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Sea level rise will be one of the greatest challenges we face in the next century.
How high seas rise and how soon has a lot to do with what happens here.
Antarctica holds the largest chunk of ice on Earth.
Its western portion alone contains enough ice to raise sea levels by more than 3 meters.
And it's in big trouble. Largely because of this, the Thwaites glacier.
Its face towers as high as a six-story building, and extends for 120 kilometers across the coast of West Antarctica, making it about the size of Florida.
It's a humongous glacier that reaches right into the heart of West Antarctica.
And that's a major problem, because in the past couple decades, it's become increasingly clear the Thwaites glacier is falling apart.
These are portraits of a vast, rugged, treacherous continent.
Which has challenged man since first he could sail beyond the limits of his horizon.
This is the Antarctic ice sheet.
It's thickest in the middle, where years and years of snowfall compacts into ice.
As the middle builds, it pushes ice out towards the oceans via glaciers.
And the part of a glacier that floats on water is its “ice shelf.”
Today, man-made climate change is warming the air and water around Antarctica, causing each side of the ice sheet to melt, but at very different speeds.
The Eastern ice sheet lies mostly on high ground, above sea level, which keeps it relatively safe from warm ocean water.
That means it's melting slowly and remains relatively stable.
But West Antarctica is different; most of it lies below sea level.
That means as it thins, water can undermine it, possibly kick-starting a more rapid collapse.
It's why West Antarctica is considered the most important piece of ice in the world when it comes to climate change.
Here's another view of the bedrock underneath Antarctica's ice sheet.
The green, yellow, and red parts are land above sea level. Like in East Antarctica.
But these blue areas in West Antarctica are all below sea level.
This area, where the bedrock slopes continuously for more than a mile down and deep into the center of Antarctica, is the Thwaites Glacier. And it could be the most dangerous glacier in the world.
Surrounded by three mighty oceans, the seas are as much a part of Antarctica, as her highest mountains.
Right now, Thwaites is barely hanging on.
In the past 30 years, the front of Thwaites' ice shelf has lost a lot of ice, causing it to retreat backwards.
With a smaller ice shelf to slow the flow of ice, the flow of the glacier speeds up.
But the bigger problem is the glacier's "grounding line", the final point where the glacier rests on the bedrock.
That grounding line has been shifting backwards as warm ocean water reaches underneath the ice shelf.
It's moved 14 kilometers since 1992.
So ice that used to be on land becomes ice that is floating on water, raising sea levels.
The downhill slope of the bedrock means that as the grounding line moves back, it lifts an even bigger slice of ice behind it off the land and into the water.
And that accelerates the flow of the glacier into the sea.
The amount of ice flowing from Thwaites has doubled over the past 30 years.
And already contributes 4 percent to global sea level rise.
And scientists have recently detected a huge cavity two-thirds the size of Manhattan down here.
Scientists believe this could mean Thwaites' collapse is inevitable.
How soon that happens is hotly debated.
The sleeping continent is awakening, slowly at first, but with ever-gathering momentum.
The complete collapse of Thwaites will take centuries and its affected by many different things, from the temperature of the ocean currents to the makeup of the bedrock.
But the research shows that humans can possibly slow or even stall its collapse by curbing greenhouse gas emissions soon.
That's important because some scientists believe collapse could start this century, while others say it's already underway.
The collapse of Thwaites would add about half a meter of sea level rise.
And trigger a much bigger catastrophe.
Because Thwaites reaches into the middle of West Antarctica, its collapse could cause the rest of the ice sheet to collapse with it, resulting in more than 3 meters of sea level rise in the next few centuries.
That would submerge not only Miami and southern Bangladesh but also parts of the Netherlands and New York City.
So while there's still a lot of uncertainty around Thwaites, one thing is clear: once it starts to collapse, it won't stop.



海面上昇が危ない!科学者たちが懸念する氷河の後退(Why scientists are so worried about this glacier)

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Minjane 2020 年 7 月 21 日 に公開    pas 翻訳    naomi チェック
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