Development of one-dimensional simplified earth system model for the future projection of carbon cycle and climate.

A simple one-dimensional Earth system model, the Four-Spheres Cycle of Energy and Mass model (4-SCEM version. 2.0), are being developed to simulate global warming due to anthropogenic CO2 emission based on our previous zero-dimensional earth system model which simulate carbon and energy coupled cycle in the simplified manner. The model consists of the Atmosphere-Earth Heat Cycle model (AEHC), the Four Spheres Carbon Cycle model (4-SCC), and their feedback processes with one-dimensional spatial resolution (18 latitudinal bands). The AEHC is a one-dimensional energy balance model, which includes the greenhouse effect of CO2, H2O, CH4 and N2O, and ocean energy balance model based on INK model. The 4-SCC is a box-type carbon cycle model, which includes biospheric CO2 fertilization, vegetation area variation, the vegetation light saturation effect, and the oceanic carbon cycle model. The following feedback processes were included in the model, (1) water vapor feedback, (2) biospheric CO2 fertilization, and temperature dependencies on (3) photosynthesis, (4) soil decomposition, (5) ocean surface chemistry. First, each model component was evaluated by off-line simulation using the CO2 concentration and future climate based on IPCC IS92a scenario. The simulated carbon cycle and climate variation were within the range of current observations. The recent NPP trends derived from the 4-SCEM and satellite data both showed the NPP increase in past 20 years with strong increases in northern mid and high latitude zones. Moreover, large increases in surface temperature in the northern mid and high latitudes were also captured by the model. The future status of the global carbon cycle and climate was simulated up to the year 2100 based on the IS92a emission scenario. The atmospheric CO2 concentration reaches around 650 ppmv in 2100. The sensitivity analysis showed that uncertainties derived from the light saturation effect of vegetation, land use CO2 emissions and ice albedo feedback were the primary cause of uncertainties in projecting future CO2 concentrations.