From the snow-dusted ridgelines of the Catskills to the rugged summits of the Rocky Mountains, Sierra Nevada and Cascades, winter is slowly disappearing. And snow is receding with it.

We know humans are altering the climate. Temperatures in south-central Colorado have risen two degrees Fahrenheit on average since 1988. In California’s Lake Tahoe region, home to more than a dozen ski areas, warmer temperatures since 1970 have pushed the snow line uphill 1,200 to 1,500 feet. Winter season lengths are projected to decline at ski areas across the United States, in some locations by more than 50 percent by 2050 and by 80 percent by 2090 if greenhouse gas emissions continue at their current rate, according to a 2017 study. Only about half of the 103 ski resorts in the Northeast will be able to maintain an economically viable ski season by midcentury, another study found in 2012.