A recent study has cautioned that a significant increase in the melting of West Antarctica’s ice shelves is inevitable in the decades ahead.
These floating tongues of ice, reaching from the primary ice sheet into the ocean, play a crucial role in impeding the glaciers situated behind them.
However, the melting of these ice shelves can result in accelerated movement of the ice behind, leading to a more substantial release into the oceans.
The study’s conclusions indicate that the potential rise in sea levels in the future might surpass earlier estimations.
“Our findings seem to increase the likelihood that [current] estimates [of sea-level rise] will be exceeded,” Dr Kaitlin Naughten of the British Antarctic Survey (BAS), the report’s lead author said.
The Intergovernmental Panel on Climate Change (IPCC) issued its most recent projections for future sea-level rise in 2021.
The estimates anticipate a global average sea-level increase ranging from 0.28 meters to 1.01 meters by the year 2100, with the melting of glaciers and ice sheets identified as a significant contributing factor.
While a one-meter rise in sea levels may not seem substantial, it poses a considerable risk to hundreds of millions of people globally, making them vulnerable to the threats of coastal flooding.
Nonetheless, the IPCC highlighted the potential for higher sea-level rises due to “ice-sheet-related processes characterised by deep uncertainty,” which were not directly factored into their estimates. A critical uncertainty lies in understanding how the ice sheet interacts with the oceans.
This recent study, featured in the journal Nature Climate Change, represents the inaugural attempt to simulate how ocean warming will impact Antarctic ice shelves based on varying levels of greenhouse gas emissions, the primary contributors to human-induced climate change.
The study reveals that the Amundsen Sea, located off the coast of West Antarctica, is expected to warm approximately three times faster than historical rates throughout the remainder of this century. Consequently, this accelerated warming will lead to a more rapid melting of ice shelves.
Significantly, the study suggests that this accelerated melting will occur even if robust measures are taken to decelerate global warming. However, Dr. Naughten emphasises that this should not dissuade efforts to transition away from fossil fuels.
“What we do now will help to slow the rate of sea-level rise in the long term,” she explains.
While the authors acknowledge the need for further research to enhance confidence in their conclusions, the study’s significance lies in understanding how ice shelf melting impacts the broader context of West Antarctica.
The Antarctic ice sheet possesses sufficient ice to elevate global sea levels by approximately 58m (190ft) in the event of complete melting.
The majority of this ice is situated in East Antarctica, which has demonstrated relative stability in recent years and is not anticipated to undergo collapse in the immediate future.
However, a substantial portion, adequate to result in a sea-level increase of approximately 5m (16ft), is situated in West Antarctica. This region is deemed less stable and has experienced a decline in mass over the recent decades.
The ice, anchored on the bedrock of the Antarctic continent, generally flows towards the oceans. In numerous locations, these grounded glaciers extend onto the ocean surface, forming ice shelves.
These ice shelves play a pivotal role in restraining the mass of ice behind them. However, the melting of these ice shelves due to warm ocean waters diminishes this restraining effect, potentially causing acceleration in the glaciers behind.
As this acceleration occurs, more ice may enter the ocean through melting, or break off to form icebergs.
Moreover, in contrast to most of East Antarctica, a substantial portion of the West Antarctic continent is situated below sea level. This topographical feature means that glaciers could retreat into progressively deeper waters, hastening the overall loss of ice.
Thwaites Glacier, flowing into the Amundsen Sea and sometimes dubbed the “doomsday glacier” due to its potential to raise global sea levels by approximately 65cm (25in) if it collapses entirely, is particularly susceptible to warming.
The glacier’s grounding line, the point where ice transitions from being in contact with the bedrock to floating, is already retreating by more than 1km per year in certain locations.
“This study worsens the outlook for Thwaites Glacier, as we simulate rapidly increasing melting beneath its connected ice shelf,” Dr Naughten said.
The processes triggered by faster ice shelf melting “could lead to the collapse of the West Antarctic Ice Sheet”, the authors suggest.
Nevertheless, additional factors will influence how the ice sheet reacts to warming and, consequently, the rate at which sea levels rise. Variables like snowfall, surface ice melting, and the velocity of glacier flow were not explicitly taken into account in this recent study.
“It looks like we’ve lost control of melting of the West Antarctic Ice Sheet,” concludes Dr Naughten.
“This is a sobering piece of research,” agrees Alberto Naveira Garabato, a professor in physical oceanography at the University of Southampton who was not involved in the latest work.
But researchers emphasise this is not a reason to give up.
Steps taken to slow the loss of ice, through cutting greenhouse gas emissions, could be vital in giving societies time to prepare for and adapt to rising seas.
“It should serve as a wake up call,” Prof Naveira Garabato explains.
“We can still save the rest of the Antarctic Ice Sheet, containing about 10 times as many metres of sea-level rise, if we learn from our past inaction and start reducing greenhouse gas emissions now.”
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