 So my name is Jonathan Bamber, I'm a professor of physical geography at University of Bristol and I'm director of the Bristol Glaciology Centre. I'm actually a physicist but also a glaciologist and I study the polar regions using satellite remote sensing techniques. The cryosphere is basically all frozen land and ice on the surface of the earth. So it's not just, so cryosphere means the cold environment or the cold component, the frozen component of the earth. So that includes seasonal snow cover, which it mainly covers quite a large part of northern hemisphere seasonally in winter. It includes sea ice, which I mentioned earlier, glaciers, ice caps, ice sheets and permafrost. Now permafrost is frozen soil where it's frozen throughout the year and there's a thin layer of soil at the surface called the active layer, which melts in summer but underneath it's permanently frozen. So those are all the components of the cryosphere, have I left anything out? Well there is river and lake ice as well, which is, so for example in parts of Arctic Canada, lake ice is very important for the hydrological cycle and the ecosystem as well because when you got frozen ground it suppresses the exchange of moisture, energy and gases like carbon dioxide between the atmosphere and the surface. So it controls all sorts of processes. So sea ice is a thin skim of ice that forms seasonally, so it's a maximum in winter in the Arctic and maximum in the southern ocean in the Arctic and it's only about one to five meters thick, something like that. And then in the summer it gets much smaller because you've got atmospheric warming and you've got changes in circulation. So it responds to both mechanical forcing and what's called thermodynamics, the warming of the surface and so that it waxes and wanes annually. It goes from a minimum of about four million square kilometers in the Arctic to something like 18 million square kilometers. So big variation and because it's floating on the surface of the ocean it doesn't really have any impact on sea level because it's in what's called hydrostatic equilibrium. It's just sitting there like a little ice cube in a glass. If you melt it, the volume in the glass doesn't change at all. Land ice is completely different. Land ice is sitting on land as the name suggests so that's glaciers and most of the ice sheets that cover Greenland and Antarctica and because they're on land they're not in hydrostatic equilibrium and they are much thicker so in Antarctica the ice is up to five kilometers thick. That's three and a half miles thick and if you melt that it goes into the ocean and it changes the mass of the ocean and therefore the ocean level goes up and if you melt both Antarctica and Greenland and I'm not suggesting this is going to happen tomorrow but if you did dump them both into the ocean global sea level will go up by something like 65 meters so that's about 200 feet so that's a plus a big effect. The principle that when you melt a piece of land ice and you melt it and it goes into the ocean is it's it's it's not even what I would really call physics it's a very basic mechanics it's it goes back to Archimedes principle which is you know he sat in a bath and the water level goes up that's it it's that simple. So I use satellite observations of primarily looking at Greenland and the Antarctic ice sheet to understand how they're behaving and how their volume and mass is changing with time particularly how it's responding to what we call external forcing that's changes in the oceans or changes in the atmosphere and I mean the technology is quite complex some of the principles are really simple but the satellites I mean it is literally rocket science you know this stuff is pretty pretty sophisticated technology. One of the main techniques we use is to measure the change in volume of the ice sheets using something called a satellite altimeter. Now altimeters measure elevate the elevation of the surface very accurately and these altimeters there are two two types that have been flown a laser and radar altimeter. They can measure changes in elevation to a few millimeters a year you know they and they're flying at altitudes of 600 miles a thousand kilometers above the surface and they're measuring you know one or two millimeters change years I mean it's pretty impressive technology and they do that over the whole continent and I mean the concept actually is quite straightforward they send a pulse of energy electromagnetic radiation down to the surface it bounces off the surface goes back to the satellite and you measure the time delay and how long it takes from the satellite back down if you know how fast the em radiation is traveling you've got an estimate or measurement of the range the distance from the satellite to the surface that's it but in between there's you know trying to measure a millimeter over a thousand kilometers it's it's quite quite difficult the other really incredible piece of technology or some approach that is used for measuring how how the ice masses are evolving is is by looking at changes in the gravity field of the earth as mass goes from the land into the ocean the gravity field locally on the surface of the earth changes and with incredibly sensitive satellite technology you can actually measure those very small changes in the gravity field and that tells you what's where the mass is going they're measuring two quite different things the altimeter is measuring the volume of an ice mass and that is not exactly the same thing as the change in mass or because because the volume to go from volume to mass you need to know the density of your snow or your ice now we know the density of ice but in Antarctica there's a layer of snow which is called fern which is up to 120 meters thick which is compressing very slowly under its own weight and that rate of compression changes with time so sometimes it's fast sometimes slow and that's got nothing to do with the mass of the ice sheet it's just snow compacting and so you have to deal with that now now the gravity measurements they they they don't measure volume they measure a change in mass but convolved or combined with the change in land ice and ocean are lots of other processes related to change in mass which if you like are contaminating the signal we're interested one of the key ones is to do with changes in the what's called the mantle of the earth this is the solid component of the earth there are there are changes in how much mantle there are in different parts of of the earth and that affects the gravity field that is nothing to do with ice but it's a signal that's superimposed on what we're interested in and so each each technique has different advantages and disadvantages different kind of corrections that you have to apply or different issues that you have to deal with and so they're actually very complementary and we learn a lot in fact what we're working on here is we're using all the techniques available combining them so that we get a complete picture about what's going on and we can sort of separate out all the other signals that aren't isolated using a combination of all the different observations and yeah and in that way actually you can learn more than just what's happening to the ice you can find out about what's happening to the solid earth and the ice ocean interactions and also what's happening at the surface in terms of variability and snowfall as well so the the lithosphere which is like the crust of the earth is elastic and what that means is that if i put something very heavy on it it actually goes down it depresses if i take the thing off it bounces back up now an elastic response is instantaneous but there is also what's called a viscous component so if i if i load the earth with a lot of ice and with Antarctica has got you know it's five kilometers thick it's a lot of ice and i take some of that off the solid earth does rebound back but part of that response is a very slow one that can take many thousands of years to fully relax one of the great things about these satellite observations is that they're telling us far more than we ever knew about how the ice sheets respond to forcing from the oceans and the atmosphere so that's that's a great bonus that the the negative is that we only really have about a 20 year record of of really high quality satellite observations that that are particularly useful for this but over the last two decades one thing that we've seen which is is sort of incontrovertible you know which nobody really argues with because all the observations show the same thing is that that mass loss from parts of Antarctica a part called west Antarctica which we believe is particularly vulnerable to um forcing from the ocean and most of the margins of the Greenland ice sheet have been losing mass at an accelerating rate so the rate of loss has increased pretty much pretty every year that we've made the observations in the 1990s um the mass loss from western Antarctica green seemed to be quite quite small close to the detection limit in the early 90s and it has increased continuously up until the present day and it's currently so 2013 you know it's a maximum in terms of mass loss there are some recent papers that have come out that showing that in just the last uh I think three or four years the volume change of Antarctica and Greenland has has doubled in other words the rate of loss has roughly doubled in that time one of the one of the great things about these both satellite technologies I've talked about that's the altimetry and the gravity mission is that they can make observations over the whole ice sheet over the whole of Greenland and and almost all of Antarctica now there's a little hole at the pole in Antarctica but you know all of Greenland for sure and um we what we see in Greenland is that there's there's big um elevation changes lowering of the elevation around the margins and a very very small increase in the interior which is what you would expect in a warming climate so this is what all the numerical models suggest that if you warm the the climate in the Arctic and and warming in the Arctic has been about double the global average over the last few decades um precipitation that and therefore snowfall does increase but all the numerical models suggest that that is outweighed by increased losses around the edges and that's pretty much exactly what what the observations are showing us a situation with the east and arctic areas um a bit more complex than for Greenland because for two reasons it's it's 10 times the size of Greenland and the signals the change in elevation and the change in mass that we're measuring with grace are much smaller than Greenland Greenland has a big signal it's well above the noise threshold east Antarctica um the signals we're looking for are quite close to sort of threshold of what we can detect and so I think it's fair to say the the jury is still out on whether east and how out of balance how much mass is being lost or gained um is happening in east Antarctica um and the best estimates that we have suggest that it's it's pretty close to balance doesn't look like it's gaining a lot or losing a lot but the error the errors on those estimates are quite large so um the the the interesting or perhaps concerning thing about west Antarctica is that um a large part of the west Antarctic ice sheet rests on bedrock that's below sea level I mean part parts of it are two and a half kilometers below sea level that's a mile and a half below sea level and that means that that part of western Antarctica is particularly vulnerable to um oceanic erosion to changes in ocean temperature and things like that and the geometry of west Antarctica suggests that it's in what we believe is a potentially unstable configuration and what that means is that if you just change change the the forcing a little bit war motion temperatures a little bit that that that instability could trigger a rapid um mass loss from the ice sheet um you know a very rapid response and a large response so large amplitude and quite fast uh that's what we mean by an instability and there are some fairly recent um very recent results that both both from observations and from a numerical modeling study that suggests that we've actually passed this this threshold of stability and that part of west Antarctic is going into a unstable regime where it's going to lose you know an increasing amount of mass and that that cannot be easily reversed what do I mean by forcing as well that the most the two key for things that act on ice sheet come from the atmosphere um so that is changes in snowfall and changes in surface air temperature or s at so in Greenland around the margins of well quite a large area around the edges of Greenland there is melting at the surface in summer and if you turn the thermometer up a bit that melting is going to increase that's pretty much an instantaneous reaction and you dump more snow on the surface and you know it's going to build up so that's that's what the atmosphere can do and another important particularly important interaction um more for Antarctic than Greenland is um around the margins of Antarctica there are um that the the the ice sheet is directly in contact with the ocean and what that means is that um you can if you if you change the temperature of the ocean or you get more warm water to these contact points the the ice can melt from beneath rather than from above at a faster rate and that can induce some of these instabilities that I talked about earlier on. Antarctic and Greenland um are you you have to think about slightly differently in terms of what might what might um make them change their mass loss or mass gain because in Antarctica the the mean annual air temperatures are pretty much everywhere except for the real northern tip are way below freezing so there's really very little surface melt in Antarctica and the big changes in Antarctica are likely to come from ocean forcing changes in ocean temperature okay in Greenland it's a somewhat different situation parts of Greenland are in contact with the ocean but but um a significant um almost almost half a little bit less than half of the mass lost by the ice sheet is lost through surface melting and that responds directly to changes in air temperature so in Greenland um there's some work that's been done and this is a bit complicated to explain that suggests that if the temperature in Greenland goes above it increases by about two degrees above pre-industrial that the ice sheet is no longer really um sustainable that it it will go into a permanent decline and the reason for that is that that um melting will at the surface will increase and go further inland to higher elevations and um gradually the top of the ice sheet will get lower and lower and in fact the elevations will go down everywhere where there's melting and as the elevation goes down the temperatures go up because of something called the lapse rate feedback you know the higher are you in the atmosphere the colder it is and so the lower you are the warmer it is so there's a positive feedback if you melt the surface and it goes down the surface gets warmer because it's at lower elevation now that positive feedback according to the neural model will will mean that for a temperature rise of two degrees above pre-industrial ruffling um Greenland may not be a sustainable ice mass so that means what does that mean it means that over possibly over thousands of years it it it will reduce in size to something very very small um the theory or the the concept it's called the small ice gap instability and so Greenland um has a I think about seat 7.3 meters of sea level equivalent in it um and I I don't know you might that's that's about what 25 feet or something you might you might think that that doesn't sound so bad but um you know the sea level rise over the last century was 15 to 18 centimeters okay and the sea level rise around about a meter um it's suggested would um displace potentially up to 200 million people so even we are very very vulnerable as a species to relatively small changes in sea level there are countries like Bangladesh the Netherlands and all the atolls in the South Pacific which would be absolutely devastated um from a sea level rise of more than a meter most of the work that I'm involved in um is about what impact the atmosphere notion might have on the cryosphere you know and and it's it's a fairly simple relationship if you warm the planet you know ice tends to melt so um but it's you know the in complex ways in Antarctica there'll be a a lag between you know warming and a response and all this sort of thing um so some of those things I'm I'm looking at but there are also other there are potential feedbacks from melting of the cryosphere on the rest of the planet on the rest of the earth system one of the one of the ones which um I mean number of scientists particularly oceanographers have been looking at for some years is the potential for um significant melting from Greenland to interfere with the large-scale ocean circulation that makes this part of Europe northwest you about three degrees warmer than it would be without the warm water coming from the Gulf Stream near the Gulf of Mexico all the way up past the coast of Scotland um and warming and then sinking in the North Atlantic in two areas called the Labrador Sea and Irminga Sea just south of Greenland where they release a lot of heat and those two areas just south of Greenland happen to be areas where the ice sheet does um dump quite a lot of fresh water and so if that amount increased the question is raised you know could that affect somehow ocean circulation it's still a very active area of research and so um I think that the the general consensus is at the minute is that the rates of input of fresh water from Greenland are not sufficient to have a a really dramatic effect on what's called the thermohaline circulation or this ocean conveyor belt but um it's you know a lot of papers being published on this and um there there is some recent work that suggests that it may have some effect it won't shut it down it won't stop there won't be some sudden kind of collapse of the the circulation but it could weaken it a little bit so some of the workers looked at the kind of they're called hosing experiments because what you're doing is you're getting a load of fresh water and you're pouring it into the ocean around the coast of Greenland and they call that a hosing experiment and so some people have studied looked at these hosing experiments where um they really dump a lot of fresh water into North Atlantic does the the circulation shut down altogether well if you put enough in it does but it doesn't look like Greenland is ever going to pump that much in but they have looked at you know sensitivity studies they're called to see yeah to see whether um it would have an effect and there are effects but they seem to be relatively subtle rather than major perturbations to the climate system if you look at uh map and I should say that I'm in a geography department so I quite like maps and I do a lot of work with maps um if you look at the southern hemisphere or the south pole and north pole they are completely different they're almost the opposite of each other the Arctic is actually the smallest ocean in the world and it's virtually landlocked so it's an ocean almost completely surrounded by land there are a few areas where water the ocean can go in and out but they're quite small they're called straits um and in the Arctic in winter that ocean is covered by this thin film of sea ice that I mentioned earlier the Antarctic it's the opposite you've got a very large continent a continent that is bigger than the contaminous USA it's one and a half times the area of Australia dumped on the south pole large continent surrounded by um the biggest ocean circulation in the world which is called the Antarctic Socomperla Socomperla current so the setting of Antarctic and Greenland is very different the changes in sea ice that we have seen during the satellite area which have made observations which is a bit longer than the ice sheets it goes back to about the mid 1970s so it's almost a 40-year record show um a pretty continuous decline in what's called multi-year ice in the Arctic and it's this this this trend very dramatic trend in reduced sea ice area in the Arctic as some people have pointed is the post-child of kind of climate change research because it's a big signal it's unequivocal the sea ice is getting smaller it's a very important component of the global energy balance because sea ice is is one of the brightest when it's covered in snow it's one of the brightest natural surfaces on the planet it is you know snow is the brightest natural surface so it reflects a lot of solar radiation remove it and you've got ocean there and so so people have been very concerned about changes in sea ice extent in the Arctic because it looks like it's on the way out but something slightly different seems to be happening um in the the southern ocean in the Antarctic because the the sea ice there doesn't seem to have got smaller if anything although it's a very small signal it's about two percent per decade it's you know it's it's it's and it's sort of moving around a bit but if anything it looks like it's getting slightly larger extending and um i mean some some people have um kind of questioned whether or asked well does that does that mean that there's an issue with some of their theories about um you know global warming and climate change but i i don't think that's the case because the warming and southern ocean is not nearly as pronounced as in the Arctic so you wouldn't expect it and the controls on sea ice extent in the Arctic and the southern ocean are completely different as i explained earlier the geography of the areas are totally different so the sea ice in um the Arctic um there's a much stronger thermodynamic in other words temperature control on on what happens to that whereas the in the southern ocean its extent is almost entirely controlled about by the location of the the Antarctic circumpolar current sea ice just can't go beyond that so there are kind of different different things driving sea ice extent in the southern hemisphere and north Antarctica as i mentioned is a huge continent um and um the the the most dramatic signals that we're seeing from the satellite data are coming from the edges um we're seeing big reductions in elevation and big mass loss around and margins of Antarctica but something else that these satellite observations that are indicating is that this this loss over time propagates inland and that's you would expect that it's it's it's uh it's not a kinematic wave um it's it's a diffusive process but over time as as the ice is drawn down at the edges and the slopes get steeper and the elevation goes down it pulls the ice from the interior um at a faster rate to the margins and so um just because we're we're the biggest signals are close to the coast doesn't mean that um ice in land is not being affected or is not potentially vulnerable to some of these changes i i've always loved playing in snow yeah um so um i did pick i did a degree in physics in fact interestingly i i did it uh in in this university so i'm in geography department now but i did and the physics department there has one of the most um i don't know famous is the right word but one of the best known theoreticians in glaciology in the world um there are some laws and principles of glaciology named after this guy called john nigh and he was actually one of my lecturers and there were other people in that department who worked in glaciology as well although it's never been that big in physics departments and um so i did physics but i was always fascinated by natural environment and how it worked and uh opportunities to work in geophysics related to glaciers and ice sheets came up for a phd and the rest is history really life on mars definitely i think that would be you know if i if i wrote a paper which said i've discovered life on mars that would certainly sell um interesting topics in so i think one of the holy grails there there were quite a few in my field one of the one of the big things we want to know is what are the ice sheets going to do in the future um but related to that and in in the department i'm in we do what's called a lot of paleo climate research that's looking at the past to help us understand what might happen in the future in when when let's say co2 levels reach levels they were a few million years ago or something like that um and one of the big challenges for our community is actually to push the satellite record which is only 20 you know do quality satellite records only 20 years push that further back in times so that we know something about what the ice sheets particularly the ice sheets because they have a long response time what they were doing um say over the last century that is a real big challenge for the community so i think the real thing um that scientists have to have to be sure they do they have to be honest when they're communicating their science and um i've had quite a lot of arguments with non-scientists about you know well we say this we say that and and the truth is that actually most scientists are skeptical about most things it's what we're trained to do you know we're trained to question everything and um in general the the science we do and the results we get aren't it's this or it's that but it's evidence and so i think we have to be honest that i can never 100 guarantee x y or z necessarily but i can say the evidence strongly suggests this or indicates something or you know if you look at all these different measures it's telling me this signal and you know the balance of evidence suggests something and so it's quite important to to be honest about the uncertainties and the things you're not sure about as well as the things you are i mean i think if i say i can't 100 guarantee that if you step out of a four-story building you're gonna die and i couldn't 100 guarantee that you know you could walk away um there is a very slim chop that that doesn't mean that you know i don't know anything about falling out of buildings um and that's that's the problem we face i think um and and there's a another issue it's also how you frame these uncertainties because if i if i say to you look you're 95 likely to be absolutely fine when you cross the road you think no that sounds fantastic come on cross the road if i said there's a one in twenty chance that you're gonna die when you cross the road you would go nowhere near one ever you know because that sounds pretty terrible and so it's it's how you frame some of these problems as well and how you frame the uncertainty and i think the language use is really important when i started my phd which was quite a few years ago back in the early 80s um um you know global warming climate change and what we're doing to the planet really wasn't wasn't on most people's horizons and i i i was studying i was doing glaciology as a phd um and you were doing it really out of interest it was curiosity driven but over time um the evidence has become more and more overwhelming that we're having a very damaging effect on the climate system um because primarily because of our love affair with um oil and fossil fuels um and i think not just in in my field i i'm very familiar with my field and and you look at any component in the cross sphere and it's they're all showing the same sort of signal that you know they're they're responding to recent change or at least they are um responding to what you would expect they're doing what you would expect them to do in a warming world put it like that and and they're pretty much all doing it but you look to any other part of the climate system you look to what's happening in the oceans and ocean certification you look what's happening to the biosphere and ecosystems and biodiversity it's the same story everywhere and so i think the evidence now is pretty incontrovert pretty compelling and uh very forceful that we're we're um making an uncontrolled experiment on the planet and we really don't know what the outcome is but i think one thing we can be sure about is that it's not going to be nice and we're not going to like it and i think the other thing that i find fascinating since i've got into this field is that if you look at the climate of when modern civilization has sort of evolved the last few thousand years you can say take the last five thousand years it's been remarkably stable it's one of the most stable periods over the last few hundred thousand years and we're starting to tinker with that and all the systems we have in place agriculture urban environment everything we've set up has all been predicated on this very very stable climate which we're now starting to tinker with you know fiddle with the dials in an uncontrolled way so i think that um yeah it's it's it's you know we're creating an extremely uncertain future in terms of what what the climate is going to do and how we're going to have to respond to it