Projecting climate change impacts on ice phenology across Midwestern and Northeastern United States lakes

Lakes are sensitive indicators of climate change as freshwater requires temperatures below 0 °C to freeze. Here, we used 34-year records for 74 lakes distributed across the Midwestern and Northeastern United States to ask the following: (i) Which physical factors affect lake ice phenology in the Northern United States?; (ii) Can an empirical statistical modelling approach be used to effectively predict ice phenology across the morphologically diverse lakes of the Northern United States?; and (iii) How much ice is forecasted to be lost in response to climate change? We find that our study lakes require 19 days with air temperatures below 0 °C to freeze, ranging from 4 days for small lakes to 53 days for larger lakes. To thaw, lakes require 22 days with air temperatures above 0 °C, ranging from 8 to 33 days. We find that 64% of the variation in ice-on dates is explained by air temperatures, and the remaining 36% of variation is explained by lake morphology, primarily mean depth. For ice-off dates, 80–90% of the variation is explained by air temperatures. By the end of the century in response to climate change, these lakes may lose 43 days of ice cover, although ranging from 12 days of less ice cover to no ice cover at all. Understanding the drivers of variability in ice phenology for lakes within regions found to be highly sensitive to climate change will promote our understanding of ice cover and ice loss, and also the widespread ecological ramifications associated with ice loss.