Increasing atmospheric CO2 and resultant climatic change would affect terrestrial carbon cycle, eventually leading to feedbacks to the anthropogenic global warming. Although flux tower measurements are finding aspects of spatial and temporal variability in carbon budget, specifying the impacts of global warming is difficult owing to natural variability and disturbances and insufficient length of measurement. Using a process-based model (VISIT: Vegetation Integrative SImulator for Trace gases), I investigated how to specify the global warming impacts on ecosystem carbon budget. (1) Detection: flux measurement data were obtained from databases and analyzed whether they contain significant long-term trends. (2) Attribution: sensitivity analysis was conducted to specify which environmental factors caused the long-term trends: e.g., CO2, temperature, precipitation, radiation, nitrogen deposition, and disturbance. (3) Prediction: near future projection up to 2050 was performed using AOGCM output for appropriate emission scenarios.
Results/Conclusions
The model-aided procedure to detect global warming impacts on terrestrial carbon cycle was successfully examined. For example, in many Asian forests, carbon budget would have been more severely affected by previous disturbances, and then effects of elevated CO2 and climate change have been relatively small. Clear impact of nitrogen deposition increase was not found; this seems different from other regions. However, the model projection showed that environmental change in the future would considerably alter the terrestrial carbon cycle, emphasizing the importance of long-term observations. Furthermore, this study carries implications to process studies such as leaf photosynthesis and soil respiration, by indicating which process is sensitive to the past and future environmental change. The future projection is expected to provide a plausible orientation to flux measurement.
