Changes to the Antarctic ice sheet at the bottom of the southern hemisphere have been triggered by sea level changes in the northern hemisphere over the past 40,000 years, a new study discovered.
Researchers from McGill University found that ice sheets at opposite ends of the Earth can influence one another by tweaking sea levels in surrounding waters.
Scientists have struggled to explain how ice sheets changed during the last ice age – the Last Glacial Period – running from 115,000 years ago to 11,700 years ago.
New models found that as the climate cooled in the norther hemisphere and more water turned to ice, sea levels in Antarctica dropped making its ice sheet grow.
Likewise, as temperatures rose again, the ice sheets in the Northern Hemisphere retreated, causing levels to rise around Antarctica and its ice sheet to retreat.
Polar ice sheets evolve on various different time scales and are in constant flux, with the ice growing and retreating depending on the climate and the surrounding water levels
Senior author Professor Natalya Gomez at the McGill University said ice sheets can influence each other over thousands of miles due to water flowing between them.
‘It’s as though they were talking to one another through sea level changes,’ she said.
The team looked at existing models, geological records, core samples from the Antarctic Ocean floor and land exposure records from shorelines.
Professor Gomez said polar ice sheets were not just large, static mounds of ice.
‘They evolve on various different time scales and are in constant flux, with the ice growing and retreating depending on the climate and the surrounding water levels.
‘They gain ice as snow piles up on top of them, then spread outwards under their own weight, and stream out into the surrounding ocean where their edges break off into icebergs,’ Gomez explained.
With this information, they were able to simulate simultaneous changes in sea levels and ice dynamics across both hemispheres over the past 40,000 years.
This time frame provides a wider picture of how climate factors affect ice sheets, as it captures the retreat following the peak of the last ice age up to 26,000 years ago.
To investigate the mechanisms involved in driving changes in the Antarctic ice sheet the researchers looked at a wide range of geological records, from cores of sediment from the ocean bottom near Antarctica to records of land exposure and past shorelines
Antarctic ice sheets lost a significant amount of ice during this time, with occasional periods of accelerated retreat, the records show.
The only possible explanation, the scientists say, were changes in sea level caused by the growth or retreat of ice sheets in the Northern Hemisphere.
Co-author Michael Weber at the University of Bonn in Germany said: ‘We found a very variable signal of ice-mass loss over the last 20,000 years, left behind by icebergs breaking off Antarctica and melting down in the surrounding oceans.
‘This evidence could hardly be reconciled with existing models until we accounted for how the ice sheets in both hemispheres interact with one another.’
The Antarctic ice sheet extends almost 5.4 million square miles, which is roughly the same size as the United States and Mexico combined.
Researchers were able, for the first time, to simulate, simultaneously, changes in both sea levels and ice dynamics in both hemispheres over the past 40,000 years
Professor Gomez added: ‘The scale and complexity of ice sheets and the oceans, and the secrets of the Earth’s past climate that are locked up in the geological record are fascinating and inspiring.
‘Our results highlight how interconnected the Earth system is, with changes in one part of the planet driving changes in another.
‘In the modern era, we haven’t seen the kind of large ice sheet retreat that we might see in our future warming world.
‘Looking to records and models of changes in Earth’s history can inform us about this.’
The findings have been published in the journal Nature.
SEA LEVELS COULD RISE BY UP TO 4 FEET BY THE YEAR 2300
Global sea levels could rise as much as 1.2 metres (4 feet) by 2300 even if we meet the 2015 Paris climate goals, scientists have warned.
The long-term change will be driven by a thaw of ice from Greenland to Antarctica that is set to re-draw global coastlines.
Sea level rise threatens cities from Shanghai to London, to low-lying swathes of Florida or Bangladesh, and to entire nations such as the Maldives.
It is vital that we curb emissions as soon as possible to avoid an even greater rise, a German-led team of researchers said in a new report.
By 2300, the report projected that sea levels would gain by 0.7-1.2 metres, even if almost 200 nations fully meet goals under the 2015 Paris Agreement.
Targets set by the accords include cutting greenhouse gas emissions to net zero in the second half of this century.
Ocean levels will rise inexorably because heat-trapping industrial gases already emitted will linger in the atmosphere, melting more ice, it said.
In addition, water naturally expands as it warms above four degrees Celsius (39.2°F).
Every five years of delay beyond 2020 in peaking global emissions would mean an extra 20 centimetres (8 inches) of sea level rise by 2300.
‘Sea level is often communicated as a really slow process that you can’t do much about … but the next 30 years really matter,’ lead author Dr Matthias Mengel, of the Potsdam Institute for Climate Impact Research, in Potsdam, Germany, told Reuters.
None of the nearly 200 governments to sign the Paris Accords are on track to meet its pledges.