One thing that’s hard to grasp about the Climate crisisThe good news is that big changes are possible quickly. In 2019I was on the Nathaniel B. PalmerThe Thwaites Glacier is seen from the helm of the 308-foot-long vessel, which is a scientific research vessel. Antarctica. One day we were sailing in clear water in front the glacier. The next day, we were surrounded in icebergs of the same size as aircraft carriers.
As we later learned from satellite images, in a matter of 48 hours or so, a mélange of ice about 21 miles wide and 15 miles deep had cracked up and scattered into the sea.
It was a frightening moment. Thwaites Glacier measures approximately the same size as Florida. It is the cork inside the entire West Antarctic Ice Sheet, which contains enough ice for sea levels to rise by 10 feet. The mélange that disintegrated was not part of the glacier itself, but a mix of icebergs and sea ice that had cozied up next to it. It was still amazing to think that it could just melt overnight.
It turns out that the ice meltup I witnessed wasn’t a random event. Scientists were involved in the experiment a few weeks back. International Thwaites Glacier PartnershipThe latest research was presented by the National Science Foundation in the U.S. and Natural Environment Research Council in Britain. It is a five-year-long, $25 million joint research program. They described cracks and fissures found in Thwaites’ eastern ice shelf. They predicted that the Thwaites ice shelf could break down like a car window in five years. “It won’t scatter out into sea as quickly as what you saw when you were down there,” Erin Pettit, a glaciologist at Oregon State University and one of the lead principal investigators in the ITGC, later told me. “But the basic process is the same. The ice shelf is breaking up and could be gone in less than a decade.”
It might not seem like much news considering the ongoing war against American democracy and death toll from Covid pandemic. But in fact, the West Antarctic ice sheet is one of the most important tipping points in the Earth’s climate system. Thwaites Glacier’s collapse will allow the rest of West Antarctic Ice Sheet to slide into sea. 250 million people live within three-foot of high tidelines globally. A global catastrophe would be a ten-foot sea level rise. It’s not only goodbye Miami, but goodbye to virtually every low-lying coastal city in the world.
However, it is difficult to predict the breakup of the ice sheets and its implications for future sea-level rise. Depending on the latest emission scenarios Intergovernmental Panel on Climate Change report, we could have as little as one foot of sea level rise by the end of the century, or nearly six feet of sea level rise (of course, rising seas won’t stop in 2100, but that date has become a common benchmark). “The difference between those [models] is a lot of lives and money,” says Richard Alley, a glaciologist at Penn State University and one of the great ice scientists of our time. Alley adds: “The most likely place to generate [the worst scenario] is Thwaites.”
Or to put it more urgently: “If there is going to be a climate catastrophe,” Ohio State glaciologist Ian Howat once told me, “it’s probably going to start at Thwaites.”
The problem is, understanding what’s going on at Thwaites is fiendishly complex. As I wrote in 2017,:
The trouble with Thwaites, which is one of the largest glaciers on the planet, is that it’s also what scientists call “a threshold system.” That means instead of melting slowly like an ice cube on a summer day, it is more like a house of cards: It’s stable until it is pushed too far, then it collapses.
Thwaites is a very different glacier from those in Greenland. One reason is that it isn’t melting from above due to warmer air temperatures. It’s melting from below, due to warmer ocean water eating away at its underbelly. The terrain beneath the West Antarctic Ice Sheet is unique. “Think of it as a giant soup bowl filled with ice,” Sridhar Anandakrishnan, an expert in polar glaciology at Penn State University, once told me. In the bowl analogy, the edge of the glacier — the spot where a glacier leaves the land and begins to float — is perched on the lip of the bowl 1,000 feet or more below sea level. Scientists call that lip the “grounding line.” Below the lip, the terrain falls away on a downward slope for hundreds of miles, all the way to the Transantarctic Mountains that divide East and West Antarctica. The ice is two miles thick at its deepest point.
This means that warm water can flow down the bowl to weaken the ice below, once it reaches below ice. Through a mechanism called “marine ice-cliff Instability,” you can get what amounts to a runaway collapse of the ice sheet that could raise global sea levels very high, very fast.
What would Thwaites’ collapse rate be in the worst case scenario? Nobody knows. The IPCC data is the best indicator of sea level rise over the next century, but Alley cautions that even six feet is too much. NotThe worst-case scenario.
“We just don’t know what the upper boundary is for how fast this can happen,” Alley says. “We are dealing with an event that no human has ever witnessed before. We have no analog for this.”
Scientists have made great strides in understanding Thwaites’ dynamics over the past few decades. Scientists discovered troughs in seabed that allowed warm waters to flow beneath the ice shelf during our 2019 cruise. Scientists have located pinning points to slow down the retreating ice by mapping the glacier’s underside. The change has been dramatic: “The net rate of ice loss from Thwaites Glacier is more than six times what it was in the early 1990s,” says Rob Larter, a geophysicist with the British Antarctic Survey who was the chief scientist on my trip to Antarctica in 2019.
The recent news about Thwaites’ eastern ice shelf breaking up in the next five years was not really a surprise to anyone who has been tracking the science closely. The sudden disintegration caused by the Larsen BAntarctica was less stable than many believed, according to scientists who discovered it on the ice shelf in February 2002. Thwaites’ cracks and fissures are a further reminder of how dynamic the changes are.
It is important to be clear that there is a significant difference between an ice shelf (or glacier) and the glacier itself. The ice shelf grows out of the glacier like a thumbnail and floats on ocean. Because it is already floating, when it melts it doesn’t in itself contribute to sea level rise (just as when ice cubes melt in your glass, they don’t raise the level of liquid).
They are crucial because they help to support glaciers. They give stability to the walls and ice walls, similar to the Notre Dame’s flying buttresses. The land-based glacier can then flow faster into the sea when it breaks up. That’s how it works. Does raise sea levels.
So yeah, if Thwaites loses a significant part of its ice shelf in five years, that’s a big deal.
Even if a large portion of the ice shelf cracks, there is still a lot of uncertainty about how it will all play out. “A first question is, if the ice-shelf breakage continues, will the whole ice shelf be lost, or will a short ice shelf remain, at least in some places?” Richard Alley emailed me. “Almost all ice-shelf ice is buttressing, generating friction that holds back the non-floating ice, so loss of part, most or all of the ice shelf will increase flow of non-floating ice into the ocean. But the most-important buttressing tends to arise closest to the grounding zone, so if a short ice shelf does remain, it may still provide important buttressing, and the speedup of flow and thinning will be smaller than they could be with full ice-shelf loss.”
This is the problem. It is hard to predict how crackups of the ice shelves will affect the flow of glaciers.
This is just one of many uncertainties scientists face when trying predict whether Miami will be underwater in 2100. There is further uncertainty in exactly where and when the ice will fracture, how much warm water will be pushed up beneath the glacier by changing winds and ocean currents, how the character of the bed the glacier rests on will speed up or slow down the glacier’s slide into the sea. The bed’s texture can also have an impact on how fast the glacier moves. “Ice is alive,” says Pettit. “It moves and flows and breaks in ways that are difficult to anticipate.”
Paradoxically, the more scientists learn about what’s going on at Thwaites, the more divergentThe latest climate models are now about the future. Take a look at the results of two models created by highly respected scientists and published side-by-side in Natureearlier in the year. One model suggests that Thwaites will remain relatively stable up to the temperature rising above 2 C. Then, all hell breaks loose. Thwaites soon falls into the sea, much like a string of dominoes being pushed off a desk. And once the collapse begins, according to this model, it will be impossible to stop — at least on any human time scale. Global sea levels could rise to 10 feet in a century, which would flood South Florida and Bangladesh, as well as many other low-lying areas around the globe.
In the other model, global sea level rise only differs by 4½ inches between a 1.5 C global temperature rise and a 3 C temperature rise (which is a little above where we are headed with under current emissions scenarios). This is largely due to the increased melt in Greenland, and mountain glaciers. As for Antarctica, the paper says explicitly: “No clear dependence on emissions scenario emerges for Antarctica.”
What can we make of this?
“The current divergence among model predictions is actually a good sign because it means that scientists are probing different parameterizations, representations of processes, and hypotheses,” WritesJeremy Bassis is a geophysicist from the University of Michigan. Bassis suggests avoiding focusing on the long-term uncertainty, and instead highlighting what scientists know about future decades. “The skill of models in predicting sea level change on decadal time scales is high, and we already have actionable projections on these time scales. We should be emphasizing that fact in discussions with community members, stakeholders, and decision-makers, so they can move ahead with important adaptation and mitigation planning.”
It is not clear, however, that the Thwaites-based dynamics are a result of ice sheet collapsing. As glaciologist Eric Rignot Put it in 2015, in Antarctica, “the fuse has been blown.” Even if we cut carbon emissions to zero tomorrow, warm water will continue to flow beneath the ice sheet for decades, destabilizing the ice and further pushing the glacier toward eventual collapse. This doesn’t means that cutting carbon pollution to zero isn’t an important goal — nothing, in fact, is more important or more urgent. “We may have a small safety margin in Antarctica, but not a large one,” says Alley. Even if there was a fuse It isIf emissions are not cut quickly, it could slow down the process to a millennium-long crack up that will allow us to adapt. Our future is written on ice.
Jeff Goodell, a contributing editor, has written extensively on the Doomsday Glacier. Listen to the audio account of Jeff Goodell’s trip to Thwaites Here.