Warming-induced increase in carbon uptake leads to earlier spring phenology

Abstract Under global warming, advances in spring phenology due to rising temperatures have been widely reported. However, the physiological mechanisms underlying the warming-induced earlier spring phenology remain poorly understood. Here, using multiple long-term and large-scale phenological datasets between 1951 and 2018, we show that warmer temperatures during the previous growing season led to earlier spring phenology in the Northern Hemisphere, with an average advancement of 2.5 days °C− 1. Correspondingly, we observed an earlier spring phenology with the increase in photosynthesis of previous growing season. Furthermore, we found a significant decline in the advancing effect of warming in previous growing season on spring phenology from cold to warm periods. These findings reveal that the observed warming-induced earlier spring phenology is driven by increased photosynthetic carbon assimilation in the previous growing season, while the slowdown in the advanced spring phenology may arise from decreased carbon assimilation when warming exceeds optimal temperatures for photosynthesis. Therefore, the vital role of warming-induced changes in carbon assimilation should be considered to accurately project spring phenology and carbon cycling under future climate warming conditions.