Each degree Celsius rise in global temperatures is likely to raise world’s sea levels by more than 2 metres within the next 2,000 years, a new study has warned.

While thermal expansion of the ocean and melting mountain glaciers are the most important factors causing sea-level change today, the Greenland and Antarctic ice sheets will be the dominant contributors within the next two millennia, according to the study published in the Proceedings of the National Academy of Sciences.

Half of that rise might come from ice-loss in Antarctica which is currently contributing less than 10 per cent to global sea-level rise.

“CO2, once emitted by burning fossil fuels, stays an awful long time in the atmosphere. Consequently, the warming it causes also persists,” said Anders Levermann, lead author of the study and research domain co-chair at the Potsdam Institute for Climate Impact Research.

The oceans and ice sheets are slow in responding, simply because of their enormous mass, which is why observed sea-level rise is now measured in millimetres per year.

“The problem is: once heated out of balance, they simply don’t stop. We’re confident that our estimate is robust because of the combination of physics and data that we use,” Levermann said in a statement.

The study is the first to combine evidence from early Earth’s climate history with comprehensive computer simulations using physical models of all four major contributors to long-term global sea-level rise.

During the 20th century, sea level rose by about 0.2 metres, and it is projected to rise by significantly less than two metres by 2100 even for the strongest scenarios considered.

At the same time, past climate records, which average sea-level and temperature changes over a long time, suggest much higher sea levels during periods of Earth history that were warmer than present.

For the new study, the international team of scientists used data from sediments from the bottom of the sea and ancient raised shorelines found on various coastlines around the world.

If global mean temperature rises by 4 degrees compared to pre-industrial times, which in a business-as-usual scenario is projected to happen within less than a century, the Antarctic ice sheet will contribute about 50 per cent of sea-level rise over the next two millennia, researchers said.

Greenland will add another 25 per cent to the total sea-level rise, while the thermal expansion of the oceans’ water, currently the largest component of sea-level rise, will contribute about 20 per cent, and the contribution from mountain glaciers will decline to less than 5 per cent, mostly because many of them will shrink to a minimum, the study found.