Global shift in a key plant trait indicates a change in biosphere function

In the face of climate change, understanding the dynamic responses of vegetation is crucial for predicting shifts in biosphere functioning. Plant functional traits, particularly leaf mass per area (LMA), are critical links between plant metabolism, vegetation responses to climate change, and the broader exchanges of energy and matter within the biosphere. Despite their importance, a comprehensive, predictive understanding of traits and biosphere changes is hampered by spatial and temporal gaps in trait observations. Here, we introduce a novel remote sensing method for the global, continuous mapping of LMA and its historical shifts. Consistent with ecological theory predicting a widespread decrease in LMA with global warming, our findings reveal a global LMA reduction of 6.5-7.6 % between 1985 and 2019, primarily due to increasing temperatures. This decrease varies among biomes, with evergreen conifer and tropical forests showing the most significant declines. Due to LMA connections with carbon metabolism in ecosystems, a global decrease in LMA points to a quickening of the carbon cycle, including largely unexplored contributions to increased global photosynthesis in recent decades. Collectively, these results signal an ongoing widespread and profound transformation in the functioning of the biosphere resulting from climate-related changes in vegetation and its traits.