Global sea levels will rise substantially more than previously thought and almost irreversibly if greenhouse gas emissions continue, according to New Zealand-led research on Thursday.
An international team led by Dr. Nicholas Golledge, of Victoria University's Antarctic Research Centre, used state-of-the-art computer modeling to simulate the Antarctic 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 (carbon dioxide) 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," Golledge said in a statement.
In its 2013 Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) predicted that the Antarctic ice sheet would contribute only 5 centimeters to global sea-level rise by the end of this century even for its warmest emissions scenario.
But Victoria University Professor Tim Naish, who was a lead author of the IPCC report, cautioned that at the time the 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 percent 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," said Golledge.
"If we lose these ice shelves, the Antarctic contribution to sea-level rise by 2,100 will be nearer 40 centimeters."
To avoid the loss of the Antarctic ice shelves, and an associated commitment to many meters of sea-level rise, the study showed atmospheric warming needed to be kept below 2 degrees centigrade above present levels.
"Missing the 2 degrees centigrade target will result in an Antarctic contribution to sea-level rise that could be up to 10 meters above present day," said Golledge.
"The stakes are obviously very high, 10 percent of the world's population lives within 10 meters of present sea level."
To restrict global warming to 2 degrees centigrade and prevent the more dangerous consequences of climate change, the United Nations climate change meeting in Paris later this year had to agree to reduce global CO2 emissions to zero before the end of the century, Naish said in the statement.
"To be on track this will require a global commitment to 30 percent reduction, below year 1990 levels, by the year 2030."
The last time CO2 concentrations in the atmosphere were similar to present levels was about 3 million years ago, when sea levels were 20 meters higher than now, said Golledge.
"We're currently on track for a global temperature rise of a couple of degrees which will take us into that ballpark, so there may well be a few scary surprises in store for us, possibly within just a few hundred years."
