For lakes across the Northern Hemisphere, winter ice is more than a frozen surface. It is a seasonal regulator that shapes underwater ecosystems and energy balance. But as the planet warms, this frozen season is disappearing faster than expected.
A new study has revealed that lake ice loss accelerates sharply once winter temperatures cross critical thresholds, leaving many mid-latitude lakes on the brink of heightened vulnerability. If emissions stay high, the winter ice-cover season of Northern Hemisphere lakes could be 40 days shorter by the end of this century.
Published in PNAS on July 27, the study was conducted by an international research team led by scientists from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences (NIGLAS), Nanjing Normal University, Bangor University, and the University of Regina.
In this study, the researchers analyzed ice phenology records and air temperature data from 724 lakes across the Northern Hemisphere between 2000 and 2022.
They found that lakes exhibit a pronounced asymmetry in their response to warming. Spring ice-off dates are far more sensitive to rising air temperature than autumn freeze-up dates, meaning the melting process accelerates considerably faster than the freezing process as the climate warms.
More critically, the researchers identified a set of winter temperature thresholds ranging from -13.7 °C to -6.8 °C. Once average winter air temperature climbs above these thresholds, the rate of ice loss increases sharply. For example, phenological sensitivity—a measure of how the timing of an environmental event is affected by climate change, especially temperature—may increase by up to 22-fold.
“Below these thresholds, ice cover responds to warming in a gradual manner,” said Dr. ZHOU Jian of Nanjing Normal University, first author of the study. “But once the threshold is crossed, the system enters a fundamentally different regime where each additional degree of warming triggers a disproportionately large loss of ice cover.”
The researchers also found that the thermal thresholds are regulated primarily by broad climatic factors, particularly winter air temperature and surface albedo—a measure of light reflectance—rather than by individual lake shape or depth. This indicates that whether a lake crosses a winter temperature threshold depends more on large-scale climatic conditions than on local lake morphology.
Looking ahead, the team projected that under a high-emission scenario, the duration of winter ice cover on Northern Hemisphere lakes will shrink by roughly 40 days by the end of this century. The proportion of lakes that have crossed critical thermal thresholds is expected to rise from 23 percent to 70 percent over the same period.
“Our findings suggest that many mid-latitude lakes are approaching a state of heightened vulnerability,” said Prof. SHI Kun from NIGLAS, co-corresponding author of the study.
“Even modest additional warming could trigger abrupt and potentially irreversible shifts in lake ice regimes, with cascading consequences for water quality, aquatic ecosystems, and northern communities that depend on stable winter ice cover,” SHI said.
According to the researchers, the findings provide a new mechanistic framework for predicting threshold-driven ice loss from northern lakes. They stress that incorporating such nonlinear thermal sensitivities into next-generation climate models is essential for reliable projections of freshwater ecosystem change.
Proceedings of the National Academy of Sciences
Rapid acceleration of ice-cover loss from Northern Hemisphere lakes above critical air temperature thresholds
27-Jul-2026