Parts of Antarctic ice sheet have different tipping points, some may have already been crossed

The various parts of the Antarctic Ice Sheet have different critical thresholds as tipping points with the drainage basins interacting with each other, according to new research by the Potsdam Institute of Climate Impact Research (PIK) and  the Max Planck Institute of Geoanthropology (MPI-GEA) published in the journal Nature Climate Change. 

When an ice sheet crosses its tipping point, the changes occurring, such as melting, become irreversible. The study found that the Antarctic Ice Sheet does not have a single tipping point but a set of different tipping systems across basins. 

In the study, researchers analysed 18 drainage basins in Antarctica for characteristics of long term loss of ice at different levels of warming. They used the Parallel Ice Sheet Model (PISM) to simulate the long term responses of different basins to the gradual increases in warming. The scientists highlighted that the changes in one basin could lead to cascading changes in other basins, concluding that the basins interact with each other. 

“Crossing a tipping point doesn’t mean immediate collapse,” said Ricarda Winkelmann, director of MPI-GEA, PIK scientist and lead author of the paper. “Large-scale ice loss in these regions unfolds over centuries, but the process may already have been set in motion in parts of the West Antarctic Ice Sheet,” she added. 

With today’s warming, which is at 1.3°C above the pre industrial average (1850-1900), 40 per cent of ice in West Antarctic is already on its way to being lost forever, according to the researchers. In East Antarctica many regions could cross critical thresholds at warming of 2°C-3°C.

“We find that ice loss in some Antarctic basins unfolds gradually with warming, whereas other basins are characterised by a tipping point, beyond which the loss of ice accelerates disproportionally to the warming and can be irreversible over centuries to millennia,” said Winkelmann.

“In East Antarctica, the ice mass is large enough to contribute ten times more to sea-level rise than its western counterpart. Massive regions like the Wilkes Basin are also increasingly at risk of substantial ice loss with sustained warming of 2 to 5°C above pre-industrial levels,” said Julius Garbe, PIK scientist and co-author of the study.

The lowest thresholds are in the Amundsen Sea basin which includes the Thwaites and Pine Island glaciers and the Ronne basin in West Antarctica. Many of these regions may be already past their tipping points with Earth warmer than pre industrial period by 1.3°C.

The Thwaites glacier is often called the ‘Doomsday Glacier’ due to its potential to significantly add to worldwide sea levels. It is one of the fastest changing ice-ocean systems on the planet. A recent study showed how the changes occurring in the Thwaites glacier can be considered a blueprint to future changes in other Antarctic glaciers. 

The melting of the Antarctic Ice Sheet would add significantly to the global mean sea level rise. The ice sheet constitutes the largest concentration of ice on the planet and if it melts completely, global mean sea levels could rise by around 58 metres. 

“Seeing how rapidly some regions in Antarctica are already responding to anthropogenic climate change, how extreme weather events are not only becoming more frequent but lead to subsequent changes in the ice dynamics, really puts into perspective the vulnerability of this vast ice sheet,” said Winkelmann, who has just returned from a field visit to Antarctica. 

“Our mapping of potential regional tipping points shows where the greatest risks lie on the long term, and which regions of the Antarctic Ice Sheet need closest monitoring. Cutting greenhouse gas emissions rapidly is imperative to prevent further destabilisation of ice basins,” she added.