Phenology and surface energy balance changes across northern lands

Plant phenological shifts – notably earlier start (SOS) and later end (EOS) of the growing season – affect surface albedo, latent and sensible heat fluxes, and ultimately the surface temperature. The magnitude and spatial variability of these effects remain uncertain. Using Earth observation and reanalysis data (2001–2021), we quantify the sensitivity of surface energy fluxes to SOS and EOS changes across northern lands (> 30° N), and we report uncertainties and convergence across multiple independent datasets. Spatially-aggregated results show that an earlier SOS is generally associated with decreased albedo by up to 0.003 d ⁻¹ (needleleaf forests and tundra), and increased latent heat fluxes by 0.47 Wm-2d-1 (spatial median), ranging from 0.15 Wm-2d-1 (croplands) to 0.68 Wm-2d-1 (mixed forests). Delays in EOS are also associated with decreases in albedo, though much smaller in magnitude, and with increases in latent heat flux – up to ∼0.14 Wm-2d-1 in mixed forests – with weaker and more variable responses across other land-cover types. Datasets reveal large spatial variability and discrepancies in the responses of the sensible heat fluxes and thus evaporative fraction. Across datasets, earlier SOS is consistently associated with increased latent heat flux, and the concurrent evidence from evaporative fraction suggests a shift towards enhanced latent cooling. These findings are consistent with a phenology-driven negative feedback on surface warming through enhanced evaporative cooling, although causal attribution from observational analyses alone is not possible.