Scientists doing climate research on Niwot Ridge in the mountains west of Boulder found a surprising trend: At 10,000 feet of elevation, conditions have become warmer and drier over the past few decades, but at 12,700 feet, conditions are actually cooler and wetter.
“We know the western U.S. has been warming. It’s concentrated in the spring at the forest site. But we see just the opposite at the high elevation site above the tree line,” said Mark Williams, the study’s principal investigator.
Williams said snowfall at the higher station has doubled in the last 60 years — the period for which scientists have been collecting precipitation and temperature data at Niwot Ridge. Temperatures, too, have dropped significantly during the winter months, from November through March.
The scientists attribute the cooling to a small-scale climatic balancing act. The warmer temperatures at lower elevations cause snow to evaporate. This moisture in the air is then drawn upward and to the west. When it reaches the continental divide, the moisture falls as snow.
The additional snowfall boosts the albedo effect, which reflects sunlight back into the atmosphere and causes the localized cooling. The higher station is above treeline, so the white snow reflects more sunlight than the tree-covered location of the lower station.
The findings are particularly surprising since the two research stations are only five miles apart, said Williams, who is a fellow at the Institute of Arctic and Alpine Research and a geography professor at the University of Colorado.