How does a block of ice nearly the size of Connecticut, which has existed for over 11,000 years disappear in less than 70 years?
In my article, "Farewell Larsen B," I discussed the findings of a NASA Jet Propulsion Laboratory study released in May, finding that the last remnant of the Antarctic Larsen B ice shelf is likely to disintegrate completely by the end of the decade. Larsen B is believed to have been stable until the 1950's when a combination of warming air and ocean water began to erode it.
A team led by Ala Khazendar at NASA JPL was responsible for the study. Dr. Khazendar focuses on combining satellite observations and additional data to model Antarctic ice shelves and their possible future behavior. One goal of his work is to quantify Antarctica's contribution to sea level rise.
As Dr. Khazendar discusses in our conversation, while he does his best to maintain a scientist's detachment through the rigor of his work, he nonetheless acknowledges that the impact of his findings are "staggering."
Can we begin with the origins of the Larson B Ice Shelf, and how it actually formed?
So, ice shelves form under certain climactic conditions and certain features of the coastline, so they tend to form mostly in embayments, like Larson B and Larson C further south. It also helps when there are what we call 'pinning points,' such as islands or higher points in the ocean floor, along which the expanding ice shelves might find points of support. They pin down the ice shelves in those areas and allow the ice shelves to grow and expand in these embayments were they are formed.
And they are ancient. This one in particular, Larson B, after two thirds of it collapsed in 2002, scientists took sediment cores from the part that was uncovered by the collapse, and from that they could calculate that it had been there for at least eleven thousand years. Maybe even longer than that.
One of the implications of the collapse of Larson B, as I understand it, is that it acts as something of a backstop for its tributary glaciers, right? It's not the collapse of Larson B in and of itself that affects sea level rise because it's already resting on the ocean, but the advance of those glaciers into the ocean affect sea level rise.
Exactly. Because the ice shelf is already in the ocean, its disintegration or eventual complete melting does not affect sea levels. As you said, the presence of these ice shelves does present resistance to the flow of the tributary glaciers. And when you remove them, in most cases the tributary glaciers will react by flowing faster and putting more ice into the ocean, and that will contribute to sea level rise.
Do you have a sense of what the difference in the pace of these tributary glaciers is before and after the disintegration of the ice shelf?
Yes. Again, in those same early studies after 2002, to document what happened and to establish this effect, some of the glaciers sped up by eight times.
That's incredible.
It is stunning. Yeah.
Over what period was the damage done to this ice shelf?
The air temperature in the Antarctic Peninsula warmed by more than two degrees Celsius since the 1950s, more than anywhere else in Antarctica. And furthermore, this warming was progressing gradually southward. These events of disintegration of ice shelves have been also moving from north to south.
There is increasing evidence that the ocean might have also played a role from underneath. So, the atmosphere was doing its thing from the top, and the ocean might have been simultaneously also affecting the ice shelf from the bottom through increased melting between the interface between the bottom of the ice shelf and the ocean. And melting is, again, part of the normal cycle of things.
This is how Antarctica gains mass, by forming snow inside, and loses mass through iceberg formations, and through melting of ice at the bottom of ice shelves with the ocean, the interface between the ice shelf and the ocean. What I'm talking about is increased melting, so melting that is out of balance has increased with time.
So, the bottom line is that a 4,800 square mile ice shelf that has been around for 11,000 years disintegrated in 70 years. That seems terrifying.
It is, yes. It is terrifying because of what might happen, and what most likely will happen to much bigger ice shelves that are fed by much bigger glaciers further south in Antarctica.
I'm working on another paper now where, using the same data, I found that another glacier in west Antarctica lost nearly 500 meters of ice in less than 7 years at the bottom. I so disbelieved it at the time that I spent a lot of time just trying to prove myself wrong by using other data sets, and every time the answer was the same.
Skepticism is a good thing. That's what we do all the time as scientists. We're skeptical of our own work and especially of other people's work. But it's a shame that people do not understand, we don't do this lightly, and how instead of just saying, "No, this cannot be," they can go and look at the data themselves. It's available for that.
That is a hallmark of science, right? The data are not packaged or withheld. It's available.
Yeah. Especially NASA. They have an open data policy. So, all the data I use in the study I downloaded from the Internet. It is available to you. It is available to everybody. They can go and download it and check what we did.
How do you balance the objectivity of a scientist, but then you're also a feeling human who recognizes the potential implications?
We try to do it with as much detachment as possible. It's imposed by the rigor of the work. We have a lot to do and you try to focus as much as possible. And then, yes, you do your study, you look at the results, you write your paper, you get reviewed by your peers, it's done, at least that part. But at the end you're a human being and you take a step back, and you look at this thing that's been around for millennia, and you say, "Wow. This is going to go soon. This is really staggering, what I'm looking at."