Causes of uncertainty in China's net primary production over the 21st century projected by theCMIP5Earth system models

Abstract

ABSTRACTNet primary production is the initial step of the carbon cycle in which atmosphericCO2is fixed by plants. The responses of net primary production (NPP) to climate change andCO2are key processes that have the potential to significantly affect the climate–carbon feedback and future atmosphericCO2levels. Understanding futureNPPchanges is important for China that became the world's largestCO2emitter since 2006. Here, we analysedNPPchanges in China under the four emission scenarios from 11 Earth system models participating in the Coupled Model Intercomparison Project Phase 5. We find a general increase ofNPPover the 21st century under the four emission scenarios, with the large percentage increase in northwestern China and Qinghai–Tibetan Plateau. However, there is a large model spread in the increase ofNPPat both country and local scales. We present a statistical approach to assess various processes to explain this large spread, and find that the large spread at the country level is predominantly attributed to inter‐model difference in parameterization ofCO2fertilization effect within each emission scenario. But the parameterization ofCO2fertilization effect not always dominates over the model spread across China. When it comes to the local scale, the model spread can be significantly contributed by inter‐model difference in parameterization ofNPPresponses to precipitation along with precipitation projection in northwestern China. Our findings provide the reasons for divergent responses of futureNPPthrough process decomposition and are the first to pinpoint that the model process dominating over the uncertainty exhibits regional dependence.