- Sea levels are rising steadily each year as the planet warms.
- Melting ice could collapse suddenly, raising sea levels abruptly.
The Earth's ice is, rightly, often in the news. As the planet and its oceans warm, our so-called cryosphere is quickly melting away.
There are two factors that lead to sea level rise: the water expanding as it gets warmer and added water from melting ice sheets and glaciers.
Melting ice that could tip sea level rise into catastrophic levels
Source: NASA Ice ViewerChart: Annie Fu/Insider
While it's easier to plan for a steady sea level rise, scientists are very concerned about what would happen if huge chunks of ice collapse and abruptly change sea levels.
Here are the sites around the world scientists are keeping a close eye on, and why they are important, according to Alex Brisbourne, a Glaciologist at the British Antarctic Survey, and Theodore Scambos, an Antarctic researcher at the University of Colorado.
Glaciers
Glaciers will be the first to go.
Though they will contribute comparatively little to sea level rise — adding about a foot to global mean sea levels if they melt completely — glaciers outside of Greenland and Antarctica have been the main contributors to higher seas over the past century, according to the UN's Intergovernmental Panel on Climate Change (IPCC).
Catastrophic collapse — Columbia Glacier in Alaska
Glaciers took centuries to freeze over, but they can disappear in a few years. When they start breaking apart, that triggers a negative feedback loop: the meltwater warms the glacier, which creates more meltwater.
The Columbia Glacier in Alaska is one of the most recognizable examples of rapid glacier collapse. This glacier has almost completely disappeared today.
"It's an example of how this will play out for many coastal glaciers," Scambos told Insider in an email.
Albedo — Presena Glacier in the Alps, Europe
Glaciers are not only important because they store water away from the oceans. Because they are light-colored, they bounce back a lot of light back into space. This effect, called the albedo of the ice, is crucial because it keeps sunlight from warming the earth.
Scientists studying the albedo of the glaciers have discovered a peculiar effect of the melt. Colorful glacial and snow algae have been growing in the glacier meltwater, creating pink and purple spectacles on the ice, like at the Presena Glacier in the Alps. The problem is that reduces the albedo of the glacier, which again encourages warming and melting.
Freshwater — Hindu Kush Himalayan glaciers, Central Asia
Glaciers are also a vital source of freshwater. Over a billion people living in central Asian countries rely on the Hindu-Kush Himalayan glaciers for drinking water, and scientists discovered recently that these glaciers are rapidly declining, causing concern.
"It's gonna peak in around 2050. Beyond that point, you start to get less melt," AB said.
Geopolitical experts are concerned this dwindling resource could cause tensions in neighboring countries.
Greenland and Antarctica
The ice sheets in Greenland and Antarctica are essentially humongous glaciers that cover the poles. They contain most of the freshwater on the Earth's surface.
The Antarctic ice sheet is much bigger than the ice sheet on Greenland. If they were to melt totally, the Greenland ice sheet would contribute about 23 feet to the sea levels, while the Antarctic ice sheet holds enough ice to raise sea levels by 190 feet. Of course, this isn't predicted to happen for centuries.
The other big difference is that the Greenland ice sheet rests on solid land above sea level, whereas much of the Antarctic ice sheet is below sea level, which makes it more vulnerable to warming ocean temperatures.
Greenland
Greenland is currently melting about twice as quickly as the Antarctic ice sheet, per the IPCC.
As the atmosphere around the North Pole warms, any ice below about 2,000 meters altitude (about 6,500 feet) is at greater risk of melting, said Brisbourne.
"The problem here is that as you melt, you're thinning the ice and that brings more ice below 2,000 meters," he said.
This is happening over the entirety of the Greenland ice sheet, as can be seen in this NASA animation.
The Ilulissat glacier, also known as Jakobshavn or its Innuit name Sermeq Kujalleq, is a glacier that scientists are following closely on the west coast of Greenland, where the ice sheet is melting more quickly.
Ilulissat Glacier, also known as Jakobshavn
Ice flows through ice sheets like very slow rivers. Carried by its weight, the ice falls from the top of the glacier to the lowest point. In a perfect equilibrium, there's enough snow fall to replenish the ice sheet, but that balance comes out of whack when the ice is melting away too quickly, snowfall is not sufficient, or rain is falling instead of snow.
When this happened, the ice sheet beings to thin and the glaciers at the edge of the sheet retreat, as can be seen below.
Antarctica
The Antarctic ice sheet, found at the South Pole, is about eight times bigger than the Greenland sheet.
Because so much of this ice sheet is below sea level, it is much more affected by the temperature of the ocean, which has been warming.
Scientists break down this ice sheet into three parts: the peninsula, west Antarctica, and east Antarctica.
Antarctic Peninsula — Larsen-A and -B
The peninsula is much more affected by the temperature of the atmosphere than other areas of the Antarctic, Brisbourne said.
In 2002, scientists watched helplessly as an ice shelf called Larsen-B collapsed into the ocean in a matter of weeks.
Between January 31 and April 13, 2002, about 500 billion tonnes of pack ice and snow disintegrated into the ocean.
This was less than a decade after another ice shelf in the area, Larsen-A, also disintegrated.
Ice shelves don't contribute to sea level rise when they melt. Because they float, they occupy the same volume in the sea, whether they are frozen or melted, just like an ice cube doesn't raise the water level in a glass when it melts.
However, ice shelves stabilize the glaciers and ice sheets that are behind them. Without their ice shelves, the glaciers that fed Larsen-A and -B glaciers started flowing much more quickly, releasing three times more ice into the ocean than they did before.
Larsen-B's collapse was likely caused by melt ponds, Brisbourne said.
Meltponds appear when the warming atmosphere causes meltwater to accumulate at the surface of the ice. As they grow, their weight cracks the ice and can lead to the collapse of the ice shelf, a process called hydrofracturing.
Because there wasn't much ice in the Antarctic peninsula to start, losing these ice shelves did not change global sea levels much.
But these losses are seen as "the canary in the coal mine" for Antarctica, said Brisbourne.
West Antarctica — The Doomsday (Thwaites) glacier and Pine Island
Scientists are much more concerned about west Antarctica. The ice sheet in West Antarctica rests on bedrock under sea level, meaning it is much more vulnerable to the warming of the ocean.
West Antarctic ice flows into several ice shelves, including the Pine Island, Dotson, and Thwaites. These act as buffers between the ice sheet and the warming oceans.
Scientists are really concerned that Thwaites is holding on "by its fingernails." This gives it its nickname — the "doomsday glacier." The ice shelf in front of Thwaites is crackling and it is thought the shelf could collapse within the decade.
"We think that potentially if we lose Thwaites area, this whole west Antarctica ice sheet part of Antarctica could follow," said Brisbourne.
That could add up to 10 feet to global sea levels.
But there's still hope.
Pine Island was collapsing more quickly than Thwaites, but it slowed down, Brisbourne said. What scientists hadn't expected is that the ice sheet would catch on a small island off the coast of Antarctica, which has slowed the speed of its collapse.
East Antarctica — Conger Ice Shelf
The east side of Antarctica is thought to be fairly stable.
"East Antarctica is a bit more like Greenland in that it sits above sea level. So it's not been influenced much by the warming ocean and the atmosphere hasn't warmed as much," said Brisbourne.
East Antarctica has enough ice to raise sea levels by about 52 meters altogether, so if it were to collapse, it'd be fairly catastrophic. But Brisbourne says scientists don't expect that to happen for a very very long time.
Still, scientists were stunned to see an ice shelf called Conger collapse on the east side of Antarctica earlier this year. Conger was not under surveillance by most scientists. Indeed, Brisbourne said most of his colleagues had never heard of it.
"It's a very small ice shelf and it is fed by a glacier that drains a very small area. So in terms of the contribution sea level rise, it's actually gonna be very small," he said.
"But again, it's one of these warning signs that in this area we're starting to see processes that we know have affected other parts of the continent and led to a fairly dramatic loss of ice," said Brisbourne.
Other effects of ice melt
There are more indirect effects of the melting ice on sea level rise.
Arctic sea ice
Every winter, water in the Arctic ocean freezes over, capping our planet in white over the winter and receding over the summer.
But the expanse of that white cap in the winter has been getting smaller every year.
Because this ice is already in the sea, it won't raise the sea level if it melts. But, like the glaciers, its declining reflective albedo contributes to more warming within the atmosphere and the ocean.
Permafrost — Russian Tundra
Permafrost, ground that is meant to stay frozen throughout the year, doesn't directly contribute to sea level rise when it thaws. But as the ground gets warmer, pools of water called thermokarsts start forming.
These are full of methane, a potent climate-worsening gas. It's not clear how much these pools could contribute to climate change.
Local sea level variation
Global mean sea level rise is only a snapshot of the whole picture.
Because sea levels are influenced by the local environment, the sea level rise can be much higher locally than it is on a global scale.
The east coast of the US, for instance, is due to have higher sea levels than the west coast, in part because of the slowing gulf stream.
Local gravity variation — Antarctica's gravity pull
Gravity is another important consideration when it comes to sea level rise.
Ice sheets are so big that they can pull water towards them, raising sea levels locally, Brisbourne said.
If Greenland melts, "sea-level rise will be greatest in the southern hemisphere, and if Antarctica melts then sea-level rise will be greatest in the northern hemisphere," wrote Pippa Whitehouse, a glaciologist from Durham University, in a blog post.
The glaciers are also weighing down the planet, squishing the Earth's crust at the poles.
That pressure will disappear when the ice sheets melt, which will influence the rotation, shape, and gravity of the Earth. This effect, called post-glacial rebound, has already started to appear. A study published in 2021 found that melting glaciers had already led to a small wobble of the Earth's axis.
Correction: January 12, 2023 — An earlier version of the story misstated the amount of sea level rise were ice on Antarctica to melt away completely. This is 58 meters (190 feet), not 58 feet. The earlier version also misspelled the name of an ice shelf, which is Dotson, not Dodson. Glaciers, ice shelves, and ice sheets were not always given the right designation. These have been corrected throughout.