The sea level is rising. There's just no doubt about that, we can measure it. What's the rate of sea level rise? Right now, it's about 3.2 millimeters per year. Something like that. It doesn't sound very big, but it's year after year, and that is getting bigger. That sea level rise is growing as well. Now, it turns out that what's happening in the Arctic has a lot to do with sea level rise. The Greenland Ice Sheet, one of our planet's two ice sheets, it is absolutely losing mass that's contributing to sea level rise, and there's evidence that that mass loss from the Greenland Ice Sheet is starting to accelerate, but also, Arctic ice caps and glaciers are losing mass. It turns out that the combined mass loss from those glaciers and ice caps is actually bigger than just Greenland. It's really these two working in combination with each other. Let's take a look at Greenland first. Here's a map of Greenland showing the ice sheet. Remember, this is one of our planet's two ice sheets. There's the Greenland ice sheet, there's the Antarctic ice sheet. By the way, the Antarctic ice sheet is also losing mass, but Greenland is the bigger player right now in terms of our two ice sheets. Now, of course, the island is largely covered with ice. How thick does that ice get? Well, the Summit at Summit Station, well, the summit of Greenland, it's about 3,200 meters, so it's about 10,000 feet. That's a hell of a lot of lives that we're talking about, but it is losing mass. Now, we can measure this. One way we can measure this is through something called the GRACE Instrument. It's actually two satellites that follow each other and what happens as they move over gravitational anomalies, the distance between the two satellites changes. We can measure that precisely and process that, and what we can do is get a handle on Gravimetric Anomalies at the earth and how they're changing with time. It's a fascinating technology, but it works quite well. It is called GRACE, it is a NASA satellite. Now, GRACE eventually died, but a new instrument is up there to replace it. Now, what you see here, this is record going back just to 2002, and you can see that line is going down. There's squiggles there because what's happening here is that there's a winter mass gain through snow and basically from snow, but then summer mass losses through melted down at the lower elevations, of course, there's iceberg calving going on as well. You see this seasonality in it, ups and downs, ups and downs, but overall it's losing mass. This is measured in gigatons of ice. A gigaton is a hell of a lot of ice, and you can see how it's going down. Absolutely how it is going down. Now, here's a question. How much would sea level rise if the entire Greenland Ice Sheet melted? Now, say at first, that's not going to happen. Not for a very, very, very long time anyhow, but the Greenland Ice Sheet is losing mass. But let's just ask the question, a philosophical question, I guess. How much would sea level rise if it all melted? The answer is about seven meters. That's a lot. That's more than 20 feet of ice, 22-23, 44 feet of ice. That's a hell of a lot. Sixty meters, that was another potentially answer here. No, that's getting closer to what the sea level would do if the Antarctic Ice Sheet melted, it would actually be bigger than that. Remember that the Greenland Ice Sheet is really the much smaller of our planet's two ice sheets. But still, Greenland Ice Sheet alone has seven meters of sea level water equivalent in it. That's a hell of a lot. Now, I mentioned ice caps and glaciers. You may have seen images like this, these before and after photographs of glaciers. This one's the McCall Glacier and that's in the Alaska Brooks Range. In the left, that was a photograph taken in 1958. You can see where the terminus of the glacier is very dirty terminus, because this glacier had been grinding up all kinds of rocks and things like that. But now on the right you see from the same vantage point, what was there in 2003. So that retreat really is very, very, very remarkable. We're seeing that sort of thing all across the Arctic and really, it's reflecting what's happening around the world. It's not just in the Arctic where glaciers and ice sheets are losing mass, it's over, really, most of the world. Now, there's always the exception. This is an analysis of Arctic Glacier mass balance from a number of different glaciers. What you can see; the X-axis on the bottom, that's a year going from 1945, this analysis goes through 2016 and on the Y-axis is the cumulative mass balance in terms of meters of water equivalent. Meters for that particular glacier. In other words, basically, how much was that glacier thinning? You can see all glaciers except one are losing mass. That's the Engabreen Glacier in Norway. It really is an outlier, isn't it? Here it is. Here's a photograph of it, and yeah, it's gaining mass. It's doing quite well. Why? Well, precipitation, it seems to be a precipitation effect, that it's getting more precipitation. Remember that when we talk about a glacier mass balance, it's really a balance between how much mass gain occurs through precipitation, largely snowfall, versus the mass losses that you get through summer melt or if this iceberg is discharging into the ocean, that effect as well. Well, this one here is doing well and what it really goes to show you is that there are always exceptions. You can always find an exception to the rule because some local topography are situated at just the right area. But definitely this is very much an exception when we talk about what's happening across the Arctic or certainly happening across the world. There's some strange things going on in the Arctic. Here's two satellite images from the Vavilov Ice Cap, that's in Severnaya Zemlya, that's in Russia. It's been exhibiting this very bizarre surge behavior. What you see on the left, there's a satellite image for June 18th of 2015 and look on the left side and you can see with this ice cap is discharging into the ocean and the ocean is blue. It's got some sea ice on it, of course. The one on the right, June 24th, 2015, look how quickly this thing showed a surge, where there's just ice being poured into the ocean. A colleague of mine, Mike Willis, who's been studying on this, describes it in another way. He says that this ice cap is just vomiting ice, in fact it's fairly descriptive term. But you're seeing these strange surge behaviors as well, and the Vavilov Ice Cap is a great example of that. How some of these ice caps can very quickly change. Now, I mentioned that the sea level rise from Arctic ice caps and glaciers combined is actually bigger from Greenland, and that's true. This is from an analysis put together from another of my colleagues, Twila Moon, who studies these things very closely. It turns out that in terms of a contribution to sea level rise, the Greenland ice sheet is about 0.11 millimeters per year, and the Arctic ice caps and glaciers together more than twice that. So you see how they're really dominating. Now you put those together and it's not nearly the total sea level rise we're seeing globally of 3.2 millimeters per year. Well, that's because there's ice caps and glaciers all over the world also contributing to sea level rise. The Antarctic ice sheet is as well, but there's something also very important, is thermal expansion of the oceans. As it turns out, the density of water is not constant, it depends on temperature, and if the water temperature goes up, basically the density of the water goes down so it occupies a larger volume, and guess what? The oceans are warming. So there's a component called thermal expansion of the oceans as well, which goes on top of the effect of this dumping water at icebergs into the ocean by mass losses from our ice sheets and our ice caps and our glaciers, and certainly the Arctic is playing a role in that. Now, here's a question. Let's think about sea ice. Remember that the Arctic Ocean is covered with lot of sea ice. Is melting sea ice a significant contributor to rising sea level? The answer is no, false, it's not, and that's because it's already floating. It's already floating, remember what sea ice is? Well, basically any ice, for the most part is about 90 percent the density of water. That's why about 10 percent of an ice flow or an iceberg sticks above the water surface. But that's just because of a difference in density as it turns out, if it melted, it would have no effect on the sea level. You could do your own experiment. You can take a glass of water, put an ice cube in it, and mark the level of the water. Come back an hour later when that ice cube has melted, the level would just be the same. It really reflects the fact that the ice is just already floating and that's the issue here, very different and we're talking about an ice sheet or a glacier or something like that and we're taking water that was on land and dumping it into the ocean, a very different thing. I hope you've learned a little bit here about what's going on in the Arctic in terms of ice caps and glaciers and the Greenland ice sheet and how they're contributing to sea level rise. Sea level rise is a very real thing and it's going to get worse as we go into the future, unless, of course, we do something about it. Thank you.
