Antarctic Ice Sheet may have reached tipping point of no return: Study

The Antarctic Ice Sheet, which has the biggest potential for sea-level rise, may be at or very close to a melting tipping point, according to a new study. In the phase beyond this point, the ice sheet cannot stop melting even if global warming is contained or reversed.

In the scientific parlance, such behaviour is called 'hysteresis'. This means the process (in this case melting) has entered an input-output loop and can keep occuring independently.

Researchers at the Norwegian research organisation NORCE Research, United Kingdom's Northumbria University and Germany's Potsdam University (PIK) have confirmed hysteresis behaviour in the the Antarctic Ice Sheet.

Ice sheets take hundreds — sometimes thousands — of years to change. But the scientific community has been observing ice loss for only 40 years, which is short to completely understand the nature and speed of the melting.

To better understand how Antarctica’s ice responds over the long term, the researchers used computer models — transient and equilibrium Parallel Ice Sheet Model simulations of Antarctic Ice Sheet — to simulate how the ice sheet behaved during the natural cycles of interglacial (warming) and glacial (cooling) over the past 800,000 years.

If Antarctica loses even a small amount of its massive ice, it could cause serious problems for coastal areas and the global economy. This analysis shows that with as little as .25 degree Celsius rise in ocean temperatures or even zero warming over current levels, the West Antarctic Ice Sheet will have led to 4 metre sea-level rise by the time it reaches equilibrium ice sheet states. Equilibrium ice sheet state refers to the final extent of the ice sheet after it has gone through the entire process of melting under current climatic conditions, which could take several years considering the slow response time of ice sheets.

"Therefore, today we are likely already at (or almost at) an overshoot scenario, supporting recent studies warning of substantial irreversible ice loss with little or no further climate warming," the researchers wrote in the report.

Heating of oceans that surround Antarctica, rather than atmospheric warming, is responsible for pushing ice sheets into interglacial state.

Moreover, the authors emphasised that once the tipping point is crossed, restoring the ice sheets to their current stable condition will be unfeasible. It would need several millenia of temperatures at or below pre-industrial conditions.

But there is hope: Urgent action to mitigate climate change may still halt this collapse. “It takes tens of thousands of years for an ice sheet to grow, but just decades to destabilise it by burning fossil fuels. Now we only have a narrow window to act,” said co-author Julius Garbe from PIK.