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Across Europe and around the world, melting glaciers are reshaping landscapes and climate systems. Researchers Elz臈 Buslavi膷i奴t臈 and Dr. Laurynas Jukna from the Institute of Geosciences at the Faculty of Chemistry and Geosciences, Vilnius University, explain how satellite data is used to monitor glacier movement, assess their response to climate change, and calculate these changes through remote sensing technologies from space.

Glaciers are often referred to as indicators of Earth's overall condition, as they reveal the extent to which human activity is transforming our planet and how it is responding to anthropogenic pressures. When we think of glaciers, we often picture them as being static鈥攎assive, motionless blocks of lifeless ice.

But is that really the case? Glaciers are actually more like living organisms: they constantly move, change, and evolve鈥攖hey are dynamic and unstable, yet highly sensitive geosystems.

What does glacial movement tell us?

Today, there are about 200,000 glaciers on Earth. A large share of them are relatively small mountain glaciers, known as ice caps. However, vast ice sheets still remain in Greenland and on the Antarctic continent鈥攖wo of the last major continental glaciers that cover an area of 1.7 million km虏 in Greenland and 14 million km虏 in Antarctica. Together, they hold 99% of Earth's ice and 68% of the planet's freshwater reserves.

It has long been observed that due to intensifying climate change, both mountain glaciers and ice sheets are melting and retreating on a global scale. According to the World Meteorological Organization (WMO), glaciers lost an average mass of approximately 273 billion tons of ice annually between 2000 and 2023, equivalent to approximately 0.75 mm per year of global sea-level rise. In 2024, glaciers around the world lost even more鈥攁n estimated 450 billion tons of ice.

As glaciers melt, their "behavior" also changes, and their mass balance becomes negative鈥攊ce loss through ablation at the lower edge of the glacier tongue exceeds mass gain from snowfall in the accumulation zone. This mass balance of a glacier is closely tied to its flow velocity; it can be understood as the difference between the snowfall input (in the accumulation zone) and the ice melt (in the ablation zone).

In some cases, increased melting and enhanced basal sliding can accelerate glacier movement and potentially reduce the accumulation of new ice mass, thus contributing further to glacier thinning and retreat. Changes in glacier flow dynamics, either acceleration or deceleration, can also signal shifts in glacier mass in the accumulation zone, where the glacier is fed by snowfall.

Therefore, 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 or the overall extent of glacier melt.

Glacier flow dynamics (speed) are typically measured in meters per year. Based on numerous studies, glacier velocity can range from less than 10 m to more than 500 m per year. Thanks to technological advances, we can now observe these changes from space.

Satellites help track glacier flow from space

Greenland is known for its massive ice sheet鈥攖he second largest in the world. In some places, it is over 3 km thick, and along its edges, it feeds as many as 22,000 individual glaciers. Among them, one of the most remarkable is Jakobshavn Glacier, which 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 tons of ice calve from the glacier and flow out through its fjord.

Jakobshavn Glacier flows from the Greenland Ice Sheet and stretches toward the Ilulissat Icefjord, near Greenland's third-largest town, Ilulissat (formerly Jakobshavn). In 2004, the fjord was declared a UNESCO World Heritage Site due to its global natural significance.

Jakobshavn Glacier is one of the fastest-moving glaciers in the world, with its flow speeds reaching up to 40 m per day. However, in recent years, a remarkable slowdown in its movement has been observed. This deceleration is clearly illustrated in a glacier velocity map created using satellite data, which shows both the direction and speed of ice flow.

By using offset tracking, i.e. comparing the intensity of satellite images taken on different dates and tracking pixel displacement, scientists can calculate how far a glacier has moved over a day or a year. According to data from the European Space Agency's (ESA) Sentinel-1 satellite, the average flow speed in different parts of Jakobshavn Glacier in 2024 was approximately 18.6 m per day鈥攏oticeably slower than in previous decades. This glacier moves fastest where it meets the Ilulissat Icefjord (shown in dark red on the map, representing the central section of the glacier located at the contact zone between land and water).