Source: Journal of Geophysical Research: Biogeosciences
Snow plays a vital role in northern and high-elevation ecosystems. It protects soil and vegetation from extreme cold and keeps the land surface cool by reflecting incoming solar energy. In the spring, snowmelt feeds rivers and replenishes groundwater. Yet springtime snow cover across the Northern Hemisphere has decreased by about 2% each decade since the 1960s. This slow but steady loss threatens the ecology, hydrology, and economies of many historically snowed-in locales.
One such place is the Marcell Experimental Forest in north central Minnesota. Situated at the southern margin of a boreal peatland forest, the ecosystem is considered especially vulnerable to climate change. It is therefore a strategic location for the Spruce and Peatland Responses Under Changing Environments (SPRUCE) whole-ecosystem experiment, operated by the Terrestrial Ecosystem Science Scientific Focus Area of Oak Ridge National Laboratory’s Climate Change Program. This experiment subjects environments to a range of elevated temperature and carbon dioxide conditions to elicit biogeochemical responses.
SPRUCE comprises 10 open-topped octagonal enclosures in a forested bog dominated by black spruce. Each hydrologically isolated enclosure stands 40 feet wide × 26 feet tall. The enclosures feature forced-air blowers that warm plot temperatures to between 4.05°F (2.25°C) and 16.2°F (9°C) above ambient air temperatures. In each plot, digital cameras continuously monitor vegetation and watch as snow piles up and disappears throughout the seasons.
Using SPRUCE digital camera imagery from 2015 to 2021, Richardson et al. researched the relationship between warming temperatures and changes to snow duration, depth, and cover. The study evaluated the snow’s response to experimental warming treatments in the enclosures, which were superimposed on natural climate fluctuations.
The results showed that snow presence, depth, and coverage were extremely sensitive to warming, especially as temperatures crested at 8°F (4.5°C) higher than the ambient air temperature. But even warming of 3.6°F (2°C) cut in half the number of days with at least 2 inches (5 centimeters) of snow cover. The reduction in snow cover resulted in higher surface temperatures, as shrub-covered ground reflected less solar energy than snow. The plots also experienced more frequent freeze-thaw cycles.
The findings indicated that at best, climate change will have a negative but linear effect: Warmer temperatures will, of course, lead to less snow and its accompanying consequences. However, the results revealed other plausible scenarios in which snow will behave nonlinearly, with steep and immediate loss of snow cover in response to any warming beyond current conditions. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2023JG007833, 2024)
—Aaron Sidder, Science Writer