Combining Satellite, Teleconnection, and In Situ Data to Improve Understanding of Multi‐Decadal Coastal Ice Cover Dynamics on Earth's Largest Freshwater Lake.

To differentiate and understand drivers behind coastal ice cover trends and variability, we advance development of a model combining satellite, in situ, and teleconnection data along the shoreline of Earth's largest freshwater lake (Lake Superior). Previous studies suggest a regime shift in Lake Superior's ice cover starting in 1998. Our study includes seven years of new data and subsequent model analysis that provide new insight into characteristics of the post‐1998 regime. In addition to providing a valuable extension to the historical ice cover record for this domain, we find the regime shift in coastal ice cover starting in 1998 is characterized by pronounced variability, and not simply a shift in pre‐1998 trends. Our findings represent an important stepping stone for future ice and climate modeling not only on Lake Superior but across the entire Great Lakes region and in other global high‐latitude coastal regions as well. Plain Language Summary: Ice cover on the Laurentian Great Lakes has become more variable over the past 25 years. To better understand this variability, we re‐develop a model from a previous study focused on a portion of the shoreline of Lake Superior. The previous study, which culminated in 2015, suggested a change in both interannual variability and long‐term trends in ice cover after 1998. At the time of the previous study, however, the extent to which those changes might continue to propagate into the future was unclear. Here, we extend the historical ice cover record through 2022 while also exploring a broad range of potential explanatory variables in a simulation model. Our analysis indicates that the post‐1998 regime is characterized by more pronounced variability than previous studies indicated, with near‐record‐high years of ice cover followed by years of very little or even no appreciable ice cover. These interannual ice cover dynamics were not evident in the historical record prior to 1998, and their persistence from 1998 through 2022 underscores the importance of not only differentiating regime shifts from trends in climate change studies, but also of the value in correctly reflecting those regime shifts in simulation and forecasting models. Key Points: For the past 25 years, ice cover along Lake Superior's shoreline has been characterized by pronounced interannual variabilityWe reproduce these dynamics in two probabilistic models (Cox survival and beta) combining satellite, in situ, and teleconnection dataCoastal ice conditions along the shoreline of Earth's largest freshwater lake reflect a regime shift that began in the late 1990s [ABSTRACT FROM AUTHOR]