Future Projections of Global Environment due to Anthropogenic CO₂ Emission: Analysis From a Simplified Carbon Cycle and Climate Coupled Model and Earth Observation Satellite Data

Abstract

Past, present and future carbon cycle was analyzed based on earth observation satellite data and a simplified carbon cycle-climate coupled model. A simple Earth system model, the Four Spheres Cycles of Energy and Mass model (4-SCEM) was developed to simulate global warming due to anthropogenic CO₂ emission. The model consists of the Atmosphere-Earth Heat Cycle model (AEHC), the Four Spheres Carbon Cycle mode (4-SCC), and their feedback processes. 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, and (5) ocean surface chemistry. The recent NPP trends derived from the 4-SCEM and satellite data were directly compared for validation. The satellite-based estimation showed the NPP increase in past 20 years at a rate of 3.8% per 10 years. Although the 4-SCEM based analysis also showed a recent increase in NPP, the result was a half (with climate feedback) or one-eighth (without climate feedback) of satellite based one. Although large discrepancies are still remained, we can conclude that the carbon cycle model with climate feedback is more reasonable than that without climate feedback. The future global carbon cycle and climate was simulated under the IS92a emission scenario. The atmospheric CO₂ concentration reaches 712 ppmv in 2100 and a peak of 910 ppmv, and becomes a steady state with 650 ppmv. Although the climate feedback effects on the future atmospheric CO₂ were not large in 4-SCEM, high sensitivity was found in the terrestrial NPP. If we include the nutrient limitation effect in terrestrial carbon cycle model, the climate feedback effect on atmospheric CO₂ may be amplified due to NPP saturation.