‘Extraordinary’ sea levels measured in warm global period

Media release

Researchers have looked back in time to uncover that even a modest climb in global temperatures could result in a significant rise in global sea levels.

Published in Nature Geoscience, a team led by Curtin University researcher Dr Mick O’Leary have examined ancient fossil shorelines of Western Australia during the Last Interglacial, a period between 128,000 and 116,000 years ago when global climate temperatures were a couple degrees centigrade higher than today’s. They discovered sea levels during this period to be a staggering three to four metres higher than its current level.

Dr O’Leary said at around 119,000 years ago, the team found evidence of an abrupt jump in sea levels from three to four metres to more than 8.5 metres, suggesting a major ice sheet collapse event occurred.

“While global temperatures and CO2 levels are fairly well understood for the Last Interglacial period, the level of the sea during this time remained a highly controversial question,” Dr O’Leary said.

“This is because tectonic movements, and the isostatic response of coastlines to shifting ice-water masses over glacial and interglacial periods, can artificially raise or lower the original shoreline position.

“But after mapping and surveying the Last Interglacial fossil shorelines from Augusta to Exmouth, my team and I were able to show that these ancient shorelines outcropped at similar elevations along this entire length of coastline and therefore have not been affected by tectonic movement.”

Dr O’Leary said the team then applied an isostatic model correcting for crustal deformation caused by glacial meltwater loading of the Indian Ocean basin.

He said knowing just how high the sea level might rise, in response to melting ice sheets under warmer global temperatures, is a critical yet poorly understood question and this study had now shed some light if such an event did occur today.

“This research shows that even a modest rise of a couple of degrees centigrade in global temperatures could result in a significant rise in global sea levels, and will also help improve our understanding of the sensitivity Greenland and Antarctic ice sheets under higher global temperatures,” Dr O’Leary said.

The research was carried out in conjunction with The University of North Carolina, Woods Hole Oceanographic Institution in Massachusetts, Columbia University, Harvard University and The University of Sydney.

For a copy of the published research report, visit http://www.nature.com/ngeo/index.html.