EXPLAINED IN 70 SECONDS
WHAT IT IS
Since satellites started collecting data in the early 1970s, there has been a trend toward less summer snow cover in the Northern Hemisphere. While most people might think of the summer as beach time, snow still covers a wide swath of land in the northern stretches of the globe. But over the past 50 years, that snow cover has been receding from a peak of 10.28 million square miles set in 1979 to a record low 3.69 million square miles set in 2013. Spring snow cover is also on the decline and this reduced snow cover is consistent with rising temperatures driving increased snowmelt.
WHY IT'S IMPORTANT
Like ice, snow has a high reflectivity, so a shorter snow season increases the amount of sunlight absorbed by the Earth’s surface. The earlier spring snowmelt thus exhibits a feedback relationship with rising temperatures, driving further temperature increases. Snowmelt also affects water supplies, and decreasing snowpack may decrease water supplies in areas around the world that rely on spring runoff. Although fall and winter snow cover has remained fairly consistent over the past 40 years, spring and summer snow cover is typically more important in influencing water supplies.