Soil Freeze–Thaw Cycles Can Advance or Delay Spring Green-Up across Northern Hemisphere

Spring green-up has advanced across much of the Northern Hemisphere, but it still shows little change or even delays in some regions, despite global warming. A new study published in Global Change Biology on Dec. 29, 2025, reveals that soil freeze–thaw cycles (FTCs) as an overlooked process can reshape the timing of the start of the growing season (SOS) each year.

SOS matters because it sets the window for photosynthesis and carbon uptake, while also influencing water and energy exchanges at the land surface. These shifts can affect regional carbon-cycle estimates, especially in high-latitude and high-elevation environments.

FTCs occur when soils repeatedly oscillate around 0°C, alternating between freezing and thawing. This can cut both ways: repeated freezing may stress roots and increase nutrient losses, while thawing can boost microbial activity, mobilize nutrients, and replenish soil moisture. This process could either advance or delay SOS within a specific biome.

To test this mechanism across the pan-Northern Hemisphere, researchers from the Xinjiang Institute of Ecology and Geography of the Chinese Academy of Sciences combined multi-source remote-sensing datasets from 2002–2022 and integrated freeze–thaw dynamics into a cross-ecosystem phenology analysis. They used pixel-level models to capture nonlinear responses and to disentangle FTC effects from other climate drivers.

They found that across the terrestrial ecosystems of the Northern Hemispheres (≥30°N), SOS advanced by about 1.9 days per decade on average. Yet more than 28% of vegetated areas experienced stable or even later growing season, with this persistence most pronounced in boreal forests, tundra, and cold high-elevation regions.

“The impacts of FTCs are not uniform but biome-specific,” said MA Xiaofei, corresponding author of the study. “In boreal forests, higher FTC frequency tended to coincide with earlier SOS—up to ~6.5–7 days. While in deserts and xeric shrublands, frequent FTCs were linked to delayed SOS.”

By elevating FTCs from a “background” fluctuation to a quantifiable driver, this study offers a clearer pathway for incorporating spring phenology into land–vegetation models. This approach could strengthen carbon-cycle projections in regions where spring’s onset remains challenging to predict.

Read the full article: https://doi.org/10.1111/gcb.70675

Contact

LONG Huaping

Xinjiang Institute of Ecology and Geography

E-mail: longhp@ms.xjb.ac.cn

Web: http://english.egi.cas.cn