Accelerated melting of the West Antarctic Ice Sheet will continue until the end of this century, no matter how much greenhouse gas emissions are cut.
Scientists from the British Antarctic Survey say this means sea level rise could be higher than currently projected, even if humanity manages to limit global warming to below 1.5C.
They have published their results in the journal Nature Climate Change this week, saying this does not mean that efforts to cut fossil fuel use are futile.
Lead Author Dr Kaitlin Naughton says: "We must not stop working to reduce our dependence on fossil fuels."
"What we do now will help to slow the rate of sea level rise in the long term. The slower the sea level changes, the easier it will be for governments and society to adapt to, even if it can't be stopped," she said.
The team ran simulation models for a range of temperature scenarios through the UK's national supercomputer.
They included conditions in the 20th century, a 1.5C scenario, a 2C scenario and the medium and high carbon emissions scenarios of RCP 4.5 and RCP 8.5.
All scenarios resulted in significant and widespread future warming of the Amundsen Sea and increased melting of its ice shelves.
The three lower-range scenarios followed nearly identical pathways over the 21st century. Even under the best-case scenario, warming of the Amundsen Sea sped up by about a factor of three and melting of the floating ice shelves which stabilise the inland glaciers followed, though it did begin to flatten by the end of the century.
The team described the results as sobering with Dr Naughton adding: "It looks like we’ve lost control of melting of the West Antarctic Ice Sheet."
"If we wanted to preserve it in its historical state, we would have needed action on climate change decades ago.
"The bright side is that by recognising this situation in advance, the world will have more time to adapt to the sea level rise that’s coming. If you need to abandon or substantially re-engineer a coastal region, having 50 years lead time is going to make all the difference."
The West Antarctic Ice Sheet has the potential to add to global sea level rise by up to 5 metres, but this study does not specify how much sea level rise estimates would have to be revised as a result of the new findings.
The IPCC has projected a sea level rise of up to 0.77 metres by 2100 if temperature increase is limited to 1.5C, with levels to continuing to rise for thousands of years as temperatures increase.
It advised that flood risk will reach catastrophic levels, even under lower emissions scenarios if coastal societies do not adapt.
This latest study suggests governments and others may need to revise upwards their plans for adapting to flood risk.
