Changes will affect regional water supplies
Long-term data from a monitoring station high in the Colorado Rockies is showing remarkable signs of climate change, according to new findings published a special issue of the journal Plant Ecology and Diversity.
The research, conducted west of Boulder, along Niwot Ridge and Green Lakes Valley, shows that the only glacier in the area has been thinning by about three feet per year during the past 15 years.
And careful surveys of alpine vegetation shows that, at one location, the plant community has changed dramatically, with a significant increase in alpine shrubs above treeline in recent decades, according to said ecologist Mark Williams, of the University of Colorado Boulder Institute of Arctic and Alpine Research.
“Places that once harbored magnificent wildflowers are being replaced by shrubs, particularly willows,” Williams said in a press release from the National Science foundation, which helped fund the new study.“The areas dominated by shrubs are increasing because of a positive feedback – patches of these shrubs act as snow fences, causing the accumulation of more water and nutrients and the growth of more shrubs,” he said, describing conditions at the study site, known as the Saddle, about 11,600 feet high and 3.5 miles from the Continental Divide.
The study area is in the National Science Foundation Niwot Ridge Long-Term Ecological Research site. It encompasses thousands of acres of alpine tundra, subalpine forest, talus slopes, glacial lakes and wetlands at the top of the Continental Divide in the Rocky Mountains. The site includes Green Lakes Valley and the University of Colorado Boulder’s Mountain Research Station.
The researchers looked at changes in the cryosphere — places that are frozen for at least one month of the year — at the Niwot Ridge site, going back to the 1960s. The decline of ice is linked with rising temperatures each summer and autumn in recent years, Williams said.
Previous research at Niwot Ridge looked closely at temperature changes over time. In 2012, Williams said a small increase in temperature can cause the climate to cross a “threshold” that triggers earlier and more intense snow melting.
As snowline moves up due to warming temperatures, so will parts of alpine tundra in the West, Williams said in 2012. “The tundra may be able to function reasonably well for several decades — it will be awhile before warming climate change pushes the tundra off the tops of mountains. But that is the direction we are heading.”
Steady ice decline
“Long-term research at Niwot Ridge offers a rare opportunity to document the continuous, progressive effects of climate change on high alpine ecosystems, from ice to nutrients to plant and animal communities,” said Saran Twombly, director of long-term research in the NSF’s division of environmental biology.
The findings show a steady decline in ice, including glaciers, permafrost, subsurface ice, lake ice, in the Niwot Ridge area during the past 30 years,” Twombly said.
The ice melt is especially evident on the area’s only true glacier.
“Things don’t look good up there,” said Williams. “While there was no significant change in the volume of the Arikaree Glacier from 1955 to 2000, severe drought in Colorado beginning in 2000 caused it to thin considerably. Even after heavy snows in 2011 and again in 2014, we believe the glacier is on course to disappear in about 20 years.”
Using ground-penetrating radar, seismometers and other measurements, the scientists documented ice loss in three rock glaciers and in subsurface areas of permafrost — frozen soil containing ice crystals.
Impacts to water supplies
The steady melting has also resulted in changes in the water cycle, with potentially serious implications for thirsty communities at the base of the Rockies. For now, there is an increased discharge of water from Green Lakes Valley in late summer and fall after the annual snowpack has melted.
The increases appear to be due to higher summer temperatures melting “fossil” ice present for centuries or millennia in glaciers, rock glaciers, permafrost and other subsurface ice.
“We are taking the capital out of our hydrological bank account and melting that stored ice,” Williams said. “While some may think this late summer water discharge is the new normal, it is really a limited resource that will eventually disappear.”
For glaciers like Arikaree and the plants their meltwaters sustain, the time left may be counted in years, not centuries nor millennia.
In addition to Williams, co-authors of a paper on the changing cryosphere published in the special issue include Nel Caine of the University of Colorado Boulder, Matthew Leopold of the University of West Australia, and Gabriel Lewis and David Dethier of Williams College.