GLACIER AREA AND VOLUME CHANGE IN GLACIER NATIONAL PARK

Glacier National Park, in northwestern Montana, is a unique and awe-inspiring national treasure that is often used by the media and public-at-large as a window into the effects of climate change. Like glaciers elsewhere, those in the Park are sensitive to changes in climate. Also, they are frozen reservoirs of water that release water from storage during late summer, after the previous winter’s snowpack has melted away. An updated inventory of glaciers and perennial snowfields (G&PS) in the Park, along with an assessment of their change over time, is essential to understanding the role that glaciers are playing in the environment of this National Park. Using nine inventories between 1966 and 2015, we assessed G&PS area and volume change. The 1966 inventory, based on U.S. Geological Survey 1:24,000 maps, shows 604 G&PS with a total area of 40.52 ± 3.6 km², including 39 named glaciers with a total area of 20.39 ± 1.8 km². Named glaciers make up only 6% of the 1966 G&PS, but represent nearly 50% of the total area. The most recent inventory, based on 2015 Worldview satellite imagery, shows a loss of 345 G&PS with a total area loss, including shrinkage of existing G&PS, of 19.79 ± 1.45 km² (49%). Estimates of volume change were made for nine of the largest glaciers in the Park by differencing historic and recent lidar-sourced digital elevation models. Results show an ice volume loss of 0.142 ± 0.02 km³ (-16.3 ± 2.5m averaged over each glacier area).

G&PS have been receding in the Park due to warming mean annual air temperatures rather than changes in precipitation, which has not changed significantly. Since 1900 air temperatures, in Glacier National Park have warmed by +1.3 C°, compared to +0.9 C° globally. Spatial variations in shrinkage rates are related to elevation and aspect. G&PS at low elevation retreat faster than those at high elevation, and those facing south to southwest retreat faster than those facing north to northeast. If air temperatures continue to increase, most, if not all of the glaciers in Glacier National Park will disappear by the end of the century.