63% of the variation in terrestrial NPP, while the rest was attributed to changes in temperature and other environmental factors. Precipitation was the major factor determining inter-annual variation in terrestrial NPP in low-latitude regions. However, in mid- and high-latitude regions, temperature variability largely controlled the magnitude of terrestrial NPP. Our results imply that projected climate warming and increasing climate extreme events would alter the magnitude and spatiotemporal patterns of global terrestrial NPP.