Glacial melting

DEFINITION: Gradual erosion of polar ice caps and mountain glaciers

The most widespread indication that the earth has been warming over time has been the steady erosion of ice in the Arctic and Antarctic and on mountain glaciers. Although a few exceptions do exist, the worldwide erosion of ice leaves little doubt that the earth has experienced steadily increasing warming for at least a century.

According to a report by Hamish D. Pritchard and his colleagues that appeared in the journal Nature late in 2009, accelerated ice flow (dynamic thinning), measured by high-resolution laser altimetry, reaches all latitudes in Greenland and has intensified on key Antarctic grounding lines, penetrating far into the interior of each ice sheet, spreading as ice shelves thin by ocean-driven melt. Mountain glaciers are in rapid retreat around the earth, with very few exceptions. By the early 2020s, the Intergovernmental Panel on Climate Change projected that between one-third and one-half of the world's existing mountain glacial mass could disappear over the next hundred years. Sometime during the twenty-first century, the last glacier may melt in Montana’s Glacier National Park.

Mass loss from the mountain glaciers, as well as massive ice shelves and sheets along the coasts of Greenland and Antarctica, is accelerating faster than expected, contributing to sea-level rises. By 2020 researchers had determined that glaciers in Antarctica were melting five times faster at that point than they were in the 1990s, with Greenland also experiencing significant ice loss. As seas gradually rise because of glacial melting and thermal expansion along some coasts, isostatic rebound, the gradual rising of land masses that have been compressed by glaciers in the past, has provoked the rise of Scotland’s coast following the last ice age. The Great Lakes, remnants of melted glaciers, also experience some isostatic rebound.

Glaciers in Rapid Retreat

Climbers have been plucked from the Matterhorn in the Swiss Alps as thawing mountainsides crumbled under them. During the summer of 2003, Mont Blanc, Europe’s tallest mountain, was closed to hikers and climbers because its deteriorating snow and ice were too unstable to allow safe passage. The mountain was crumbling as ice that once held it together melted during a record-warm summer in Europe. The continent continued to face dangerous levels of ice melt in subsequent decades; in 2022 the Swiss Alps saw their most severe melting on record, which nearly doubled the record from 2003 and exposed areas of rock that had been covered in ice for thousands of years. At that time, scientists estimated that glaciers in the Swiss Alps would lose 80 percent of their mass by 2100.

The U.S. Geological Survey (USGS) has collected a digital library that describes the state of more than 67,000 glaciers around the world. Using historical photographs, images from space satellites, precision laser measurements, and other tools, the USGS has created an archive that tells a story of glacial retreat around the world. Generally, the only glaciers gaining mass during this time were in wet maritime areas of the world, such as parts of Norway and Sweden, where melting was offset by increased snowfall, another facet of climate change in that region. For much of the world, however, glacier melting remained a dire issue. The rate of ice loss doubled from 1988 to 2002 and continued to increase in subsequent decades. While the Earth lost an average of 760 billion tons of ice per year for most of the 1990s, by 2023 annual ice loss had risen to roughly 1.2 trillion tons per year.

Global Effects of Ice Melt

The snow-and-ice crown of Mount Kilimanjaro in equatorial Africa may vanish by the mid-twenty-first century. Kilimanjaro will no longer live up to its name, which in Swahili means “mountain that glitters.” Nearby Mount Kenya’s ice fields lost three-quarters of their mass during the twentieth century. By the end of the twenty-first century, Glacier National Park in Montana may lose the last of its permanent glaciers. The USGS noted that between 1966 and 2017, glaciers in Montana had reduced by as much as 85 percent. The original 150 glaciers within Glacier National Park had been reduced to 37 by 2002, and most of these were small remnants of once-mighty ice masses. The number of glaciers had reduced further by the early 2020s, with only twenty-five active glaciers remaining in the park in 2022.

Millions of people around the world may face severe water shortages as glaciers around the world melt. Ecuador, Peru, and Bolivia, where major cities rely on glaciers as their main source of water during dry seasons, could be among the most intensely affected. Areas of the Himalayas face grave danger of flooding initially, as glaciers melt, followed by water shortages from the ebbing of glacier-fed rivers that supply water to one-third of the world’s population, mainly in India and China.

Evidence from Antarctica suggests that melting ice may flow into the sea much more easily than earlier believed, perhaps leading to an accelerating rise in sea levels. A study published in the journal Science in 2003 suggested that seas might rise as much as several meters during the next several centuries, given projected global warming based on continuing usage of fossil fuels at the levels of the early twenty-first century. Glaciers tracked by the World Glacier Monitoring Service lost the ice equivalent of four feet of liquid water in 2018 alone. Additional studies have provided further evidence of this trend, as the important Pine Island Glacier of the West Antarctic Ice Sheet has been receding into the ocean at a faster pace. This mass of ice could influence the entire region in years to come. Another Antarctic glacier, the Thwaites Glacier, sometimes referred to as the "doomsday glacier" due to its massive size and the threat it poses as it melts, also experienced major ice loss in the 2010s and into the 2020s. In 2021 scientists raised concerns that the ice shelf under the melting glacier, which was already responsible for roughly 4 percent of annual global sea level rise, could collapse within three to five years.

Bibliography

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Freedman, Andrew, and Chris Mooney. "Earth is Now Losing 1.2 Trillion Tons of Ice Each Year. And It’s Going to Get Worse." The Washington Post, 25 Jan. 2021, www.washingtonpost.com/climate-environment/2021/01/25/ice-melt-quickens-greenland-glaciers/. Accessed 17 July 2024.

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"Overview of Glacier National Park's Glaciers." National Park Service, 20 June 2024, www.nps.gov/glac/learn/nature/glaciersoverview.htm. Accessed 17 July 2024.

Pritchard, Hamish D., et al. “Extensive Dynamic Thinning on the Margins of the Greenland and Antarctic Ice Sheets.” Nature 461 (October 15, 2009): 971–75.