According to a recent study, Antarctic glaciers are losing ice more quickly due to meltwater running beneath them, which could result in sea level rises that are much worse than expected.
Meltwater running beneath glaciers is causing them to lose ice more quickly, according to US researchers mapping Antarctic ice sheets using a new approach.
Scientists studying climate change caution that the present models projecting significant changes in sea level do not take this meltwater into account, which could imply that already concerning estimates of rising sea levels are underestimated.
The study’s authors, who published their findings in the journal Science Advances, caution that by the year 2300, the two glaciers they are focusing on would be solely responsible for rises of 1.5 meters (5 feet).
In addition, the researchers alerted the climate community to the possibility that the modeling community was underestimating sea-level rises, which might wipe out coastal populations in the ensuing decades. Their work acted as a “wake-up call” for this community.
In order to predict their contributions to sea-level rises, climate scientists at the Scripps Institution of Oceanography at the University of California, San Diego (UCSD) analyzed the retreat of two glaciers in eastern Antarctica through the year 2300 under various emission scenarios.
This most recent study took into account the impact of subglacial discharge, or the movement of meltwater from beneath glaciers out to sea, in contrast to earlier models of the Antarctic ice sheet.
The combined mass of the two glaciers under consideration, Denman and Scott, is sufficient to raise world sea levels by almost 1.5 meters.
With a high emissions scenario (e.g., the IPCC’s SSP5-8.5 scenario, which assumes no new climate policy and features 20 percent higher CO2 emissions by 2100), the researchers’ model found that the contribution of these glaciers to sea-level rise due to glacial meltwater increased by 15.7 percent by the year 2300, from 19 millimeters (0.74 inches) to 22 millimeters (0.86 inches).
The surrounding glaciers are perched atop a continental trench that is more than two miles deep. The researchers predict that if their retreat reaches the trench’s steep slope, it will accelerate the glaciers’ contribution to sea level rise.
The melting that takes place when the glacier rests on its continental bedrock produces subglacial meltwater.
Friction from the ice scraping against the bedrock and geothermal heat seeping through the crust from the Earth’s core are the primary sources of heat that melt glacial ice.
According to the researchers’ model, the glaciers retreated below this barrier around 25 years earlier than they did without the additional influence of the meltwater.
The study’s co-author and researcher at Scripps’ Institute of Geophysics and Planetary Physics, Dr. Jamin Greenbaum, issued the following warning: “I think this paper is a wake-up call for the modeling community.”
“It demonstrates that you cannot accurately model these systems without accounting for this process.”
A major finding of the study, in addition to the underappreciated and understudied contribution of subglacial discharge to the acceleration of sea level rise, is the significance of our actions in the upcoming decades in limiting greenhouse gas emissions, according to Dr. Greenbaum.
The glaciers did not retreat completely into the trench during the model’s low emissions scenarios, preventing the ensuing runaway contributions to sea level rise.
Dr. Greenbaum clarified, “If there is a doomsday story here, it isn’t subglacial discharge.”
“Emissions continue to be the real end of the story, and humanity is still in control of the situation.”
Dr. Tyler Pelle, a postdoctoral researcher at Scripps and the study’s principal author, clarified that precise modeling was also essential for alerting the millions of people who live along coastlines.
“The welfare of coastal communities depends on knowing when and how much global sea levels will rise,” Dr. Pelle stated.
“Without precise sea-level rise projections, we cannot effectively prepare our communities, as millions of people reside in low-lying coastal zones.”
Previous research has indicated that subglacial meltwater is a frequent feature of glaciers worldwide. It is found beneath a number of other major Antarctic glaciers, such as the vast Thwaites Glacier in West Antarctica, which is around 14 times larger than either Great Britain or India.
The ice shelf of a glacier is a long, floating tongue of ice that extends beyond the furthest portion of the glacier that is still in contact with solid ground, known as the “grounding line,” and is thought to melt more quickly when glacial meltwater flows out to sea.
According to the researchers, it accelerates ice shelf melting and glacial retreat by generating ocean mixing, which brings in more ocean heat into the space beneath a glacier’s floating ice shelf.
Sea levels rise as a result of the upstream glacier accelerating due to the increased melting.
According to Dr. Greenbaum, the scientific community as a whole largely accepts the theory that subglacial discharge contributes to further ice shelf melting.
Many scientists were doubtful if the process’s effect was significant enough to raise sea levels, which is why it has not been included in predictions of sea level rise thus far.
According to Dr. Pelle, subglacial discharge initially came to his attention in 2021 when his team noticed that, given the local ocean temperatures, the ice shelf of East Antarctica’s Denman Glacier was melting more quickly than was normal.
Strangely, despite nearly comparable ocean conditions, the ice shelf of Denman’s neighbor, Scott Glacier, was melting far more slowly.
The research team combined models for three different environments: the ice sheet, the area between the ice sheet and bedrock, and the ocean to test whether glacial melting could reconcile the melt rates observed at the Denman and Scott ice shelves and whether subglacial meltwater might accelerate sea-level rise.
After getting married, the researchers used a NASA supercomputer to run a number of projections up until the end of the twenty-third century.
Three primary scenarios were included in the projections: a low emissions pathway (SSP1-2.6), a high emissions pathway (SSP5-8.5), and a control scenario that included no additional ocean warming.
The researchers produced forecasts for each scenario both with and without the influence of the current rates of glacier melting.
The model’s simulations showed that the melt rates at Denman and Scott Glaciers could be harmonized by include subglacial discharge.
According to Dr. Pelle, “[The model showed] a strong subglacial discharge channel drained across the Denman Glacier grounding line, while a weaker discharge channel drained across the Scott Glacier grounding line,” which explains why Scott Glacier was melting so much more slowly than Denman.
He said that the reason for its rapid melting was the Denman discharge channel’s strength.
With or without subglacial discharge at 2300, the contributions to sea-level rise for the control and low-emissions model runs were nearly nil or even slightly negative.
In contrast, the model indicated that subglacial discharge raised these glaciers’ contribution to sea level rise from 19 millimeters (0.74 inches) to 22 millimeters (0.86 inches) in 2300 under a high emissions scenario.
The two glaciers receded into the two-mile-deep trench underneath them by 2240 in the high emissions scenario with subglacial discharge, about 25 years earlier than in the model runs without subglacial discharge.
The Denman and Scott Glaciers’ annual sea-level rise contribution skyrocketed to a peak of 0.33 millimeters (0.01 inches) per year once their grounding lines retreated past the trench’s lip. This represents nearly half of the Antarctic ice sheet’s current annual sea-level rise contribution.
According to the scientists, the trench’s steep slope is the cause of this sudden surge in the contribution of sea level rise. As the glacier retreats downslope, its ice shelf starts to lose ever bigger slabs of ice from its leading edge.
Further glacial retreat results from the process of ice loss swiftly exceeding ice accumulation near the interior of the ice sheet.
Scientists worry that terrain like the trench beneath the Scott and Denman Glaciers, which they refer to as a “retrograde slope,” could start a positive feedback loop whereby glacial retreat leads to further retreat.
Although not as dramatic as the Denman-Scott trench, large portions of the West Antarctic Ice Sheet, like the massive Thwaites Glacier, also include retrograde slopes that raise concerns about wider instability of the ice sheet.
The majority of Antarctic glaciers, if not all of them, including the Thwaites, Pine Island, and Totten glaciers, have subglacial meltwater implied beneath them, according to Dr. Pelle.
We have demonstrated that subglacial discharge may be hastening the retreat of all these glaciers, which is causing the sea level to increase.
“We must model these other glaciers immediately in order to gauge the extent of the impact that subglacial discharge is having.”
The UC San Diego group is actively proposing a study proposal to apply their new model to the entire Antarctic ice sheet, living up to their words.
In order to allow the amount of subglacial meltwater to dynamically react to these additional parameters, future iterations of the model can potentially try to tie the subglacial environment with the ice sheet and ocean models.
According to Greenbaum, their existing model maintained a constant subglacial meltwater level for the course of the model runs; altering this value to reflect the subglacial environment more dynamically would probably make the model more realistic.
According to Dr. Greenbaum, “this also means that our results are probably a conservative estimate of the effect of subglacial discharge.”
“Having said that, we are unsure of the precise rate at which this process will accelerate sea level rise; hopefully, it won’t be excessive.”
The National Science Foundation (NSF) and NASA are funding part of Dr. Greenbaum’s future fieldwork in Antarctica, which will directly examine the effects of subglacial meltwater in the East and West Antarctic ice sheets.
Dr. Greenbaum and his associates will be visiting the ice shelves of Denman and Thwaites Glaciers in East Antarctica and West Antarctica, respectively, in cooperation with the Australian Antarctic Division and the Korea Polar Research Institute. They will be searching for concrete proof that subglacial freshwater is leaking into the ocean beneath the glaciers’ ice shelves and causing warming.