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Some good news for the sea level rise in the future



  Speed ​​of the last ice current around the Antarctic. The Thwaites Glacier is one of the smaller purple regions on the left side of this image.
Enlarge / Speed ​​of the last ice current around the Antarctic. The Thwaites Glacier is one of the smaller purple regions on the left side of this image.

Glaciers are moody things with a variety of personalities. Some are quite stubborn and refuse to melt too much while the earth's climate warms. Others are quite sensitive and may shrink more than you would expect if you push them too far.

Much of this is related to the shape of the underlying rock. Some glaciers that touch the sea have bedrock falling down when you drive inland. As the glacier begins to retreat downhill, seawater can flow in and make the ice easier and swim, which makes it faster.

Every marine glacier has a "grounding line" ̵

1; the point where the ice is resting on solid ground instead floats like a canoe pushing away from the shore. If you hear of an "ice shelf", this is the floating part of the glacier. The position of the grounding line along the bedrock is the place where topography plays such a big role. A new study by a team led by Eric Larour of NASA shows this The bedrock can also move and make these sensitive glaciers a little less sensitive.

The idea is not new: the retreat of these glaciers can be accelerated or slowed down through a series of processes, including changes. As the sea level rises, the limp state obviously increases and ice loss is accelerated, and there are stranger factors: glaciers Actually exert an attraction on the sea water and pull a hill near water as the glacier shrinks. This attraction also shrinks, which actually makes the water slosh away – lowering sea level at the coast.

Bedrock also responds to changes in the mass of ice on top of the land surface (which is why the land is roughly cup-shaped below Greenland's ice cover). If you lose ice, the ground will jump up. And in this case, this means that the ground at the grounding line below a sensitive glacier can jump up to the ice to get the friction that slows the retreat.

The question is how much effect does this have? Many models used to simulate changing glaciers attempt to incorporate these processes, but are limited to coarser resolutions. In this new study, the researchers have modeled the Antarctic to a resolution of 1 kilometer. It turns out that this makes a pretty big difference.

The study focuses on the Antarctic Thwaites Glacier, one of the continent's most sensitive and vulnerable continents, which plays an important role in determining how quickly future sea-level rise will increase. Several versions of the model were run to simulate the next 500 years, each time adding another process to investigate the effects.

The two biggest effects were the rebound bedrock, followed by gravitational pull, which slowed Thwaites Glacier's shrinkage. The higher resolution of the model showed that these processes were stronger in the immediate vicinity of the glacier than in coarser models that spread over larger areas. Together, they reduced the movement of the Glacier Earth Line by nearly 40 percent in 2350 and reduced their contribution to sea-level rise by 25 percent.

This result suggests that these processes may be important and helpful in the long run. For glaciers like Thwaites, there was very little difference in this century. By 2100, there was only a 1% change in sea level rise. Major changes in mass were needed before the ground could recover, or a weaker attraction could become significant factors.

A sobering indication of sea-level rise is that it will continue for a long time in the future, even if global warming is successfully halted. Ice plates just take a long time to respond to a warmer world. This study shows that complex factors such as moving rocks in the coming decades need not have much impact on sensitive glaciers, but they need to be adequately considered if you want to project those changes for several centuries – where they can do something good news.

Science, 2019. DOI: 10.1126 / science.aav7908 (About DOIs).


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