The response of global net primary productivity (NPP) to CO_2 increasing and climate change: Evaluation of coupled model simulations

摘要

Three experiments from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) are used to estimate the impact of climate change MdCO_2 increasing on global net primary productivity (NPP). One is the standard 1 %/yr increase of CO, concentration until it quadrupled the pre-industrial level at the 140 year experiment (lpctCO_2) and the others are two diagnosis experiments, which are used to isolated the impact of climate change alone (esmFdbkl) and CO_2 concentration changes alone (esmFixClim 1) on surface carbon fluxes. The experiments were carried out with several coupled climate models. Although there are large variations in the magnitude of the precipitation flux among the models, the majority of the models show an obvious seasonal patterns of NPP, surface air temperature and precipitation flux. During 140 year long simulations, global NPP increasing steadily when CO_2 concentration quadrupled and climate changed together or CO, increasing alone, the growth rates can reach up to 0.31 %/ yr(MPI-ESM-LR simulated). However, there is a down trend of global NPP when climate changed alone. NPP changes are not consistent around the world, influenced by CO, increase and climate change, higher NPP are most distributed in southern Africa, Amazon basin and southeast coastal regions in the northern hemisphere, CO, increase due to climate change also has a positive impact on global NPP at the end of the simulation. Nevertheless, no matter what the situation, climate change alone or climate change resulted from CO, increase both are not good for NPP accumulation on global scale. The relationship between annual NPP and climatic variables shows temperature rising in the growth season has significant effects on NPP increase in the mid and high latitudes of northern hemisphere, while NPP in arid or semi-arid regions in the southern hemisphere is mainly limited by precipitation.