The Thwaites Glacier is West Antarctica's second-largest sea-flowing ice stream and has long been a concern for climate researchers.

Satellite observations over the past ten years show it to be one of the fastest shrinking ice masses on the southern continent.

According to previous estimates, as a result of global warming, it will have retreated completely in 200 to 900 years.

After that, its waters will add one to three meters to the overall rise in global sea levels.

It would now be important for the inhabitants of threatened sections of coast to know when which level will be reached.

Thwaites Glacier is a significant source of uncertainty for such forecasts.

Ulf von Rauchhaupt

Editor in the “Science” section of the Frankfurter Allgemeine Sunday newspaper.

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Nature Geoscience

A published study shows that the retreat of the 100-kilometer-wide ice tongue on the Amundsen Sea – and thus its contribution to sea-level rise – will probably not be slow and steady.

This is indicated by measurements by a team led by marine geologist Alastair Graham from the University of South Florida.

The researchers from England, Sweden and the USA were on board the American research icebreaker "Nathaniel B. Palmer" in the Amundsen Sea at the end of 2019 and had used a southern hemisphere summer with particularly little sea ice to study the seabed directly in front of the glacier edge for the first time at a depth of around 700 meters with the Swedish robotic submarine "Rán".

The section examined is around 40 kilometers in front of the current so-called baseline of the Thwaites Glacier - i.e. the contact line between the glacier ice and the sea floor.

There, the sonar data obtained documented a total of more than 160 parallel grooves, which the receding edge of the ice had left there in time with the tides, when the base line still ran through the examined area up to two hundred years ago.

This groove pattern allowed the researchers to estimate the rate of retreat at times long before modern measurements began, and thus to make statements about the longer-term dynamics of glacier retreat.

According to this, the glacier did not shrink evenly in the past, but in the meantime at a rate of 2.1 kilometers per year - twice as fast as in the years between 2011 and 2019, from which the shrinkage is known from satellite measurements.

"Our measurement results suggest that pulses of very rapid retreat have occurred at Thwaites Glacier over the past two centuries," Graham is quoted as saying in his university's press release.

"Possibly only in the mid-20th century."

A renewed acceleration of the loss of water bound in Antarctic land ice via the Thwaites Glacier is therefore almost certain, especially since the glacier is still held by a bump, behind which it will eventually have retreated.

Beyond that, the subsoil drops to greater depths, opening up a basin into which warm ocean water will then flow, rapidly undermining the glacier.

This process and the associated increase in global levels cannot be stopped by any climate protection measure.