Climate-driven changes to the cryosphere are having unprecedented impacts in the Arctic and the Subarctic, where permafrost, snow and freshwater ice dominate the terrestrial landscape and are host to unique and interconnected habitats and ecosystems. Rates of permafrost thaw are now higher than at any other time on record, therefore impacting northern infrastructure dependent on permafrost stability and increasing greenhouse gas emissions to the atmosphere through thermokarst lakes formation. Increasing temperatures and its related impacts are changing groundwater flow of northern river systems, altering the Arctic snowpack’s properties, and causing reduction in year-round ice cover of High Arctic lakes. The warming climate is also threatening the habitats of certain polar microbes, causing cascading effects throughout other microbial communities within connected hydrologic habitats. The discovery of new and diverse bacterial and viral communities in northern freshwater systems could bring about a better understanding of carbon cycling in northern ecosystems. This chapter presents a selection of Sentinel North’s research advances related to the physical and biogeochemical impacts of permafrost degradation; the microbial and viral diversity of Northern lakes and ponds and how they respond to climate change; the changing hydrological regime and snowpack properties; and the development of new innovative technology to monitor the changing terrestrial environments.