DOI: 10.25923/cfhv-c239

L. R. Mudryk¹, A. Elias Chereque², C. Derksen¹, K. Luojus³, and B. Decharme⁴

¹Climate Research Division, Environment and Climate Change Canada, Toronto, ON, Canada
²Department of Physics, University of Toronto, Toronto, ON, Canada
³Arctic Research Centre, Finnish Meteorological Institute, Helsinki, Finland
⁴Centre National de Recherches Météorologiques, Météo-France, Toulouse, France

Headlines

• Snowpack at the peak of the 2024/25 snow season was higher than normal over much of the Arctic and remained high through May.
• Despite the higher-than-normal snowpack remaining in May, by June snow cover extent dropped below normal, consistent with values typical of the past 15 years.
• June snow cover extent over the Arctic today is half of what it was six decades ago.
• Loss of snow cover directly contributes to amplified warming in the Arctic, while also affecting permafrost deterioration, timing of freshwater availability, and ecosystem health.

Overview

Snow cover in the Arctic helps to regulate the climate and maintain the health of the established ecosystem. Reductions in snowpack depth or coverage reduce the amount of insulation between the ground and the air, which can, for example, alter ground temperatures and affect permafrost conditions (Goodrich 1982). Winter snowpack also functions as a temperature-stable habitat for small animals, vegetation, and microbial life (Jones et al. 2011). Even following the snow cover season, the timing of snowmelt has impacts on river discharge timing and magnitude, surface and sub-surface water availability, vegetation phenology, and fire risk (Meredith et al. 2019). Loss of snow cover also contributes to amplified Arctic warming through the surface albedo feedback (Forster et al. 2021).

In this essay, multiple data sets derived from satellite observations and snowpack models driven by historical weather conditions are used to assess Arctic seasonal snow cover (see Methods and data). Collectively, this approach provides a reliable picture of Arctic snow cover variability over the last five to six decades. We characterize snow conditions across the Arctic land surface using three quantities: how much total land area is covered by snow (snow cover extent – SCE), how much of the year snow covers the land surface (snow cover duration – SCD), and how much total water is stored in solid form by the snowpack (snow water equivalent – SWE; the product of snow depth and density). We examine each of these quantities in turn for the 2024/25 Arctic snow season (August 2024 to July 2025).

Snow cover extent and duration

Snow cover extent anomalies over the 1967-2025 period are shown separately for the North American and Eurasian sectors of the Arctic in Fig. 1. In 2025, Arctic SCE was close to normal across both the Eurasian and North American sectors during May but by June had dropped below normal (baseline periods listed in figure captions). Weekly SCE anomalies (Fig. 2) indicate that Eurasian Arctic SCE was already below normal in April (Fig. 2a; see also the discussion of SWE below), and while it recovered slightly during May, by June it dropped to values typical of recent years (typical recent values illustrated in Fig. 2 by the average anomalies seen over the 2010-24 period). Across North America, SCE was very close to normal until the end of May (Fig. 2b), after which it fell sharply to values even lower than those typical of recent years.

Corresponding SCD anomalies (Fig. 3) indicate a mix of early and late snow onset over Eurasia but primarily late onset over North America, except for central Alaska (Fig 3a). Snow melt at the end of the 2024/25 snow season was earlier than normal over northern Europe and eastern Siberia, but later than normal over the central portion of the continent (Fig 3b). Across the North American Arctic, melt was later than normal over the western parts of the region but earlier than normal over the central and eastern parts. Across broad portions of the southern Canadian Arctic Archipelago the 2024/25 snow season ranked as the shortest in the 27-year record.

Snow mass and snow water equivalent

Snow mass across the Arctic typically peaks each year during April, when snowfall has accumulated since the preceding autumn but before increasing temperatures during May and June lead to melt. Snow mass anomalies for April 2025 (Fig. 4) were above the 1991-2020 baseline across both the North American and Eurasian Arctic. The spatial patterns of monthly SWE (Fig. 5) illustrate how this accumulation varied regionally from just before peak (March) through to the end of the melt period (June). Higher-than-normal SWE anomalies are apparent across broad portions of both continents in March and remain through both April and May. For Eurasia, the absence of SWE over parts of northern Europe in April is consistent with the below-normal SCE during April (Fig. 2a). By June the SWE remaining across much of the rest of Eurasia is also gone, consistent with the sharp decrease in SCE during the last week of May (Fig. 2b) and June SCE anomalies (Fig. 1). For North America during June, the western portion of the Canadian Arctic Archipelago has strongly above-normal SWE while in the eastern portion and Baffin Island SWE is below normal.

Long-term changes and summary

For the Arctic as a whole, May SCE has declined 15% since 1967 (-2.5 %/dec) while June SCE has declined 50% since 1967 (-8.7 %/dec). The onset of snow melt over the recent period (2010-24) has occurred 1-2 weeks earlier during May and June compared to historical conditions (1967-81) for both the Eurasian and North American Arctic sectors (Fig. 2c). Corresponding declines in snow mass for the pan-Arctic region (total SWE over the region) are also large and significant in May and June (snow mass has declined by about 13% and 33%, respectively, since 1981), but during April, near the annual snow mass peak, the decline is small (about 3% since 1981) and not significant. This small April trend may reflect the complex regional picture of snowpack changes expected across the Arctic under climate change. While peak snowpack is expected to decrease on the western portions of both the North American and Eurasian Arctic, increases are expected over the eastern portions due to increased precipitation in the form of snowfall (Brown et al. 2017; also see essay Precipitation for a description of how pan-Arctic precipitation has increased).

In summary, peak seasonal snowpack during the 2024/25 snow season was above average across both continents. Over parts of Eurasia, snow cover extent was already below normal in April, and it remained below normal throughout the remainder of the season (Fig. 2a). Over broad portions of North America, above-normal SWE persisted for most of May, keeping snow cover extent near normal until the end of the month when it dropped even lower than values typically seen over the recent period (Fig. 2b).

Methods and data

SCE anomalies (Figs. 1 and 2) were calculated from the NOAA Climate Data Record of Northern Hemisphere SCE (Robinson et al. 2012) using a 1991-2020 baseline period. Weekly anomalies of total snow cover area over land were computed separately for the North American and Eurasian Arctic sectors (land regions at latitudes > 60° N). For Fig. 1, the data were grouped by month and standardized (each observation was differenced from the mean and divided by the standard deviation and thus unitless) using the baseline period to calculate both the mean and standard deviation.

SCD fields (Fig. 3) were calculated from the IMS Daily Northern Hemisphere Snow and Ice Analysis at 24 km (U.S. National Ice Center 2008). Anomalies in the total number of days with snow cover were computed separately for each half of the snow season: August 2024 to January 2025, referred to as “onset period,” and February 2025 to July 2025, referred to as “melt period.” IMS availability starts in 1998, so a 1998/99 to 2022/23 baseline period was used. Anomalies for each of the two seasons were presented as percent differences from the climatological number of snow-free days in the baseline period.

Snow mass and SWE data (Figs. 4 and 5) were derived from four daily frequency data sets: (1) the European Space Agency Snow Climate Change Initiative (CCI) SWE version 3.1 product, a combination of satellite passive microwave brightness temperatures and climate station snow depth observations (Luojus et al. 2024); (2) SWE output from the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2, GMAO 2015); (3) SWE output from the ERA5-Land analysis (Muñoz Sabater 2019); and (4) SWE output from the Crocus physical snowpack model (Decharme and Barbu 2024) driven by ERA5 meteorological forcing. Monthly SWE anomalies were calculated for each product relative to the 1991-2020 baseline period and the ensemble-mean SWE field was presented as percent differences from its average over the baseline period (Fig. 5). For April, snow mass was derived by aggregating the SWE field of each product across Arctic land regions (> 60° N) for both North American and Eurasian sectors. For each data product, these snow mass values were standardized relative to the baseline period and then averaged to produce an ensemble-mean time series. Greenland is not represented consistently among the SWE data products and is not added to the SCE of either Arctic sector nor is it included in calculations of snow mass.

Acknowledgments

Some data generated using modified ERA5-Land information (Muñoz Sabater 2019) downloaded from Copernicus Climate Change Service. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.

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December 4, 2025