Environment

Melting of ancient Antarctic ice sheet drove a 3-meter sea level rise

Melting of ancient Antarctic i...
Scientists at Australia's University of New South Wales Sydney set out to study the behavior of the West Antarctic Ice Sheet during a period known as the Last Interglacial
Scientists at Australia's University of New South Wales Sydney set out to study the behavior of the West Antarctic Ice Sheet during a period known as the Last Interglacial
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Scientists at Australia's University of New South Wales Sydney set out to study the behavior of the West Antarctic Ice Sheet during a period known as the Last Interglacial
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Scientists at Australia's University of New South Wales Sydney set out to study the behavior of the West Antarctic Ice Sheet during a period known as the Last Interglacial
Fine layers of volcanic ash helped scientists piece together the history of an Antarctic ice sheet
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Fine layers of volcanic ash helped scientists piece together the history of an Antarctic ice sheet
Trace gas bubbles in the ice samples collected by researchers in the Antarctic
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Trace gas bubbles in the ice samples collected by researchers in the Antarctic
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Scientists digging into the ancient history of Antarctica's ice sheets have uncovered evidence of an "extreme" melting event that drove rapid and significant sea level rise. Taking place more than 100,000 years ago, the scientists see this ice melt as a cautionary tale for climate change, largely because it was likely set off by a temperature increase of less than 2° C (3.6° F), the upper limit of the goal laid out by the Paris Climate Agreement.

The work was led by scientists at Australia's University of New South Wales Sydney, who set out to study the behavior of the West Antarctic Ice Sheet during a period known as the Last Interglacial, which took place around 129,000-116,000 years ago. At this time, ocean temperatures were likely less than 2° C warmer than they are today, which makes it an ideal period to study how global warming could impact sea levels and melting ice in the region.

To do this, the team took advantage of what are known as blue ice areas, which are created by strong winds that roll over the mountains and blow the top layer of snow away, in turn eroding the exposed ice. When this happens, ancient ice flows upwards towards the surface, presenting scientists with a time capsule and a window into the ice sheet's ancient history.

“Instead of drilling kilometers into the ice, we can simply walk across a blue ice area and travel back through millennia. By taking samples of ice from the surface we are able to reconstruct what happened to this precious environment in the past,” says Professor Chris Turney, who led the research team.

Isotope measurements of the samples enabled the team to piece together the sheet's history, and in doing so they noticed a gap in the record, which occurred right before the Last Interglacial. This gap happens to coincide with an extreme rise in sea levels that took place around the same time, suggesting that the ice melted away into the surrounding waters. This conclusion was supported by examinations of fine volcanic ash and trace gases in the samples, along with the DNA of the bacteria trapped inside the ice.

Trace gas bubbles in the ice samples collected by researchers in the Antarctic
Trace gas bubbles in the ice samples collected by researchers in the Antarctic

Some scientists believe that at some time during the Last Interglacial, global mean sea levels were around six to nine meters (20 to 30 ft) higher than they are today, with some scientists suspecting they could have been as much as 11 m (36 ft) higher. A number of factors are thought to have contributed to this, including melting glaciers, thawing of the Greenland Ice Sheet and expanding oceans as a result of warmer waters. The team says this new study indicates West Antarctica had a big role to play, singlehandedly causing a rise in sea levels of more than three meters (9.8 ft).

“We now have some of the first major evidence that West Antarctica melted and drove a large part of this sea level rise,” says Professor Turney.

What concerns the scientists with regard to the future is how vulnerable the West Antarctic Ice Sheet appears to be to warmer waters. This is because it rests on the seabed rather than the ground, like the East Antarctic Ice Sheet, and ocean water fills cavities underneath it that melts the ice from below.

“The West Antarctic Ice Sheet is sitting in water, and today this water is getting warmer and warmer,” says Turney.

To explore how things could pan out if the planet continues to warm as expected, the team used the data they collected to run model simulations and explore effects on the ice shelves, which sit against the sheets and slow the rate of ice flow from the continent.

Their results point to a 3.8-m (12.5-ft) increase in sea levels within the first thousand years of a 2° C warmer ocean, while the ice shelves would collapse completely within the first 200 years. This, the team believes, could set off an irreversible chain of events that includes the melting of the East Antarctic Ice Sheet, sending sea levels even higher.

“Our study highlights that the Antarctic Ice Sheet may lie close to a tipping point, which once passed may commit us to rapid sea level rise for millennia to come," says study co-author Professor Christopher Fogwill, from the UK's University of Keele. "This underlines the urgent need to reduce and control greenhouse gas emissions that are driving warming today."

From here, the researchers hope to cast a wider net with their techniques to see which other parts of the sheet were impacted and how fast they may have melted.

“We only tested one location, so we don’t know whether it was the first sector of Antarctica that melted, or whether it melted relatively late," says Turney. "How these changes in Antarctica impacted the rest of the world remains a huge unknown as the planet warms into the future. Testing other locations will give us a better idea for the areas we really need to monitor as the planet continues to warm."

The research was published in the journal Proceedings of the National Academy of Sciences.

Source: University of New South Wales

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8 comments
Malcolm Jacks
Has anyone thought that a 100 years plus depletion of the earths oil and gas alone is causing global warming? The depletion of oil and gas which for millions of years has acted as a lubricant to the earths mantle acted in preventing the mantle from causing friction, without that lubricant the earths mantle is now causing that friction, which in-turn creates heat.
and also that friction causes more earth quacks and eruptions.
Both of these syndromes have been noticeable increase lately.
Brian M
Curious times we are living in , we have global warming (man made supposedly) yet we are well overdue for another ice age (ignoring human global warming) , the magnetic poles are shifting with a possibility of a flip. Could we see a change of tilt of the planet causing less sunlight a trigger for a possible snowball earth again or least another ice age?

Perhaps we really need to be looking at a system to better control the warming and cooling of the earth via near orbit or far orbit blinds or other technology. Its a case of not if, but when.
piperTom
SO! The people of the Last Interglacial gave up all electric generation and scraped internal combustion engines entirely... and they STILL had a huge rise in sea level! Very sad. The good news is - it took a thousand years. I also infer some even better news: the industrial age has caused aggregate wealth to increase 10 fold in the last century; we look forward to the computer/ space age to drive another 10 fold increase in the next century. Ergo, our very rich descendants will be far better able to deal with global warming than we are. Benign neglect is our very best answer to climate change!
ljaques
Right. And mankind should not stand up, as it creates friction with the wind, increasing Anthropomorphic Global Warming, Kumbaya. // Do any of the Alarmists get that this last warming (interglacial) happened even without man using any subterranean oil? Yup, no cars, trains, planes, or powered boats. Yessiree, the cycle is warm, to cool, to cold, to cool, to warm, to cool, etc. just like night and day/summer and winter. The magnetic poles were shifting back then, too, no doubt. And the sun had its cycles of cooler and warmer, causing this change, as it always has. Isn't that COMFORTING?
bwana4swahili
Does anyone actually believe the Antarctic ice won't totally disappear!? It has happened many times in the past and WILL again. Adapt or die has always been nature's way.
El Nacho
@Brian M ("we are well overdue for another ice age") I dunno. The present interglacial warm period, the Holocene, only started some 11,400 years ago. The past four interglacial warm periods prior to our current one all lasted an average 20,000 years. So wouldn't that mean we could have around 8,000 years of natural warming until we're all plunged back into the next Ice Age?
Readout Noise
Yes, the Earth has warmed before, cyclically - but never at this RATE. The problem with the current period of global warming is not its extent, but its rapidity. Thanks to us, it's happening on a timescale of decades, not millenia. Just check out the scientific evidence for this, rendered as graphs of warming rate for the last many thousand years. They slowly drift up, and down...but they shoot up like a rocket once you get to the last century!

That rapidity of change gives current ecosystems insufficient time to adapt, species insufficient time to migrate, humans insufficient time to completely rebuild away from low-lying coastal areas. Instead of the boundaries of forests and grasslands gradually shifting in latitude with the usual millenium-scale climate variations, the rapidly changing climate is overtaking them completely.

In 2019, globally, we succeeded in lowering our CO2 emissions, principally by substituting natural gas for coal (both are fossil fuels, but gas is more efficient). We must continue to lower our greenhouse gas emissions, moving away from fossil fuels altogether over time.
Worzel
One of the paradoxes of a returning glacial period is, that it first gets warmer. It's this warming that helps in precipitating the next glacial period. Warmer climate, results in more evaporation, which in turn causes more rain and more snow. The heavier snow falls take longer to melt, and the snow reflects sunlight which causes local cooling. This local cooling, causes the snow to take longer to melt, and so on. This is a positive feedback process, and results in an exponential cooling rate, and increase in permanent snow cover. The claim that human produced gasses are causing the climate warming is a political myth, otherwise known in common language, as, 'A Lie!' 75% of the land area of the planet is now desert, and human deforestation is increasing that area rapidly. Trees cool the climate, remove them and the climate heats up, and can eventually produce hot desert. If one was serious about cooling the climate, then the obvious solution would be to reduce desert areas. This is something that both China, and India are attempting to achieve. However, the 20,000 years of interglacial period claimed by 'El Nacho' is erroneous, as over the last 10 cycles, they have been around half that, so our present interglacial period is due to end in the near future. Another of the characteristics of the end of the interglacial period is, an increase in earthquake and volcanic activity, caused by the changing loads on the tectonic plates from ice melt. The volcanoes put debris into the atmosphere, which blocks sunlight, and also causes cooling. Added to that are characteristic extensive forest fires, that do the same. So all the elements of a change from interglacial to glacial are present. Information from deep sea and lake bed core drillings, has shown that the change has occurred in as little as 20-50 years in the past.