Assessment of the impacts of biological nitrogen fixation structural uncertainty in CMIP6 earth system models

Abstract. Biological nitrogen fixation is the main source of new into natural terrestrial ecosystems and consequently in cycle many earth system models. Representation biological varies, because tight coupling between carbon cycles, previous studies have shown that this affects projected changes net primary productivity. Here we present first assessment performance models contributing to CMIP6 compared observed observation-constrained estimates fixation. We find 9 out 10 represent global total within uncertainty recent estimates. However, 6 overestimate amount tropics therefore extent latitudinal gradient distribution. For SSP3-7.0 scenario future climate change, project increases over 21st century up 80 %. while historical range amongst large (up 140 kg N ha−1 yr−1 at grid cell level 43–208 Tg globally) does not explanatory power for variations model ensemble productivity or coupled nitrogen–carbon cycle. Models with shared structures can significant both other parts without differing their This points systematic challenges representation carbon–nitrogen severe limitations using evapotranspiration response elevated atmospheric dioxide environmental changes.