Glaciers in Antarctica are being thrown out of balance | Polarjournal
The floating Filchner-Ronne ice shelf’s grounding line lies several hundred kilometres south of its front (visible in this 2017 aerial picture). Image: Nathan Kurtz / NASA

If we maintain the current climate, the rate of melting of the Antarctic glaciers will reach a point of no return within 400 years on average, but each additional tenth of a degree of warming brings us closer to this deadline.

The large Antarctic ice shelf meets the shore and then floats out to sea, forming a grounding line specific to each glacier. A line which, although apparently stoic, is the result of the flow of ice from upstream and its melting on contact with the ocean. In other words, it is stable as long as the formation of ice upstream is sufficient to compensate for the flow of ice downstream.

But global warming is altering this balance, favouring the melting of ice to the detriment of its storage. As a result, the grounding lines of Antarctic glaciers are retreating. European researchers are concerned that these lines reflect the state of the climate and the rise in sea level. Their work was published in two articles in the journal The Cryosphere on 7 September.

Let’s start with the good news

We learn that successive warming could destabilise the grounding lines, causing their perpetual and inevitable retreat on a human scale, and that this point of no return has not been reached. “Taking into account the history of the climate and the geometry of the Antarctic, which also determines the speed at which the ice flows, the lines have not entered an irreversible phase of retreat,” says Olivier Gagliardini, a glaciologist at the Institut des Géosciences de l’Environnement and the CNRS. Which sounds like good news.

But it is not all good news. The second study explores the future effects on glaciers of the degrees already added to the global temperature. “Even without increasing warming, we will end up pushing these lines towards areas where they will cross a tipping point,” he notes. Researchers put the deadline at 300 to 500 years for West Antarctica, if the climate remains as it is today. However, the additional degrees of warming to come will bring this point of no return closer.

In black, the average glacier grounding line recorded in 2015; in blue, the maximum retreat of this line in 10,000 years, assuming the present climate. Image : TiPACCs

“To return to the original state, we would need to reinject much more energy than was supplied to trigger the instability, which would mean a colder climate for longer to return to the initial equilibrium,” imagines Olivier Gagliardini.

Only the most optimistic scenario (SSP1-1.9) from the international panel of climate experts proposes a slow cooling of the climate from 2040 onwards. That’s possible if, and only if, global carbon absorption exceeds emissions by 2050, preceded by the stabilisation of our emissions, from now on.

Camille Lin, PolarJournal

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