Climate change is messing with the seasons in a Rocky Mountain forest

Since 1968, researchers have gathered air samples from near the summit of Colorado’s Niwot Ridge in the Rocky Mountains, and tracked carbon dioxide levels in the conifer forest below. They’ve amassed the world’s third-longest record of atmospheric carbon dioxide, and that record provides a troubling glimpse of how forests respond to a warming world. The biological start of spring in the Niwot forest was about 10.5 days earlier in 2002 than it was in 1980, and cool fall temperatures are coming later. “It’s shocking,” said researcher Pieter Tans. “It was more than I expected.” That bodes ill for the Northern Hemisphere’s mountain forests: An earlier spring usually means a hotter, drier summer, with water-stressed trees that are easier prey for insects, disease, and forest fires. Trees hurting for water also photosynthesize more slowly, pulling less carbon dioxide from the air than a healthy forest would.