Projections suggest an uneven rise in global sea-level

Projections suggest an uneven rise in global sea-level

Reporting in the journal Geophysical Research Letters, researchers have looked ahead to the year 2100 to show how ice loss will continue to add to rising sea levels.

Co-author Jonathan Bamber, of Bristol University, says that this is ‘the first study to examine the regional pattern of sea level changes using sophisticated model predictions of the wastage of glaciers and ice sheets over the next century’.

Scientists have known for some time that sea level rise around the globe will not be uniform, but in this study the team of ice2sea researchers shows in great detail the global pattern of sea-level rise that would result from two scenarios of ice-loss from glaciers and ice sheets.

The team, from Italy’s University of Urbino and Bristol, found that ice melt from glaciers and from the Greenland and Antarctic ice sheets, is likely to be of critical importance to regional sea-level change in the Equatorial Pacific Ocean, where the sea level rise would be greater than the average increase across the globe. This will affect, in particular, Western Australia, Oceania and the small atolls and islands in the region, including Hawaii.

The study focused on three effects that lead to global mean sea-level rise being unequally distributed around the world. Firstly, the earth’s crust is till deforming in response to the loss at the end of the last ice age, 10,000 years ago, of the billions of tonnes of ice that covered much of North American and Europe.

Secondly, the warming of the oceans leads to a change in the distribution of water across the globe. And thirdly, the sheer mass of water held in ice at the frozen continents of Antarctica and Greenland exerts a strong gravitational pull on the surrounding liquid water, raising adjacent sea levels. As the ice melts this pull decreases and water is redistributed elsewhere around the globe.

Researcher Professor Giorgio Spada says the research has defined patterns known as sea level fingerprints. ‘This is paramount for assessing the risk due to inundation in low-lying, densely populated areas,’ he explains.

‘We believe this is due to the effects of the melting polar ice relatively close to Europe – particularly Greenland’s ice. This will tend to slow sea-level rise in Europe a little, but at the expense of higher sea-level rise elsewhere.’

The team considered two scenarios in its modelling, the ‘most likely’ or ‘mid-range’, and the one closer to the upper limit of what could happen.

‘The total rise in some areas of the equatorial oceans worst affected by the terrestrial ice melting could be 60cm if a mid-range sea-level rise is projected, and the warming of the oceans is also taken into account.’

Fellow researcher David Vaughan, ice2sea programme coordinator, says that in the past couple of years programmes such as his have made great strides in predicting global average sea-level rise. ‘The urgent job now is to understand how global sea-level rise will be shared out around the world’s coastlines. Only by doing this can we really help people understand the risks and prepare for the future.’

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