Widespread loss of safe lake ice access in response to a warming climate

different (p < 0.05), distributions between ice quality categories had higher absolute difference values. When combined with warming, the absolute difference between 1˚C black ice and 4˚C white ice exceeded 0.99, indicating a nearly complete difference between the empirical cumu- lative distribution functions of the two distributions (S3 and S4 Figs). This stark variation of the distributions and empirical cumulative distribution functions (ECDF) implies that ice quality increased the transition period of unsafe lake ice more significantly than warming, with higher maximum values. That is, the period of unsafe ice presence is projected to be much longer when ice quality degrades. 4. Discussion This research investigated how projected warming average air temperatures and changing ice quality throughout the 21st Century will result in longer periods when lake ice cover is present but not safe for human use. Studies in winter limnology have primarily focused on changing phenology and duration [3] and decreasing ice thickness [1,4]. Using CESM2-LE, our projec- tions suggest a shift toward lake ice that will be unsafe for human use for a mean of approxi- mately 5, 17, or 29 days longer per year for black ice, 50% white ice, and 100% white ice, respectively, at 4˚C of warming. We determined that ice quality increased the transition period of unsafe ice more than did warming air temperatures alone. 4.1 Lake ice is projected to become increasingly unsafe Ice quality impacts the carrying capacity of lake ice, which interacts with air temperatures both

in the creation of white ice [5,7] and its flexural strength [9,10]. As density decreases with degrading ice quality, lake ice can support less weight and becomes more than 50% weaker at temperatures near 0˚C [10]. Ice quality can quickly degrade in warm years, where most or all of the ice column can become white ice throughout the ice cover season, resulting in danger- ous ice conditions, including drownings [5,15]. While the duration of safe lake ice use has been analyzed for transportation efforts [21], the unsafe transition period adds important Table 2. Unsafe transition period standard deviation. Warming Ice Formation Standard Deviation Ice Melt Standard Deviation 100% Black Ice 0˚C 11.5 7.9 1˚C 12.2 8.3 2˚C 12.4 8.6 4˚C 13.3 9.1 50% White Ice 0˚C 17.3 10.1 1˚C 18.7 10.8 2˚C 19.3 11.4 4˚C 21.1 12.4 100% White Ice 0˚C 23.7 12.1 1˚C 25.8 13 2˚C 27 13.6 4˚C 30 15 The standard deviation of the transition periods shown for each warming scenario and ice quality ratio. Values are in units of days. Warming is in degrees Celsius. The value of 0˚C is the historical period of 1851–1880. https://doi.org/10.1371/journal.pone.0313994.t002 PLOS ONE Changing ice conditions inhibit safe use PLOS ONE | https://doi.org/10.1371/journal.pone.0313994 December 11, 2024 10 / 19