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

n = 2743), 4.7±4.4 (SD, n = 2674), and 5.9±5.4 (SD, n = 2512) days when average air temper- ature warms by 1˚C, 2˚C, and 4˚C, respectively. Finally, when ice quality was 100% white ice, the transition period extended by 6.3±4.9 (SD, n = 2643), 7.2±5.5 (SD, n = 2580), and 8.8±6.6 (SD, n = 2379) days under warming of 1˚C, 2˚C, and 4˚C, respectively (Table 1, Fig 3). Additionally, the standard deviation of the transition period increases with warming sce- narios and across ice quality ratios, which implies that the variability of the transition period increases with both warming and degrading ice quality (Table 2). For example, the standard deviation of black ice during the ice formation period increases from 11.5 to 13.3 days between the historical period and 4˚C. The standard deviation of white ice, on the other hand, increases from 23.7 to 30.0 days between the same period. The standard deviation during the melt period is overall shorter compared to the ice formation period; however, the values increase with both warming and degrading ice quality (Table 2). Fig 2. Unsafe transition period conceptual model. The conceptual model depicts the thickening of lake ice after formation for a historical period (black line) and a future warming scenario (orange line). The horizontal lines indicate the required thickness that the ice must reach prior to use under different ice quality categories (black ice: >10 cm (solid black line), a mix of black and white ice: 15 cm (dashed line), and white ice: >20 cm (white line)). The blue

shaded area represents the period of safe ice use. The yellow shaded area represents the period of unsafe ice use for the historical period, while the red region represents the increasing length of the ice cover period for the future warming scenario. For this instance, the red shaded region is the difference between the transition period for white ice for the warming scenario and the historical black ice scenario. The panels at the bottom show various ice categories as sampled from Paint Lake and Lake Simcoe during the winter of 2023–2024. From left to right, they are 100% black ice, 50% black ice and 50% white ice, and almost entirely white ice. https://doi.org/10.1371/journal.pone.0313994.g002 PLOS ONE Changing ice conditions inhibit safe use PLOS ONE | https://doi.org/10.1371/journal.pone.0313994 December 11, 2024 7 / 19