Glaciers and Ice Sheets in a Warming World

By Dr Catriona Nguyen-Robertson MRSV

This article follows the 2023 Howitt Lecture, co-hosted by the Royal Society of Victoria and the Geological Society of Australia (Victoria Division), delivered by Professor Andrew Mackintosh, Head of the School of Earth Atmosphere and Environment at Monash University.

Melting ice off the Antarctic coast. Photograph: Cassie Matias via Unsplash.

Amidst the frozen landscapes that have been part of Earth’s geography for millennia, a transformation is underway as ice sheets and glaciers succumb to climate change. The delicate dance of freezing and melting of these ice formations, once viewed as frozen in time, is yielding to the planet’s rising temperatures. From the remote corners of Antarctica to the towering ranges of the Himalayas, the alarming spectacle of accelerating ice loss casts a stark shadow over ecosystems, coastlines, and the equilibrium of our global environment. 

The melting ice is a chilling reminder of the urgent need to address the consequences of climate change. Glaciologists like Professor Andrew Mackintosh reconstruct past glacier and ice sheet changes to improve their predictions of the future – and, so long as we do not slow down carbon emissions, the future looks bleak.

Changing ice – a delicate dance no longer so balanced

Glaciers around the world range from ice that is several hundred to several thousand years old. In polar and high-altitude alpine regions, snow accumulates on glaciers and turns into ice over time. As ice builds up, it begins to flow outwards and downwards under the pressure of its own weight, flowing slowly over the land. The glaciers grow, while also moving and melting as part of their natural life cycle. If the accumulation of snow and ice equals or is greater than the amount melting, a glacier will remain in balance or even grow.

But since the early 1900s, many glaciers around the world have been rapidly melting – too quickly to counter. For 17 years, Andrew worked in the Southern Alps of New Zealand, watching the ice retreat. Every year, glacier “watchers” like him take to the skies to photograph snow and ice clinging to high peaks along the length of the Alps following the summer. They know the landscape well and they even have their favourite glaciers – but those glaciers are clearly and irreversibly disappearing. 

There is grief among glaciologists as they watch the ice melt. Andrew helped launch the monitoring programme at Brewster glacier in 2004 at a time when the ice was thick and healthy – 20 years on, it ‘doesn’t have the characteristics of a happy, living glacier’, he says. ‘It looks like something that is just decaying and won’t be with us much longer.’

Two other glaciers close to his heart are the Franz Josef Glacier, or, as it is known in Māori, Kā Roimata-a-Hine Hukatere, and Fox Glacier, or Te Moeka o Tuawe. For much of their history, people – including Andrew – have been able to walk on the glacier, right up to the terminus to see the frozen towers of ice. But now, some glaciers in the Southern Alps have shrunk so much that they are hard to see and cannot be stepped on; many will be gone within decades. 

Tourists trek over Franz Josef Glacier/Kā Roimata-a-Hine Hukatere in New Zealand. The Māori name for the glacier translates roughly to ‘Tears of the Snow Maiden’. The legend goes that the Māori princess Hine Hukatere climbed the mountains with her lover Wawe. Tragically, he was swept away by a devastating avalanche, leaving Hine shattered by grief and guilt. The gods, witnessing Hine’s anguish, froze her tears, transforming them into a colossal river of ice. The glacier has been in ‘retreat’ since 2008, with no signs of slowing, and Andrew notes that the melting ice looks like her tears rushing down the slopes as she cries. Photograph: Jackman Chiu via Unsplash 

Using computer modelling, Andrew can predict what may remain of New Zealand’s glaciers by 2100. With global warming limited to 1.5-2.0°C (RCP 2.6) in a “peak” scenario, the glaciers will have retreated but remained connected and still act functioning entities that follow a cycle of building and shrinking.1 If we continue along the current trajectory as the worst-case scenario (RCP 8.5), most glacier ice will be gone.1 The outcome depends on what we do from this point on. Either way, much of the ice will simply vanish in the coming decades.

The outlook is similarly grim for glaciers elsewhere. In fact, there is ‘near universal retreat of glaciers all over the world,’ Andrew says. ‘The scale of retreat is confronting, even to a glaciologist. It’s unprecedented – and I don’t use that word lightly’. 

In the last few decades, there have been extreme glacier melts. When an ice cube is exposed to warm water or air, it melts. It is therefore no surprise that a warming climate is causing glaciers and ice sheets to melt. Andrew has been concerned to see over recent years that ice is not merely retreating up mountains, but the mountain glaciers are being completely stripped of ice both horizontally and vertically. The ice is becoming thinner and breaking apart more easily. Thinning makes the situation worse – the less ice there is, the faster it will melt and the harder it is to build back up. 

As glaciers decrease in size and become thinner, their slopes become more unstable. Last year, there were two major avalanches as Tian Shan in Kyrgyzstan and the Dolomites in Italy within the space of about a week as glaciers collapsed. The glaciers were there – and then suddenly they were not. Scientists like Andrew are concerned that similar events are likely to become more common as the planet warms.

It can be difficult to disentangle natural and anthropogenic causes of glacier retreat, but human-induced climate warming appears to be the chief factor in their decline. For example, human-caused climate change made the 2018 extreme mass glacier loss in New Zealand’s Southern Alps at least 10 times more likely than natural climate variability.2 As warming and extreme heat events continue and intensify, there will be an increasingly visible human fingerprint on extreme glacier mass-loss years in the coming decades.

Consequences when the ice melts

As temperatures rise and ice melts, more water flows to the seas from glaciers and ice caps, contributing to global sea level rise. Glaciers hold about 2.1% of all of Earth’s water, frozen as ice.3 Excluding the Arctic and Antarctic ice sheets, if all the world’s glaciers melted completely, sea levels would rise by 40cm.4,5 While this may not sound like much, Andrew warns that the two ice sheets hold much more.

The fate of the world’s biggest ice sheet is uncertain – it lies in our hands. Antarctica is covered by a vast ice sheet that is nearly twice the size of Australia’s land mass. While it is not yet contributing significantly to sea level rise, it is the riskiest. It holds most of the Earth’s glacier ice, and if the entire sheet were to melt, sea levels would rise by nearly 60 m.6 In addition, the Arctic ice sheet has been showing great signs of vulnerability. Over the past 30 years, the oldest and thickest ice in the Arctic has declined by 95%.7 If emissions continue to rise, the Arctic could be ice-free in the summer by 2040.7

It is very difficult to predict the future of ice sheets with modern observations such as satellite imagery because they cover a very short period. Andrew may be equipped with data for the past 40 years, but these ice systems have been in place for millions of years. He uses computer modelling and radar to explore the water and rock underneath. The East Antarctic ice sheet is thought to be more stable as much of it sits above sea level, meaning that warming oceans cannot reach it and the only melting is from warmer air, which is a much slower process. In contrast, the WAIS sits below sea level and is of greater concern. 

While glaciers and the ice sheets of the poles may seem distant here in Australia, the resulting sea level rise when they melt poses a great threat everywhere. A 2014 report by the Climate Council referred to coastal flooding as a “sleeping giant”.8 Over $226 billion dollars of our infrastructure (residential, commercial, industrial, etc.) is potentially exposed to flooding and erosion hazards if sea levels rise 1.1m, which is quite possible by the end of the century.8 Globally, sea level rise poses an existential risk to low-lying islands and coastal cities. 

Snow and ice loss also have immediate consequences for people. Climate change is predicted to drastically reduce the discharge of snow and ice meltwater in the Himalayas, which could have far-reaching consequences for flood risk and for water security. More than 60 million people in Asia live downstream of five major rivers that originate in the Himalayas, and their food security will be threatened by the melting ice in the coming decades.9 For example, record temperatures in 2022 hastened melting of the Shisper Glacier, creating a lake that swelled and burst through an ice dam. A torrent of water and debris flooded the valley below, damaging fields and houses, wrecking two power plants, and washing away parts of the main highway and a bridge connecting Pakistan and China.

Given current projections, global temperature rise, and inaction by major global political and industry leaders, a sea level rise of 1.5 m is a realistic estimate that will likely occur within the century. Even a few metres of sea level rise will redraw the map of the world, with profound consequences for millions of people. Many island nations will be below the tideline, and much of Amsterdam, Alexandria, Bangkok, Ho Chi Minh City, Kolkata, and Venice, among other highly populated cities will be underwater.10 If there are to be glaciers and ice anywhere on Earth in the next century, we need to make ambitious cuts to our carbon emissions.


  1. Anderson, B., et al. (2021). Modelled response of debris-covered and lake-calving glaciers to climate change, Kā Tiritiri o te Moana/Southern Alps, New Zealand. Global and Planetary Change, 205.
  2. Vargo, L., et al. (2020). Anthropogenic warming forces extreme annual glacier mass loss. Nature Climate Change, 10. 856–861.
  3. U.S. Geological Survey. How much of the Earth’s water is stored in glaciers?
  4. Heiko Goelzer, et al. (2020). The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6. The Cryosphere, 14(9).
  5. Hélène Seroussi, et al. (2020). ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century. The Cryosphere, 14(9)
  6. Australian Antarctic Program (2021). Ice Sheets.
  7. Osborne, E, et al. 2018. Arctic Report Card. National Oceanic and Atmospheric Administration.
  8. Steffen, W, et al. (2014). Counting the Costs: Climate Change and Coastal Flooding. Climate Council.
  9. Immerzee, W.W.,l et al. (2010). Climate Change Will Affect the Asian Water Towers. Science, 328 (5984): 1382 DOI: 10.1126/science.1183188
  10. Climate Central. (2021). Sea level rise and coastal flood risk maps – a global screening tool by Climate Central.

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