The findings suggest that in the past, a rise of 3–4°C was enough to trigger a mass discharge of icebergs – known as a Heinrich event – from the Laurentide Ice Sheet in what is now Canada.

A team of scientists led by Shaun Marcott of Oregon State University reconstructed past ocean temperatures and used computer modelling to re-create what probably happened at various times during Heinrich events that took place in the past.

‘There is now better evidence that the climate was getting colder prior to the Heinrich events, causing surface ocean waters to cool, but actually causing warmer water in the subsurface,’ Marcott said. ‘We tried to demonstrate how this warmer water, at depth, caused the base of the ice shelf to warm and collapse, triggering the Heinrich events.’

The results, which were published in the Proceedings of the National Academy of Sciences, have implications for the future of the West Antarctic Ice Sheet. According to the scientists, if water were to warm by about 2°C under the ice shelves that are found along the edges of much of the ice sheet, it could increase the rate of melting to more than ten metres a year, causing many of the ice shelves to melt in less than a century.

 ‘We don’t know whether or not water will warm enough to cause this type of phenomenon,’ Marcott said. ‘But it would be a serious concern if it did, and this demonstrates that melting of this type has occurred before.’

September 2011