Climate Change: Spring Snow Cover

February 14, 2020

Records from the last five decades show that on average, spring snow is disappearing earlier in the year than it did in the past, with the most rapid declines in snow-covered area occurring in June, a month when, historically, Siberia, Alaska, and northern Canada remained partially snow covered.

Two rows of small maps showing snow anomalies across the Northern Hemisphere in the late 1970s versus the late 2010s

June snow cover each year from 1975-1979 (top row) and from 2015-2019 (bottom row) compared to the 1980-2010 average. Historically, large parts of the high latitudes of the Northern Hemisphere were well covered with snow as late as June (blue areas). Four decades later, June snow cover has declined significantly. NOAA Climate.gov image, based on maps from Rutgers Snow Lab. 

Across the Northern Hemisphere, the total area covered by snow during March and April—the end of the snow season for much of the mid-latitudes—has also shrunk over time.

Explore this interactive graph: Click and drag either axis to view different parts of the graph. To squeeze or stretch the graph in either direction, hold your Shift key down, then click and drag. This graph (source data) shows average area covered by snow in the Northern Hemisphere during March and April as the difference from the 1981-2010 average.

Measuring snow extent

Beginning in the 1960s, weekly maps of snow extent in the Northern Hemisphere were prepared from satellite imagery. Now, satellites provide daily maps of snow cover for both hemispheres. Ground observations, precipitation gauges, and weather stations with pressure-sensitive “pillows” measure the amount of snow on the ground and validate the satellite maps. The graph above shows how the average extent of snow cover each March and April compares to the long-term average extent for those months. Despite occasional positive anomalies tied to natural variability in atmospheric circulation patterns, springtime Northern Hemisphere snow cover has declined. 

Impacts of snow loss

About one-third of Earth’s land surface is covered by snow for some part of the year. The bright white covering affects global conditions by reflecting solar energy away from surfaces that would otherwise absorb it. Therefore, the earlier decrease in snow cover increases the amount of sunlight absorbed by Earth, and in turn, surface temperatures. In step with earlier dates of spring budburst for many plant species, reduced spring snow cover is a sign that winter conditions are lasting for a shorter period while growing seasons are getting longer.

Close up photo of a willow ptarmigan midway between brown summer plumage and white winter plumage, nestled in a shrub with snow piled on its branches

A willow ptarmigan mid-way between its brown summer and all-white winter plumage. In the cold season, these Arctic birds burrow under an insulating layer of snow that piles up in willow thickets. Lack of snow leaves them exposed to the elements and to predators. NPS photo by Tim Rains.

At regional and local scales, water resource managers, flood forecasters, and farmers are intensely interested in knowing how much water is in snow and when it will melt. Locally, snow provides moisture to soil and plants. On a larger scale, runoff from melting snow feeds streams and rivers that supply water for agriculture and cities. Knowing when and how quickly snow will turn to water is essential for forecasting if water from snowmelt will soak into the ground or cause flooding. In managed watersheds, earlier melting of snow can change when and how much water is available for various uses.

Recognizable patterns of climate variability such as the El Niño-Southern Oscillation and the Arctic Oscillation can affect the amount of snow that falls each year. In different phases of these back-and-forth patterns, some regions receive abnormally large or small amounts of snow. On average, however, despite variations in mid-winter snowfall, Northern Hemisphere snow is melting earlier in the year.

References

Mudryk, L., Luojus, K., Helfrich, S. (2018). Terrestrial snow cover in the Arctic [in State of the Climate in 2017]. Bulletin of the American Meteorological Society, 99(8), S87–S88.

Robinson, D.A. (2018). Northern Hemisphere continental snow cover extent [in State of the Climate in 2017]. Bulletin of the American Meteorological Society, 99(8), S22–S23.

Robsinson, D. (2015). Northern Hemisphere Continental Snow Cover Extent: 2018 Update (pdf).

Rutgers University Global Snow Lab, Data History. Accessed August 29, 2011.

United States Department of Agriculture National Resources Conservation Service, SNOTEL Data Collection Network Fact Sheet. Accessed August 29, 2011.

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