How Ice A Half A World Away Affects Southern California Sea Levels
Monday, June 17, 2019
San Diego researchers are among many scientists around the world trying to understand how a warming climate is affecting the world’s major ice sheets. Two Scripps Institution of Oceanography researchers are studying the changes in different parts of the world about the change that could affect local oceans. As part of our reporting from the Climate Change Desk, KPBS Environment Reporter Erik Anderson discussed the issue with glaciologist Helen Fricker and physical oceanographer Fiamma Straneo.
Q: What is driving the change in the world’s major ice sheets?
Fricker: There are two drivers behind what is increasing sea level rise. The first one is that the average temperature of the ocean is increasing. And because of that, the entire ocean volume is expanding. And there’s only one way for that to go because the basins are all fixed so it just rises up. So that’s a well- known, well-constrained number. We know roughly what that’s doing, something like 1.5 milliliters per year. The other component is the extra water that’s being added as the ice sheets of Greenland and Antarctica melt. And as that ice is lost around the edges of both continents, it goes into the ocean and sea level goes up. So that’s the extra math.
Q: Are there any other factors?
Fricker: The mountain glaciers that are outside of Greenland and Antarctica to the Himalayas, the Andes, Patagonia. These are all contributing to sea level because once ice melts it has to go somewhere. And it ends up in the ocean. That is also a very well-constrained number — it is something on the order of a half a meter. That’s the maximum we can get from all those glaciers once they melt so we have a finite cap. We know that number. But the numbers that we aren’t so sure of is how much will come from Greenland and how much will come from Antarctica, and on what time scale.
Q: Why is this a concern now, when it wasn’t such a big concern 10 or 20 years ago?
Fricker: The changes that we’re seeing in the Antarctic and Greenland ice sheets have really kicked in in the last decade or two. We are now seeing signals that appear to be starting to accelerate. We’re getting an increase in the amount of mass coming off ice sheets. Which means their component, and their contribution, to mass sea level rise, is going up.
Q: Why does the pace of change seem to be quicker in Greenland?
Straneo: Greenland is changing faster right now. Antarctica accounts for about 10% of global sea level rise. Greenland is about twice that 20% … Some of the things we think are influencing the flow of the glaciers have to do with the fact that the air temperatures have been warming. There’s increased surface melting. You can picture the ice is also warming. So there are processes that are happening above the ocean that can weaken the ice and facilitate it flowing faster.
Q: What is happening to the ice in Greenland?
Straneo: (This is) video that we’ve taken from a helicopter flying at the edge of glaciers in Greenland. And (it shows) the glaciers are flowing literally into the ocean. This is a larger glacier. You can see this highly crevassed ice. It’s breaking up as its flowing into the ocean. And the way we’ve managed to make measurements of what the ocean conditions are right at the edge of the glacier is to find patches of open water as the ice moves. The floating ice in front of the glacier and we release probes.
Q: Is it difficult to measure the changes that are underway?
Straneo: What we really need are measurements as close as we can get to where the ice meets the ocean. But that’s probably one of the most challenging places to get observations on the planet. In Antarctica, its glaciers are sitting thousands of feet below sea level. With ice shelves that extend hundreds of miles. In Greenland, things are a bit small ... but the edge of these glaciers that flow into the ocean is really a dramatic place. Big icebergs are breaking off. Ice has been speeding up and it’s just a very hostile environment, yet that’s exactly where we’d like to make measurements.
Q: How fast will sea level rise and how much will it go up?
Fricker: That’s the big sort of holy grail question about both of these ice sheets: How much ice are we going to lose and how quickly are we going to lose that ice. Because when you start to think about, half-a-meter or one-meter of sea level rise over the next several decades, it really matters how many decades we are talking about and how many tens of centimeters we’re sort of talking about. Because if you think about cities and planning and people living near the ocean, it’s going to affect a lot of communities. We need to know for planning purposes how quickly we need to start making these changes.
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