It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Scientists have established the most reliable estimates to date of past temperature variations in Antarctica.
They highlight significant differences in behaviour between West and East Antarctica.
This study makes it possible to test and consolidate future climate projections.
Antarctica has experienced significant temperature changes, especially since the last glacial period. An international collaboration including scientists from the CNRS1 has now challenged previously accepted estimates of these variations, using new measurements published on June 4, 2021 in Science. Their study highlights differences in behaviour between East and West Antarctica, connected in particular to differing variations in their altitude.
Surface temperatures in Antarctica have risen sharply since the last glacial period. Understanding this increase is key to understanding changes in climate at any given time and to testing our ability to model them. A study involving French scientists now provides the most reliable estimates to date of past temperature variations in Antarctica. Whereas warming since the last glacial period was until now estimated at +9 °C across the entire continent, the new measurements reveal a variation of +10 °C in West Antarctica and between +4 and +7 °C in East Antarctica.
Scientists previously estimated past temperatures using an isotopic thermometer, in other words, by analysing the ratio of different isotopic forms of water. However, the accuracy of this method relies on a calibration that is hard to implement in Antarctica. Now, two new independent methods have been developed in order to overcome this problem. The first consists in measuring the temperature in the boreholes resulting from coring2. The tremendous thickness of the Antarctic ice sheet means that records are well-preserved and can be used to reconstruct past temperatures. The second method is based on the process of snow densification, which is temperature-sensitive and can be measured by analysing the air trapped in ice cores. The two measurements gave similar results, confirming their reliability.
This work highlights the impact on temperature changes in Antarctica caused by variations in the altitude of the ice. It demonstrates the significant differences between East Antarctica, whose elevation has increased slightly since the last glacial period, and West Antarctica, where it has decreased considerably. The data was compared with climate models3 in order to better understand past temperature changes and improve confidence in future projections.
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CAPTION
Temperature probe developed at the Institute of Environmental Geosciences (OSUG, CNRS / IRD / UGA / Grenoble INP) to collect data from the EPICA borehole at Concordia.
Antarctica's 'Sleeping Giant' Might Flood the World. Here's How to Stop It Tony Ho Tran Wed, August 10, 2022 David Merron via Getty
Are you a fan of the 1995 film Waterworld starring Kevin Costner? Great news: There’s a distinct possibility that it’ll become a reality in the future if humanity can’t get its act together to prevent climate catastrophe!
In a new paper published August 10 in the journal Nature, a team of Australian scientists found that sea levels could rise a staggering five meters by the year 2500 if we fail to meet the goals set in the Paris Climate Agreement. Specifically, the ice melt would come from the East Antarctic Ice Sheet (EAIS), one of two massive ice sheets on the southernmost continent that scientists have ominously dubbed a “sleeping giant” due to its potential to wreak havoc on sea level rise.
The Paris Agreement’s goal is to limit global temperature rise to two degrees Celsius or below (ideally 1.5 degrees Celsius). If it rises any higher, things could get very dicey, very quickly.
“The EAIS is 10 times larger than West Antarctica and contains the equivalent of 52 meters (170.6 feet) of sea level,” Nerilie Abram, an earth scientist at Australia National University and co-author of the paper, said in a press release. In other words, the ice shelf has more than enough water to flood the world well into “Waterworld” territory if it completely melts.
“If temperatures rise above two degrees Celsius beyond 2100, sustained by high greenhouse gas emissions, then East Antarctica alone could contribute around one to three meters (three to 10 feet) to rising sea levels by 2300 and around two to five meters by 2500,” Abram explained.
There is some glimmer of hope, though. If we manage to keep global warming in check and meet the Paris Agreement targets, then the sleeping giant ice shelf is only expected to contribute less than half a meter of sea level rise by 2500. That’s not nothing, but it’s certainly a lot less than the 16 feet rise that would spell disaster to coastline communities and ecosystems across the globe.
An illustration showing regions of the Americas that would be completely flooded if sea levels rose by five meters. ROWLEY ET AL. 2007
The Inflation Reduction Act, which was passed on August 7, is also expected to be the largest investment by the U.S. in fighting global warming to date. With a $369 billion investment in clean energy, it’s slated to reduce U.S. greenhouse gas emissions by 40 percent below 2005 levels by 2030. By the end of the decade, emissions could be reduced by as much as 50 percent.
However, our timeline to accomplish this is shrinking faster than an ice cube under the summer sun. In fact, compounding issues related to climate change including sea level rise due to ice melt elsewhere and warming ocean waters are exponentially increasing the chances of the EAIS melting faster.
“We used to think East Antarctica was much less vulnerable to climate change, compared to the ice sheets in West Antarctica or Greenland, but we now know there are some areas of East Antarctica that are already showing signs of ice loss,” Abram said. “This means the fate of the world’s largest ice sheet very much remains in our hands.”
Fate of the world's biggest ice sheet is in our hands, scientists say
Mountains protruding above the surface of the East Antarctic Ice Sheet. Credit: Jan Lenaerts
The fate of the world's biggest ice sheet still rests in our hands if global temperature increases are kept below the upper limit set by the Paris Agreement on climate change.
A new study led by Durham University, UK, shows that the worst effects of global warming on the East Antarctic Ice Sheet (EAIS) could be avoided if temperatures do not rise by more than 2°C above pre-industrial levels.
Staying below this limit would see the EAIS—which holds the vast majority of Earth's glacier ice—contribute less than half a meter to sea level rise by the year 2500, the researchers say.
However, they add that if warming continues to increase beyond the 2°C limit, we could potentially see the EAIS contribute several meters to sea-level rise in just a few centuries.
The research team, which included scientists from the UK, Australia, France and the U.S., has published its findings in the journal Nature.
To assess the sensitivity of the EAIS, they looked at how the ice sheet responded to past warm periods, as well as examining where changes are currently occurring.
They then analyzed a number of computer simulations made by previous studies to examine the effects of different greenhouse gas emission levels and temperatures on the ice sheet by the years 2100, 2300 and 2500.
Scientists overlooking the edge of Mawson Glacier, East Antarctica. Credit: Richard Jones
Lead author Professor Chris Stokes, of the Department of Geography, Durham University, UK, said: "A key conclusion from our analysis is that the fate of the East Antarctic Ice Sheet remains very much in our hands.
"This ice sheet is by far the largest on the planet, containing the equivalent of 52 meters of sea level and it's really important that we do not awaken this sleeping giant.
"We used to think East Antarctica was much less vulnerable to climate change, compared to the ice sheets in West Antarctica or Greenland, but we now know there are some areas of East Antarctica that are already showing signs of ice loss. Satellite observations have revealed evidence of thinning and retreating, especially where glaciers draining the main ice sheet come into contact with warm ocean currents."
The team's analysis shows that if warming continues beyond 2100, sustained by high emissions, then East Antarctica could add several meters to global sea level rise over the coming centuries. This would add to the substantial contributions from Greenland and West Antarctica and threaten millions of people worldwide who live in coastal areas.
Iceberg towers calved from the East Antarctic Ice Sheet. Credit: Nerilie Abram
Professor Stokes added: "Restricting global temperature increases to below the 2°C limit set by the Paris Climate Agreement should mean that we avoid the worst-case scenarios, or perhaps even halt the melting of the East Antarctic Ice Sheet, and therefore limit its impact on global sea level rise."
When world leaders met at the 2015 UN Climate Change Conference in Paris, they agreed to limit global warming to well below 2°C and pursue efforts to limit the rise to 1.5°C.
According to the most recent Intergovernmental Panel on Climate Change (IPCC) report, published last year, human activity has already increased global mean temperatures by about 1.1°C since pre-industrial times.
The Durham-led study showed that with dramatically reduced greenhouse gas emissions and only a small rise in temperature, the EAIS might be expected to contribute around two centimeters of sea level rise by 2100—much less than the ice loss expected from Greenland and West Antarctica. Indeed, some research shows that snowfall has increased over East Antarctica in the last few decades and, if this continues, it will offset some of the expected ice losses over the next century.
Scientists drilling a shallow ice core at the surface of the East Antarctic Ice Sheet. Credit: Nerilie Abram
If the world instead continues on a pathway of very high greenhouse emissions, the researchers could not rule out the possibility of the EAIS contributing nearly half a meter to sea levels by 2100, but viewed this as very unlikely.
If emissions remain high beyond 2100 then the EAIS could contribute around one to three meters to global sea levels by 2300, and two to five meters by 2500.
Crucially, if the target of the Paris Agreement is met, significant ice loss from East Antarctica could be reduced or even prevented, with the EAIS's contribution to sea-level rise remaining below half a meter by 2500.
The researchers also reviewed how the ice sheet responded to past warm periods, when carbon dioxide concentrations and atmospheric temperatures were only a little higher than present.
They said that unlike the very rapid and extreme warming that we have experienced over the last few decades, that can only be explained by greenhouse gas emissions from human activity, past warming occurred over much longer timescales and was largely caused by changes in the way the Earth orbits the Sun.
A field camp on the surface of the East Antarctic Ice Sheet, Princess Elizabeth Land.Credit: Nerilie Abram
For example, the last time that carbon dioxide concentrations exceeded the current value of 417 parts per million was during a period known as the mid-Pliocene, around three million years ago. Temperatures were only 2-4°C higher than present at that time—in the range of the temperature changes we could experience later this century—but global mean sea level eventually reached 10-25 meters higher. Worryingly, evidence from sea-floor sediments around East Antarctica indicates that part of the ice sheet collapsed and contributed several meters to sea level rise during the mid-Pliocene.
Even as recently as 400,000 years ago, not that long ago on geological timescales, there is evidence that a part of the EAIS retreated 700 km inland in response to only 1-2°C of global warming.
Sky over Vanderford Glacier, Wilkes Land, East Antarctica. Credit: Richard Jones
Professor Nerilie Abram, a co-author of the study from the Australian National University in Canberra, said: "A key lesson from the past is that the East Antarctic Ice Sheet is highly sensitive to even relatively modest warming scenarios. It isn't as stable and protected as we once thought.
"We now have a very small window of opportunity to rapidly lower our greenhouse gas emissions, limit the rise in global temperatures and preserve the East Antarctic Ice Sheet.
"Taking such action would not only protect the East Antarctic Ice Sheet, but also slow the melting of other major ice sheets such as Greenland and West Antarctica, which are more vulnerable and at higher risk.
"Therefore, it's vitally important that countries achieve and strengthen their commitments to the Paris Agreement."
The terminus of Vanderford Glacier, Wilkes Land, East Antarctica. Credit: Richard Jones
The research was led by Durham University working with King's College London, and Imperial College, London (UK); the Australian National University, University of New South Wales, University of Tasmania and Monash University (Australia); Université Grenoble Alpes (France); the University of Colorado Boulder, NASA Goddard Space Flight Center and Columbia University (U.S.).Antarctic ice's deep past shows it could be more vulnerable to warming
East Antarctic Ice Sheet could raise sea levels by up to 16 feet
Fiona Jackson For Mailonline -
An ice sheet that holds about 80 per cent of the world's glacier ice has the potential to cause global sea levels to rise by up to 16 feet (five metres) by 2500.
Scientists have predicted that melting of the East Antarctic Ice Sheet (EAIS) will result in this increase if temperatures continue to rise at the current rate.
This warming of about 0.32°F (0.18°C) per decade is the result of humanity's increase in greenhouse gas emissions since the Industrial Revolution.
Researchers from Durham University modelled the effects different temperatures and levels of emissions would have on the ice sheet in the next few centuries.
If no change is made to slow the warming, the EAIS could contribute up to ten feet (three metres) to global sea levels by 2300.
The melting could be limited significantly if emissions targets are met that see global temperature rise limited to 3.6°F (2°C) above pre-industrial levels.
The EAIS could then only contribute about 0.8 inches (two centimetres) of sea level rise by 2100, and 1.6 feet (0.5 metres) by 2500.
Thickness of ice in Antarctica, showing the location of the East Antarctic Ice Sheet (red outline), which holds the equivalent of 52 metres of sea level rise (alongside the UK and Ireland at the same scale). Wilkes Land (highlighted) has been referred to as East Antarctica’s ‘weak underbelly’, where some glaciers appear to be thinning, retreating and losing mass due to warm ocean currents
Scientists have predicted that melting of the East Antarctic Ice Sheet (EAIS) will result in this increase if temperatures continue to rise at the current rate. Pictured: Ice cliff at the terminus of Vanderford Glacier, Wilkes Land, East Antarctica
WHY IS CURRENT GLOBAL WARMING DIFFERENT TO HOTTER PERIODS IN HISTORY?
Previous periods of warming, that are similar to what the Earth is experiencing today, occurred over hundreds of thousands of years.
About 300,000 years ago, during the mid-Pliocene, temperatures were only between 1.3°F and 3.6°F (2°C and 4°C) higher than present.
This period of warming occurred gradually over 300,000 years and is thought to have been caused by changes in the way the Earth orbits the sun.
The Earth's average surface temperature has increased rapidly by about 1.8°F (1.0°C) since the late 1800s.
This can be explained by the increase in our greenhouse gas emissions since the industrial revolution.
Lead author Professor Chris Stokes said: 'We used to think East Antarctica was much less vulnerable to climate change, compared to the ice sheets in West Antarctica or Greenland, but we now know there are some areas of East Antarctica that are already showing signs of ice loss.
'Satellite observations have revealed evidence of thinning and retreating, especially where glaciers draining the main ice sheet come into contact with warm ocean currents.
'This ice sheet is by far the largest on the planet, containing the equivalent of 52 metres of sea level and it's really important that we do not awaken this sleeping giant.'
Ice sheets in Greenland and West Antarctica were already predicted to lose ice in the centuries to come.
Greenland is far away from the North Pole so is exposed to warm air, and West Antarctica is affected by warm ocean currents as it sits below sea level.
However the EAIS is home to the staggeringly cold South Pole, and it is located on land that shields it from the sea's warmth, so it was widely assumed to be more solid.
But in 2020, evidence was found that a part of the EAIS retreated 435 miles (700 km) inland just 400,000 years ago - not that long ago on geological timescales.
This was in response to only 1.8-3.6°F (1-2°C) of warming.
In the study, published today in Nature, researchers from the UK, Australia, France and the USA examined how the EAIS responded to periods of warmth and high carbon dioxide concentrations in the past.
Around three million years ago, during the mid-Pliocene, temperatures were only between 3.6°F and 7.2°F (2°C and 4°C) higher than present.
This range of temperature change is one we could experience later this century.
However, global sea levels in the mid-Pliocene were between 33 and 82 feet (10 and 25 metres) higher than they are now.
Evidence from sea-floor sediments around East Antarctica indicates that part of the ice sheet collapsed and contributed several metres to this.
Carbon dioxide concentrations in that period also only slightly exceeded the current value of 417 parts per million.
This period of warming occurred over a very long timescale - about 300,000 years according to NASA - and is thought to have been caused by changes in the way the Earth orbits the sun.
However current global warming has only been felt for the last few decades, which can only be explained by greenhouse gas emissions from human activity.
Next, the team analysed computer simulations made by previous studies to examine what effects different levels of emissions and temperatures would have on the ice sheet.
If warming continues at its current rate, sustained by high greenhouse gas emissions, the EAIS could contribute nearly half a metre to sea levels by 2100.
Additionally, if it continues beyond 2100, it could contribute around three to ten feet (one to three metres) to global sea levels by 2300, and 7 to 16 feet (two to five metres) by 2500.
This would add to the substantial contributions from Greenland and West Antarctica and thermal expansion of the ocean, threatening millions of people worldwide who live in coastal areas.
In 2020, evidence was found that a part of the EAIS retreated 435 miles (700 km) inland just 400,000 years ago - not that long ago on geological timescales. This finding suggested it was at risk to retreating further as a result of current climate change. Pictured: Scientists drilling a shallow ice core at the surface of the East Antarctic Ice Sheet
Professor Nerilie Abram, from the Australian National University, said: 'We now have a very small window of opportunity to rapidly lower our greenhouse gas emissions, limit the rise in global temperatures and preserve the East Antarctic Ice Sheet
However, in 2015 new targets were agreed upon by world leaders that attended the UN Climate Change Conference in Paris.
They agreed to limit global warming to well below 3.6°F (2°C) and pursue efforts to limit the rise to 2.7°F (1.5°C) by reducing their countries' greenhouse gas emissions.
The international researchers found that, if these targets are met, the worst effects of global warming on the world's largest ice sheet could be avoided.
The EAIS might be thus expected to contribute only about 0.8 inches (two centimetres) of sea level rise by 2100 and 1.6 feet (0.5 metres) by 2500.
Some research shows that snowfall has increased over East Antarctica in the last few decades and, if this continues, it will offset some of the expected ice losses over the next century.
However the researchers say sea levels will still rise due to unstoppable ice losses from Greenland or West Antarctica.
If the Paris Agreement targets for global temperature increase are met, the worst effects on the world's largest ice sheet could be avoided. The EAIS might be thus expected to contribute only about 0.8 inches (two centimetres) of sea level rise by 2100 and 1.6 feet (0.5 metres) by 2500. Pictured: Iceberg towers from the East Antarctic Ice Sheet
Professor Nerilie Abram, a co-author of the study from the Australian National University in Canberra, said: 'A key lesson from the past is that the East Antarctic Ice Sheet is highly sensitive to even relatively modest warming scenarios. It isn't as stable and protected as we once thought.
'We now have a very small window of opportunity to rapidly lower our greenhouse gas emissions, limit the rise in global temperatures and preserve the East Antarctic Ice Sheet.
'Taking such action would not only protect the East Antarctic Ice Sheet, but also slow the melting of other major ice sheets such as Greenland and West Antarctica, which are more vulnerable and at higher risk.
'Therefore, it's vitally important that countries achieve and strengthen their commitments to the Paris Agreement.'
Professor Stokes added: 'A key conclusion from our analysis is that the fate of the East Antarctic Ice Sheet remains very much in our hands.'
Startling satellite images show 'spike melt' of ice in Greenland over three days
Greenland experienced a 'spike melt' from July 15 through 17, which saw its massive ice sheet lose enough water to fill 7.2 million Olympic-sized swimming pools.
The dramatic event was captured in a satellite image that reveals how 18 billion tons of runoff water completely changes the landscape.
The European Union's Copernicus satellite captured the the climate change-induced melt that shows areas of blue water flowing along the bedrock surface.
It was due to a heatwave gripping the country that enveloped the area in a steady 60 degrees when temperatures are typically no more than 50 degrees around this time of year, according to CNN that first reported on the matter.
Although there have been numerous melts in previous years, the recent one is two times the larger than normal and experts warn it has greatly contributed to an increase in the global sea level.
Greenland's dramatic melt that took place on July 15-17 was captured in a satellite image. The shades of blue are actually melted ice that is making its way through the bedrock surface and out to sea
Friday, May 14, 2021
Antarctica’s Doomsday Glacier: How Doomed Are We?
Two new papers offer radically different predictions of the glacier’s future — and thus for the future of low-lying cities around the world. Here’s how to understand the divergent projections
I came face to face with the Doomsday Glacier (a.k.a. Thwaites glacier) in 2019, on a trip to Antarctica aboard the Nathaniel B. Palmer, a 308-foot-long icebreaker operated by the National Science Foundation. I had dubbed the Florida-sized slab of ice its nickname in an article I’d written a few years earlier, and the name stuck. Nevertheless, I was unprepared for how spooky it would be to actually confront the 100-foot-tall wall of ice from the deck of a ship. Locked up here in the West Antarctic ice sheet was enough water to raise global sea levels nearly 10 feet. As I wrote in a dispatch from Antarctica on the day we encountered Thwaites, it was both terrifying and thrilling to know that our future is written in this craggy, luminous continent of ice.
Our world is heating up fast. And as every kid knows, on hot days, ice melts. The question is how quickly. At Thwaites, the melting is mostly a result of warm ocean water attacking it from below, which is stressing and fracturing both the ice shelf that protects the glacier and the glacier itself. Just how fast Thwaites and the other big glaciers that make up the West Antarctic ice sheet will all fall apart is one of the most important scientific questions of our time. And it is a question upon which the future of virtually every coastal city in the world depends. “We know there are tipping points in Antarctic ice sheets, and we also know that Antarctica is the biggest wildcard in the future sea level rise projections,” says Andrea Dutton, a professor of geology at the University of Wisconsin-Madison and a 2019 MacArthur Fellow. “Basically, it all comes down to ‘when will we reach that tipping point?’ ”
Last week, two new papers were published simultaneously in the science journal Nature that offer radically different visions of the Doomsday glacier, as well as radically different visions of how climate models work and what they can tell us about the future. But they agree on one thing: “Both papers make it very clear that human decisions are important, and that limiting warming can limit sea level rise,” says Richard Alley, a glaciologist at Penn State and one of the most respected ice scientists in the world. But beyond that, the two papers may as well be describing life on different planets.
The first paper might be called the Holy Shit vision of Antarctica’s future. In this scenario, led by Rob DeConto, a climate modeler at the University of Massachusetts-Amherst (Dutton and Alley and 10 other scientists are co-authors), the West Antarctic ice sheet remains fairly stable as long as warming stays below 2 C, which is the temperature threshold identified in the Paris climate agreement. Beyond 2 C, however, all hell breaks loose. Thwaites begins to fall into the sea like a line of dominoes pushed off a table and soon takes the rest of the West Antarctic ice sheet with it. And once the collapse begins, it will be impossible to stop – at least on any human time scale. In a century or so, global sea levels could rise 10 feet, which would swamp much of South Florida and Bangladesh and many other low-lying regions of the world.
In fact, it could happen even faster than that, says Alley: “We just don’t know what the upper boundary is for how fast this can happen. We are dealing with an event that no human has ever witnessed before. We have no analogue for this.” All in all, the paper makes a very strong argument that cutting emissions today may avert a centuries-long climate catastrophe. DeConto’s paper also warns against betting on a quick techno-fix like CO2 removal. Unless it is widely deployed by 2070, which, the way things are going, is highly unlikely given the cost and scale-up of the technology that is required, it will be too late
The second paper might be called the What, Me Worry? vision of Antarctica’s future. Unlike the DeConto study, which is based on a single model, the second paper, which was led by Tamsin Edwards, a climate scientist at King’s College London, involved 84 people working at 62 institutes in 15 countries. Edwards and her co-authors use an “emulation” technique to compare the outcome of the different climate models, making the results less dependent on assumptions built into any one scenario, creating what amounts to a statistical average of climate-model outcomes.
In this study, the Doomsday glacier isn’t very doom-y at all. There’s no collapse, no tipping point, no big jumps in sea level rise. In fact, although the paper makes clear that the rate of CO2 emissions over the next few decades is clearly important, the difference in global sea level rise from the melting of all land glaciers, not just Thwaites, only differs by 4 ½ inches between a 1.5 C global temperature rise and a 3 C temperature rise (which is a little above where we are headed with current commitments under the Paris agreement). And much of that comes from increased melt in Greenland and mountain glaciers.
As for Antarctica, the paper says explicitly: “No clear dependence on emissions scenario emerges for Antarctica.” Or as Alley put it to me, a tone of mild astonishment in his voice: “For Antarctica, the Edwards paper basically says, Antarctica doesn’t matter to us and our decisions don’t matter to Antarctica.”
So let me roughly sum up where we are with our scientific understanding of sea level rise risk from Antarctica after more than three decades of serious climate change research: One study tells us that if we don’t cut CO2 emissions fast we will condemn the world to a century of rising seas that will flood every major coastal city and reshape the global map. The other study tells us that the likely difference between dramatically cutting CO2 emissions and cruising along on the current path is 4 ½ inches of water. That means more coastal flooding, more erosion, more salt-water intrusion into drinking wells, but it’s a long way from Waterworld.
What to make of all this? Well, for one thing, the discrepancy between the papers demonstrates not only how little scientists really understand about what is going on in Antarctica, but also what a low priority our society has put on funding research to better understand it. For another, modeling ice sheets is just plain hard, in part because it requires high-resolution models, and in part because a lot of the important events in the story of ice happened 20,000 years ago (or more), for which data is sparse.
Finally, there is a big difference in perspective between the two studies: The Edwards paper only looks at sea level rise out to 2100, whereas the DeConto paper stretches out to 2300. Even in the DeConto paper, Antarctica doesn’t really start to fall apart until 2120 or so. As always, what you see depends on the lens you look through. There’s also the question of how additional snowfall from a warmer atmosphere may offset some or all of the melting from warmer ocean water. (Warmer air holds more moisture, and thus can result in more snow.) As Edwards tells me via email, “We are not yet sure how much we have control over Antarctica, because snowfall has a counteracting effect that may also increase in future.”
The most important distinction, however, is that the DeConto paper includes a mechanism called Marine Ice Cliff Instability, or MICI (scientists pronounce it “Mickey,” like the mouse) and the Edwards paper doesn’t.
MICI is best understood as a hypothesis about how ice sheets behave in a rapidly warming world. The gist of it is that, in some conditions, ice sheets don’t simply melt — they collapse. Warm ocean water can get beneath the glaciers, causing them to fracture and destabilize. When the ice shelves that keep the glaciers wedged in place break up, the glaciers themselves become vulnerable. According to the MICI hypothesis, ice cliffs above about 100 meters high or so don’t have the structural integrity to stand on their own, and without ice shelves to buttress them, they will collapse, or calve, into the sea (there’s a more detailed explanation of MICI in my 2017 article on the Doomsday Glacier).
This is more or less what’s happening right now at a few glaciers in Greenland, including Jakobshaven, the fastest flowing glacier in the world. A few years ago, I flew across the front of Jakobshaven in a helicopter and watched huge chunks of ice calve into the water, creating an army of icebergs that float out into Glacier Bay, where climate-catastrophe tourists take pictures of them and post them to their Instagram accounts.
The calving front at Thwaites is roughly 10 times bigger than Jakobshaven. If Thwaites’ ice shelf breaks up and starts behaving like Jakobshaven, a whole lotta real estate is gonna get wet real fast.
MICI may be a radical idea, but it is not new. It has been around since at least the 1960s, when climate scientist John Mercer first traveled to Antarctica and realized that the land beneath the ice in West Antarctica was shaped like a bowl, which means that if warm water got under the ice and began to destabilize the glacier, it could trigger a runaway retreat that could dump a lot of ice into the Southern Ocean very quickly. Richard Alley took up the idea in the early 2000s, understanding it could be a mechanism to explain why sea levels were so high during the Pliocene era, 3 million years ago, when levels of CO2 in the atmosphere were about the same as they are today. In 2016, DeConto co-authored a paper with Dave Pollard, a climate modeler at Penn State, that modeled the implications of MICI in Antarctica for the first time. The paper added more than three feet to sea level rise projections and scared the bejesus out of climate scientists everywhere.
The MICI hypothesis also prompted the formation of the International Thwaites Glacier Collaboration, a five year-long, $50 million joint research effort between the U.S. and the U.K., which began in 2018 (my trip to Thwaites in 2019 was with scientists participating in this joint research venture). Among the key questions scientists are asking: How much warm water is getting under Thwaites ice shelf? (Quite a bit, according to a new paper by Swedish oceanographer Anna Wåhlin, which is based on measurements she made while we were in Antarctica together.) How quickly is the glacier losing its grip on the bedrock near the current ice front? How quickly is the ice shelf breaking up?
“In the last few years, we have seen a lot of dynamic change at Thwaites and other glaciers in the region,” says Robert Larter, a geophysicist with the British Antarctic Survey who was the chief scientist on the Palmer on my trip to Antarctica. According to one recent study, the net ice-mass loss from Thwaites and nearby glaciers is now more than six times what it was 30 years ago, which Larter calls “mind-boggling.”
None of this research is conclusive, and most of it is still too new in include in climate models. For the moment, MICI remains an outlier idea, one that mainstream climate modelers have yet to fully embrace, despite the risks that civilization faces from it.
“If you want to be generous,” Alley tells me, “You could say that climate modelers really want to make their models carefully, make sure they are calibrated precisely, and they don’t know what to do with MICI.”
It’s also true that there are still a lot of unanswered questions about exactly how MICI works. “Yes, ice cliffs can fail,” says Ted Scambos, the lead U.S. glaciologist in the Thwaites research project. “But is a runaway failure realistic?” And just because ice cliff collapse is happening at Jakobshaven, it doesn’t mean it will necessarily happen at Thwaites. “Jakobshaven is not physically the same as all Antarctic glaciers, nor does their model include all possible physics (e.g. negative feedbacks or other factors that limit the rate and extent of cliff collapse),” Edwards tells me via email. “It’s far too simple to say, ‘Clearly MICI exists so why don’t you believe in it?’ ”
“The reason nobody is rushing off an unstable marine cliff in search of what DeConto and Pollard have done is because nobody thinks there is any good reason to single out MICI and make it the cause of instability in glaciers,” says Gavin Schmidt, a climate modeler and director of the NASA Goddard Institute for Space Studies in New York. “Is MICI a large part of why glaciers calve? It’s not inconceivable, but it’s also not inconceivable that it could be other factors.”
Finally, some of the resistance to MICI may simply be a failure of imagination. No human has ever witnessed the rapid collapse of a glacier in Antarctica like Thwaites; ergo, it can’t happen. Alley himself thinks about it simply in terms of risk. “Maybe we’ll get lucky and the ice cliffs won’t disintegrate in Antarctica quite as fast as we predict,” he says. “But if you are even a little bit worried that scientists might have made mistakes in their calculations about what is going on in Antarctica, then maybe we should pay attention to this.” He compares Thwaites and other glaciers in West Antarctica with drunk drivers. “They are out there, they are scary, and they don’t behave as you expect them to,” Alley says. “That’s why it’s a good idea to have a seatbelt in your cars.”
In the end, climate modelers are a little like sci-fi writers. They use facts and physics to spin out possible futures. DeConto’s paper imagines we are moving into a new world that will behave very differently from the world we have lived in so far. Edwards’ paper imagines that the rest of the 21st century will look pretty much like it does today, only hotter, and with a little less ice. Both visions are based in science. Both visions are plausible. And both visions are fraught with deep uncertainty about where we are going.
I hope we live in Edwards’ world, but I fear we live in DeConto’s.
Wednesday, July 13, 2022
New research shows how the Antarctic ice sheet retreated over 10,000 year
Our latest research looks at how the Antarctic ice sheet advanced and retreated over the past 10,000 years. It holds stark warnings, and possibly some hope, for the future. The current imbalance
Future sea-level rise presents one of the most significant challenges of climate change, with economic, environmental and societal impacts expected for coastal communities around the globe
While it seems like a distant issue, the changes in Antarctica may soon be felt on our doorsteps, in the form of rising sea levels.
Antarctica is home to the world’s largest single mass of ice: the Antarctic ice sheet. This body of glacier ice is several kilometres thick, nestled on top of solid land. It covers entire mountain ranges beneath it.
The ice sheet “flows” over the land from the Antarctic interior and towards the surrounding ocean. As a whole it remains a solid mass, but its shape slowly deforms as the ice crystals move around.
While the ice sheet flows outward, snowfall from above replenishes it. This cycle is supposed to keep the system in balance, wherein balance is achieved when the ice sheet is gaining the same amount of ice as it’s losing to the ocean each year.
GETTY IMAGES The Antarctic ice sheet has been retreating for over 10,000 years.
However, satellites keeping watch from above show the ice sheet is currently not in balance. Over the past 40 years, it has lost more ice than it has gained. The result has been global rising sea levels.
But these historical observations span only four decades, limiting our understanding of how the ice sheet responds to climate change over much longer periods.
We wanted to look further back in time – before satellites – and even before the first polar explorers. For this, we needed natural archives. Digging up Antarctica’s past
We brought together various natural archives to unearth how the Antarctic ice sheet changed over the past 10,000 years or so. These included:
LIZ CARLSON
Antarctica will be the largest source of future sea-level rise.ice cores collected from Antarctica’s remote interior, which can show us how snow accumulated in the past rocks collected from exposed mountain peaks, which reveal how the ice sheet has thickened or thinned with time
sediment cores collected from the seafloor, which reveal how the ice sheet margin – where the edge of the land ice meets the ocean – advanced or retreated lake mud and old beaches, which reveal how the coastline changed in response to the ice sheet growing or shrinking.
When we started our research, I wasn’t sure what to expect. After all, this period of time was long considered fairly dull, with only small changes to the ice margin.
Nevertheless, we studied the many different natural archive one by one. The work felt like a 1000-piece jigsaw puzzle, full of irregular-shaped pieces and seemingly no straight edge. But once we put them together, the pieces lined up and the picture was clear.
Most striking was a period of ice loss that took place in all regions of Antarctica about 10,000 to 5000 years ago. It resulted in many metres of sea-level rise globally.
BAILEY BERG/FOR THE WASHINGTON POST Understanding how and why the Antarctic ice sheet changed in this fashion offers lessons for the future.
In some regions of Antarctica, however, this ice loss was then followed by ice gain during the past 5000 years – and a corresponding global sea-level fall – as the ice sheet margin advanced to where it is today. A warning
Understanding how and why the Antarctic ice sheet changed in this fashion offers lessons for the future.
The first lesson is more of a warning. The period of ice loss from 10,000 to 5000 years ago was rapid, occurring at a similar rate to the most dramatically changing parts of the Antarctic ice sheet today.
We think it was likely the result of warm ocean water melting the underside of floating ice shelves – something that has also happened in recent decades. These ice shelves hold back the ice on land, so once they’re removed the ice on the land flows faster into the ocean.
In the future, it’s predicted ice loss will accelerate as the ice sheet retreats into basins below sea level. This may already be under way in some regions of Antarctica. And based on what happened in the past, the resulting ice loss could persist for centuries. Bouncing back
The second lesson from our work may bring some hope. Some 5000 years ago the ice sheet margin stopped retreating in most locations, and in some regions actually started to advance. One explanation for this relates to the previous period of ice loss.
Before the ice began melting away, the Antarctic ice sheet was much heavier, and its weight pushed down into the Earth’s crust (which sits atop a molten interior). As the ice sheet melted and became lighter, the land beneath it would have lifted up – effectively hauling the ice out of the ocean.
Another possible explanation is climate change. At Antarctica’s coastal fringe, the ocean may have temporarily switched from warmer to cooler waters around the time the ice sheet began advancing again. At the same time, more snowfall took place at the top of the ice sheet.
Our research supports the idea that the Antarctic ice sheet is poised to lose more ice and raise sea levels – particularly if the ocean continues to warm.
It also suggests uplift of the land and increased snowfall have the potential to slow or offset ice loss. However, this effect is not certain.
The past can never be a perfect test for the future. And considering the planet is warming faster now than it was back then, we must err on the side of caution.
Richard Selwyn Jones is a Research Fellow at Monash University, Australia.
Half of Antarctica’s ice shelves could collapse in a flash, Live Science reports. The article points out that this could result from ongoing global warming.
As meltwater rushes through the cracks in the Antarctic ice shelves, it can destroy the ice shelves in minutes or hours. This is amplified by the warming atmosphere, and as the warming continues, this phenomenon may happen more often than not. A study published back in August showed that at least half of the ice shelves are at risk of having this happening.
The study suggested that around 50% to 70% of the ice shelves holding Antarctic glaciers in place could become weak and even collapse with surges of meltwater. Ching-Yao Lai, a postdoctoral researcher in the Department of Marine Geology & Geophysics at Columbia University’s Lamont-Doherty Earth Observatory in New York and lead author of the study said, “What we find is that the amount of melting is important, but where the melting happens is also important.”
Christine Dow, the Canada Research Chair in Glacier Hydrology and Ice Dynamics at the University of Waterloo, wasn’t involved with the study but shared her thoughts with Live Science:
“The time frame over which this process could happen is the biggest question.”
“Mass loss from Antarctica (2003–2019). (Top) Mass change for Antarctica. (Bottom) Mass changes at the grounding line. Highest mass loss rates are in West Antarctica and Wilkes Land, East Antarctica. Map and grounding line mass change have been smoothed with a 35 km median filter for improved visualization.” Image courtesy NASA/Science.
Punching Through The Ice
Antarctic ice shelves that are confined to the open water create a barrier that slow-moving glaciers move up against. These buttressing ice shelves were a focal point for the study and they often have cracks on their surfaces as the shelf pushes against the curving shoreline. Also, the shelves stretch out as they flow across the ocean water. “Usually near the front of ice shelves, it gets stretched the fastest and this kind of breaking occurs,” Lai explained.
When the atmosphere is warm, the surface of an ice shelf may start to melt, and when this happens, the meltwater will pool into the cracks and create hydrofracturing, which is a process where excess water puts pressure on the ice. This makes the cracks deeper and can trigger the collapse of that shelf.
Dow explained that the meltwater “can punch through the ice to the ocean in a matter of minutes to hours, as long as there’s enough water available to keep on filling the crevasse and keep up the pressure,” adding that “the crack in the ice then fills up with ocean water.”
This could lead to the shelf breaking apart, which is what scientists believe happened to an ice shelf named Larsen B — it lost 1,255 square miles of ice over a period of a few weeks in 2002.
Lai and her team created a machine learning model to see which buttressing ice shelves were the most vulnerable to collapse. The algorithm can be trained to recognize visual features based on past images it’s analyzed. Lai and her team taught their model to recognize surface fractures in the ice using satellite images of two shelves — Larsen C and George VI — both located in the northwest region of Antarctica. Then they applied the model to a complete map of Antarctica.
After this, the researchers saw which fractures would be at risk of hydrofracture. Dow pointed out that even though researchers had used this analysis at specific ice shelves before, this application is “the first time it has been applied to the Antarctic as a whole.”
The Next Question
The research team is not done asking questions and seeking answers. They wonder, “How does this hydrofracture process contribute to the sea level rise?” To answer this question, her team will pair their model of ice cracks with climate predictions and a model of how ice flows over the bedrock of Antarctica.
Lai pointed out that the research will help the authors see how fast and how much sea-level rise could change due to cracks forming in ice sheets in combination with rising atmospheric temperatures.
The researchers don’t have an exact timeframe yet, but some scientists think that climate change will further accelerate massive hydrofracturing events within a matter of decades.
Final Thoughts
This year has been a really unusual year for many people. We’ve had the global pandemic, Trump and his drama, Black Lives Matter protests (which I support because killings of unarmed black people are abhorrent), the Pentagon released footage of UFOs, a mysterious monolith popping up at random places and then vanishing, and even a former Israeli space security chief saying extraterrestrials exist and claiming that Trump knows about it.
It’s been a helluva year, and so much has happened that the news about Antarctica’s heatwave back in February was probably forgotten. It got up to 64 degrees Fahrenheit, which is pretty much unheard of. And it isn’t stopping there — Antarctica has been simmering for 30 years — much longer than many have realized. The focus of the world is mostly on political games, whether it’s Trump and his drama or other countries with their own issues. Although many nations that took part in the Paris agreement did so because they are concerned with the direction our planet is headed in, I think we have some severe wakeup calls coming as Antarctica’s ice shelves start to collapse.
As a whole, we are simply not doing enough to stop the heating of our planet. Some are trying, but we all need to get involved, and quite frankly, people who are starving, jobless, and who are trying to survive don’t really care about Antarctica or climate change. There are entire nations that look the other way on issues such as child slavery. There are leaders who are corrupt and don’t care about the wellbeing of their citizens. There are many issues in the world, but ongoing global warming and melting ice shelves will make most of them worse
This mentality has to change, and it starts with all of us.
SPACE Wed, June 21, 2023 Satellite images show that the amount of sea ice floating around Antarctica remains too low during the winter season.
Antarctica may be in serious trouble. Satellite images show that the amount of sea ice floating around the pristine polar continent remains far below long-term averages despite the south polar region moving into its peak winter period.
Researchers at the British Antarctic Survey (BAS) observed with trepidation in late 2022 and early 2023 as satellite images revealed that sea ice attached to the coast of Antarctica had been disappearing month after month at a pace never seen before. And they continued to observe in near horror as this sea ice failed to sufficiently replenish after the colder months arrived. As of mid-June 2023, sea ice extent in Antarctica was about 0.9 million square miles (2.28 million square kilometers) below the average from 1981 to 2010 for that part of the year, according to the U.K. weather authority Met Office, and about 0.4 million square miles (1.15 million square km) below the previous June record low from 2019.
This development is a worrying deviation from a previous trend that saw Antarctica hold quite steady against progressing climate change, which has long been decimating its northern counterpart, the Arctic. Scientists now worry that the frozen southernmost continent, which plays a crucial role in stabilizing the global climate, may be reaching its tipping point, a point of no return beyond which the polar ecosystem as we know it won't be able to survive.
"In the Arctic, we have seen a steady decline [of sea ice] over time," Peter Fretwell, a remote-sensing scientist at the BAS, told Space.com. "Antarctica, up until 2016, was steady, even getting more sea ice, which we couldn't understand. But since 2016, it's gone down, and it's going down even more at the moment. Something has happened, and it's gone down suddenly very much."
The amount of floating ice surrounding the polar continent dropped to an all-time low in late February this year, shrinking to 691,000 square miles (1.79 million square km). That's 50,000 square miles (130,000 square km) below the previous record low of February 2022, according to NASA, which followed a previous record low from 2021.
The problem is, as Fretwell said, that "what happens to Antarctica doesn't just stay in Antarctica." The warming polar seas affect weather patterns all over the world and accelerate the melting of Antarctic glaciers that, in turn, will lead to faster sea level rise around the globe.
Penguins on an Antarctic iceberg.
"Climate change is affecting the polar regions faster than anywhere else in the world. They're really at the frontline of climate change," Fretwell said. "But we know that sea ice drives deep water currents around the world, and it has consequences around the world."
The three consecutive years of unprecedented sea ice loss also bode ill for many of the continent's species that are unlikely to survive anywhere else. Fretwell and his team are currently scouring satellite images for evidence of the impacts on populations of animals that are known to rely on sea ice for breeding.
For example, changes in sea ice previously decimated one of the largest colonies of the iconic emperor penguin. That colony lost three generations of chicks after sea ice in the Halley Bay in the Weddell Sea broke up too early in the season in 2016, 2017 and 2018. Emperor penguin chicks huddle on the sea ice while their parents fish for food, as they can't enter the frigid water before developing their outer feathers. When the sea ice disintegrates underneath the colony, the chicks drown or freeze to death.
Eight years of melting of the Pine Island Glacier.
The alarming decrease of sea ice is also a bad omen for Antarctica's glaciers, which would, without the buffer of coastal sea ice, become directly exposed to the warming ocean waters. A flurry of recent studies has explored the condition of the melting Thwaites glacier, a vast frozen river flowing into the Amundsen Sea. Dubbed the Doomsday glacier, Thwaites is one of the most vulnerable ice masses in Antarctica. Currently contributing 4% to the global sea level rise, Thwaites could single-handedly increase global sea levels by 26 inches (65 centimeters) if it were to melt completely, according to estimates.
Previous studies have shown that the Thwaites Ice Shelf, a stable floating mass of ice that protects the continental glacier, may completely collapse by the early 2030s, a process that might accelerate if the current trend of vanishing sea ice continues. But Fretwell thinks that all is not lost yet.
"There is still time to stop this oil tanker of climate change," Fretwell said. "But there is not much time. We now have decades of warming oceans and warming temperatures wired into the system, so if we stop putting carbon in the atmosphere, the world will still continue to heat for decades to come."
Humankind's failure to stop emitting greenhouse gases might result in a new Antarctica, one completely different from the continent that we know today. And researchers have no way of knowing how close to this new world we have come.
"With tipping points, you never know whether you've come past one," Fretwell said. Sea ice levels "might come back, but right now, we are in a horrible state of wondering whether it's going to come back or continue on this track."
