Comment on tc-2021-52

Abstract

Arctic snow and ice cover are vital indicators of climate variability and change, yet while the Arctic shows overall warming and dramatic changes in snow and ice cover, the response of these high-latitude regions to recent climatic change varies regionally. Although previous studies have examined changing snow and ice separately, examining phenology changes across multiple components of the cryosphere together is important for understanding how these components, and their response to climate forcing, are interconnected. In this work, we examine recent changes in sea ice, lake ice and snow together at the pan-Arctic scale using the Interactive Multisensor Snow and Ice Mapping System 24 km product from 1997 -2019, with a more detailed regional examination from 2004 -2019 using the 4 km product. We show overall that for sea ice, trends towards earlier open water (-7.7 d decade -1 , p < 0.05) and later final freeze (10.6 d decade -1 , p < 0.05) are evident. Trends towards earlier first snow-off (-4.9 d decade -1 , p < 0.05), combined with trends toward earlier first snow-on (-2.8 d decade -1 p < 0.05), lead to almost no change in the length of the snow-free season, despite shifting earlier in the year. Sea ice-off, lake ice-off and snow-off parameters were significantly correlated, with stronger correlations during the snow/ice-off season compared to the snow/ice-on season. Regionally, the Bering and Chukchi Seas show the most pronounced response to warming, with the strongest trends identified toward earlier ice-off and later ice-on. This is consistent with earlier snow/lake ice-off and later snow/lake ice-on in west and southwest Alaska. In contrast to this, significant clustering between sea ice, lake ice and snow-on trends in the eastern portion of the North American Arctic show an earlier return of snow and ice. The marked regional variability in snow and ice phenology across the pan-Arctic highlights the complex relationships between snow and ice, and their response to climatic change, and warrants detailed monitoring to understand how different regions of the Arctic are responding to ongoing changes.