By Michon Scott
Most of the planet’s seasonal snow cover occurs in the Northern Hemisphere, although isolated areas of snow cover exist south of Earth’s equator and outside of Antarctica. Since continuous satellite records began in the early 1970s, Northern Hemisphere snow cover has declined overall. The largest losses have occurred in spring and summer, outweighing modest autumn and winter gains. Though the overall trend is significant, it does not capture all the details, such as how snow cover changes vary by location and season.
Snow cover 101
Most seasonal snowfall occurs in the Northern Hemisphere (everything north of the equator), but many snow-cover surveys focus on the Arctic Circle (everything north of 66.5°N) or on high northern latitudes (north of 60°N). Considerable quantities of Northern Hemisphere snow fall outside of the Arctic Circle, though the regions—and their snow totals—overlap. In addition, planet-wide changes that affect the Arctic often affect Northern Hemisphere snow totals and trends as well.
Across the Northern Hemisphere, snow’s seasonal advance and retreat is one of the most dramatic changes on Earth’s surface. In winter, snow can cover up to 46 million square kilometers (about 18 million square miles). That is nearly five times the area of the United States, including Alaska. In summer, snow cover can drop as low as 2 million square kilometers (about 780,000 square miles). In many locations, snow comes and goes multiple times between autumn and spring.
In simplest terms, higher temperatures mean less snow, but the relationship is often complex. In cold regions, higher temperatures can increase snowfall by boosting atmospheric moisture. For instance, the Arctic Report Card 2025, covering conditions from October 2024 through September 2025, reported both the highest temperatures and some of the highest precipitation amounts on record over that period. How long snow persists on the ground depends on multiple factors, including sunny (as opposed to cloudy) conditions, and weather events such as wind or rain, which also can diminish snow cover. In general, though, higher temperatures correlate with snow retreat, and snow melt can then become a self-reinforcing cycle.
Even without melting snow, rising temperatures can change snow cover characteristics in ways that promote retreat and continued warming. A freshly fallen snow crystal has many facets, each of which has the potential to bounce sunlight back into the atmosphere. In fact, fresh crystals make pristine snow one of the brightest natural surfaces on Earth. Such snow reflects up to 90 percent of the sunlight that reaches it. Fresh snow’s reflectiveness—its albedo—helps keep the planet cool, but albedo drops slightly as snow warms. As the snowpack heats up, snow crystals lose their sharp edges and many light-reflecting facets. As the snow grows warmer, the crystals begin clumping together. If the snow surface acquires a layer of soot or dust, it darkens even more. The snow remains brighter than other surfaces such as rock or soil but nevertheless loses some of its reflectiveness.
In short, snow can transform at the microscopic scale (snow crystal changes) and the macroscopic scale (advance and retreat of snow cover over millions of square kilometers). Increasing snow cover, on average, can reflect more sunlight back into space and help cool the planet. Decreasing snow cover can lead to more sunlight absorption and help warm the planet.
If Northern Hemisphere snow cover keeps reaching the same general highs and lows year after year, that reinforces climate stability. If snow cover instead changes over the long term, the change nudges global climate. Snow loss amplifies warming, but it operates alongside other major drivers such as land-use changes and greenhouse gas emissions.
Greenhouse gases and global temperatures
Snow can only fall and persist on the ground under certain conditions, including sufficiently cold temperatures. Greenhouse gas emissions pose problems for snow cover by boosting global temperatures. Measurements of atmospheric carbon dioxide, which began at Mauna Loa in 1958, have shown a steady increase since that time. The Bulletin of the American Meteorological Society (BAMS) reported in its State of the Climate in 2024 that atmospheric concentrations of the three main greenhouse gases—carbon dioxide, methane, and nitrous oxide—all matched the highest levels on record or set new records. Meanwhile, temperatures continued to climb. BAMS reported that 2024 was the second consecutive year with record-high global temperatures. The 10 years leading up to 2024 were the 10 warmest years in the instrumental record.
BAMS State of the Climate is a peer-reviewed report published several months after the year in question ends. Observations continue, however, with even more timely statistics. As of January 2026, NOAA’s Global Monitoring Laboratory reported continued increases in greenhouse gas concentrations. Meanwhile, NOAA’s National Centers for Environmental Information reported that 2025 was the third-warmest year on record
Warming rates intensify in the polar regions, especially in the Arctic (north of 60°N), in a phenomenon known as Arctic amplification. The Arctic Report Card 2025 reports that the Arctic region has warmed about twice as fast as the global average since 2006, and that the October 2024 through September 2025 “water year” had the highest surface air temperatures across the Arctic since records began in 1900.
Understanding snow cover change in relation to climate takes more than a long record of greenhouse gas emissions and temperature. It also requires a long record in snow cover itself.
A long-term database
NSIDC offers a wealth of snow data products distributed through the NASA Distributed Active Archive Center and the National Oceanic and Atmospheric Administration (NOAA) NOAA@NSIDC. Many of these data sets span decades. NSIDC also operates Snow Today, with in-depth information on snow cover in the western United States and other locations. Meanwhile, a long-term archive of Northern Hemisphere snow conditions is available from Rutgers University Global Snow Lab. (NOAA@NSIDC distributes a Rutgers snow product.)
Rutgers offers snow statistics and visualizations extending from the 1960s to present, derived from snow cover extent maps produced by NOAA. The database has been employed in myriad peer-reviewed studies, and in reports from BAMS State of the Climate, NOAA Arctic Report Card, and the Intergovernmental Panel on Climate Change.
The decades-long database maintained by Rutgers reveals overall trends, but above all, it reveals a complicated situation, such as how snow cover varies by season and location.
Location and landscape
Location drives where snow falls and sticks in the first place, and unsurprisingly, location and landscape affect where snow cover lasts the longest.
Mountainous regions often make hospitable snow environments—so much so that glaciers often form in those regions, thanks to long-lasting snow cover. Still, mountain snowpack has shown declines. A 2022 study examined mountain snowpack data spanning 1982 to 2020. The authors found overall declines in global mountain snowpack, but with exceptions. The general downward trend was 3.6 ± 2.7 percent in extent, with a loss of 15.1 ± 11.6 days in snow cover duration. The authors identified the greatest declines in winter, but also found a positive trend in spring, particularly in the High Mountain Asia region.
A 2023 study examined snow cover changes across the Northern Hemisphere from 1967 to 2021. The authors found rapid declines in the Arctic and at lower latitudes, but also found snow cover increases in multiple locations, especially in eastern Canada. Another 2023 study examined snow cover changes in the Arctic. The authors found the strongest decrease in spring. This strong springtime decline fits with other findings about snow cover changes across the Northern Hemisphere.
Rising greenhouse gas concentrations and rising temperatures naturally have an impact on snow cover. A 2024 study examined evidence of human influence on snow loss. The authors investigated 169 major Northern Hemisphere river basins over the period of 1981 to 2020. They identified clear declining trends in 82 of those basins and further linked the trends in 31 of those river basins to human activities. The authors noted, though, that the changes were nuanced, writing, “[T]he relationship between forcing and snowpack is not unidirectional: warming, for example, can enhance cold-season precipitation and snowfall extremes, potentially offsetting warming-driven losses.”
Snow trends do not vary solely by location. Long-term data records also show variations by season.
Changing seasons
Because the Arctic comprises just a portion of the Northern Hemisphere, trends across these regions are not identical, although there is significant overlap.
The 2023 study on Arctic snow cover found sharp declines in spring, so much so that the authors recommended strengthening the Intergovernmental Panel on Climate Change (IPCC) confidence level for Arctic springtime snow loss from “high confidence” to “very high confidence.” (The IPCC has already assigned “very high confidence” to springtime snow cover losses across the Northern Hemisphere.)
The Arctic Report Card 2025, released on December 16, 2025, described terrestrial snow cover conditions over the “water year” beginning October 1, 2024, and ending September 30, 2025. The authors reported above-average snowpack through May 2025, then a rapid decline in snow cover in June. June 2025 snow cover extent, the authors noted, was only half what it was six decades earlier. These mixed results—higher snow cover extent in winter and much lower snow cover extent in spring into summer—continue the pattern reported in previous report cards.
Meanwhile, data available from the Rutgers University Global Snow Lab reinforces findings of strong snow cover reductions in spring across the Northern Hemisphere. The data extend back to November 1966, and the unbroken monthly record extends back to 1972.
Global Snow Lab’s monthly snow extent observations from January 1972 through December 2025 show reductions, but not in all months. Northern Hemisphere snow cover trends upward from September through January, and downward from February through August. The graphs below show monthly trends from January 1972 through December 2025. Most monthly trends over that period are statistically significant—meaning they are unlikely to arise from random variability—whether they are upward or downward. Only the monthly trends for January, February, and September lack statistical significance. To learn how statistical significance is calculated—whether for sea ice or snow—see What is the value of sea ice time series data?
Sharp declines for seasonal snow cover begin in the Northern Hemisphere spring. Gains begin in autumn. Overall, the declines outweigh the gains.
Rain on the snow parade
Faster melt of snow is not the only consequence of increasing warmth. Higher temperatures also correlate with more precipitation falling as rain. A 2023 study using reanalysis data—a combination of observations and weather forecasts—found an increase in Arctic rainy days from 1980 to 2016. The study also detected lengthening of the rainy season, which the authors tied to more days with temperatures above freezing.
More precipitation falling as rain means many of the same problems as premature snow melt, and the problems may be intensified. In these cases, the cooling benefits of reflective snow cover are reduced or do not occur at all.
In some cases, falling rain lands not on bare ground but on snow. That rain might subsequently freeze and form a hard crust. NSIDC leads the Arctic Rain on Snow Study (AROSS), which examines the impacts of such events. As part AROSS, NSIDC graduate student Zaria Cast led a 2025 study identifying locations and seasons of increasing rainfall across the Arctic from 1979 to 2023. Cast and coauthors detected the biggest transitions from snow to rain during summer over land—except for the Greenland Ice Sheet. The Greenland Ice Sheet typically receives little rain, but rain events have increased in recent years.
What it means and why it matters
When Arctic precipitation falls as rain and lands on snow, the rain-on-snow events pose particular challenges for Arctic inhabitants. An icy crust over a snow surface can complicate travel, increase avalanche risks by forming slippery ice lenses within snow layers, and prevent grazing animals from feeding by forming an impenetrable barrier of ice.
When high-latitude Northern Hemisphere precipitation falls as rain on bare ground, or falls as snow that melts quickly, it reduces the region’s ability to reflect sunlight. The Arctic is an ocean basin largely surrounded by land. As Northern Hemisphere snow cover retreats earlier in spring, the land areas around the Arctic Ocean absorb more sunlight, prompting more melt and continuing the cycle. Warming land areas around the Arctic Ocean contribute to sea ice decline, which further boosts warming conditions in the region. At present, sea ice decline might be the leading contributor to Arctic amplification.
Together, snow and ice act like a planetary air conditioner. Reduce that cooling influence, and additional warming follows.
Effects of snow loss are not limited to temperature and reflectivity. In places where snowpack has historically—even prehistorically—been a recurring feature of the landscape, plant and animal species have typically adapted to seasonal or perennial snow cover. Hare, fox, and ptarmigan species, for instance, have evolved the ability to blend in with snowy landscapes, and unusual snow declines can leave these animals conspicuous to sharp-eyed predators. Plants that evolved according to a longstanding cycle of snowmelt and runoff face an uncertain future as needed water resources dwindle. Human populations can wind up high and dry, too. Estimates vary, but recent studies indicate that more than a billion people worldwide rely on snowmelt for farming and drinking, and some 2 billion people are at risk of decreased snow supply of vital water resources.
Snow cover losses may worsen in the future. The 2024 study on human influence on snow reached a sobering conclusion, namely that snow’s sensitivity to rising temperatures may grow in the future, with modest amounts of warming contributing to greater snow declines.
Northern Hemisphere snow cover shows important variations by season and location, but decades of observations point to a clear overall pattern: snow cover is declining, especially during the spring melt season. That shift has implications for ecosystems, water resources, and the climate system itself.
References
Boisvert, L.N., M.A. Webster, C.L. Parker, and R.M. Forbes. 2023. Rainy days in the Arctic. Journal of Climate 36(19): 6855-6878. https://doi.org/10.1175/JCLI-D-22-0428.1.
Cast, Z.I., M.C. Serreze, E. Cassano, and A.P. Barrett. 2025. Seasonal characteristics and trends in precipitation partitioning in the Arctic. EGUsphere https://doi.org/10.5194/egusphere-2025-3482.
Derksen, C., and L. Mudryk. 2023. Assessment of Arctic seasonal snow cover rates of change. The Cryosphere 17(4): 1431-1443. https://doi.org/10.5194/tc-17-1431-2023.
Druckenmiller, M.L., R.L. Thoman, and T.A. Moon, Editors. 2025. Arctic Report Card 2025. https://doi.org/10.25923/nrzf-j897.
Dunn, R.J.H., J. Blannin, K.M. Willett, N. Gobron, G.A. Morris, M. Ades, R. Adler, M. Alexe, R.P. Allan, J. Anderson, O. Anneville, … C.-Z. Zou. 2025. Global climate. Bulletin of the American Meteorological Society 106(8): S11-S172. https://doi.org/10.1175/bams-d-25-0102.1.
Gottlieb, A.R., and J.S. Mankin. 2024. Evidence of human influence on Northern Hemisphere snow loss. Nature 625: 293-300. https://doi.org/10.1038/s41586-023-06794-y.
Jia, Y., R. Lund, J. Kong, J. Dyer, J. Woody, and J.S. Marron. 2023. Trends in Northern Hemispheric snow presence. Journal of Hydrometeorology 24(6): 1137-1154. https://doi.org/10.1175/jhm-d-22-0182.1.
Lindsey, R. 2011. Greenland Ice Sheet getting darker. Climate.gov.
Mankin, J.S., D. Viviroli, D. Singh, A.Y. Hoekstra, and N.S. Diffenbaugh. 2015. The potential for snow to supply human water demand in the present and future. Environmental Research Letters 10: 114016. https://doi.org/10.1088/1748-9326/10/11/114016.
NOAA Global Monitoring Laboratory. Trends in CO2, CH4, N2O, SF6. Accessed November 10, 2025.
Notarnicola, C. 2022. Overall negative trends for snow cover extent and duration in global mountain regions over 1982-2020. Scientific Reports 12: 13731. https://doi.org/10.1038/s41598-022-16743-w.
Sturm, M., M.A. Goldstein, and C. Parr. 2017. Water and life from snow: A trillion dollar science question. Water Resources Research 53:3534-3544. https://doi.org/10.1002/2017WR020840