Thermodynamic Control of Global Seasonal Snow Decline

Seasonal snowfall is declining globally, yet the relative roles of precipitation variability versus warming‐induced phase transitions remain poorly quantified. We develop a physically based attribution framework that decomposes snowfall trends (1983–2023) into hydrological (precipitation‐driven) and thermodynamic (phase‐driven) components, constrained by a wet‐bulb‐temperature‐based phase relationship. Across most seasonal snow regions, snowfall decline is primarily driven by thermodynamic phase shifts rather than changes in precipitation amount. Regions near the rain–snow transition exhibit the strongest sensitivity to warming, consistent with systematic snowline retreat. Results are robust across independent data sets, including ERA5 reanalysis and the satellite‐based GPCP v3.3 products. These findings indicate that precipitation‐phase transitions exert pivotal control on contemporary snowfall loss, suggesting that projected precipitation increases are unlikely to offset warming‐driven reductions in snowfall. This has critical implications for future hydrological regimes and cryosphere‐climate feedbacks.