Alaska's Shrinking Glaciers

Alaska is one of the most heavily glaciated areas in the world outside of the polar regions. Approximately 23,000 square miles of the state are covered in glaciers—an area nearly the size of West Virginia. Glaciers have shaped much of Alaska’s landscape and continue to influence its lands, waters, and ecosystems. Because of their importance, National Park Service scientists measure glacier change. They have found that glaciers are shrinking in area and volume across the state. 

The effects of climate change are felt more in high-latitude regions like Alaska than in most other regions of the world. Over a 50-year interval—between the 1950s and early 2000s—glaciers within Alaska national parks shrank by 8%. From 1985 to 2020, glacier-covered area in Alaska decreased by 13%, indicating that the rate of glacier loss accelerated in recent decades. As our climate continues to warm, glacial retreat will likely accelerate, profoundly impacting the landscape of Alaska and our parks for generations to come. 

Glaciers are formed by centuries of snow accumulation. As the snow compacts, air is squeezed out and glacial ice forms. These “rivers of ice” slowly flow downslope. Geographic location, temperature, and precipitation are the primary components of how glaciers form and why they change. To form, the temperature needs to be cold enough that snow accumulates without melting. Glaciers around the world were generally much larger during the last ice age, a period that peaked about 23,000 years ago (Last Glacial Maximum) and ended more than 10,000 years ago. Since the end of the Little Ice Age (about 1300-1850 CE), glaciers have retreated to roughly their current locations. 

Alaska’s high-latitude and high-elevation mountain ranges have historically had average annual temperatures cold enough to sustain glaciers. However, global air temperatures are increasing, and Alaska and other high-latitude regions are warming faster than the average global rate. Average annual air temperatures across Alaska have increased significantly since 1950. As temperatures warm, the elevation at which snow and ice remain frozen is getting higher, with more rain and less snow at lower elevations. With warming spring and autumn seasons, snow melts earlier and arrives later. These factors collectively impact a glacier at all elevations, from summit to the terminus, but the effects are most visible at the lowest elevations, where most glacier termini are rapidly retreating. 

Glaciers erode and transport huge amounts of rocky debris as they grind their way through mountain slopes. Lateral moraines are crested piles of glacially transported rock and debris deposited along the glacier edges as it flows. Medial moraines form where two glaciers flow together. They consist of rock that has fallen from the mountain walls onto the glacier or exposed rock entrained into the ice. Terminal moraines are the rock that is left at the toe of a glacier as the ice melts and the end of the glacier retreats. 

Glaciers have interested scientists for hundreds of years. Alaska Natives sometimes used glaciers as travel routes and incorporated them into oral histories. Because they are such important components of the landscape, we are interested in how they change over time. We use several methods to measure glaciers.

Glaciers are more than an attractive ornament in Alaska’s landscape: they comprise a significant portion of the landcover in our nine glaciated national parks and their presence exerts substantial influence over physical and ecological processes on much of the adjacent, non-glacierized landscape. The National Park Service cannot manage glacier shrinkage, in the specific sense that the drivers of glacier change are global in scope. But what we learn about glacier change has direct implications for how we manage the parks, largely because glaciers are such an integral part of these landscapes. 

 As glaciers shrink and change, we are already seeing impacts on downstream hydrology, tourism and recreational opportunities, public safety, vegetation patterns, and wildlife behavior. Even the land itself has changed. As glaciers recede, the Earth’s crust rises as the weight of the glacier is removed—this is called post-glacial rebound. Post-glacial rebound occurs slowly (at rates sometimes exceeding an inch per year) and can continue for thousands of years after the ice has melted. Meanwhile, unstable hillslopes newly exposed by glacier retreat are made vulnerable to landslides.  

Even at the global scale, Alaska’s glacier changes matter. Meltwater from Alaska’s glaciers is estimated to comprise about one quarter of the total global glacier melt contribution to contemporary sea level rise. The glacier-derived freshwater inputs to the oceans provide nutrients that support algal blooms and can change ocean circulation patterns as the freshwater lens pushes warmer, more dense saltwater deeper. 

For all these reasons, monitoring, understanding, and predicting glacier change is a critical ongoing activity for National Park Service scientists. The NPS Inventory & Monitoring Program has primary responsibility for measuring glacier changes of the sort described here. It conducts regular measurements of glacier change using a combination of direct field measurements and remote sensing (the use of data from satellites and aircraft). We also work with academic partners to predict the scope of potential future glacier change. Preliminary results suggest that by the year 2100, glacier cover in Alaska’s national parks will be about half of what it is now, with the important caveat that the rate of future change is critically dependent on the choices our society makes today.  

Primary sources used to create this story include:

Loso, M., A. Arendt, C. Larsen, J. Rich, and N. Murphy. 2014.  Alaskan national park glaciers - status and trends: Final report . Natural Resource Technical Report NPS/AKRO/NRTR—2014/922. National Park Service, Fort Collins, Colorado.  

Roberts-Pierel, B. M., P. B. Kirchner, J. B. Kilbride, and R. E. Kennedy. 2022.  Changes over the last 35 years in Alaska’s glaciated landscape: A novel deep learning approach to mapping glaciers at fine temporal granularity . Remote Sensing 14(18): 4582.  

 Secondary sources include: 

Black, T. and D. Kurtz. 2022.  Maritime glacier retreat and terminus area change in Kenai Fjords National Park, Alaska, between 1984 and 2021 . Journal of Glaciology 69(274): 1-15. 

Brinkerhoff, D., M. Truffer, and A. Aschwanden. 2017.  Sediment transport drives tidewater glacier periodicity . Nature Communications 8(1): article 90.

Cogley, J. G., R. Hock, L. A. Rasmussen, A. A. Arendt, A. Bauder, R. J. Braithwaite, P. Jansson, G. Kaser, M. Möller, L. Nicholson, and M. Zemp. 2011.  Glossary of Glacier Mass Balance and Related Terms , IHP-VII Technical Documents in Hydrology No. 86, IACS Contribution No. 2, UNESCO-IHP, Paris. 

Gardner, A. S., M. A. Fahnestock, and T. A. Scambos. ITS_LIVE Regional Glacier and Ice Sheet Surface Velocities. Available at:  doi:10.5067/6II6VW8LLWJ7  (accessed 1 October 2020; data archived at National Snow and Ice Data Center, October 1, 2020).

Giffen, B., D. Hall, and J. Chien. 2014. Chapter 11:  Alaska: Glaciers of Kenai Fjords National Park and Katmai National Park and Preserve,  pp. 241-261 In J. Kargel, G. Leonard, M. Bishop, A. Kääb, and B. Raup (eds). Global Land Ice Measurements from Space. Springer Praxis Books. Springer, Berlin, Heidelberg. 

Kaluzienski, L., J. Amundson, J. Womble, A. K. Bliss, and L. Pearson. 2023.  Impacts of tidewater glacier advance on iceberg habitat . Annals of Glaciology pp.1-11.

Kaufman, D. S., N. E. Young, J. P. Briner, and W. F. Manley. 2011.  Alaska Palaeo-Glacier Atlas (Version 2) . Developments in Quaternary Sciences 15: 427-445.

Kim, Y., J. Kimball, J. Du, C. Schaaf, and P. Kirchner. 2018.  Quantifying the effects of freeze-thaw transitions and snowpack melt on land surface albedo and energy exchange over Alaska and Western Canada . Environmental Research Letters 13: 075009. 

Larsen, C. F., E. Burgess, A. A. Arendt, S. O’Neel, A. J. Johnson, and C. Kienholz. 2015.  Surface melt dominates Alaska glacier mass balance . Geophysical Research Letters 42(14): 5902–5908.

Larsen, C. F., R. J. Motyka, A. A. Arendt, K. A. Echelmeyer, and P. E. Geissler. 2007. Glacier changes in Southeast Alaska and northwest British Columbia and contribution to sea level rise. Journal of Geophysical Research 112(F1): F01007.  Loso, M. G., C. F. Larsen, B. S. Tober, M. Christoffersen, M. Fahnestock, J. W. Holt, and M. Truffer. 2021.  Quo vadis, Alsek? Climate-driven glacier retreat may change the course of a major river outlet in southern Alaska . Geomorphology 384: 107701.

Loso, M. G., A. Arendt, C. Larsen, N. Murphy, and J. Rich. 2013.  Status and trends of Alaska national park glaciers: What do they tell us about climate change?  Alaska Park Science 12(2): 19-25. 

McNabb, R. W. and R. Hock. 2014.  Alaska tidewater glacier terminus positions, 1948-2012 . Journal of Geophysical Research: Earth Surface 119(2): 153-67.

Pan, C., P. Kirchner, J. Kimball, Y. Kim, and J. Du. 2018.  Rain-on-snow events in Alaska, and their frequency and distribution from satellite observations . Environmental Research Letters 13: 075004. 

Tober, B. S., J. W. Holt, M. S. Christoffersen, M. Truffer, C. F. Larsen, D. J. Brinkerhoff, and S. A. Mooneyham. 2023.  Comprehensive radar mapping of Malaspina Glacier (Sít’ Tlein), Alaska—the world’s largest piedmont glacier—reveals potential for instability . Journal of Geophysical Research: Earth Surface 128(3): e2022JF006898.

Womble, J. N., P. J. Williams, R. W. McNabb, A. Prakash, R. Gens, B. S. Sedinger, and C. R. Acevedo. 2021.  Harbor seals as sentinels of ice dynamics in tidewater glacier fjords . Frontiers in Marine Science 8: 634541.