Scientists say melting of Earth’s widest glacier began in the 1940s

By James Gamble via SWNS

Earth's widest glacier began melting as far back as the 1940s, reveals a new study.

Antarctica's Thwaites Glacier, which measures around 80 miles on the western edge of the continent, is losing 50 billion tonnes of ice more than it's receiving in snowfall - placing its stability in a precarious position.

The huge glacier currently accounts for around four percent of global sea-level rise and is now believed to have been in retreat for more than 80 years.

American researchers warn that if the glacier were to collapse entirely, it would have catastrophic consequences for the planet.

Accelerating ice loss at the Thwaites Glacier has been observed since the 1970s, though until now it has been unclear as to when this melting first began.

In a recent study published in the journal PNAS, climate scientists at the University of Houston (UH) suggest significant glacial retreat began in the 1940s and, once underway, never stopped.

The results coincide with previous work that studied glacial retreat on Pine Island Glacier, which similarly found it began in the 1940s.

Study author Dr. Rachel Clark, who graduated last year from UH with a doctorate in geology, said we can no longer afford to ignore glacial retreat.

"What is especially important about our study is that this change is not random nor specific to one glacier," she explained.

“It is part of a larger context of a changing climate. You just can’t ignore what’s happening on this glacier.”

The researchers say the glacial retreat was likely sparked by an extreme El Niño climate pattern - in which sea surface temperatures are warmed every few years.

Thwaites Glacier has never recovered since and, according to the research team, is currently contributing to four percent of global sea-level rise.

“It is significant that El Niño only lasted a couple of years, but the two glaciers, Thwaites and Pine Island, remain in significant retreat,” Dr. Julia Wellner, a UH associate professor of geology, said.

The US lead investigator of the Thwaites Offshore Research project, or THOR, an international collaboration whose team members are authors of the study, added: "Once the system is kicked out of balance, the retreat is ongoing."

The researchers' findings also make it clear that the retreat at the glaciers’ grounding zone, or the area where the glaciers lose contact with the seabed and start to float, was due to external factors.

Dr Claus-Dieter Hillenbrand, the UK's lead investigator of THOR and co-author of the study, added that the findings demonstrated that ice loss in the Antarctic was mainly influenced by external factors.

She said: "The finding that both Thwaites Glacier and Pine Island Glacier share a common history of thinning and retreat corroborates the view that ice loss in the Amundsen Sea sector of the West Antarctic ice sheet is predominantly controlled by external factors, involving changes in ocean and atmosphere circulation, rather than internal glacier dynamics or local changes, such as melting at the glacier bed or snow accumulation on the glacier surface."

Co-author James Smith, a marine geologist at the British Antarctic Survey added: “A significant implication of our findings is that once an ice sheet retreat is set in motion, it can continue for decades - even if what started it gets no worse.

“It is possible that the changes we see today on Thwaites and Pine Island glaciers – and potentially across the entire Amundsen Sea embayment – were essentially set in motion in the 1940s.”

The researchers utilized three primary methods for their study, one of which involved marine sediment core collection from the Thwaites Glacier.

The team's core collections - which occurred in 2019 and drew closer to the glacier than ever before - were used to reconstruct the glacier's history from the early Holocene epoch of around 11,700 years ago to the present day.

X-rays of the sediment were taken to gather details from its history, whilst geochronology - the science behind dating earth materials - was used to conclude that significant melting began in the 1940s.

The researchers used a radioactive isotope that's naturally buried in the sediment cores as the most important isotope in her geochronology.

This process is similar to radiocarbon dating, which measures the age of organic materials as far back as 60,000 years.

“But the isotope has a short half-life of about 20 years, whereas something like radiocarbon has a half-life of about 5,000 years,” Dr. Clark explained.

“That short half-life allows us to build a timeline for the past century that’s detailed."

This methodology is important, as although satellite data exists to help scientists understand glacial retreat, these observations only go as far back as a few decades - a time frame too short to determine how the Thwaites Glacier responds to ocean and atmosphere changes.

Pre-satellite records are needed for scientists to understand the glacier’s longer-term history, which is why sediment cores are used.

Thwaites Glacier plays a vital role in regulating the West Antarctic ice sheet stability and, thus, global sea-level rise, according to Antarctic researchers.

“The glacier is significant not only because of its contribution to sea-level rise but because it is acting as a cork in the bottle holding back a broader area of ice behind it,” Dr. Wellner highlighted.

“If Thwaites is destabilized, then there’s potential for all the ice in West Antarctica to become destabilized."

If the Thwaites Glacier were to collapse entirely, the research team warns global sea levels are predicted to rise by 65 cm (25 in) - which would destroy the lives of many living close to the ocean.

“Our study helps to better understand what factors are most critical in driving thinning and retreat of glaciers draining the West Antarctic ice sheet into the Amundsen Sea,” Dr. Hillenbrand added.

“Therefore, our results will improve numerical models that attempt to predict the magnitude and rate of future Antarctic ice sheet melting and its contributions to sea levels.”