This is a satellite overlay image of the Jakobshavn Glacier in southwest Greenland. The glacier drains about 6.5% of the Greenland Ice Sheet and produces approximately 10% of all icebergs that break off and drift away from Greenland’s coast. Every year, about 35 billion tonnes of ice calve from the glacier and flow out through Ilulissat Icefjord, named for its proximity to Greenland’s third-largest town.
Measuring the speed at which these glaciers move is a critical component of climate models. Given the common idiom “at a glacier’s pace” one would expect glaciers to be large nearly-static walls of ice. The reality is otherwise. As researchers Elzė Buslavičiūtė and Dr Laurynas Jukna from the Institute of Geosciences at the Faculty of Chemistry and Geosciences, Vilnius University, Lithuania put it:
Glaciers are actually more like living organisms: they constantly move, change, and evolve – they are dynamic and unstable, yet highly sensitive geosystems.
The speed at which glaciers descend, and the rate of sea level change, can be tied to measurements that are now possible via ESA’s Copernicus satellite program. By comparing glacier images over time, they can deduce the actual speed of glacier movement with a precision of meters per second. That results in “flow diagrams” like below, where the vector arrows show flow direction and color shows flow speed. The abrupt transition from dark red is the point where the glacier moves from land to water in Ilulissat Icefjord:
Here’s the problem: Historically, the glacier’s flow rate has been 40 meters per day, but it’s now slowed to 18.6 meters per day. What does this mean? When a glacier decelerates, as Jakobshavn is doing, it usually means there has been a reduction in snowfall over the accumulation zone — the catchment area for snow and ice that feeds specifically into Jakobshavn. Note that as the flowing ice enters Ilulissat Icefjord it speeds up (red) because of the downward slope. The speed slows the nearer you approach the ice cap that feeds it (field of arrows).
Glacier speed is typically measured in meters per year. Based on numerous studies, glacier speed can range from less than 10 m to more than 500 meters per year. Thanks to technological advances, we can now observe these changes from space. Of course, decelerating glaciers like Jakobshavn are not the problem — it’s the accelerating glacier that scientists are concerned about.
By monitoring glacial motion, scientists can assess the impact of climate change on glacier dynamics and estimate the potential amount of ice entering the ocean, and the overall extent of glacier melt.
There are about 200,000 glaciers on Earth. A large share of them are small mountain glaciers (ice caps), but vast ice sheets remain in Greenland and the Antarctic. They cover an area of 1.7 million km² in Greenland and 14 million km² in Antarctica. Together, they hold 99% of the Earth’s ice and 68% of the planet’s freshwater reserves.
And that ice is melting. Both ice caps and ice sheets are melting around the globe. According to the World Meteorological Organization (WMO), glaciers lost an average mass of approximately 301 billion tons of ice annually between 2000 and 2023. That’s equivalent to 0.75 mm per year of sea-level rise. In 2024, glaciers around the world lost even more — an estimated 496 billion tons of ice!
The Vilnius research provides another tool to incorporate with existing climate models. It will produce data for all the glaciers Copernicus can see, and lead to more accurate predictions of sea level rise.
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