Climate change causes functionally colder winters for snow cover-dependent organisms

Refugia are habitats that allow organisms to persist when the environment makes persistence impossible elsewhere. The subnivium—the interface between snowpack and ground—is an important seasonal refugium that protects diverse species from extreme winter temperatures, but its future duration is uncertain with climate change. Here, we predict that subnivium duration will decrease from 126 d (2010–2014) to 110 d (2071–2100), which we have inferred using past and future duration of frozen ground with snow cover (D_sc) derived from remotely sensed datasets and climate projections. Concomitantly, duration of frozen ground without snow cover (D_fwos) at mid-latitudes is predicted to increase from 35 d to 45 d, with notable increases in the western United States, Europe, the Tibetan Plateau and Mongolia. In most areas, increasing winter temperatures were more important than precipitation for decreasing D_sc and increasing D_fwos. Thus, counter-intuitively, warming climate will cause longer D_fwos at mid-latitudes, causing functional winter cooling for subnivium-dependent organisms.