by I am strolling on the steep bank of a white-water raging torrent, and although the canyon is only about the width of the highway, the flow of the river is greater than that of the London Thames. The rush and deafening roar of the cascading water is incredible – a humbling reminder of the raw power of nature.
As I round a corner, I am stunned by a sight that is completely surreal: A gaping crack has opened in the river bed, and the water is being swallowed up in a huge whirlpool, sending up huge sponges of spray. This might sound like a computer-generated scene from a blockbuster action movie – but it’s true.
A moulin is forming right in front of me on the Greenland ice sheet. Only that should really be happening here – current scientific understanding does not accommodate this reality.
As a glaciologist, I have spent 35 years investigating how meltwater affects the flow and stability of glaciers and ice sheets.
This gaping hole opening up at the surface is just the beginning of the meltwater’s journey through the bowels of the ice sheet. As it enters moulins, it bores a complex network of tunnels through the ice sheet that extends hundreds of meters down, all the way to the ice sheet bed.
Once it reaches the bed, the meltwater drains into the ice sheet’s subglacial drainage system – like an urban stormwater network, albeit one that is constantly changing and supporting. It carries the meltwater to the ice edges and eventually ends up in the ocean, with major consequences for the thermodynamics and flow of the overlying ice sheet.
Scenes like this and new research into the mechanics of the ice sheet are challenging traditional thinking about what happens in and under ice sheets, where observations are extremely challenging but have huge implications. They suggest that the world’s remaining ice sheets in Greenland and Antarctica are much more vulnerable to climate warming than models predict, and that the ice sheets may be destabilizing from within.
This is a tragedy for the half a billion people who live in vulnerable coastal regions, as the Greenland and Antarctic ice sheets are effectively huge reservoirs of frozen fresh water locked in at over 65 meters (over 200 feet) of equivalent rise global sea level. . Since the 1990s their loss of mass has been increasing, contributing mainly to future sea level rise and as the wild card.
How do narrow cracks become gap masses in the ice
Moulins are near-vertical conduits that catch and undulate the melt runoff from the surface of the ice each summer. There are thousands across Greenland, and they can grow to significant sizes due to the thickness of the ice combined with the extremely high rates of surface melting. These gaping chasms can be the size of tennis courts on the surface, with hidden chambers in the ice below that could swallow cathedrals.
But this new moulin that I have seen is really far from any crevasse areas and melt lakes, where current scientific understanding demands that they should form.
In a new paper, Dave Chandler and I show that ice sheets are littered with millions of tiny hairline cracks that hold open the meltwater from the rivers and streams that intercept them.
Because glacial ice is so fragile at the surface, such cracks are ubiquitous throughout the melting zones of all glaciers, ice sheets, and ice shelves. But because they are so tiny, they cannot be detected by satellite remote sensing.
Under most conditions, we find that flow-fed hydrofracturing like this allows water to penetrate hundreds of meters down before the freeze closes, without the crack going to the bed to form a full-fledged mole. But, even these partial depth hydrofractures have a significant impact on ice sheet stability.
As the water pours in, it damages the ice sheet structure and releases its latent heat. The ice structure heats up and moves and, therefore, flows and melts faster, just like heated candle wax.
The current-driven hydrofractures mechanically damage the ice and transfer heat into the interior of the ice sheet, destabilizing it from within. Ultimately, the internal fabric and structural integrity of the ice sheets are becoming more vulnerable to climate warming.
Emerging processes that accelerate ice loss
In the last two decades, that scientists have been seriously tracking the melting and flow of ice sheets, melting events have become more common and more intense as global temperatures rise – made worse by the warming of the Arctic which is almost four times more than the global average.
The ice sheet is also flowing and icebergs are calving much faster. It has lost about 270 billion metric tons of ice per year since 2002: over a centimeter and a half (half an inch) of global sea level rise. Greenland is now, on average, adding about 1 millimeter (0.04 inch) to the sea level budget each year.
A study carried out in 2022 found that, even if atmospheric warming is stopped now, at least 27 centimeters – almost 1 foot – of sea level rise is inevitable due to Greenland’s imbalance over the past two decades. ‘climate.
Understanding the risks we face is essential. However, the current generation of ice-sheet models used to assess how Greenland and Antarctica will respond to future warming do not account for the amplification processes being detected. This means that the models’ estimates of sea level rise, which are used to inform Intergovernmental Panel on Climate Change (IPCC) reports and policy makers around the world, are conservative and underestimating rates of sea rise. global in a warming world.
It’s just our new result. Recent studies have shown that:
In recent months, other papers have also described previously unknown feedback processes operating under ice sheets that computer models cannot currently account for. These processes often occur at a scale too fine for models to pick up, or the simple physics of the model means that the processes themselves cannot be captured.
Two such studies independently identify enhanced submarine melting at the landline in Greenland and Antarctica, where large outlet glaciers and ice streams sink into the sea and begin building their beds as floating ice shelves. These processes greatly accelerate the ice sheet response to climate change and, in the case of Greenland, could double future mass loss and contribute to sea level rise.
Current climate models show the risks
Along with other applied glaciologists, “structured expert judgement” and some honest modellers, I argue that the current generation of ice models used to inform the IPCC are not keeping up with the sudden changes being observed in Greenland and in Antarctica, or the risks associated with it. before us.
Ice sheet models do not include these evolving feedbacks and respond over millennia to strong warming disturbances, leading to sluggish sea level forecasts that are lulling policymakers into a false sense of security. We have come a long way since the first IPCC reports in the early 1990s, which treated polar ice sheets as completely static entities, but we still fall short of capturing reality.
As a dedicated field scientist, I am well aware of how privileged I am to work in these sublime environments, where what I observe inspires and inspires. But it also fills me with speculation about our low-lying coastal regions and what lies ahead for the 10% or so of the world’s population that live in them.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. The Chat is trusted news from experts. Try our free newsletters.
It was written by: Alun Hubbard, University of Tromsø.
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Alun Hubbard acknowledges funding from the Research Council of Norway (Centres of Excellence: CAGE & iC3), the Academy of Finland (PROFI4: Arctic Interactions) and is also affiliated with Oulun Yliopisto (University of Oulu), Arctic Basecamp and La Venta Esplorazioni Geografiche.
