Freshwater ice is an integral part of the hydrologic regimes of cold environments. It controls the ecology of related aquatic systems and is important economically, through the facilitation of winter transport and via generation of extreme hydrologic events. Given projected changes in future climate, concern has been raised about related changes in freshwater ice. This paper reviews the status and trends in records of lake and river ice around the circumpolar North from traditional observations, remote sensing and paleo-sources. The temporal and spatial variability in trends are evaluated with relation to climatic conditions. Rapid changes experienced in freeze-up and break-up timing for high-latitude lakes, compared to those at more southerly locations, are particularly notable. Also considered are the nature and implications of changes in future freshwater-ice regimes that will have cascading effects on cold-region hydrology and a suite of hydro-ecological conditions including UV radiation receipts, habitat quality and availability, fisheries productivity and contaminant pathways. Overall, the duration and event timing of river and lake ice are proving to be useful indicators of climate change. Considering the scope and significance of ice-cover changes on northern hydro-ecology, a recommendation is made to place more emphasis on long-term and spatially diverse monitoring of freshwater ice.

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