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More than 50% of global lakes periodically freeze, and their lake ice phenology is sensitive to climate change. However, spatially detailed quantification of the changes in lake ice at the global scale is not available. Here, we map ice cover in >33,000 lakes throughout the North Temperate Zone (23.5°–66.5°N) using 0.55 million Landsat images from 1985 to 2020. Over this period, we found a remarkable reduction in median ice cover occurrence (ICO) (61% to 43%), which was strongly related to warming terrestrial mean surface temperatures (R2 = 0.94, p < 0.05). Lakes in Europe showed the most pronounced ice loss (median ICO decreased from 50% to 24%), and extensive lake ice losses were also detected in the northern US, and central and eastern Asia. An overall increase in ice cover was identified from P2 (1999–2006) to P3 (2007–2014) due to regional decreased temperatures associated with the "global warming hiatus." Thehigh‐resolution mapping of lake ice here provides essentialbaseline information whichcan be used to elucidate ice loss‐induced environmental and societal impacts. Plain Language Summary: Widespread reductions in lake ice have been detected recently worldwide, yet spatially detailed characterization of global lake ice is currently unavailable. Using 0.55 million Landsat satellite images from 1985 to 2020, we provide the first long‐term wall‐to‐wall mapping of lake ice cover over the entire Northern Temperate Zone, comprising >33,000 lakes representing 48% of the global lake area in total. We track spatially detailed changes in lake ice across the entire Northern Temperate Zone, and examine how ice change patterns have differed geographically and temporally in response to climate change. Key Points: We provide the first long‐term wall‐to‐wall mapping of lake ice cover over the entire Northern Temperate ZoneWe found a remarkable reduction in median ice cover occurrence (61‐43%)Extensive lake ice retreats were found in central and southern Europe, the northern US, and central and southeastern Asia [ABSTRACT FROM AUTHOR]

The Qinghai‐Tibet Plateau possesses the largest alpine lake system, which plays a crucial role in the land‐atmosphere interaction. We report first observations on the thermal and radiation regime under ice of the largest freshwater lake of the Plateau. The results reveal that freshwater lakes on the Tibetan Plateau fully mix under ice. Due to strong solar heating, water temperatures increase above the maximum density value 1–2 months before the ice break, forming stable thermal stratification with subsurface temperatures >6°C. The resulting heat flow from water to ice makes a crucial contribution to ice cover melt. After the ice breakup, the accumulated heat is released into the atmosphere during 1–2 days, increasing lake‐atmosphere heat fluxes up to 500 W m−2. The direct biogeochemical consequences of the deep convective mixing are aeration of the deep lake waters and upward supply of nutrients to the upper photic layer. Plain Language Summary: The Qinghai‐Tibet Plateau possesses the largest alpine lake system, which plays a crucial role in the land‐atmosphere interaction. Data on thermal properties of Tibetan lakes during the ice‐covered season are extremely scarce. The first observations on the thermal and radiation regime under ice of the largest freshwater lake of the Plateau reveal that freshwater (and apparently the majority of brackish) lakes gain an extremely large amount of solar radiation penetrating the highly transparent ice cover. As a result, lakes fully mix under ice and get heated up to >6°C. The accumulated heat makes a crucial contribution to ice cover melt. The quick release of the heat to the atmosphere during 1–2 days after the ice breakup strongly increases lake‐atmosphere heat fluxes, potentially affecting regional weather conditions. Warm and well‐mixed conditions are favorable for aquatic life in the extreme environment of Tibet. Key Points: An abnormal thermal regime under the ice cover of Tibetan lakes is revealedThe lakes get heated above their maximum density temperature by extremely high level of solar radiation penetrating the ice coverThe stored heat shortens the ice‐covered period and is quickly released into the atmosphere after ice‐off, affecting local climate [ABSTRACT FROM AUTHOR]

Extreme climate events can have significant consequences on ecosystems and by extension human populations. Over 50 million of the world's lakes typically freeze each winter, and the absence of winter ice cover, in lakes where ice has historically been present, can be characterized as an extreme event. We quantified the effects of extreme climate events on lake ice cover using 78‐year ice records from 122 lakes to show that (1) extreme ice‐free years are becoming more frequent and severe, (2) winter air temperature is a significant predictor of ice cover that was driven by large‐scale climate oscillations, (3) extremes in temperature are closely related to extremes in ice cover, and (4) ice‐free years are forecasted to result in significant loss of ice‐cover in the future. Without drastic reductions in carbon emissions, we can expect the widespread loss of lake ice cover could have significant socioeconomic and biological implications. Plain Language Summary: Climate change is expected to have a large impact on humans and our natural systems. Freshwater lakes are an important resource and each year, millions around the world freeze during the winter months. However, climate change is expected to threaten the freezing of some of these lakes. We explored 122 lakes that typically freeze over winter and that had records of freeze/thaw since 1939. We asked, do extremes in winter air temperature affect extremes in lake ice cover and what would that mean for the future? Winter air temperature was found to closely predict ice‐free years for lakes. Years with abnormally hot winters were also years where many lakes remained ice‐free. Projecting into the future, we predicted that lakes will continue to experience more ice‐free years. With a reduction in carbon emissions, there will be a modest increase in ice‐free years, but if carbon emissions continue as they are currently, there could be a large increase in ice‐free lakes. This study highlights lake ice as another victim of climate change. The loss of lake ice will have impacts to natural systems and also socioeconomic implications for human populations that are dependent on it. Key Points: Observed recent increases in ice‐free years for 122 lakes since 1939Extremes in winter air temperature were observed to closely relate to extremes in ice‐free cover for lakesUsing climate change scenarios, ice‐free years for lakes are predicted to increase significantly in the next decades [ABSTRACT FROM AUTHOR]

During the winter of 2014, a weak polar vortex brought record cold temperatures to the north-central (“Midwest”) United States, and the Great Lakes reached the highest extent of ice coverage (92.5%) since 1979. This event shut down the generation of seismic signals caused by wind-driven wave action within the lakes (termed “lake microseisms”), giving an unprecedented opportunity to isolate and characterize these novel signals through comparison with nonfrozen time periods. Using seismic records at 72 broadband stations, we observe Great Lakes microseism signals at distances >300 km from the lakes. In contrast to conventional oceanic microseisms, there is no clear relationship between the frequency content of the seismic signals (observed from ~0.5–5-s period) and the dominant swell period or resonance periods of the lakes based on their bathymetric profiles. Thus, the exact generation mechanism is not readily explained by conventional microseism theory and warrants further investigation. [ABSTRACT FROM AUTHOR]

Abstract: Detailed observations of thermal structure over an entire winter in a large lake reveal the presence of large (10–20 m) overturns under the ice, driven by diurnal solar heating. Convection can occur in the early winter, but the most vigorous convection occurred near the end of winter. Both periods are when our lake ice model suggest thinner ice that would have been transparent. This under‐ice convection led to a deepening of the mixed layer over time, consistent with previous short‐term studies. During periods of vigorous convection under the ice at the end of winter, the dissolved oxygen had become supersaturated from the surface to 23 m below the surface, suggesting abundant algal growth. Analysis of our high‐frequency observations over the entire winter of 2015 using the Thorpe‐scale method quantified the scale of mixing. Furthermore, it revealed that changes in oxygen concentrations are closely related to the intensity of mixing. [ABSTRACT FROM AUTHOR]