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Journey to Antarctica: Reckoning With Uncertainty

A conversation with chief scientist Rob Larter about the existential guessing game at the bottom of the world

Chief Scientist Rob Larter (third from left) discussing ocean surveying plans with scientists aboard the Nathaniel Palmer in Antarctica

Chief Scientist Rob Larter (third from left) discussing ocean surveying plans with scientists aboard the Nathaniel Palmer in Antarctica

Linda Welzenbach/Rice University

This is the eighth dispatch in a series from Jeff Goodell, who is in Antarctica investigating the effect of climate change on Thwaites Glacier.

Rob Larter was 23 when he made his first visit to Antarctica. The son of a public health inspector and a secondary-school teacher, Larter grew up in the gentle green landscape of England’s West Midlands. “When I saw Antarctica for the first time,” he recalls, “I thought, ‘this is a really a bleak place.’” Today, as a geophysicist at the British Antarctic Survey, Larter probably knows as much about the past, present and future of the continent as anyone on the planet.

I met Larter three weeks ago, when I boarded the Nathaniel Palmer, an icebreaker and research vessel that was about to embark on a two-month cruise to West Antarctica to explore the risks of the collapse of Thwaites glacier, one the most important tipping points in the earth’s climate system. The cruise is part of a five-year-long collaboration between the U.S.’ National Science Foundation and the U.K.’s National Environment Research Council. Larter, a gentle but forceful man, introduced himself as chief scientist on the trip, in charge of managing all experiments on the ship, from tagging seals to mapping uncharted regions of the ocean floor.

Larter and I talked in his cabin on the third deck of the Palmer while the ship rolled in a heavy swell. A long passage from Chile to Antarctica, as well as a medical emergency aboard the ship, meant we were still a few days away from reaching Thwaites. Larter was eager to begin deciphering the mysteries embedded in Antarctica’s ice. “There is only one true story,” he had said during a meeting on the Palmer earlier that morning. “As scientists, our job is to tell it.”

Rolling Stone: This cruise is the beginning of a five-year-long emergency research project to study changes in Thwaites glacier. Why is studying Thwaites so urgent?
Rob Larter: Because what happens in Antarctica — and at Thwaites glacier, in particular — has enormous consequences for the world. Until recently, scientists studying the response of glaciers to climate change thought Antarctica was fairly stable. But in the late 1990s, they realized they were wrong. One of the places where change is happening fastest is Thwaites, which is in a remote part of West Antarctica. Thwaites has been called “the weak underbelly” of the West Antarctic ice sheet, and that’s a pretty good way to describe it. It flows out from a very large and vulnerable drainage basin in West Antarctica. If Thwaites were to collapse, the whole West Antarctic ice sheet could be in trouble.

West Antarctica holds enough water for, what, 10 feet of sea level rise?
Yes, for West Antarctica as a whole. But we don’t know yet what the conditions needed for West Antarctica to collapse. So we don’t really know how close we are, or how fast it could happen.

What are the two or three most important questions you want to answer on this trip?
We want to get a really reliable, accurate picture of the sea bed offshore from Thwaites, because that will reveal any places where the ice margins stabilized over the past few centuries, or where a more extensive ice shelf was pinned on shallow banks. It will also show us the deep channels that route warm, dense water into the cavity beneath the ice shelf, the glacier’s floating extension. And we want to analyze sediment cores at very high resolution to look at what Thwaites has been doing in the past. In particular, we’re interested in understanding how much warm water has been coming onto the continental shelf in front of Thwaites for the decades and centuries before we have instrumental observations.

A few weeks ago, a new research paper was published about West Antarctica that attracted a lot of attention. It described a cavity in Thwaites glacier about the size of Manhattan – further evidence that Thwaites may be falling apart faster than anyone realizes. Did that surprise you?
Not really. When people talk about a cavity, they are really just talking about ocean space beneath an ice shelf. These exist in many places around Antarctica. But this new study is significant because it’s based on the latest satellite imagery data over the grounding line region of Thwaites. The major driver of the retreat of Thwaites is the relatively warm ocean water that is coming in from underneath the ice shelf and melting the ice at the grounding line. That thins the ice shelf. A thinner ice shelf provides less resistance to the flow of the glacier upstream, which leads to acceleration of the glacier into the sea. Overall, that means more loss of ice.

How fragile is Thwaites? A number of scientists I’ve talked to suspect the runaway collapse of Thwaites may already be underway — and that there is no stopping it.
It’s hard to say. Dramatic changes at Thwaites have been going on for more than 20 years. The flow rates are increasing. There is very little ice shelf left. For Thwaites, a lot critically depends on the rate at which the incursion of warm water beneath the glacier is increasing. If [the incursion] were to slow or switch off, the rate of retreat would slow. But even if that were to happen, we could still be in trouble, because the grounding line is now on a retrograde slope. The base of the glacier gets deeper as you go back towards the interior of Antarctica. Since the 1970s, it’s been recognized that this is likely an unstable situation. If we’re already in that state, there are many people who would say the eventual collapse of Thwaites may be unstoppable.

Penn State’s Richard Alley, one of the most respected glaciologists of our time, says we can’t rule out 15 feet of sea level rise by the end of the century. In that kind of extreme scenario, a lot of that water comes from West Antarctica.
That’s because of something called marine ice cliff instability. It’s the idea that any ice cliff over 100 meters high is unstable and will collapse. If that happens at Thwaites, it’s particularly troubling, because the glacier is on a reverse slope, which means that the ice cliff gets taller the farther back you go. If it starts to collapse, it could go much faster than what people generally suppose. How fast, we don’t really know.

Chief Scientist Rob Larter examining a sediment core in Antarctica

Chief Scientist Rob Larter examining a sediment core in Antarctica. Photo credit: Linda Welzenbach/Rice University

What did Antarctica look like in deep time?
Well, it depends how far back you go. Antarctica was the cornerstone of Gondwana, the supercontinent that existed about 500 million years ago. About 180 million years ago, during the Jurassic period, South America and Africa broke off. Then India, then Australia and New Zealand. Antarctica was in more or less its present form and location about 90 million years ago. But it was much warmer then. Dinosaur fossils have been found in Antarctica from this period, and there was lush vegetation.

The big ice sheets emerged about 34 million years ago. And they developed quite abruptly. [This] was probably caused by declining carbon dioxide levels in the atmosphere, which cooled the climate. But the final trigger could have been the development of the Antarctic Circumpolar Current, which circles around Antarctica and cuts off ocean heat transported from the tropics to the continent.

One of the fascinating things about the research you’re doing on this trip is how you’re using the past to understand the future. Which brings up the question: If Thwaites is collapsing, how will we know it?
That’s a very good question. In recent years, we have found out a lot more about how ice sheets behave, but unfortunately, the level of confidence in some ways has gone down, because we have found out about new processes, like marine ice cliff instability. Right now, we have probably magnified the uncertainty. But that’s better than going along in ignorance of something.

There are a lot of unknowns in all this, and the geological record shows you that. An event called Meltwater Pulse 1A, which occurred about 14,500 years ago, is a good example. The best evidence implies a sea level rise of about 50 feet in 350 years. That is just incredible. That is 14 feet per century. That is like losing the West Antarctica ice sheet every century, for three centuries in succession. That’s very, very fast compared to anything that we know can happen in human experience. If it were to happen today, it would have a devastating impact to coastal cities. To me, this is an indication that there are thresholds in the system that you can trigger huge changes very quickly. But nobody really understands how it happened in the past — or if it could happen again.

I think it’s a cautionary signpost for anyone thinking about the implications of climate change, because it’s saying, “maybe there are things out there that we still don’t know.” Until we know where this happened, and what the processes were, how can we ever say it can’t happen again?

This interview has been edited for length and clarity.

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