The detection and quantification of global land change by satellite observations are the grand challenges to improve the understanding of global environmental change. In this study, we develop a new vegetation index, which can be used as a proxy of the fractions of tree canopy and short vegetation, based on the simple linear regression between microwave vegetation optical depth (VOD) and optical leaf area index (LAI). Although we use no high-resolution reference data, the newly developed vegetation index successfully detects and quantifies the global land change which has been reported by the previous estimations based on high-resolution reference data. We find that the relationship between VOD and LAI is non-stationary and the temporal change in the VOD-LAI relationship is the important signal to detect and quantify global change in the terrestrial ecosystem.