End of an (ice) age

Jackson Glacier at Glacier National Park.

Several National Parks, including Redwood, the Grand Canyon, and Glacier are named after their most iconic feature. They were established with an eye to the future to protect unique or superlative biological and geological features. In protecting a park’s namesake, whether that is old-growth redwoods or a pristine snowy peak, a whole ecosystem and its diverse components can also be protected from exploitation or excessive degradation. But at Glacier, the glaciers are disappearing.

A glacier is essentially a perennial slow-moving river of ice, formed from the long-term compaction of snow, flowing slowly down a mountainside. The weight of the glacier gradually propels it downslope, while its mass is renewed by new annual snowfall. Technically “official” glaciers have a minimum size of 25 acres. Glaciers are fantastic geologic agents: they carved out Puget Sound in Washington and the stunning Yosemite Valley in the Sierra Nevada for example.  

About a century and a half ago, there were estimated to be nearly 150 glaciers present in Glacier National Park. But by 2015, that number had declined to only 26. The trends at Glacier in northwest Montana track patterns elsewhere: glaciers are shrinking and snowpack is declining. Data from several benchmark glaciers in the northwestern US show mass loss of glacial ice over the last four decades. In the uneven distribution of climate change impacts across the globe, high latitude (particularly Arctic) and alpine regions appear to be warming to a greater degree than other regions.

Left: Map of some of the named glaciers in Glacier National Park and the adjacent Flathead National Forest. Right: Change in the area occupied by Chaney Glacier between 1966 and 2015. Map and figure from USGS.

Change in the Clements Glacier at Glacier NP.
Images from USGS Repeat Photography Gallery.

Glacial growth and retreat is a natural geologic cycle. Currently, the Earth is in an interglacial period, at the warm peak of an alternating cycle of cooling and warming that has alternated periodically over the last 2.6 million years. About 10,000 years ago the last major glacial period ended and the glaciers that covered much of the land in the northern hemisphere melted and retreated, sending sea-levels hundreds of feet higher.

So is the loss of glaciers today part of a normal cycle? Probably not, because today’s rate of atmospheric CO₂ increase (due to human production of greenhouse gases) is unprecedented in recent geologic history. A global increase of 1 to 2°C that may have occurred over centuries or millennia in the past is now on our doorstep in a matter of decades. And because large-scale biological and geological processes can temporally lag the events that drive them, we have probably locked in additional warming for years even were we to cease all additional greenhouse gas emissions tomorrow.

The glaciers and snowfields of Glacier National Park provide the source waters for rivers that flow to the Pacific Ocean, the Gulf of Mexico, and Hudson Bay. The park straddles the continental divide, the cross-roads of the watersheds that collectively cover most of North America. Glacial melt is a particularly important source of water to mountain ecosystems in the late summer when the non-glacial snowfields have already melted.

Long-term change in snowpack throughout the western United States. Red circles indicate areas
 with snow decline. Image from EPA.

Change in the size of the Grinnell Glacier at Glacier NP.
Images from USGS Repeat Photography Gallery.

Driving through the park this month, I saw the lingering snowfields of the higher peaks, with perhaps a glacier or two tucked into the mountains. The melting water fed rapidly flowing streams, waterfalls, and lakes. The only glacier I definitively saw was Jackson Glacier from a viewpoint along the “Going-to-the-Sun” road. Views of other glaciers required more committed backcountry hikes that I didn’t have the time for on the trip.

By emitting so many greenhouse gases into the atmosphere in such a short time, we may be ushering in an era of unprecedented warming across the planet that may affect everything from species distributions to ocean acidification and sea-level rise. The threats to glaciers are a global phenomenon, requiring global action to address. More locally, at Glacier NP and other alpine ecosystems, it remains to be seen how the loss of glaciers will affect ecosystem processes over the coming centuries.   

References

Glacier National Park website

National Snow and Ice Data Center. 2017. All About Glaciers.

US Geological Survey. Retreat of Glaciers in Glacier National Park. 

US Geological Survey. Repeat Photography Gallery.

Snowfield and Bird Woman Falls as seen from the
"Going-to-the-Sun" road at Glacier National Park.