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The global carbon cycle has feedbacks on the global climate, and climate-carbon cycle interactions are explicitly represented in earth system models (ESMs). In ESMs, leaf area index (LAI) is a key variable for projecting future environmental changes, but it might be one of the most difficult to precisely predict. In this research, historical LAI changes reproduced in the ESM named 'Model for Interdisciplinary Research on Climate ESM (MIROC-ESM)' are analyzed, focusing on impacts of CO2 fertilization effects, climate change, and land-use change. The model showed reasonable seasonality of LAI in global scale although the absolute value of this index was larger than the observation. The CO2 fertilization effect increases global LAI, and this was found to be nearly ubiquitous. However, an LAI increase is partially offset by the influence of historical climate change induced by anthropogenic greenhouse gas emissions. In addition to these environmental change impacts, human perturbations of the carbon cycle through land-use change dramatically altered global LAI. Although land-use change may have both positive and negative impacts on LAI, most regions showed negative impacts in the historical simulation, and land-use change had greater impacts than environmental change. Further study is recommended, such as long-term observation, modeling, and simulations of historical LAI change, toward improving modeling of future climate change.
