In a California forest torched by wildfire last summer, researcher Anne Nolin examines a handful of the season’s remaining snow, now darkened by black specks from the burned trees above.

Spring heat waves had already melted much of the year’s limited snowfall across California and parts of the West when Nolin visited in early April. But she and her colleague are studying another factor that might’ve made the snow vanish faster in the central Sierra Nevada — the scorched trees, which no longer provide much shade and are shedding flecks of carbon.