February 7, 2022

expert reaction to glaciers maybe not containing as much ice as previously thought

A study, published in Nature Geoscience, has looked at glaciers maybe not containing as much ice as previously thought. 

Prof Martin Siegert, co-director of the Grantham Institute – Climate Change and the Environment, Imperial College London, said:

“This is a very interesting study. It shows that the contribution of glaciers (as opposed to ice sheets) is much less than we’d appreciated previously. As the contribution to sea level from the worlds massive ice sheets is now (today) greater than from the glaciers, it is the ice sheets that will likely drive sea level in this century and beyond; and since they are losing six times more mass today compared with 30 years ago we should be extremely worried about future sea level rise.

“While glaciers contain enough ice to raise sea level by 25cm or so, there is enough ice in ice sheets to raise sea level by over 60 metres. It remains possible that with unstable changes in West Antarctica, Greenland and East Antarctica that over one metre of sea level rise could occur this century, and many more metres beyond that.”

Prof Andrew Shepherd, Director of the Centre for Polar Observation and Modelling, University of Leeds, said:

“This is a first class study – the team have extended their previous work on updating ice sheet thickness measurements to mountain glaciers and it will prove to be just as important for climate science.

“Although mountain glacier melting is a big chunk of sea level rise today, it will soon be dwarfed by accelerating ice losses from Antarctica and Greenland, and so their maximum sea level contribution isn’t our main concern. The effect of glacier melting on water resources is a much bigger issue for society. Because there is less ice stored in the worlds glaciers than we had thought they will disappear earlier than expected, and so the communities that depend on their ice and water will experience the worst effects of climate change sooner.  In Iceland for example – which was named after its glaciers by the Vikings a thousand years ago – the landscape will change irrevocably as most of its ice will be lost within a couple of centuries.  In every corner of the planet, the seasonality of river water levels will change dramatically as glaciers melt away.”

Prof Eric Wolff, Royal Society Professor of Earth Sciences, University of Cambridge, said:

“This is a great new inventory of how much ice there is in glaciers worldwide, excluding the great ice sheets of Greenland and Antarctica. This is an important basis for estimating how they will change in the future. It has local implications for people who rely on the glaciers  to provide water resources. If all these glaciers melted then sea level would rise by 26 cm, which is important but less worrying than the much larger rises that could come from the Antarctic and Greenland Ice Sheet if they were to retreat rapidly.”

Dr Bethan Davies, Senior Lecturer in Quaternary Science at Royal Holloway, University of London, said:

“The really important finding of the paper for human societies is that there is less ice in the low latitudes, mainly in South America, where glaciers provide a dependable and very important downstream water supply. The Andes are mountain ‘water towers’, providing water to downstream communities. Cities like La Paz (2.2 million inhabitants) are very dependent on the water provided for glaciers, which reliably release water, providing a buffer for droughts. As the glaciers shrink, the amount of water they can provide downstream declines, meaning that droughts are more likely. These glaciers have a low volume so negligible importance for sea level, but critical for downstream water supply in the dry season.

“I don’t believe that the smaller ice volume for glaciers will result in a substantial reduction in the amount of sea level rise we can expect from glaciers, but it will result in reduced water resources and water availability in some important mountain water towers.”

Prof Jonathan Bamber, Director of the Bristol Glaciology Centre, said:

“This is an important and thorough study of the potential contribution glaciers could make to sea level rise. It is important because over the last century glaciers were a dominant source of sea level rise and are projected to make a significant contribution over the next century. But by how much, depends on how much is stored in them presently. This study lowers that number by 20%, which means that they will disappear faster than expected, also adversely affecting water resources in areas where glacial melt is an important water source in summer.

“It is also important because it suggests that there remains considerable uncertainty in the global glacier volume. This is one estimate, which while careful and thorough, makes some important assumptions regarding ice flow and how it relates to ice thickness. Changing these assumptions would change the estimate. Nonetheless, it looks like the earlier glacier volume numbers were over estimates.”

Dr Andrew Sole, Senior Lecturer in Physical Geography at the University of Sheffield, said:

“Millan and co-authors present an update to existing estimates of the volume of ice stored in the world’s glaciers and ice caps (excluding the Greenland and Antarctic ice sheets) using satellite derived measurements of surface ice flow and a model of glacier motion. This approach is required because it is unfeasible to measure the ice thickness of all glaciers directly.

“Due to their greater sensitivity to climate change, glaciers and ice caps are expected to be the main cryospheric contributor to sea level rise in the 21^st century (Edwards et al., 2021). Quantifying the volume of water stored in glaciers and ice caps is therefore important for modelling sea level rise over the coming decades. In addition, meltwater runoff from many of these ice masses provides essential water resources, so knowing how much water they hold is also crucial as a starting point for modelling the impact their future demise will have on downstream populations and ecosystems.

“Millan and co-authors estimate that the potential sea level rise contribution of glaciers and ice caps, were they to melt completely, is 257 ± 85 mm; 20% less than the most recent similar global assessment (Farinotti et al., 2019). Regionally, Millan et al. suggest there is 37% more ice present in the Himalaya, but 27% less ice stored in the Andes. Interestingly, Farinotti et al.’s estimate for the Himalaya was 27% less than the previous assessment.

“These significant fluctuations in ice volume estimates as satellite observations improve and computational power increases, hopefully represent a gradual zeroing in on the real value, though there remain significant uncertainties in converting measured ice flow to ice volume, and given the rapid rate of mass loss from many glaciers and ice caps, the true value is a moving target.”

Prof David Hannah, Professor of Hydrology and Chair-holder for the UNESCO Chair in Water Sciences at the University of Birmingham, said:

“Notwithstanding the high level of uncertainty of glacier thickness model results in this study, it remains critically important to remember that mountain glaciers are shrinking under climate change. Retreating glaciers and snowpack loss threaten the ecosystem services that glacier-fed rivers provide to high-altitude communities and people downstream. These include provisioning of water for agriculture, hydropower, and consumption. 

“Comprehensive and high-resolution satellite observations such as these continue to revolutionise our understanding of Earth’s ice. While this study finds mountain glaciers worldwide contain 20% less ice than previously thought, their melting has already raised the global sea level by 3 cm since the 1960s, raising the risk of storm-surge flooding for coastal communities. This is without considering melting in Antarctica and Greenland, which contain almost all of Earth’s ice on land, and are on track to double the frequency of coastal flooding in many of the world’s largest coastal cities this century.”

Dr Ella Gilbert, Post-doctoral research assistant at the University of Reading, said:

“Losses from glaciers currently drive a large chunk of ongoing sea level rise, so if this paper’s conclusions are true, it could be good news that they contain less ice to add to sea levels. It’s bad news though for people who live in areas where glacier thickness is less than previously thought, like the Andes, and who rely on glacial meltwater for water resources.

“It’s important to remember however that ultimately the majority of sea level rise will come from thermal ocean expansion and ice losses from Antarctica and Greenland. These ice sheets contain a lot more ice in total and studies show that losses there are currently progressing along a worst-case-scenario kind of trajectory (cf. Slater et al., 2020, doi: 10.1038/s41558-020-0893-y).

“Plus, there’s still uncertainty in the estimates – this paper looks at ice thickness in just one year (2017/18) and the technique has its limitations. The authors also report some of the largest differences between their results and previous estimates in regions where measurements are scarce and uncertainty is high (e.g. Greenland/Antarctica, both -25% SLR contribution).

Overall, potentially interesting results, but it’s important to put it into the wider context.”

Dr Thomas Slater, University of Leeds, said:

“Comprehensive and high-resolution satellite observations such as these continue to revolutionise our understanding of Earth’s ice. While this study finds mountain glaciers worldwide contain 20% less ice than previously thought, their melting has already raised the global sea level by 3 cm since the 1960s, raising the risk of storm-surge flooding for coastal communities. This is without considering melting in Antarctica and Greenland, which contain almost all of Earth’s ice on land, and are on track to double the frequency of coastal flooding in many of the world’s largest coastal cities this century.”

‘Ice velocity and thickness of the world’s glaciers’ by Romain Millan et al. was published in Nature Geoscience at 4pm UK time on Monday 7 February.

DOI: https://doi.org/10.1038/s41561-021-00885-z

Declared interests

Prof Wolff: No competing interests

Dr Slater: I have no conflict of interest to declare

Dr Sole: No interests to declare

None others received.