Cryoset shows ice loss from glaciers

When one thinks of the damage that climate change is doing, what likely comes to mind is giant chunks of ice leaving one of the polar ice sheets and crashing into the ocean. While Greenland and Antarctica are losing ice mass, so are most glaciers around the world, but it is difficult to measure how much ice they are shedding.

Thanks to ESA’s CryoSat satellite and a breakthrough way of using its data, scientists have discovered that glaciers worldwide have shrunk by a total of 2% in just 10 years, and that is due to higher air temperatures.

A paper, published in a journal Geographical Research PapersDescribes how scientists used a specific technique to process cryosat data to find that glaciers lost 2,720 gigatons of ice between 2010 and 2020.

Their research also shows that higher air temperatures are responsible for 89% of this ice loss.

Glaciers are found on all continents except Australia. They provide an essential source of fresh water. For example, glaciers alone in high mountain Asia provide water to more than 1.3 billion people. Glaciers are also important for industries such as hydropower.

The death of glaciers worldwide, therefore, causes serious problems for local populations and those who rely heavily on outflow water.

In addition, ice loss from glaciers contributes more to sea level rise than ice loss from any of the giant ice sheets on Greenland and Antarctica.

Although mountain glaciers are key indicators of climate change and important to society, estimates of global glacier mass loss have been limited to a few scientific studies. This is because there are numerous practical challenges in mapping and monitoring glaciers, which lie in complex rugged terrain, and because there are no specific satellite missions dedicated to doing this.

“I’m sure most people have seen photographs taken at different times that show how the glacier terminus has retreated over time. And we can see this from satellite images as well,” said Noel Gormelon of the University of Edinburgh, UK.

“But we need to measure how the volume of the glacier is changing to understand what’s really happening.”

The research team turned to ESA’s CryoSat satellite, which carries a radar altimeter to measure the height of the ice surface. This works well for measuring sea level and sea ice height, which is used to measure how ice thickness varies, and the vast polar ice sheets.

However, the footprint of this type of instrument is too coarse to measure and monitor mountain glaciers.

“Several years ago, we developed a technique for processing cryosat data, called swath processing, which revolutionized the use of cryosat data over complex glaciated regions. It revealed a wealth of new details on glaciers,” Dr. Gormelon noted.

Livia Jacob of EarthWave in the UK explained, “We have been able to use this technique to study glaciers around the world and we can report that, in total, mountain glaciers have lost 2% of their volume between 2010 and 2020.

“That adds up to a total of 2,720 gigatons. This can be imagined as an ice cube larger than the highest mountain in Europe, which is quite impressive. Importantly, we also found that the air temperature, which causes the ice surface to causing melting. 89% loss of this snow.”

While warmer air temperatures are responsible for this declining “surface mass balance,” the research team found that something called “ice discharge” is responsible for the other 11% of ice loss.

This is associated with glaciers that terminate at the coast, where warm ocean waters are largely responsible for thinning the ice flow front.

Dr. Gormelon said, “The relative contribution of reduced surface mass balance and increased ice discharge to sea-level change is well known for the Greenland and Antarctic ice sheets. Now we know more about how the atmosphere and ocean are combining to melt glaciers. Much work remains to refine and incorporate this knowledge into our glacier projections.”

ESA’s Stephen Plummer explains, “Innovative work using Cryosat in swath altimetry mode demonstrates the value of its altimeter for monitoring glaciers, thus achieving one of the mission’s secondary objectives.

“This work laid the foundation for the glacier mass balance intercomparison exercise, GLAMBI, which reconciles different estimates of glacier mass balance from several satellite and in-situ methods. It also helped guide the design of the Copernicus Sentinel Expanding Crystal mission. To monitor ground ice Therefore, to ensure continuity in monitoring glaciers globally.”