Climate change may lead to substantial rise in sea level

Melbourne, October 19

A jump in global average temperatures of 1.5 degrees Celsius to 2 degrees Celsius will see the collapse of Antarctic ice shelves and lead to hundreds and even thousands of years of sea-level rise, a new research has warned.

An international team led by Dr Nicholas Golledge, who holds a joint position at Victoria University's Antarctic Research Centre and GNS Science in New Zealand, predicted how the Antarctic ice sheet will respond to future atmospheric warming.

Using state-of-the-art computer modelling, Golledge and his colleagues simulated the ice sheet's response to a warming climate under a range of greenhouse gas emission scenarios.

They found that all but one of the scenarios (that of significantly reduced emissions beyond 2020) would lead to the loss of large parts of the Antarctic ice-sheet, which in turn would result in a substantial rise in global sea level.

"The long reaction time of the Antarctic ice-sheet — which can take thousands of years to fully manifest its response to changes in environmental conditions — coupled with the fact that CO2 lingers in the atmosphere for a very long time means that the warming we generate now will affect the ice sheet in ways that will be incredibly hard to undo," said Golledge.

In its 2013 Assessment Report the Intergovernmental Panel on Climate Change (IPCC) predicted that the Antarctic ice sheet would contribute only 5 cm to global sea-level rise by the end of this century even for its warmest ('business as usual') emissions scenario.

But Professor Tim Naish, who worked with Golledge on this latest study and who was also a lead author of the IPCC report, cautioned that at the time that report was written there was insufficient scientific knowledge on how the Antarctic ice sheet might respond to future warming, meaning the IPCC sea-level projections could have been too modest.

"Our new models include processes that take place when ice sheets come into contact with the ocean. Around 93 per cent of the heat from anthropogenic global warming has gone into the ocean, and these warming ocean waters are now coming into contact with the floating margins of the Antarctic ice sheet, known as ice shelves.

"If we lose these ice shelves, the Antarctic contribution to sea-level rise by 2100 will be nearer 40 centimetres," said Golledge.

To avoid the loss of the Antarctic ice shelves, and an associated commitment to many metres of sea-level rise, the study shows atmospheric warming needs to be kept below 2 degrees Celsius above present levels.

"Missing the 2 degrees Celsius target will result in an Antarctic contribution to sea-level rise that could be up to 10 metres above present day," said Golledge.

"The stakes are obviously very high — 10 per cent of the world's population lives within 10 metres of present sea level," he said.

The new research is published in the journal Nature. — PTI