Global Patterns and Drivers of Recent Decoupling Between Extratropical Spring Phenology and Temperature

While spring phenology has been widely studied, the magnitude and drivers of its decoupling from thermal cues across extratropical biomes remain poorly understood. Using satellite data from 1982 to 2021, we show that the onset of vegetation green-up (GSOS) generally lags the onset of the thermal growing season (TSOS). This mismatch (ΔSOS) has increased by 1.51 days per decade (p < 0.001) since 1996, largely driven by shrublands and grasslands. GSOS in these biomes exhibits lower sensitivity to spring temperature but stronger responses to shotwave radiation and precipitation, with higher ratios of heat accumulation to winter chilling associated with delayed green-up under reduced chilling. Phenological decoupling is strongly biome dependent: in warm-dry grasslands and shrublands (ΔSOS > 15 days), warming-driven advances in TSOS are increasingly decoupled from GSOS, as declining precipitation and enhanced evaporative demand intensify moisture limitation and delay green-up; in temperate forests (both coniferous and broadleaf), warming together with enhanced shortwave radiation promotes faster GSOS advancement relative to TSOS, thereby dampening the mismatch. These contrasting pathways reveal an accelerating yet heterogeneous phenology-temperature decoupling, with far-reaching consequences for ecosystem synchrony, seasonal carbon uptake, and land-climate feedbacks. Our results underscore the need to incorporate non-thermal drivers and biome-specific controls into phenological and Earth system models to better constrain future climate-biosphere interactions.