Glaciers collapsing: meltwater raises sea level and depletes vital water supplies

Glaciers are melting at an unprecedented rate. This has two serious effects: the influx of meltwater into the sea raises the sea level, increasing coastal flooding; it also threatens the drinking-water and irrigation needs of communities that use glacier meltwater as their primary water source. Researchers studied global glacier melt patterns to understand how rapid this will happen and how it will affect our future.

“Our study shows that the world’s glaciers are melting more rapidly than ever before – and this affects the sea and water supplies. The meltwater raises sea level, threatening low-lying coastal areas. In addition, millions of people are losing a crucial source of drinking-water, especially in Asia, where mountain glaciers supply major rivers. If this melting continues at the current rate, it could have catastrophic repercussions for both cities and agriculture,” explains Shfaqat Abbas Khan, Professor, Department of Space Research and Technology, Technical University of Denmark (DTU Space), Kongens Lyngby.

Smaller glaciers melt more rapidly

Glaciers are an obvious indicator of climate change. When they melt, this not only affects sea level but also the people who use the meltwater for drinking-water and irrigation. Understanding how rapidly glaciers are disappearing and how this affects our planet is therefore crucial.

“This study on mass changes of glaciers is one of the most comprehensive ever. From 2000 to 2023, melting has accelerated tremendously – and is progressing much more rapidly today than it did 25 years ago,” says Shfaqat Abbas Khan.

A significant finding is that smaller glaciers melt faster than large ice sheets, currently contributing more to raising sea level than the ice sheets in Greenland and Antarctica.

“We found that smaller glaciers contribute more to raising sea level than the large ice sheets. These glaciers respond much more rapidly to climate change than the large ice sheets.”

Since 2000, glaciers have lost considerable ice, with the extent varying by location. In some places, up to 39% of the ice has disappeared, and the global average is about 5%.

“The glaciers are melting more rapidly than previously. They have already lost 18% more ice than the Greenland Ice Sheet has lost – and more than twice as much as Antarctica,” notes Shfaqat Abbas Khan.

Previous models were crude

Small mountain glaciers are common all over the world, including the Alps, Himalayas and Andes. They are disappearing rapidly, and their meltwater is essential for millions of people. When these glaciers vanish, water shortages will become a reality in many regions. Understanding exactly what is happening and how rapidly is therefore crucial.

“We cover the entire planet. We go into the field and take measurements – and use those data to validate satellite data. Satellites cover the entire Earth, but they measure differently: some register gravity, which changes when a glacier loses mass, and others measure the height of glaciers and how this changes,” explains Shfaqat Abbas Khan.

The researchers combine several methods to clearly determine how glaciers are melting. They carry out field measurements on the glaciers themselves, but this only covers selected areas, so they supplement these with satellite data measuring changes globally. Satellites use either radar or lasers to record changes in the height of glaciers, and other satellites measure how the Earth’s gravity field changes as ice masses disappear.

“Previous models were crude – an entire ice sheet was represented as one large block. Today, supercomputers enable us to delve into the details. We can simulate how each individual glacier reacts to temperature increases, changes in precipitation and other factors,” says Shfaqat Abbas Khan.

Plenty of historical data

The researchers combine satellite data with advanced computer models that can show how each individual glacier is developing over time. By integrating the data obtained by using different methods, researchers can predict what will happen to the glaciers by 2100.

“We compare observations to improve understanding of local areas. The next step is to model the predictions for 2100. At DTU, we fine-tune our models with the latest data from around the globe,” explains Shfaqat Abbas Khan.

One challenge is that the data from satellites, field measurements and computer models do not always agree. Large quantities of historical data are therefore used to calibrate the models. The longer the time period for which researchers have data, the better they can identify long-term trends and differentiate between natural variation and anthropogenic climate change.

“Our current study covers 23 years, but we are working on extending this to 50 years. In Greenland, we can include extensive historical data. The longer the time series, the clearer the shift becomes – nothing like this has happened in 100 years,” observes Shfaqat Abbas Khan.

Less water for crops, animals and people

By combining field measurements, satellite data and computer models, the researchers have created the most comprehensive global overview of glacier melting to date. This enables them to predict the effects of the vanishing ice – both for sea-level rise and for the many people who depend on meltwater from mountain glaciers.

“All measurements point in the same direction: the glaciers are melting everywhere on Earth and at an unprecedented pace,” warns Shfaqat Abbas Khan.

Small glaciers, such as those in central Asia, South America and the Alps, are melting more rapidly than in many other places. In some places, up to 39% of the ice has disappeared since 2000, with major effects for millions of people who use the meltwater for drinking-water and irrigation.

“The melting has accelerated by 36% since 2012, so the glaciers are disappearing more and more rapidly. Every year, about 273 gigatonnes of ice vanish from the glaciers. Think of an ice cube one kilometre on each side – that is one gigatonne. Every year, 273 of these ice cubes melt and end up in the ocean, causing the sea level to rise,” emphasises Shfaqat Abbas Khan.

Lose ability to re-establish themselves

The ice melt affects some areas more severely than others. Alaska accounts for 22% of the total ice loss, the Canadian Arctic for 20% and Greenland’s peripheral glaciers for 13%. In central Europe, the Caucasus and New Zealand, up to 39% of glacial ice has vanished since 2000, significantly affecting water supplies.

“In Asia, mountain glaciers are the lifeblood of millions of people who depend on the meltwater for drinking-water and irrigation. When the ice disappears, so does this vital resource. Increasingly more areas are losing ice mass, leading to potentially catastrophic consequences. Many rivers in China, India and the rest of Asia receive most of their water from melting glaciers. Disappearing glaciers mean less water for crops, animals and millions of people,” explains Shfaqat Abbas Khan.

The massive changes already underway have several dramatic effects. Rising temperatures mean that the snow, which normally accumulates to build up the glaciers, now falls as rain instead. This shift causes glaciers to melt faster because they are no longer replenished during winter.

“The temperature rise is just one factor. When snow turns to rain, the glaciers lose their ability to replenish themselves, causing them to melt even more rapidly,” says Shfaqat Abbas Khan.

Huge ice shelves hang over the sea

While mountain glaciers melt from above, the large ice shelves in Antarctica and the Arctic are threatened from below. Even a slight increase in sea temperature can cause ice shelves to collapse, initiating a self-reinforcing process in which even more ice calves (breaks off) into the sea.

“Huge ice shelves hang over the sea, making them extremely vulnerable. A slight increase in sea temperature can cause them to collapse, triggering a self-reinforcing effect that can release substantial water,” explains Shfaqat Abbas Khan.

Much of the ice disappears from glaciers by calving.

“New calculations reveal that calving alone has removed about 10 gigatonnes of ice per year from glaciers in the Northern Hemisphere and as much as 43 gigatonnes from the Greenland Ice Sheet,” emphasises Shfaqat Abbas Khan.

These dramatic changes in ice mass have global effects. Because of gravity, sea-level changes are not evenly distributed globally. For instance, the melting of Antarctica’s ice raises sea level more in Denmark than in Australia.

“Antarctica contains enough ice to raise the global sea level by 65 metres, but Denmark’s sea level could rise by up to 100 metres, whereas Australia might only rise by 60 metres because the rise is inversely proportional to the distance from the melting source.”

How rapidly will this occur?

Global warming causes the sea to rise in two ways: meltwater from glaciers and ice sheets flows into the sea, and the seawater expands as it gets warmer – potentially even more if melting continues at its current rate.

“The sea rises not only because of meltwater; warm water also occupies more space. By 2100, the global sea level may rise at least one metre, perhaps even more,” suggests Shfaqat Abbas Khan.

The researchers’ models indicate that the glaciers are melting more rapidly than previously. Even before 2040, meltwater is expected to raise the sea level by 3–7 cm. In the worst case, up to half of global glacier ice could vanish by 2100.

“Millions of people already experience the effects of rising sea level and extreme weather. When glaciers melt and heavy rains fall, rivers overflow, resulting in devastating floods in many regions.”

The researchers are certain that the large glaciers and ice sheets will collapse. The only question is how rapidly this will happen. New models suggest that major ice sheets could collapse within the next few decades.

“Large glaciers will collapse – this is not a question of if but when. It could happen in 50 years or 20. New models enable us to predict the exact time frame more accurately” warns Shfaqat Abbas Khan.

Sea level not rising in Greenland

In contrast to the affected coastal areas, the bedrock in Greenland is rising more rapidly than the sea level, such that the average global sea-level rise does not affect Greenland in the same way as elsewhere.

“Ironically, Greenland is one of the few places not suffering from sea-level rise. The bedrock rises more rapidly than the sea. However, this displacement creates new earthquakes, which can strongly affect villages,” notes Shfaqat Abbas Khan.

For Greenland, the considerable melting also means that the large icebergs in the fjords create problems for transport and mining. The ice cannot just melt away without causing practical challenges.

“Icebergs calve into the sea, especially around Nuuk. Some people dream of extracting minerals in Greenland, but the fjords are packed with ice – and ships cannot enter. This is a logistical nightmare,” says Shfaqat Abbas Khan.

Although the changes may seem abstract to people who do not witness them, they are eerily clear to the researchers working directly with the data. The landscape is changing rapidly, and the melting is accelerating at an alarming pace.

“Every time I return, the landscape looks different. Sometimes I can barely find my equipment because the ice has changed so much. I wish more people could see it with their own eyes. This ice is melting really rapidly.”

Fearing cutbacks

In 2022, Pakistan experienced devastating floods that submerged one third of the country and killed 1,700 people. Millions of families were forced to leave their homes, infrastructure was destroyed and vast agricultural areas were washed away.

According to Shfaqat Abbas Khan, this type of disaster is expected to recur repeatedly if we do not act quickly.

Meanwhile, political decisions in several countries threaten climate research and the necessary initiatives. In countries such as the United States, which increasingly focus on using more fossil fuels, comprehending and addressing the severe damage caused by climate change becomes considerably more challenging.

“The shift towards using more oil and coal in the United States is a disaster. We fear that they will cut back climate research and satellites that monitor glaciers, setting us back decades. We are at a crossroads. If we do not act now, the catastrophic effects of the disappearing ice will be far worse. The question is whether we are prepared to take responsibility while there is still time,” says Shfaqat Abbas Khan.

United States is very vulnerable

The coming decades will be decisive in how the massive changes already underway are addressed. Sea-level rise will affect coastal areas globally, but the effects will not be evenly distributed. Because of gravity, the ice melting in Antarctica will cause the greatest sea-level rises in the Northern Hemisphere .

“When Antarctica melts, it affects the Northern Hemisphere the most because of gravity: mass attracts water. When the mass disappears, the attraction disappears, and the water moves to the opposite side of the Earth,” explains Shfaqat Abbas Khan.

Even a relatively small rise in sea level can have enormous effects. The East Coast of the United States is a very vulnerable area in which millions of people will be directly affected, especially in low-lying and densely populated states such as Florida.

“When an ice sheet collapses, I think politicians will have to act. The Arctic and Antarctic are vast blocks of ice with colossal potential. Even a one-metre rise in sea level can submerge large parts of Florida – and that is precisely what we are witnessing now,” concludes Shfaqat Abbas Khan.