Our directory of things of interest

University Directory

Ice loss

  • Written by  David Sugden
  • Published in Polar
Iceberg on the West Antarctic Ice Sheet Iceberg on the West Antarctic Ice Sheet Guido Amrein
07 Jun
2016
David Sugden, Professor Emeritus of the School of GeoSciences at the University of Edinburgh, shares his concerns surrounding melting ice in Antarctica, particularly the West Antarctic Ice Sheet

For nearly 40 years we have known that the West Antarctic Ice Sheet is susceptible to the sudden loss of ice into the ocean, a process termed marine instability. The reason is that the 2,000 metre-high centre of the ice dome overlies a marine basin with a depth of 1,500 metres below present sea level.

The risk is that warm ocean water will melt the floating margins, thin the ice, and lead to a speed up in ice velocities as the ice retreats into deeper and deeper water. This loss of ice into the ocean would cause a global sea level rise of up to five metres if the ice sheet disappeared.

The issue is important because the latest IPCC predictions of sea level rise by 2100 under warm scenarios range from 53 to 98 centimetres and are due to a combination of thermal expansion and the melting of glaciers. Marine instability was excluded from the predictions because there was too much uncertainty about the process.

But the record of marine instability at the end of the last ice age shows that a rise in sea level exceeding one metre per century is possible. The real concern is that glaciologists are alarmed at the loss of ice from the Pacific margins of the West Antarctic Ice Sheet as revealed by satellite imagery. Some think it may have passed the point of no return.

One approach to this problem is to ask what happened to the ice sheet in the past during interglacial periods such as 130,000 and 205,000 years ago when the world was warmer than at present. Such conditions are a pointer to what we might experience by the end of the present century.

Scientists working on raised shorelines believe that sea levels 130,000 years ago were four to six metres higher than at present and look to the loss of the West Antarctic Ice Sheet as a source of water. Marine biological evidence agrees. Bryozoa and octopuses on the Pacific and Atlantic coasts of West Antarctica show similarities that imply a marine seaway existed across West Antarctica within the last million years or so. A collapse of the ice sheet during an interglacial period would expose such a seaway.

We risk losing the marine portions of the West Antarctic Ice Sheet. If so, we have to plan for an additional rise in the global sea level of three metres

Geographers from the universities of Edinburgh and Northumbria have recently published a paper in Nature Communications (doi: 10.1038/ncomms10325) in which they provide a new insight into West Antarctica during interglacial periods. They outline field evidence to show that the minimal configuration of the West Antarctic Ice Sheet in a warmer world involved regional ice sheets ~500 kilometres across that survived on three mountain blocks in West Antarctica, with marine seaways in between. The loss of ice raised global sea levels by about three metres. The research studied the geomorphology of three massifs in the southern Ellsworth Mountains in the heart of the Weddell Sea embayment.

The team studied boulders dropped by the ice sheet on the mountains and dated them using cosmogenic isotopes. Cosmic rays bombard the Earth’s surface and build up cosmogenic isotopes in surface rocks. Measure these and you can show how long a boulder has been exposed and sometimes how long it has subsequently been buried by ice.

The team found that while the ice sheet elevation fluctuated, there was evidence of persistent ice sheet conditions for 1.4 million years, a discovery demonstrating that at least a sizeable ice sheet survived several warm interglacial periods.

No evidence was found of complete deglaciation. There are two possible explanations. First, the main ice dome survived intact for 1.4 million years in which case the West Antarctic Ice Sheet has played little part in sea level change. Second, a regional ice sheet survived on the Ellsworth-Whitworth mountain block during warm interglacial periods, in which case the contribution to sea level rise would have been three metres.

This latter scenario is supported by the evidence of higher than present sea levels during interglacial periods and the biological evidence of a seaway across West Antarctica in the last million years.

The implications of this work are troubling. If the world continues on its warming trajectory, then we risk losing the marine portions of the West Antarctic Ice Sheet. If so, we have to plan for an additional rise in the global sea level of three metres, a future with frightening implications for the coastal populations of the world.

David Sugden is Professor Emeritus of the School of GeoSciences at the University of Edinburgh. For photographs and a weekly account of months living in a small tent while doing the fieldwork, see ellsworthblueice.wordpress.comThe research was funded by the Natural Environment Research Council to the universities of Edinburgh and Northumbria, the Scottish Universities Environmental Research Centre, and the British Antarctic Survey which supported the two field campaigns.

This was published in the June 2016 edition of Geographical magazine.

Related items

Subscribe to Geographical!

geo line break v3

Free eBooks - Geographical Newsletter

Sign up for our weekly newsletter today and get a FREE eBook collection!

geo line break v3

University of Winchester

geo line break v3

EDUCATION PARTNERS

Aberystwyth University University of Greenwich The University of Derby

TRAVEL PARTNERS

Ponant

Silversea

Travel the Unknown

DOSSIERS

Like longer reads? Try our in-depth dossiers that provide a comprehensive view of each topic

  • Natural Capital: Putting a price on nature
    Natural capital is a way to quantify the value of the world that nature provides for us – the air, soils, water, even recreational activity. Advocat...
    The Human Game – Tackling football’s ‘slave trade’
    Few would argue with football’s position as the world’s number one sport. But as Mark Rowe discovers, this global popularity is masking a sinister...
    Essential oil?
    Palm oil is omnipresent in global consumption. But in many circles it is considered the scourge of the natural world, for the deforestation and habita...
    Mexico City: boom town
    Twenty years ago, Mexico City was considered the ultimate urban disaster. But, recent political and economic reforms have transformed it into a hub of...
    Diabetes: The World at Risk
    Diabetes is often thought of as a ‘western’ problem, one linked to the developed world’s overindulgence in fatty foods and chronic lack of physi...

MORE DOSSIERS

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...

Nature

Natural capital is a way to quantify the value of…

Tectonics

The reason for the unusual location of Mount St Helens…

Climate

Most plants thicken their leaves in response to higher carbon…

Climate

Not just the preserve of flatulent cows, methane is causing…

Climate

As the United States’ Supreme Court delays a landmark climate…

Geophoto

Of Britain's 15 national parks, the New Forest is probably…

Energy

The Treasury has announced that it is considering imposing a…

Tectonics

Major earthquakes are triggering seismic activity half the world away

Climate

Marco Magrini finds that a warming world also means a…

Wildlife

Unchecked tourism is potentially reducing the number of cheetah cubs that…

Oceans

A relocated military base in Okinawa, Japan will cause ‘irreversible’…

Climate

The ongoing recovery of the planet’s ozone layer is being…

Oceans

The Ocean Cleanup has launched System 001, a floating barrier…

Nature

New videos reveal how plants respond to wounds, sending forth…

Geophoto

The recent heatwave had everyone longing for a drop of…

Wildlife

The demand for horseshoe crab blood – vital for testing…

Climate

One of the problems in getting accurate climate science out…

Wildlife

Italy is divided over the future of its wolves and…

Energy

A Scottish tidal power project in the Pentland Firth has…

Oceans

The world’s first full global analysis of beaches reveals the…