Most of the time, when we talk about melting sea ice, the focus is on the Arctic Ocean. There are a few reasons for this, the biggest one being that sea ice is a much larger part of what happens there, compared to the continent of Antarctica. It’s also a bit easier to measure what’s going on up there. Multiple countries have naval activity under the ice, and they keep track of thickness so they know where their submarines can or cannot surface. There are also many more people living in the Arctic circle, so more people pay attention to what’s happening there, because it affects their daily lives.
There are also three very big considerations when it comes to the rate and impact of global warming. The first is the albedo feedback loop – ice melts, exposing more water, which absorbs more heat, which melts more ice, and so on. Melting sea ice speeds the rate at which warming happens. The second is that as more and more water is exposed for more of the year, the warmth rising from the water pushes arctic air south, leading to the “polar vortex” events with which we’ve become familiar. And last but certainly not least, the ice and low temperatures of the Arctic play a big role (along with salt concentration, also affected by meltwater) in driving the big oceanic currents that bring oxygen into the abyss, and keep northern regions like western Europe nice and warm. As the planet warms and ice melts, it’s expected that those currents will change, causing a huge change in weather patterns all around the planet on top of those we’re already seeing. I will be writing more about that very soon.
All of that is why we most often hear about Arctic sea ice. This post is about what’s happening on the other side of the planet. Ice around Antarctica plays many of the same roles, and it is also being closely monitored, but it gets a bit less press. The biggest news we tend to see is when a particularly large ice shelf breaks up, and that’s what this news is about – a breakup that we’ve been waiting for, and that we’ve been hoping would happen slowly, and not soon.
Scientists have discovered a series of worrying weaknesses in the ice shelf holding back one of Antarctica’s most dangerous glaciers, suggesting that this important buttress against sea level rise could shatter within the next three to five years.
Until recently, the ice shelf was seen as the most stable part of Thwaites Glacier, a Florida-sized frozen expanse that already contributes about 4 percent of annual global sea level rise. Because of this brace, the eastern portion of Thwaites flowed more slowly than the rest of the notorious “doomsday glacier.”
But new data show that the warming ocean is eroding the eastern ice shelf from below. Satellite images taken as recently as last month and presented Monday at the annual meeting of the American Geophysical Union show several large, diagonal cracks extending across the floating ice wedge.
These weak spots are like cracks in a windshield, said Oregon State University glaciologist Erin Pettit. One more blow and they could spiderweb across the entire ice shelf surface.
“This eastern ice shelf is likely to shatter into hundreds of icebergs,” she said. “Suddenly the whole thing would collapse.”
The failure of the shelf would not immediately accelerate global sea level rise. The shelf already floats on the ocean surface, taking up the same amount of space whether it is solid or liquid.
But when the shelf fails, the eastern third of Thwaites Glacier will triple in speed, spitting formerly landlocked ice into the sea. Total collapse of Thwaites could result in several feet of sea level rise, scientists say, endangering millions of people in coastal areas.
“It’s upwardly mobile in terms of how much ice it could put into the ocean in the future as these processes continue,” said Ted Scambos, a glaciologist at the University of Colorado Boulder, and a leader of the International Thwaites Glacier Collaboration (ITGC). He spoke to reporters via Zoom from McMurdo Station on the coast of Antarctica, where he is awaiting a flight to his field site atop the crumbling ice shelf.
“Things are evolving really rapidly here,” Scambos added. “It’s daunting.”
Pettit and Scambos’s observations also show that the warming ocean is loosening the ice shelf’s grip on the underwater mountain that helps it act as a brace against the ice river at its back. Even if the fractures don’t cause the shelf to disintegrate, it is likely to become completely unmoored from the seafloor within the next decade.
Other researchers from the ITGC revealed chaos in the “grounding zone” where the land-bound portion of the glacier connects to the floating shelf that extends out over the sea. Ocean water there is hot, by Antarctic standards, and where it enters crevasses it can create “hot spots” of melting.
Without its protective ice shelf, scientists fear that Thwaites may become vulnerable to ice cliff collapse, a process in which towering walls of ice that directly overlook the ocean start to crumble into the sea.
This process hasn’t been observed in Antarctica. But “if it started instantiating it would become self-sustaining and cause quite a bit of retreat for certain glaciers” including Thwaites, said Anna Crawford, a glaciologist at the University of St. Andrews.
This would continue the already measurable acceleration of sea level rise, as NASA reported in 2018:
We’re a very long way away from the scenario in my “flooded Manhattan” stories, and there’s no guarantee it’ll ever get to that point, but we are already seeing things like “ghost forests”, caused by salt creeping into the groundwater as seas rise, and multiple island nations are understandably concerned about their looming inundation. On the whole, I think adapting ourselves to sea level rise could be one of the easier climate problems to solve. It will require a lot of construction work, but that’s one thing that we’re generally quite good at, around the world. As always, I think the bigger problem is ensuring just treatment of those affected as part of a broader fight for environmental justice.
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