Mountains are not just impressive geographic formations that entice us to hike and ski. They are also home to fascinating landforms which spark astonishment and awe: Glaciers. But as immortal as these icy giants might look, the last few centuries has seen their powers diminish.

At a science fair, organised by the Austrian Science Fund last summer, many visitors remained standing in front of a time-lapse sequence depicting Austria’s biggest glacier, the Pasterze, in a pavilion run by climate change researchers and glaciologists. “Sad”, “oh no, how dreadful” or “I can’t even watch” were some of the reactions. What triggered these emotions?

The time-lapse sequence showed the Pasterze over eight months, between April and December of 2016. It was clear to the naked eye what was happening: The glacier was moving. Contrary to popular opinion, glaciers are not rigid, unmoving structures. Glacier ice flows down a mountainside thanks to the forces of gravity. It’s warmer in the lower realms of the glacier than at the top, so the ice moving further down melts. This is a completely natural process that has nothing to do with the extinction of glaciers due to climate change. The movement is very slow: On average, the Pasterze moves around 10 meters a year. Compared to other glaciers, that is neither particularly fast nor particularly slow.

A glacier is balanced when it gets as much “nutrition” in the form of snow on its upper areas – the so-called accumulation zone – as it has melting in its lower parts – the ablation zone – over the course of a year. In reality, most glaciers are never perfectly balanced and their size fluctuates from year to year. However over the past few decades most glaciers have continuously shrunk, loosing a significantly greater amount of ice than they gained.

It is not only those living in the Alps who can detect these changes. Around the world glaciers are a prime example of the impact of ever-increasing climate change, with several fascinating series of  photographs which contrast old and new images to show the glaciers changing size.

But why are the glaciers melting? Is humankind responsible for this loss? And how far away will the impact of melting glaciers be felt? Only nearby, or is there reason to fear impacts further afield?

Since what was known as the Little Ice Age ended around 1850, glaciers around the world have lost around one fifth of their volume. If we look for reasons behind this, it is hard to ignore the human contribution to rising global temperatures. Researchers at the University of Innsbruck have used computer simulations to help show that around a quarter of all the glacier-melting that took place between 1850 and 2010 can be attributed to human activity.

But that relatively small percentage should not spark a sigh of relief. The percentage of glacial change that can be attributed to us is changing fast. In the middle of the 19th century human impact was hardly noticeable but over the last two decades we have become responsible for over two-thirds of overall melting. This trend will only continue because glaciers react very slowly to climate change. Just as they were at the end of the Little Ice age, glaciers are actually still larger than suits predominant climate conditions. That is, their melting is not keeping pace with rising temperatures.

It also means that their ablution zones are much bigger than their accumulation zones. In other words, the glaciers are starving. In colder regions, the glaciers are supposedly drawing back and becoming smaller, then eventually reaching a new balance. At least, that’s how the theory goes. Because progressively rising temperatures are making it increasingly difficult for the glaciers to attain a balanced state.

Researchers at the University of Bremen estimate that 36 percent of the ice currently stored in glaciers will melt over the next few years, so that the glaciers can reach a new balance that is in keeping with the current temperatures. That means that glacial shrinkage will only begin to show the impact of past industrial-age emissions during the next few decades.

So even if we don’t produce any more greenhouse gas emissions at all, it won’t matter: A third of glacier ice will still melt. The situation looks even more critical when taking into account a study led by researchers in Geneva that looks at the impact of greenhouse gas emissions to be produced in future decades. By the year 2100, between 76 and 97 percent of the ice in the European Alps will have disappeared.

In other areas – such as in the Himalaya in central Asia – the percentages of lost ice are smaller because the glaciers there are bigger and can pull back to higher, colder elevations to survive. Over the earth’s history, glaciers have always melted away and then grown again. After a glacier is gone, a new landscape arises in the immediate vicinity, and this area too must find its natural balance. The disappearing ice leaves behind brittle rock and loose stones, increasing the potential for scree slides, rock falls, avalanches and slips. Lakes form and new ecosystems evolve. The results vary in different locations and are the subject of intensive research.

One important function a glacier fulfils is as a storage and delivery system for water, particularly during drier seasons. Months-long dry spells in the outer tropics can be eased by glacial water supplies. This makes glaciers important for regional agriculture, hydropower and irrigation, which in turn means they are of social and economic importance. When a glacier melts, the level of short-term water supply rises. But in the long term, the melt threatens the very basis of regional water supply.

This threat is particularly significant in the South American Andes and in the Himalayas; the latter often being referred to as Asia’s water tower. Their surroundings include catchment areas for great rivers like the Ganges, the Brahmaputra and the Indus, which provide water to over half a billion people. Yet now, as in the past, our understanding of how changes in the glaciers will impact the local water balance remains limited. That is because it is not just the glaciers that are important but also precipitation patterns (consider, for example, the monsoons) as well as the annual snow melt.

Additionally, the aforementioned lakes that are evolving as the glaciers pull back also represent a growing danger. Should their levels rise above a certain threshold, there could be a sudden and uncontrolled emptying of these so-called proglacial lakes – and this could cause major damage downhill.

But the consequences of glacial melt are not just local, or even just regional. On a global level they raise  sea levels. Certain glaciers are thought to have contributed to at least a seven centimetre rise in sea levels during the 20th century, making them the greatest contributor to expanding oceans. 

In the past 20 years, this has changed a little bit. The giant ice sheets in Greenland and Antarctica are currently competing with the earth’s glaciers for the title of biggest contributor to rising sea levels. While progressive glacial melting could add a potential 30 centimetres to the world’s oceans, these ice sheets have the potential to add up to 66 meters as they melt. Presently though, the glaciers still react far faster to climate change and will remain the most meaningful contributors to sea levels over the next few decades.

Glaciers in the far north and in the Arctic are the ones that are supplying the most extra water to oceans. That’s no surprise as the glaciers there are far larger. What is surprising though is that sea levels in these areas are actually falling while they rise disproportionately in areas far away, such as in the Southern hemisphere and in the Tropics.

There are two reasons for this. Firstly, it is because when a glacier melts, the land underneath it, freed of the heavy weight, slowly rises. To anyone living there it seems as though sea levels are actually falling when it is actually the land that is rising.

Secondly, the huge ice masses effect a gravitational pull on everything around them, including the water in the oceans. That means that sea levels along an ice-covered coast tend to be slightly higher than they would be, if the ice was not there. When the ice mass shrinks, so does it’s gravitational force and then so do the sea levels. And because sea water doesn’t evaporate into air, or otherwise disappear, it is displaced - so the sea levels much further away from the ice mass rise instead.

The people who suffer are those on low-lying tropical islands and coastal nations: They feel the full force of the melting glaciers (and ice sheets) far away. The many real life problems caused by the world’s melting glaciers are hard to put a number on. The actual figure is probably inestimable. And as the glaciers disappear, we are also waving goodbye to an utterly unique land form.