A new study by Colorado and Utah researchers indicates desert dust kicked up by human activity blows to the mountaintops, where it accelerates snowpack melt and interferes with the life cycle of plants.

Current mountain dust levels are generally five times greater than they were prior to the mid-19th century, due in large part to increased human activity in the deserts, according to the study.

This year, 12 dust storms have painted the mountain snowpack red and advanced the retreat of snow cover, likely by more than a month across Colorado. Under climate change, warming and drying of the desert Southwest is likely to result in greater dust accumulation in the mountains.

"It is striking how different the landscape looks as result of this desert-mountain interaction," said Chris Landry, director of the Center for Snow and Avalanche Studies, Silverton, Colo., who contributed to the study along with Tom Painter, an assistant professor of geography and director of the Snow Optics Laboratory at the University of Utah. "Visitors to the mountains arriving in late June will see little remaining snow, even though snow cover was extensive and deep in April, and the snow that remains will be barely distinguishable from the surrounding soils."

The dust's impact on snowpack has consequences for water users, the study says.

"Earlier snowmelt by desert dust depletes the natural water reservoirs of mountain snowpacks and in turn affects the delivery of water to urban and agricultural areas," Painter said.

The new research, published this week by the Proceedings of the National Academy of Sciences, now shows that this early snowmelt also affects the life cycles of alpine plants and that the dust effect on these plants differs from the effect of climate warming.

In an alpine basin in southwest Colorado's San Juan Mountains, the researchers simulated dust effects on snowmelt in experimental plots to measure dust's acceleration of snowmelt on the life cycles of alpine plants. The timing of snowmelt signals to mountain plants that it is time to start growing and flowering. When dust causes early snowmelt, plant growth does not necessarily begin soon after the snow is gone. Instead, plants delay their life cycle until air temperatures have warmed consistently above freezing.

"Climate warming could therefore have a greater effect on the timing of growth and flowering," said Heidi Steltzer, a Colorado State University researcher who led the study.

The study asserts that the transfer of desert dust to the mountains has environmental consequences for alpine plants, wildlife and people. Human use of desert landscapes is linked to the life cycles of mountain plants and changes the environmental cues that determine when alpine meadows will be in bloom, possibly increasing plants' sensitivity to climate warming.

"Desert dust alters the ecology of alpine landscapes from staggered to more synchronized plant growth. With increasing dust deposition from drying and warming in the deserts under global warming, the composition of alpine meadows could change as some species increase in abundance, while others are lost, possibly forever," Steltzer said.

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