Three decades of multi-dimensional change in global leaf phenology

Changes in the phenology of vegetation activity may accelerate or dampen rates of climate change by altering energy exchanges between the land surface and the atmosphere(1,2) and can threaten species with synchronized life cycles(3-5). Current knowledge of long-term changes in vegetation activity is regional(6-8), or restricted to highly integrated measures of change such as net primary productivity(9-13), which mask details that are relevant for Earth system dynamics. Such details can be revealed by measuring changes in the phenology of vegetation activity. Here we undertake a comprehensive global assessment of changes in vegetation phenology. We show that the phenology of vegetation activity changed severely (by more than 2 standard deviations in one or more dimensions of phenological change) on 54% of the global land surface between 1981 and 2012. Our analysis confirms previously detected changes in the boreal and northern temperate regions(6-8). The adverse consequences of these northern phenological shifts for land-surface-climate feedbacks(1), ecosystems(4) and species(3) are well known. Our study reveals equally severe phenological changes in the southern hemisphere, where consequences for the energy budget and the likelihood of phenological mismatches are unknown. Our analysis provides a sensitive and direct measurement of ecosystem functioning, making it useful both for monitoring change and for testing the reliability of early warning signals of change(14).