On a hot August afternoon, glaciologist Mauri Pelto picks his way across a steep slope of fragmented rock deep in Washington State’s Cascade Mountains. We’re a two-hour drive northeast of Seattle, and we’re far from any defined trails. After a day and a half of hiking, fording creeks, thrashing through tight forest, and climbing chutes, this rocky rise is all that separates us from our destination: the shrinking Columbia Glacier.

The North Cascades, the most remote portion of this mountain range, is the most glaciated region in the Lower 48. Pelto’s been making this trek every year since 1982, when he began an ambitious 50-year project to track the behavior of these glaciers. Their ice is a crucial lifeblood of this