The Jakobshavn glacier gained a little mass due to an influx of cold water. However, according to researchers, this is only a temporary condition.
Glacier growth in Greenland? – The most important thing at the beginning:
- Jakobshavn, the island's largest glacier, is currently growing
- Several research teams involved in analyzing complex relationships
- Overall, the Greenland ice sheet continues to lose large amounts of ice
- One has to distinguish between long-term and short-term phenomena: glacier growth: short-term; Glacier melt: long term
It is widely believed that once a glacier has melted, it will not come back. Glaciers across the Arctic are shrinking due to global warming. Or maybe not? It's not that simple.
Jakobshavn glacier is growing
Oceans Melting Greenland (OMG) project recently showed that the Jakobshavn Glacier is growing again, at least on the edge. In a study in “Nature Geoscience,” the researchers report that the ice has increased in mass again since 2016. The reason for this is comparatively colder water, which has slowed down the melting process. This appears to have reversed the glacier melt. But even as Jakobshavn, the island's largest, grows, the Greenland ice sheet is still losing large amounts of ice.
Shrinking and growing of glaciers difficult to predict
When you read this news, you briefly feel hopeful, but NASA scientists clarify that climate change is not a linear process.
Josh Willis, oceanographer at NASA's Jet Propulsion Laboratory and lead scientist on the OMG project: “It used to be thought that once glaciers started shrinking, nothing could stop them. We found out that’s not true.”
Other Arctic glaciers could also grow similarly. In a world that is constantly warming, such events are a sign that the seasonal shrinking and growing of glaciers is more complicated and therefore more difficult to predict than previously thought, Willis continued.
It's not just the warmer air that plays a role. “The water is also warming up,” says Willis. “The seas play an important role in the melting of Greenland’s ice. More than 90 percent of the heat retained by greenhouse gases heats the oceans. So we know that this slowdown will pass in the long run. If that happens, the glacier will shrink even faster than before.”
Ala Khazendar, a glaciologist on the OMG project and lead author of the study, said: “This all points to how sensitive glaciers are to rising sea temperatures.”
Why is the Jakobshavn Glacier currently growing?
Below the glacier fresh and salt water mixes. This accelerates melting, which means that so-called calving - the breaking off of large masses of ice - occurs more frequently in glaciers that end in the sea or inland waters. Jakobshavn is currently growing due to an influx of unusually cold water from the North Atlantic. Temperatures here have fallen by two degrees Celsius at a depth of 250 meters since 2014. This slowed the melting of the glacier and even allowed some ice to grow. The influx of cold water is caused by the natural cycle that takes place in the Atlantic. Here, colder and warmer water alternate about every 20 years. So cooler water is currently reaching the west coast of Greenland, but at some point this will reverse again.
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From a holistic perspective, glacier melting continues, which also causes the ice sheet to shrink and thus contributes to sea level rise.
The influence of the sea has so far been underestimated?
Jakobshavn and other glaciers extend out to sea. The water temperature therefore has a direct influence on the size and movements of the glaciers. This could possibly mean that overall they are shrinking more slowly than expected. According to Willis, experts had previously assumed that glacier melt was largely controlled by the seafloor. The ice wedges itself into underground elevations, preventing the glaciers from moving.
“But the surprising thing is the sea. It basically reversed the retreat of that glacier. We never thought that the sea could play such an important role. We found out that you also have to pay attention to what the sea is doing,” says Willis.
Considering that global warming will continue, the future of the glacier looks poor despite current growth. Ice loss will be greater in warm periods than growth in cold periods. Between 2000 and 2010 alone, the Jakobshavn Glacier lost more pieces of solid ice than any other area of the Greenland ice sheet. This corresponds to an amount that raises global sea levels by almost one millimeter. If the island were to melt completely, it would mean a sea level rise of seven and a half meters.
Monitoring seasonal growth and shrinkage
In 2016, OMG began monitoring the seasonal growth and shrinkage of ice to better predict sea level rise. Now the researchers want to test Willis' hypothesis. For the most part, climate research is limited to air and atmosphere. OMG, on the other hand, explores the water and glaciers directly. The OMG team now wants to measure the ice cover using radar scans. With this technology, this can be recorded with an accuracy of up to one meter.
NASA's GRACE-FO mission records movements of terrestrial water masses. It will show later this year how much mass Greenland has lost in the last two years.
Josh Willis said: “This can help us learn whether this effect is more widespread and could have a positive impact on mass balance. […] We don’t know how to place the Jakobshavn results in the overall Greenlandic context until we have this additional data.”
David Holland, a professor at New York University, has spent twelve years researching the interactions between the Jakobshavn Glacier and the sea. He also suspects that this interaction could be widespread from the Arctic to the Antarctic and thus agrees with Willis' ideas.
“In summer you can see Jakobshavn growing instead of shrinking,” says Holland. “I think the question is more: Why does the glacier do what it does? In my opinion, the sea is the dominant factor that controls this.”
Different views and opinions
Martin Truffer from the University of Alaska measures glacier movements using ground radar scans. He was a little surprised by Holland's observation. Truffer believes that warming air contributes to glacier growth.
“It is important to know that these glaciers can react much more quickly to short-term temperature changes. We used to think that such ice sheets react very slowly. “But this shows that glaciers can react very quickly to the climate,” he says. “It remains to be seen whether this will spread or not,” said Truffer.
Truffer sees the spread of this effect also depending on the water temperatures, which, according to Willis, will only be available from the GRACE mission over the next few months.
“The temperature of the air is probably important, as is any snowfall,” adds Willis. “Warmer air will lead to more melting and more ice loss. Colder air could result in less ice loss. But we know that what we saw was caused by the sea because the retardation [of melting] and ice accretion are concentrated where the ice meets water. The increase becomes smaller the further inland you go.”
Complex interactions and connections
As you can see, some insights need to be gathered here in order to get a clearer statement. The interactions between glacier, water temperature and air conditions are obviously very complex. Additionally, research shows that rainfall in Greenland increased from 1979 to 2012, also leading to sudden periods of melting. There is also evidence that the warmer temperatures have affected the snow line on the island. The ice therefore came into direct contact with the air and melted.
According to Willis, the findings and results of his latest study are not mutually exclusive. Even though the data here shows that the Jakobshavn Glacier has grown, it is still impossible to say exactly how much and why. According to Willis, there are a number of possible explanations.
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Far-reaching consequences
In Antarctica, ten percent of coastal glaciers are currently in retreat. Between 1991 and 2016, the sea warmed an average of 60 percent more per year than predicted by the Intergovernmental Panel on Climate Change.
The consequences of this are clearly felt, from raw material extraction, shipping routes and fishing to considerations and territorial claims from Russia to China.
If glaciers like Jakobshavn lost less ice, fewer dangerous icebergs could drift south into the Atlantic, where they repeatedly cross shipping routes. It could also mean that calving underwater creates more ice floes. Every year, around 20 billion tons of ice break off from the Jakobshavn Glacier alone and float out to sea. In 2017, more than 1,000 icebergs drifted across the sea below the 48th parallel, where they pose an enormous danger to shipping.
Source: National Geographic
Article image: Shutterstock / Mathias Berlin
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