Ice Melt Means Uneven Sea Level Rise Around the World

By Alex Kirby, Climate News Network

LONDON – Scientists say the sea level rise caused by climate change during the rest of this century will not affect all parts of the world equally, because of the ways sea, land and ice interact.

They say parts of the Pacific are likely to see the highest rise. This region is where many low-lying island countries most vulnerable to sea level rise, like the Seychelles, are already struggling. Their peoples will need evacuation if the scientists’ high-end predictions are correct. Northern Europe, on the other hand, will experience a below-average increase.

Researchers have found that ice melt from glaciers and from the Greenland and Antarctic ice sheets is likely to be critically important to regional sea-level change in the equatorial Pacific ocean.
Credit: Christine Zenino via Climate News Network.

The team, from Italy’s University of Urbino and the University of Bristol, U.K., report their findings in a paper, The gravitationally consistent sea-level fingerprint of future terrestrial ice loss, published in Geophysical Research Letters online.

Scientists have known for some time that sea level rise around the globe will not be uniform. The team investigated how ice loss will continue to add to rising sea levels until the year 2100. The researchers, from the European Union’s Ice2sea project, show in detail the global pattern of sea level rise that would result from two scenarios of ice-loss from glaciers and ice sheets.

Improved projections of the contribution of ice to sea level rise produced by Ice2sea will feed into the fifth assessment report of the Intergovernmental Panel on Climate Change. In 2007, the IPCC’s fourth report highlighted ice-sheets as the most significant remaining uncertainty in projections of sea-level rise.

The researchers found that ice melt from glaciers and from the Greenland and Antarctic ice sheets is likely to be critically important to regional sea-level change in the equatorial Pacific ocean.

Legacy of the Ice Age

There the rise will be greater than the global average increase, affecting in particular western Australia, Oceania and the small atolls and islands in the region, including Hawaii. Another area which should expect an above-average increase is the east coast of South Africa and Madagascar.

The study focussed on three effects that lead to the unequal distribution of sea level rise. First, land is both subsiding into and emerging from the sea because of a massive ice loss at the end of the last Ice Age 10,000 years ago, when billions of tonnes of ice covering parts of North America and Europe melted.

How Do We Know: Greenland’s Melting Ice Sheet

This caused a major redistribution of mass on the Earth, but the crust responds to such changes so slowly that it is still changing shape. Secondly, the warming of the oceans changes the distribution of water across the globe.

The third effect is the way the sheer mass of frozen water on Antarctica and Greenland exerts a gravitational pull on the surrounding liquid water, pulling in enormous amounts and raising the sea-level close to the coasts. As the ice melts its pull decreases and the water previously attracted pours away, to be redistributed around the globe.

Co-author Professor Giorgio Spada said: “The most vulnerable areas are those where the effects combine to give the sea-level rise that is significantly higher than the global average.” In Europe the level would rise, but it would be slightly lower than the average.

“We believe this is due to the effects of the melting polar ice relatively close to Europe — particularly Greenland’s ice”, he said. “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. One was the “most likely” or “mid-range” and the other closer to the upper limit of what could happen.

Stark contrast

Professor Spada said: “The total rise in some areas of the equatorial oceans worst affected by the terrestrial ice melting could be 60cm (23.6in) if a mid-range sea level rise is projected, and the warming of the oceans is also taken into account.”

Another co-author, Jonathan Bamber, professor of physical geography at Bristol University, U.K., told the Climate News Network: “Northern Europe will be influenced by mass loss from Greenland, and places like Scotland and Scandinavia will probably see close to zero sea level rise from the melting ice, leaving aside thermal expansion of the sea.

“But if you take the high-end scenario, there’s a reasonable chance the rise could reach a metre in the western Pacific.”

Professor David Vaughan, Ice2sea programme coordinator, said: “The urgent job now is to understand how the 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.”

A spokesman for the Association of Small Island States (Aosis), told a U.N. climate conference two years ago that whole nations would be washed away by sea level rise.

He said the people of Kiribati, Tuvalu, most of the Cook Islands, the Marshall Islands and the Maldives, which are just a few meters above sea level now, could be lost. 

Alex Kirby, a former BBC environment correspondent, is a founding journalist of Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.