 Cryosphere means the cold environment or the cold component, the frozen component of the earth. So that includes seasonal snow cover, which 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 we have different measurements, they are very complementary and all are more sensitive to different processes so we can get a good picture. 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. With satellite data they have completely revolutionised the way we look at polar regions, they make the whole place accessible. The other really incredible piece of technology or sort of approach that is used for measuring how the ice masses are evolving 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 where the mass is going. We've got cryosat and Operation Ice Bridge and those using altimetry to figure out the surface of the ice sheet. Altimeters measure the elevation of the surface very accurately and these altimeters there are two types that have been flown, a laser and radar altimeter. They can measure changes in elevation to a few millimeters a year and they're flying at altitudes of 600 miles, a thousand kilometers above the surface and they're measuring one or two millimeters change a year. It's a pretty impressive technology. So one of the great things about these both satellite technologies I've talked about, that's the altimetry and the gravity measurements, is that they can make observations over the whole ice sheet, over the whole of Greenland and almost all of Antarctica now. There's a little hole at the pole in Antarctica but all of Greenland for sure and what we see in Greenland is that there's big 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. Greenland is losing mass faster, you know, if you look over the last 10 years, one to 10 a decimal from grace, because I have it off the top of my head, but you know, from 2002 to 2002 now, you know, you have a mass loss is about 270 gigatons per year. There's 210 or so outlet glaciers in Greenland, marine terminating and wow, 99% of them are retreating, you know, 90% of them is accelerated. So we're seeing, you know, the details may be different, but the overall pattern is the same. We're going to report results this week of the collapse of an ice shelf and the formation of a new tidewater glacier in northeast Greenland, way over there, 79 north, which most of us did not think we would see that happening maybe in our lifetime. The ice shell works a little bit like, it's like if you have a cork in a bottle of champagne, you know, it's like stopping the champagne, you break the ice shelf and the champagne comes out. And so the glacier has been observed to once the ice shelf, you know, collapsed and it breaks up in pieces, they have been sort of flowing faster in the ocean. In the 1990s, the mass loss from Western Antarctic Green seems to be quite, quite small, close to the detection limit in the early 90s. And it has increased continuously up until the present day. For Antarctica, we're seeing the mass loss is increasing. And we're seeing, for sure, like Western Antarctica, the mass loss is accelerating, is increasing with time. 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 there's been a paper, a good colleague of mine, a very good scientist that said we may have already committed to more than three meters of sea level rise from West Antarctica. If we haven't, we're pretty close to it, and the scholarship is strong on that. 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 the forcing a little bit, warm ocean temperatures a little bit, that that instability could trigger a rapid mass loss from the ice sheet. It might retreat faster if climate warming continues at this pace, it might retreat slower. We don't know that absolutely for sure. But the fuse is already blown. There are some fairly recent, very recent results that both from observations and from a numerical modelling study that suggests that we've actually passed this threshold of stability, and that part of West Antarctica is going into an unstable regime where it's going to lose an increasing amount of mass, and that that cannot be easily reversed. All the observations we've collected in the past decades are actually pointing towards shorter time scales at what the models are able to replicate. It's true for the sea ice decay, most of the models are not able to replicate that. It's true for the decay of glaciers and ice sheets. They're going on a pace faster than what the models projected and faster than even the present day models are able to replicate. 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 a pretty continuous decline in what's called multi-year ice in the Arctic. This trend, very dramatic trend in reduced sea ice area in the Arctic, as some people have pointed, is the post-child of climate change research, because it's a big signal. It's unequivocal. Sea ice are getting smaller and smaller and it's a very important component of the global energy balance. But something slightly different seems to be happening in the Southern Ocean, in the Antarctic, because the sea ice there doesn't seem to have got smaller. If anything, although it's a very small signal, it's about 2% per decade, and it's sort of moving around a bit, but if anything, it looks like it's getting slightly larger. There's been an increase in wind away from the continent, so that that wind kind of does two things. One, it pushes the ice further away from the continent, so it makes it extend further north than it ever did in the past. And the second thing that it does is that when it pushes ice away from the continent in the winter, then areas of cold water which are adjacent to the continent become ice factories, essentially. And so more new ice is being produced all the time as the winds are increasing. For 24 consecutive years, alpine glaciers around the world, every continent, have lost mass. One year, maybe one glacier or one continent has a good year, but overall, globally, glacier mass balance is declining. For most of my students, they weren't even alive the last time glaciers had a good year, a positive balance. What glaciers do is that they act as sponges, basically. So in the winter, they hold that snow that falls, and then they release that snow in the dry time of the year, which is typically the summer. So what glaciers do is they tend to even out the annual precipitation that falls, and essentially allow areas to carry on to have agriculture, for example, in the summer, when otherwise there'd be areas that are very, very dry. Glaciers are kind of like an insurance policy. They accumulate snow during wet seasons and wet periods, and then they melt and release that during droughts and dry seasons, but they're getting smaller, so their ability to do that becomes less and less. So this has tremendous implications for people who live in areas that depend on those water resources. I think perhaps the biggest impact is on agriculture, because if you think of the prairies that stretch east from the Rockies, there's huge areas that are fed by the rivers that flow from the Rockies. We're most concerned about the sea level rise aspect, which is not useful. The sea level rise around about a meter, it's suggested would displace potentially up to 200 million people. 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 from a sea level rise of more than a meter.