Retreat of Glaciers in Glacier National Park
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In Glacier National Park (GNP) some effects of climate change are strikingly clear. Glacier recession is underway, and many glaciers have already disappeared. The retreat of these small alpine glaciers reflects changes in recent climate as glaciers respond to altered temperature and precipitation. It has been estimated that there were approximately 150 glaciers present in 1850, around the end of the Little Ice Age. Most glaciers were still present in 1910 when the park was established. In 2010, measurements of glacier area indicate that there were 25 remaining glaciers larger than 25 acres. There is evidence of worldwide glacial glacier recession (1,2) and varied model projections suggest that certain studied GNP glaciers will disappear between 2030 (3) to 2080 (4). USGS scientists in Glacier National Park are incorporating standardized methods and emerging technologies to understand glacier-climate interactions to advance the understanding of alpine glaciers and to provide a scientific foundation for land managers.
Citations: (1) Oerlemans, 1994, Science | (2) Roe et al., 2016, Nature Geoscience | (3) Hall and Fagre, 2003, Bioscience | (4) Brown et al., 2010, Global and Plan
WHAT IS A GLACIER? A glacier is a body of snow and ice that moves. Glacier movement is detected by the presence of crevasses, cracks that form in the ice as the glacier moves. Glaciers are dynamic – changing in response to temperature and precipitation. A glacier forms when winter snowfall exceeds summer melting. It retreats when melting outpaces accumulation of new snow. A commonly accepted guideline for glacier activity and movement is that a glacier must be 0 .1 km2 (100,000 m2), or about 25 acres in size. Below this size, the ice is generally stagnant and does not move, unless it is on a steep slope.
While the glaciers that carved GNP’s majestic peaks were part of a glaciation that ended about 12,000 years ago, current glaciers are considered geologically new, having formed about ~7,000 thousand years ago. These glaciers grew substantially during the Little Ice Age (LIA) that began around 1400 A.D and reached their maximum size at the end of the LIA around A.D.1850. Their maximum sizes can be inferred from the mounds of rock and soil left behind by glaciers, known as moraines (Key, 2002), which provide a scientific baseline for comparison to current glacial extent.
WHY ARE THEY MELTING? Glaciers, by their dynamic nature, respond to climate variation and reveal the big picture of climate change. Unable to adapt, like living creatures, GNP’s relatively small alpine glaciers are good indicators of climate, the long-term average of daily weather conditions. While occasional big winters or frigid weeks may occur, the glaciers of GNP, like most worldwide, are melting as long term mean temperatures increase. Glaciers are like a visual checking account of the status of the cold part of the ecosystem. Analysis of weather data from western Montana shows an increase in summer temperatures and a reduction in the winter snowpack that forms and maintains the glaciers. Since 1900 the mean annual temperature for GNP and the surrounding region has increased 1.33°C (Pederson et al. 2010), which is 1.8 times the global mean increase. Spring and summer minimum temperatures have also increased (Pederson et al. 2010), possibly influencing earlier melt during summer. Additionally, rain, rather than snow, has been the dominant form of increased annual precipitation in the past century (Selkowitz et al. 2002). Despite variations in annual snowpack, glaciers have continued to shrink, indicating that the snowpack is not adequate to counteract the temperature changes.
In conjunction with the past century’s long-term temperature increase, ocean-driven climate trends (Pacific Decadal Oscillation) influence GNP’s regional climate. Tree-ring based climate records reveal PDO effects that have resulted in 20-30 year periods of hot, dry summers coupled with decreased winter snowpack (Pederson et al. 2004). These periods have induced rapid recession, as high as 100 m/yr between 1917-1941, and influence the current rate of recession. Even during cooler phases of the PDO cycle, glaciers have continued to shrink, albeit at a slower rate.
WHAT ARE THE EFFECTS OF LOSING GLACIERS? The loss of glaciers in GNP will have significant consequences for park ecosystems as well as impacting landscape aesthetics valued by park visitors. While winters will still deposit snow in the mountains, this seasonal snow will not function the same as glacial ice since it melts early in the summer season. Glaciers act as a “bank” of water (stored as ice) whose continual melt helps regulate stream temperatures and maintains streamflow during late summer and drought periods when other sources are depleted. Without glacial melt water, summer water temperatures will increase and may cause the local extinction of temperature sensitive aquatic species, disrupting the basis of the aquatic food chain (Pepin and Hauer 2002). Such changes in stream habitat may also have adverse effects for the threatened native bull trout (Salvelinus confluentus) and other keystone Salmonid species (Pederson et al. 2010).
What is the status of glaciers at Glacier National Park?
Other impacts of climate change in GNP:
- Mountain snowpacks hold less water and have begun to melt at least two weeks earlier in the spring. This impacts regional water supplies, wildlife, agriculture, and fire management (Mote, 2005).
- Loss of alpine meadows will put some high-elevation species at risk as habitats become greatly diminished or eliminated (Peterson, 1998).
- Mountain pine beetle infestation will likely spread further, causing areas of forests to die which will impact wildlife and stream habitat, wildfire risk, and recreation use (Western Forestry Leadership Council, 2009).
- Fire frequency and burned area may be increased as fire season expands with earlier snowpack melt out and increasing number of hot days (Westerling et al. 2006).
Large fires may greatly impact regional air quality, increase risk to people and property, and negatively affect tourism.
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