# 25. Ice and climate change

They’re calving into water, but it’s fresh water lakes rather than seawater with tides Flying over it, you get to see these snow-covered mountains, you get to see some of the ice breaking up into crevasses as they begin to flow over a bend Wherever they’ve got a drop over a sudden break in the slope, they often break up into these deep crevasses And of course, they’re covered with snow, but if you were to fall into that, you fall down 50 or 100 meters and be lost But you can see the flow streaks, these medial moraines follow it down to where the calving occurs It’s a bad picture from an aircraft There’s a lake there and the icebergs are calving into the lake You see it here as well You see these various moraines, medial moraines going down and then they break off into the little lake down there Now, there’s been a trend in the amount of ice in mountain glaciers, and it’s negative most places This shows a number of different parts around the world where you’ve got mountain glaciers, and it’s kept track of their mass since 1960 The units here are meters of water equivalent So it’s not how deep the snow or the ice is on the glacier, but if you were to melt it into liquid how deep it would be That’s a convenient reference because snow can be of different densities, and even compacted snow, depending on how tight it’s been compacted, may not reach the full density of ice So for this kind of mass balance calculation, it’s more convenient to, in the end, describe it as a loss in a depth of water equivalent A little bit hard to follow the colors, but in Patagonia where I was just pointing, we’ve had some of the largest drops, 35 meters of water equivalent, a decrease in the thickness of those mountain glaciers Alaska and the coast mountains have decreased rapidly as well And the Northwestern USA, for example, Glacier National Park, named after its glaciers, is having one of the most rapid decreases The word there is if you want to see the glaciers in Glacier National Park you better go there in the next five years because they’re diminishing pretty rapidly However, there are some glaciers that are not changing very much For example, in the arctic, and again, I’m not sure of the color codes here, but it looks like Europe and the Andean glaciers this would be the Southern Andes, this would be the rest of the Central Andes they are not changing so dramatically, at least not until the last few years So it’s a mixed story, but mostly strongly negative for the trends on those mountain glaciers To wrap-up I wanted to go back and look at Greenland We’ve already talked about it a little bit, but just to summarize some of the changes that are occurring in Greenland Here are some of the glaciers coming off of the main Greenland Ice sheet as a function of time from 2000 till almost the present day We looked at the Jakobshaven one We’ve spent some time talking about those I haven’t shown you the other ones Oh, I did show you the Petermann up in the northwestern part For the most part these are negative Some very strongly negative, some not so strongly But generally the glaciers are retreating This is in units of square kilometers So the base of it, it’s not keeping track of thickness now, but the area as it decreases Generally negative And we saw Petermann’s glacier So when that drops off, they decrease the area estimate of the Petermann glacier And some would argue well that’s not a significant loss because that’ll refill eventually, but that’s how they’ve done the calculation And then we looked at Jakobshaven before and saw that its calving front was retreating with time as well, and that shows up on the time plot also Now, there’s another thing we can investigate about Greenland, and that is the amount of surface area up on the ice sheet that has meltwater in the middle of the summer And what’s shown–so you can fly a satellite over, look down, and by the way light reflects off the ice sheet, you could determine whether or not the snow is wet whether

it’s got meltwater mixed in with the snow And in 1992 the pale area was shown to have melt water in the warm season And now, 2005, even this deeper red area It’s only the diminishing white area that is free of melt water, and that’s an indication that the climate is changing as well What happens to that melt water, some of it just stays there and refreezes the next winter Some of it runs off in this rather remarkable called a moulin, which is basically a hole that develops in the ice sheet that allows surface waters that are melting in the summer to drain and fall a distance of perhaps a kilometer or so down to the base of the glacier And then it’ll flow along the base of the glacier out to the sea So this is an example of one of those moulins Up on the Greenland ice sheet, water then draining down into this hole that takes it down to the bottom of the glacier Any questions on that? It’s a summertime, of course Recently we’ve got a new technology to keep track of what’s happening to Greenland and other things around the world It’s called the GRACE satellite, and maybe you can make out the acronym here Gravity Recovery And Climate Experiment That’s GRACE And it consists of two satellites moving around the planet very close to each other with a laser beam going from one to the other doing accurate laser ranging So you know within a millimeter or so the distance between those two satellites as they move Well, as the Earth is not uniform in its density, the continents have mass, other things have mass concentrations that make the gravity field of the planet a little bit irregular And by sending a satellite around that feels that gravity, and keeping track of how the distance between the two satellites varies during the orbit, they can map out these gravitational anomalies around the surface of the Earth And this is an exaggerated what they’ve done is take a globe, and in three dimensions kind of made it nobly so that it shows you where the higher mass concentrations are So this kind of irregular gravity field is what GRACE can detect as it goes around Now that satellit’s all that’s been in orbit for a few years now, and one of the applications of it is to look at not just the gravity concentrations near Greenland, but how they’ve been changing in time That’s what shown in this diagram So two plots are shown, one for Southeast Greenland, that would be this area here The other for Northwest Greenland up here The time runs from 2002 to 2010, and this is the centimeter of water equivalent thickness removed from, ormissing from that part of Greenland over that period of time And for Southeast Greenland, putting a straight line through there, you get about minus eight centimeters per year of water equivalent loss And for Northwest Greenland it’s about minus seven centimeters per year So the two values are roughly consistent That tells you that the overall mass of the Greenland ice sheet is decreasing You can do calculations with these numbers and figure out how long it would take before it would all be lost. It’d be quite a number of years because these ice layers are quite thick, a kilometer or more But nevertheless, it represents quite a bit of mass loss And when that water melts and goes into the sea, of course, that raises sea level a little bit And that’s a calculation you can do as well If you know the area of Greenland and how much this is decreasing per unit time, you can use the surface area of the oceans to compute how much that is going to raise sea level Any questions on that? Well that’s the end of the story on modern ice, current ice on the planet We could take a few minutes if there are any questions about any of the things that I’ve covered with regards to ice in the climate system Anything?