Thwaites: Antarctica’s most worrying glacier

Thwaites Glacier covers an area of the West Antarctic ice sheet that is the size of the British Isles. In recent years, scientists have observed dramatic changes in the glacier that can be directly attributed to climate change and which will potentially have a devastating impact on people all over the world.

The glacier is in a keystone position within the vast West Antarctic ice sheet and its removal would have a huge impact on all of the other glaciers around it. If all of the ice surrounding Thwaites in the West Antarctic ice sheet were to come down with it, global sea levels could rise by as much as 3 metres.

But what does this mean for us in the UK? The Thames Barrier was designed to cope with a once in a thousand-year breach. With mid-range carbon emissions estimates, this could be reduced to one in 10 years by 2100. London is still adjusting to the removal of ice in Scotland 10,000 years ago which means it subsides by a couple of millimetres each year, amounting to 20cm of relative sea-level rise by 2100. Add another 80cm resulting from climate change and we may see one metre of sea-level rise which will reduce the existing Barrier’s protection down to one flood every 10 years. For this reason, a replacement is currently being considered by the Environment Agency, taking the most accurate projections into account.

Graph: IPCC AR6 2021 sea level projections

The International Thwaites Glacier Collaboration was put together by the UK and US, with scientific support from Germany, Sweden and Korea to investigate this “Doomsday” glacier. It is the most complex and extensive field project that has ever been undertaken in Antarctica, weaving in a variety of interconnected projects and requiring support from multiple aircraft, stations and ships. The projects range from climate and glacial modelling, to examining the processes that lead to ice sheet loss, and how history can inform us about present and future changes in the ice sheet.

The last Antarctic research season was disrupted by the covid-19 pandemic, but it is still hoped that all field work will be completed by 2025. Described by the BBC as “the most remote camp site on Earth”, living conditions on the ice are fairly basic, living in 2-person pyramid tents for weeks and meeting in a larger mess tent for team discussions. Storms can not only delay the collection of data, but also risk all of the equipment being buried in the snow and lost forever. Teams must mark everything with flags so that when the storm clears they can find it, digging everything out by hand.

One of the Thwaites field projects, MELT, has managed to access the grounding zone, where the base of the glacier comes into contact with the seabed. This is the area that’s experiencing the most intense melting and the scientists want to find out what the conditions are like so that they can predict how it will affect the glacier as a whole.

Dr Pete Davis, a British Antarctic Survey oceanographer, explained that the major challenge of the Thwaites Glacier grounding zone is that it’s below 650m of ice. The only way to reach it is to make an access hole through the ice, using hot water drilling. The scientists melt 10,000 litres of water, heat it to 90 degrees and then pump it through the drill into the ice as quickly as possible. It took them 24 hours to drill through the ice to reach the grounding zone.

They were then able to drop an underwater remotely operated vehicle through the hot water borehole to explore the environment beneath the ice shelf. This Icefin robot (pictured below) is equipped with sensors that can measure temperature, salinity and how fast the ocean is moving above and below it. Its onboard camera and sonar imaging allow scientists to see the remote sub ice shelf environment for the very first time, including anemone-like creatures which may have never been seen before.

The MELT project was unique in being able to gather a huge amount of data from an extremely hard to access region. Crucially, scientists have been able to measure exactly how much heat there is at the grounding line which will help them to predict the future behaviour of the ice sheet. They discovered that the water within a few metres of the base of the ice is 2 to 3 degrees above freezing, and circulation means that it delivers a large amount of heat (by glacier standards) to the base of the ice, causing tens of metres of melting each year. This data will be fed into current and future climate models to provide more accurate projections of future sea level rise for policymakers.

University of Houston geologist, Prof Julia Wellner, also uses the hot water boreholes to collect samples of the sediment beneath the ice. Combining these samples with others collected from the research vessel in different locations, she aims to map the path of past glacial retreat which could help her understand how Thwaites will react in the future.

Working on a relatively recent timescale dating back to 1900, the scientists want to fill in the data gap to see what was happening to the ice before satellite imagery was available.

Analysis of the sediment cores with CT scans, geochemistry, radiocarbon dating and other isotopic dating can determine when the changes in the sediment happened and the environmental conditions at that time.

The scientists also used sonar to map the sea floor in the area around Thwaites Glacier, allowing them to understand where the glacier retreated and how the ice used to flow. Working with oceanographers, they looked at how warm water is getting to the base of the ice today. Did that happen in the past, or have previous warm water conditions not caused the same level of instability?

Sediment cores and sonar mapping of the seafloor are now being used to reconstruct glacial history. This insight, combined with MELT data on the current warm water flowing around Thwaites, will help them to predict how Thwaites will retreat in the future and which environmental conditions could exacerbate or alleviate the ice loss.

In summarising the results of the research so far, US Science Coordination Lead for the ITGC, Dr Ted Scambos of the University of Colorado said:

“There’s a visceral sense of how massive this glacier is that we’ve set in motion and the fact that it truly has the capacity, all by itself, to impact sea level rise across the planet. It’s really sobering when you’re out there.”

The data shows that Thwaites has retreated rapidly in the past with much slower pushes from climate change. Now humans are driving really rapid changes in climate and, although we’re in the early stages of seeing the effects of climate change, the Thwaites scientists say that the pace of change must be slowed right now. CO2 emissions need to be dramatically reduced in the near future because, long after emissions have ceased, the warming will continue due to the quantity of carbon that is already in the atmosphere. This means that the melting of the ice sheets will continue at the same rate, sea levels will continue to rise and the amount of rise will be proportionate to the total amount of CO2 that we have put into the atmosphere. Earlier constraint on CO2 emissions will reduce the likelihood that we’ll reach the catastrophic tipping points that would result in the loss of Thwaites, the West Antarctic ice sheet and Greenland, resulting in a sea level rise of 3 - 5 metres or more.

Questions

James Gray MP - If an iceberg melts, will the land rise due to the reduced mass that is bearing down on it?

TS - As the ice melts, the release of weight will allow the land underneath to rise slightly which mitigates the effects a little, but not enough to change the overall result of sea level rise. The problem with Thwaites is that as the glacier retreats inland, the continent is below sea level and the band of ice gets thicker. The ice sheet is currently 800m deep but we’re rapidly retreating past that to the area that is 1200m deep. The pressure from the increased depth of ice will cause the ice sheet to flow much faster towards the sea and that’s the tipping point when really big sea level rise occurs.

Lord Lea of Crondall – What is a feasible target for saving Thwaites Glacier?

TS – I wouldn’t guess as to what greenhouse gas level will save Thwaites. Saving it is probably not possible at this point. Models show that we’re looking at slowing the pace rather than stopping ice loss from Antarctica.

Thwaites is unusual because its ice shelf is grounded fairly deeply on the seabed. The process begins in the central Pacific Ocean where increased warming causes changes in the atmosphere which influence the winds around Antarctica. The band of westerly winds around the continent increase in speed and shift slightly to the south. An increase in westerly winds pushes the surface of the ocean and the sea ice, causing it to drift westward but also outward due to the Coriolis effect. As the sea ice and surface water moves outwards and away from the Antarctic continent, it tends to draw deeper water inward. This warm, deep water can access the edge of the glacier where it begins to float, undermining it and speeding up Thwaites’ retreat.

Baroness Jay of Paddington – We’re all clinging to the hope that there will be outcomes from COP26 that will make a difference in the polar regions. Is there anything specific from COP that you hope will affect your work?

DV – Everything that we can do in getting towards net zero gives us more likelihood of preventing rapid sea level rise in future. But in the meantime, coastal infrastructure will need to be increased or replaced. The vulnerable areas of coastline around the world will then have the best possible chance of survival. It’s hard to say that a particular level of emission will mitigate this risk, but the less carbon we put into the atmosphere the more chance those areas will have to survive over the centuries. Sea level is one aspect of global climate change impact but it’s not the most immediate. The key thing to remember is that the effects continue long after emissions have ceased.

Brendan O’Hara MP – Thwaites Glacier melt would be a 3m rise in sea level and I’ve heard that just a 20% melt of Greenland’s ice would create a further 2m rise. A total of 5m sea level rise would be unthinkable. Is it inevitable or reversible, and how long would it take for a change in human behaviour to stop or reverse it?

TS – 5m in total will take centuries, but will that level of sea level rise happen in 500 years or the next 200 years? We’re likely to overshoot our target of 1.5 degrees warming for several decades before technology gets to the point where the CO2 levels off or starts to decline. That will require action to remove CO2 from the atmosphere biologically, or via other methods. I think we can be proud of ourselves as human beings if greenhouse gases are flat or declining by the end of the century.

After that, it will take a long time before the ice sheet will stop retreating, but we can slow it down. Sea level rise will happen, so it’s really about adaptation and whether we’re going to be overwhelmed by changes that are happening too quickly around our coastlines, or whether we can improve sea defences at a cadence that doesn’t break the bank for the countries of the world.

Baroness Neville-Jones – It’s striking how the warming is focussed on this area of Antarctica, so could we expect to see further heating in other areas of the Antarctic? Is this a fore-runner, or the centre of activity?

PD & JW – West Antarctica is the focus of the activity because the ice sheet is grounded below sea level, so Thwaites is reacting the quickest and it’s the area of greatest concern in the short term, until about 2050. Its neighbour Pine Island Glacier is showing the same behaviour and in the Antarctic peninsula we’re getting atmospheric warming because it’s further north – both the Larsen A and Larsen B ice shelves have collapsed entirely. East Antarctica is not reacting as quickly and most of its glaciers are quite stable at the moment. Its topography and ocean circulation means that the warming is kept away from the ice shelves, but local changes in wind or circulation patterns would result in the same situation as West Antarctica. It’s certainly possible that the behaviours we see in West Antarctica could extend to other areas of the continent.