Ice Loss and Glacial Retreat
Glacial melt is one of the strongest indicators of climate change. Scientists have observed a significant melt acceleration recently, showing how climate change is indeed causing more glaciers to melt.
Glaciers have lost 70.5 trillion gallons of water each year since 2000
On average, glaciers lost over 70.5 trillion gallons of water annually from 2000-2019, showing researchers how a warming planet has an impact on glacial melt.
Glaciers and ice sheets are stuck in a melting loop
When glaciers and ice sheets melt and release freshwater into the saltwater-filled oceans, the freshwater floats to the surface, becoming warmer before rubbing on the glacier and melting it even more.
Glacial inventories are how scientists measure glacial loss
Glacial inventories are carefully-measured databases of the world’s glaciers and ice sheets. They form the basis of how we understand the history of glaciers and predict their melting.
What We Know
It is basic science that warming temperatures melt ice. However, glaciers are much more complicated. Glaciers are made up of packed snow and ice over thousands of years. When glaciers move (at a rate of a few inches per year), they collect rock and debris. Because glaciers are so complex, their melting rate depends on factors in addition to warmer temperatures, including ocean water temperatures, land and ocean terrain, and their own meltwater. The Greenland and Antarctic Ice Sheets are large glacial masses covering enormous areas. While glaciers are found across the world, there are only two ice sheets.
Both warm air and warm ocean temperatures are melting these glaciers and ice sheets. Josh Wills, the lead NASA researcher on the Greenland ice sheet melting said:
"The glaciers are being melted by heat from above and below simultaneously."
In addition to normal ocean temperatures, glacial meltwater melts glaciers more. When the fresh meltwater flows into the ocean, it floats to the surface because freshwater floats in saltwater. It becomes warmer as it does so because it mixes with the warm ocean water. Then, this warm water at the surface rubs against the glaciers, melting them even more.
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As the graph above shows, glaciers across the world have been melting. Between 2000 and 2019 alone, the world's glaciers lost 267 metric gigatons each year — that's 70.534 trillion gallons of water annually, for a total of 1.411 quadrillion gallons. In addition, recent studies have found that glacial loss has been accelerating, further indicating a warming climate.
How We Know
There are many glacier inventories that scientists use to track glaciers and ice sheets across the world. These inventories have been carefully created by scientists from around the world. The Intergovernmental Panel on Climate Change has created a glacier inventory which consists of all the glaciers in the world, minus the ice sheets. Other glacier inventories have measured the two ice sheets. These inventories are used to measure how climate change has melted glaciers and predict future glacial melt.
Hugonnet, Romain, Robert McNabb, Etienne Berthier, Brian Menounos, Christopher Nuth, Luc Girod, Daniel Farinotti, et al. “Accelerated Global Glacier Mass Loss in the Early Twenty-First Century.” Nature 592, no. 7856 (April 2021): 726–31. https://doi.org/10.1038/s41586-021-03436-z.
Pfeffer, W. Tad, Anthony A. Arendt, Andrew Bliss, Tobias Bolch, J. Graham Cogley, Alex S. Gardner, Jon-Ove Hagen, et al. “The Randolph Glacier Inventory: A Globally Complete Inventory of Glaciers.” Journal of Glaciology 60, no. 221 (July 10, 2017): 537–52. https://doi.org/10.3189/2014JoG13J176.