Two new studies claim the rise could take place in less than 100 years, writes Dick Ahlstrom, Science Editor
The world could be facing a staggering six-metre rise in sea level in less than 100 years if the results of two new studies are correct. This would swamp a third of the world's population and, closer to home, leave cities such as Dublin, Cork and Belfast under water.
The two studies from the US combine the latest in computer modelling with ancient data on climate recovered from corals and other sources.
These show that the northern hemisphere is now almost as warm as it was 130,000 years ago, when the sea level was six metres higher than it is today.
The studies, published this morning in the journal Science, point out that melting Greenland and Arctic ice could not have accounted for the entire six- metre difference in sea level.
They argue that between 2.2 metres and 3.4 metres of the six-metre difference probably arose from northern ice melt, while the remainder came from the massive ice sheets covering Antarctica.
"Although the focus of our work is polar, the implications are global," said lead author of one study from the US National Centre for Atmospheric Research, Dr Bette Otto-Bliesner. "These ice sheets have melted before and sea levels rose. The warmth needed isn't that much above present conditions."
The two studies attempted to model temperature and ice conditions in 2100. Greenhouse gas increases in the coming decades could warm the Arctic by three to five degrees by that year. This in turn would push temperatures to where they were 130,000 years ago when sea levels were six metres higher than today.
The computer model was used to project backwards in time, and its results matched up well with the data recovered from ancient coral reefs, ice cores and other natural climate records, the authors note. "Getting the past climate change correct in these models gives us more confidence in their ability to predict future climate change," said Dr Otto-Bliesner.
Similar natural indicators were sampled in Antarctica including marine diatoms, a form of phytoplankton, and beryllium isotopes found under the west Antarctic ice sheet.
These indicated that parts of the land ice disappeared in that part of the world too, contributing to sea level rise.
Current models predict a sea level rise of less than one metre by 2100, the authors said, with perhaps a five-metre rise over the next 1,000 years. "The record of past ice sheet melting indicates that the rate of future melting and related sea level rise could be faster than widely thought."
Such change in such a short time would be catastrophic, the director of NUI Galway's Environmental Change Institute, Prof Emer Colleran said. "The six- metre rise is remarkable."
An estimated one third of the world's population lives at or very close to sea level, and a six- metre change would cause many coastal countries to disappear.
Many of Ireland's largest cities would be in jeopardy including Dublin, Belfast, Waterford and Cork. The centres of all of these could be submerged given a six- metre rise.
Prof Colleran urged caution in response to this estimate, however. "There is a risk when going back to very old data when trying to model. It is a completely different world today," she said.
She would be happy if such reports prompted discussion about global warming.
Perversely, a reduction in fossil fuel use could result in an acceleration of warming, she points out. These fuels release particulates into the atmosphere. "We are being protected if you like by the level of particulates in the atmosphere."