Listening Script Vocabulary
(Section 4: You will hear a talk discussing glaciers and ice sheets. First, you will have some time to look at questions 31 to 40 [20 seconds]. Listen carefully and answer questions 31 to 40.)
Good morning everyone. I'm a radio glaciologist. That means that I use radar to study glaciers and ice sheets. And like most glaciologists right now, I'm working on the problem of estimating how much the ice is going to contribute to sea level rise in the future. So today, I want to talk to you about why it's so hard to put good numbers on sea level rise, and why I believe that by changing the way we think about radar technology, we can get much better at it.
When most scientists talk about sea level rise, they show a chart with steadily rising numbers. This is produced using ice sheets and climate models. However, beyond that, such a chart comes with a warning - unless the West Antarctic Ice Sheet collapses. And in that case, we would be talking about dramatically higher numbers. They'd literally be off the chart. And the reason we should take that possibility seriously is that we know from the geologic history of the Earth that there were periods in its history when sea level rose more quickly than today. And right now, we cannot rule out the possibility of that happening in the future.
So why can't we say with confidence whether or not a significant portion of a continent-scale ice sheet will or will not collapse?
Well, in order to do that, we need models that we know include all of the processes, conditions and physics that would be involved in a collapse like that. And that's hard to know, because those processes and conditions are taking place beneath kilometres of ice, and satellites are unable to observe them. In fact, we have much more comprehensive observations of the surface of Mars than we do of what's beneath the Antarctic ice sheet. And this is even more challenging in that we need these observations at a gigantic scale in both space and time.
In terms of space, Antarctica is a continent. And in the same way that in North America, the Rocky Mountains, Everglades and Great Lakes regions are very distinct, so are the subsurface regions of Antarctica. And in terms of time, we now know that ice sheets not only evolve over the timescale of millennia and centuries, but they're also changing over the scale of years and days. So, what we want is observations beneath kilometres of ice at the scale of a continent, and we want them all the time.
So how do we do this? Well, we're not totally blind to the subsurface. I said in the beginning that I was a radio glaciologist, and the reason that that's a thing is that airborne ice-penetrating radar is the main tool we have to see inside of ice sheets. So, most of the data used by my group is collected by aeroplanes with antennas underneath the wing. These are used to transmit radar signals down into the ice. And the echoes that come back contain information about what's happening inside and beneath the ice sheet. While this is happening, scientists and engineers are on the aeroplane for eight hours at a stretch, making sure that the radar's working. And I think this is actually a misconception about this type of fieldwork, where people imagine scientists peering out the window, contemplating the landscape, its geological context and the fate of the ice sheets.
Now, a radargram is a vertical profile through the ice sheet, kind of like a slice of cake. It shows the surface of the ice sheet at the top, on the bottom is the bedrock of the continent itself, and the layers in between are kind of like tree rings, in that they contain information about the history of the ice sheet. And it's amazing that this works this well. The ground-penetrating radars that are used to investigate infrastructures of roads or detect landmines struggle to get through a few metres of earth. But we can look through three kilometres of ice. And there are sophisticated, interesting, electromagnetic reasons for that, but let's say for now that ice is basically the perfect target for radar, and radar is basically the perfect tool to study ice sheets.