About 115,000 years ago Homo sapiens still lived in clusters of hunter-gatherers, largely confined to Africa. We still shared the globe with the Neanderthals, though it is not clear that we had not met them yet.
And although these different hominids did not know it, the earth was at the end of a great warm period. It was one that came pretty close to our present climate, but with a big discrepancy – the seas were 6 to 9 meters higher at that time.
In this ancient time, sometimes referred to as Eemian, the oceans were about as warm as they are today.
And last month, there has been fascinating new research indicating that northern hemisphere glaciers have already declined as much as in Eemian, driven by dramatic warming in the Arctic regions.
The finding emerged when a research team on Baffin Island in northeastern Canada examined the remains of ancient plants that had appeared beneath the rapidly retreating mountain glaciers.
And they found out that the plants were very old and probably were last. At these sites were bred about 1
This is the last time that the areas were actually covered by ice, the scientists believe.
"It's very difficult to find another explanation, except that at least that's the case. O In an area where we work, the last century is as warm as in the last 115,000 years," said Gifford Miller, a geologist at the University of Colorado in Boulder, who led the research on Baffin Island.
But if Miller is right, there is a big problem. We have geological records of the sea level of the Eemian. And the oceans were 20 to 30 feet (6 to 9 meters) higher according to scientists.
Some additional water probably came from Greenland, whose ice currently contains over 6 meters (20 feet) of potential sea-level rise. But it could not only have been Greenland, because the entire ice sheet had not melted then.
Therefore, the researchers also suspect the collapse of the most vulnerable part of the Antarctic, the West Antarctic ice sheet. This region could easily provide another sea level rise of 10 feet (3 meters) or more.
"There is no way to reach tens of meters of sea-level rise without getting tens of meters of sea-level rise from the Antarctic," said Rob DeConto, an Antarctic expert at the University of Massachusetts.
An attempt to understand how the Antarctic will fall
Scientists are now intensively discussing which processes could have happened when – I will play again. After all, the Antarctic West has already shown that it is retreating.
Some researchers, including DeConto, believe they have found a key process – the so-called "Marine Ice Cliff Collapse", which can release sea levels very rapidly from the West Antarctic.
But they are being challenged by another group whose members suspect that the changes in the past have been slow – and will happen again.
To understand the dispute, consider the vulnerable situation of the West Antarctic itself.
Essentially, it is a huge block of ice that is mostly in very cold water. Its glaciers are facing the ocean in all directions, and toward the center of the ice sheet the seabed drops rapidly, even if the surface of the ice sheet itself becomes much thicker, about two miles thick altogether.  One and a half miles of this ice rests below sea level, but there is still much ice over that.
So, when the Gateway Glaciers begin to move backwards – especially a glacier called Thwaites the largest of them – the ocean would have quick access to much thicker ice.
The idea is that this whole area was not a block of ice during the Eemian, but an unnamed sea. Somehow the ocean came in, overturning the outer defenses of the glaciers and gradually grading the entire West Antarctic over and on its way to melting.
DeConto, along with his colleague David Pollard, built a model that looked at the Eemian, and another ancient warmth called Pliocene, to understand how this can happen.
In particular, they contained two processes that make it possible to remove glaciers. One, referred to as the "sea ice shield instability," describes a situation in which a partially submerged glacier becomes deeper and deeper as one moves toward the center.
In this configuration, warm water can cause a glacier to move backwards and downwards getting thicker ice to the sea – and thicker ice will flow out faster.
The loss is absorbed.
The instability of the marine ice is probably already in progress in the West Antarctic, but in the model that was not enough. DeConto and Pollard also added another process currently under way in Greenland on a large glacier called Jakobshavn.
Jakobshavn moves backwards down an underwater slope, just as it is feared for the much larger Thwaites Drift. But Jakobshavn does something else as well. It constantly breaks off thick pieces at the front, almost like a loaf of bread, and exits slice by slice.
This is because Jakobshavn no longer has an ice-board, a floating extension that has grown over the sea at the front of the glacier and stabilizes it. The shelf collapsed when Greenland had warmed over the last two decades.
Jakobshavn presents itself as a steep vertical sea front. Most of the glacial ice is under water, but more than 100 meters in length – and that's the problem for DeConto and Pollard. That's too much to uphold.
Ice is not steel. It breaks. And breaks. And breaks.
This additional process, called the "collapse of the sea ice cliffs," leads to a complete catastrophe when applied to Thwaites. If Thwaites one day loses his own ice shelf and shows a vertical front to the sea, you would have ice cliffs hundreds of feet above the water surface.
DeConto and Pollard say that such cliffs would constantly fall into the sea. And when they added this calculation, not only was the sea-level rise in Eemia restored, but the forecast also increased how much ice the Antarctic could yield in that century – more than three feet.
Since there are other drivers of sea-level rise, as in Greenland, this meant that we could see a total of six feet in this century, which is about twice the previous projection. And in the next century, ice loss would get worse.
"We pointed out that if the type of calving we see in Greenland today would start in Antarctica in an analogous environment, then by the way Antarctica has a good idea thicker ice, it is a much larger ice sheet, the consequences might be truly monumental for sea-level rise, "said DeConto.
In addition, the process is essential to understanding the past – and thus how we can replicate it.
"We can not recover six meters of sea-level rise early in the Eemian without considering a brittle fracture in the ice sheet model," said DeConto.
A massive debate on ice cliffs at sea
Tamsin Edwards is unconvinced. As a glaciologist at Kings College London she is – along with a number of other Antarctic experts – lead author of a study published Wednesday Nature (the same journal published in DeConto and Pollard 2016) questions her model. detail.
Using a statistical technique to study the results, Edwards and her co-workers conclude that tumbling the ice cliffs is not necessarily necessary to reproduce past warm periods.
They also offer lower sea-level rise Antarctica in this century. If they are right, the worst case is again about 40 centimeters or just over three to four feet.
"Things may not be as terrible as the last study predicted," Edwards said. "But they are still bad."
It's a new science, she said, and without further modeling, it's unclear how ice cliffs will ultimately affect sea-level rise.
But what happened in the Eemian? Edwards believes it took a long time to lose West Antarctica. That it was not fast. After all, the entire geological period was millennia long.
"We are an impatient crowd, humans, and the ice sheet does not respond in a decade, they are slow beasts," she said. [19659003DeContentStewardofKnowledgeLearned
"The Edwards study illustrates the need for more detailed statistics than we originally used for our 2016 model edition, but the models are evolving rapidly and have changed significantly since 2016," he said in a written statement.  But he does not retire to the icy sea cliffs, the new criticism, DeConto said, implies that "these processes are not important for future sea-level rise. And I think that's some kind of dangerous message. "
He certainly has his allies. Richard Alley, a noted glaciologist at Penn State University, who has published with DeConto and Pollard, wrote in an e-mail that" Cliff Retreat is not some weird and unexpected physical process; it now happens in some places, in the past, and is expected where high enough temperatures in the sea or in the air around the ice flowing into the sea occur.
The Eemianer – but worse?
There is one important thing to consider – the Eemian occurred without people emitting much greenhouse gases.
The atmospheric carbon dioxide was far lower than today Earth orbit changes around the sun causing more sunlight to fall on the northern hemisphere.
The big difference this time is that people are heating things up much faster than is thought to have happened in the geological past.
And that makes a big difference, said Antarctic explorer Ted Scambos, who directs the US side of an international multimillion-dollar mission to study Thwaites Glacier, and is a senior researcher at the National Snow and Ice Data Center in Colorado.
"The current pace of climate change is very fast," said Scambos, and the Warming could cause glaciers to behave differently than in the past.
Accordingly, Scambos says he considers the current debate fruitful – "it's the discussion that needs to happen" – but it does not diminish his concern for the fate of Thwaites Glacier if he retreats far enough.
"There is no model that will not accelerate the glacier r if it gets into those conditions," said Scambos. "It just has to be."
The humans were in the Eemian Sea near the Antarctic – and in modern times we have never seen a glacier as big as the retreat of Thwaites. It is possible that something will happen for which we have no precedents or predictions.
Just last week, scientists reported, for example, a large cavity opening under one part of the glacier – something models could not have predicted
It's now a tremendous effort to at least find out what could happen – before it actually does happens. It will help determine if people who are now organized and industrialized and master fossil fuels are ready to advance a reiteration of our own geological history.
2019 © The Washington Post
This article was originally published by The Washington Post .