"This is our planet, the Earth." "It's unique in the solar system, perhaps even in the universe." "I'm Iain Stewart and I want to show you how our planet works." "In this series, I am exploring the four powerful forces that have worked together to create our world." "Wow!" "Volcanoes, the oceans, the atmosphere." "But this week it's ice." "Ice may be nothing more than frozen water but it holds extraordinary power." "Since human beings have been on the planet, nothing has done more than ice to shape our world." "It has carved the landscape, unleashed terrible catastrophes and ice has driven the climate of the whole planet." "It's even changed the course of human evolution, yet it may also threaten our future." "Only now are we beginning to understand the power of this remarkable substance." "Welcome to the world of ice." "The Alps." "One of the world's great mountain ranges." "Its peaks reach almost five kilometres into the sky." "It's a vertical landscape of snow and ice where even waterfalls can freeze." "If you want to understand the power of ice to transform our world, this is a great place to begin." "Okay, I may not be the best ice climber in the world, but what a way to really experience ice." "(GRUNTING)" "I'm 500 feet above a glacier." "That's, what, 1 50 metres up, and I'm climbing a frozen waterfall." "And what I'm looking for are nice, clean bits of ice to put my ice axe into." "This is amazing stuff, you know, because... (GRUNTING) ...it's so solid and it can hold my weight." "It really is surprising how solid ice is, or I hope it is." "I find it astonishing that hundreds of tons of cascading water can be stopped dead in its tracks." "But this frozen waterfall is nothing compared to the ice that's all around me in the form of glaciers." "I'm climbing right next to one of the largest in France, the Argentiere." "Glaciers are ice at its most powerful." "They're nature's bulldozers, capable of completely reshaping the landscape." "Thing is, that giant icicle I've just climbed up is made of frozen water, it formed this year, whereas that glacial ice up there, formed over thousands of years in a completely different way." "Glaciers are not formed from frozen water." "They are made from snow." "Every snowflake is formed from dozens of delicate ice crystals." "No one has ever found two that are the same." "Individual snowflakes may be fragile but put enough together and they can create one of the most awe-inspiring sights in nature." "(RUMBLING)" "Every year, around a million avalanches thunder down the Earth's mountains." "But however devastating avalanches may appear to us, when it comes to reshaping the Earth, they barely even scratch the surface." "It's only when snow turns into ice that it becomes so powerful it can change our world." "On this ice cliff you can actually see the transformation of snow into ice as it happens." "Each year's snowfall creates distinct layers, many metres deep." "Now, above me is the fresh snow from this winter, and down here, this brown line, is the melt from the summer before." "So as you go down through these layers, the snow gets older and older." "It's kind of like the rings of a tree with each layer being a new layer of snowfall, and it's the weight of all those snowfalls building up that starts to compress the individual snowflakes together." "The further down the layers you go, the harder the snow becomes until you reach here." "This is a really distinctive set of snow." "It's called neve and it formed several years ago." "It's really hard, I mean, I have to dig at it with my ice axe." "It's amazing stuff." "It's kind of like a bubbly fibreglass." "It's beautiful." "And what it's telling us is we're getting close to true ice." "The more the snow is compressed, the more air is forced out of it." "Removing air is what turns fluffy snow into rock hard ice." "This is it." "I've come down about 20 metres to the base of the cliff and this is pure glacial ice." "All those snowflake crystals in there have been squeezed down and it gives this weird texture." "I mean, it's just frozen water but it's like solid rock." "Look at that." "And it's got this glassy feel to it." "It's almost transparent." "It might take 20 years or so, but now the air has gone, this ice is tough enough to take on the hardest rock." "When enough ice forms, it slowly starts to slide downhill and becomes a glacier." "And over the last few million years, the time that humans have been around, it's ice that has been the dominant force shaping our world, even changing the climate." "Recorded from deep within the ice, these are the sounds of a glacier groaning and creaking as it slides down the mountain." "(RUMBLING)" "(CREAKING)" "(DEEP RUMBLING)" "They may move too slowly for the human eye to appreciate, but as a speeded-up film of the Argentiere glacier shows, ice is very much on the move." "Instruments underneath the Argentiere reveal that it's travelling at half a metre a day." "Here in Europe, ice is confined to high mountain ranges." "But in the polar regions, it's cold enough for ice to cover vast areas of land." "In Antarctica, a single ice sheet buries a continent bigger than the United States." "The ice sheet is a staggering four kilometres thick so only the peaks of high mountains, called nunataks, can poke through." "This is a world where ice doesn't so much carve out a landscape, it is the landscape." "This ice world is so huge that some of its greatest wonders can only be seen from space." "These are megadunes of ice, carved by centuries of relentless winds." "Each dune is six kilometres from the next." "Together they cover an area twice the size of Great Britain." "The polar ice even creates its own climate." "The air is so cold that it holds almost no moisture so, in fact, Antarctica is the biggest and driest desert on Earth." "But beneath the ice is another even more magical world, one that's been lost for more than 1 0 million years." "This satellite image reveals a huge area of flat ice, flat because it's floating on top of an enormous lake." "It's called Lake Vostok." "It lies beneath three kilometres of ice." "The lake has been isolated from the rest of the planet for millions of years." "It may even be home to forms of life we've never seen." "And thanks to radar, for the first time we can reveal the complete landscape that lies buried beneath Antarctica's ice." "It's a strange and unfamiliar world of islands and mountains that's never been seen by humans." "We may take it for granted that snow and ice are very much part of our world and that glaciers and ice sheets seem to be a permanent feature of the landscape but, in fact, nothing could be further from the truth." "As far as Earth is concerned, ice is pretty unusual." "For most of our planet's long history, about 90% of it, there's been virtually no ice at all." "Even the dinosaurs, that hung around for 200 million years, never saw anything like this." "We're living at an unusual time." "Technically speaking, we're in the middle of an ice age right now, but, fortunately, a relatively warm part of one." "Throughout Earth's four-and-a-half-billion year history, ice ages have come and gone, sometimes reaching as far as the equator." "But they don't happen very often, and when they do, they don't last that long, usually no more than a few million years." "The most recent one, the one we're living in right now, is believed to be the result of a rather remarkable chain of events." "First, around three million years ago, the continents of North and South America collided." "The result, a warm ocean current that flowed around the equator was cut off, so now the warm water travelled north." "Today we know this current as the Gulf Stream." "Strange as it may seem, it was this warm current that tipped the planet into an ice age." "As the warm waters evaporated, this supplied more moisture to the cold northern regions of the planet, so more snow fell." "And slowly the Northern Hemisphere iced over, triggering a global cooling." "Over the last three million years, the ice has advanced and retreated more than 50 times in a cycle governed by small changes in Earth's orbit." "If I was standing here 20,000 years ago, there'd be over a kilometre of ice above my head." "And even though much of that has melted and retreated away, permanent ice still covers 1 0% of the planet's surface, so ice is still well and truly with us." "Although a few million years is just the blink of an eye in the planet's life, this recent ice age has had an extraordinary influence on our world, and on us." "As we'll discover, it changed the climate across the planet, and in doing so, it drove human evolution." "And it carved out many of the most dramatic landscapes we know today." "If you head to Yosemite National Park in California, you get a good idea of just how effective ice is at shaping the landscape on a gigantic scale." "Glaciers are responsible for carving out many cliffs but few are as epic as this one, El Capitan." "It's ice that has made El Capitan into the greatest challenge in rock climbing." "And for Leo Holding, one of the world's top climbers, nothing quite matches it." "HOLDING:" "We call El Cap the Big Daddy." "This is 1,000 metres high and it's damn near vertical the whole way." "Your initial reaction is terror." "The scale of it is really intimidating even to extremely experienced climbers." "There's basically no easy way up it." "It's the hardest cliff to climb in the world." "STEWART:" "Two million years ago, Yosemite Valley looked very different." "A landscape of steep V-shaped valleys carved out by rivers." "But then glaciers formed in these mountains." "Slowly they flowed down the valleys, grinding sideways into the hard granite rock, gradually steepening the sides of the valley." "When the ice retreated, it left behind a deep U-shaped valley." "The classic signs of glacial activity are everywhere." "There are huge boulders plucked from the cliffs and carried for kilometres by the ice." "Waterfalls reveal where ancient river valleys were cut off mid-stream." "Sheer cliffs like this are absolutely typical of recent glacial activity." "The rock face is almost vertical." "HOLDING:" "El Cap is so amazing." "The rock, it's just bullet hard, nothing loose at all." "The only way to get up it is when you find these cracks and you can wedge your fingers into them, twist your feet into the corner... (GRUNTING) ...and claw your way upwards." "(EXHALING)" "STEWART:" "The ice took a mountain of granite and over tens of thousands of years, cut one side of it away, which is why this cliff is so steep." "I've been climbing for the last few hundred feet." "Crack's about to run out." "When the cracks run out, you get into these blank faces that are almost impossible to climb." "In fact, you can see it's so smooth, the rock, you hold onto virtually nothing." "STEWART:" "The glacier moved across the granite, grinding it with a force of over 1 00 kilograms on every square centimetre." "It polished the rock up a treat." "(GRUNTING)" "Whoo!" "I'm slipping, I'm slipping." "I'm right at the limit of friction." "Oh, it's just so smooth and slippery." "You have to keep your weight close into the wall." "(THUNDER RUMBLING)" "STEWART:" "But when bad weather closes in, this rock face becomes a climber's nightmare." "It's getting really wet and this glassy rock is just turning into an ice rink." "In fact, I might fall off here." "Oh, my God!" "In fact, there's quite a good chance I'm going to fall off." "STEWART:" "It would be reckless to keep on climbing." "Oh!" "Jesus Christ!" "STEWART:" "Leo must find one of the few refuges that El Capitan has to offer." "Might have to..." "It's all right, we're nearly there." "Even when it's raining, it's just such an awesome sensation to be up here." "Okay, Dave, I'm safe." "Brilliant, what an awesome climb." "Magical place." "It's like Mother Nature created this place for rock climbers." "STEWART:" "Some climbers prepare to spend the night on El Capitan, hoping to climb the next day." "It's easy to imagine that the ice age shaped only remote mountain ranges but it also left a legacy that has affected millions of people." "Take for example Manhattan, the island at the centre of New York." "When you look at it from a distance, it's actually got a very distinctive profile." "There are two clusters of skyscrapers with much lower buildings in the middle." "This is a direct result of the ice age." "Twenty thousand years ago, this part of America was at the edge of a vast ice sheet." "It covered much of the Northern Hemisphere." "The ice would have towered over any modern skyscraper." "When it retreated, just as in Yosemite, the ice left behind these boulders and rock smoothed and polished by ice." "The ice exposed a hard bedrock called schist, solid enough for sinking deep foundations" "to support tall buildings." "Without this bedrock, New York couldn't have been built so high." "The one part of the skyline that dips is the one place where the ice sheet deposited loose sand and gravel, no good for building towering skyscrapers." "Ice has bulldozed and carved the world we know on a colossal scale." "But what is it that gives something as brittle as ice supremacy over the hardest and most resilient rocks to be found on the planet?" "I've come to one of the only places on Earth where you can really see ice in action, not just by looking at it from afar but by getting up so close you can see its inner workings." "It's thanks to this glacier that we've started to unravel the mysteries of ice's great power." "In Norway's Arctic Circle lies the Svartisen Glacier." "I'm here because the Svartisen has something unique." "You can see how it works not just from the outside, but from the inside." "It's one of the only glaciers in the world with a back door." "This is part of a 50-kilometre-long network of tunnels." "They were built for a big hydroelectric power station but they'll also lead me right inside the glacier." "I usually study volcanoes, and in a way, glaciers are just like volcanoes." "They're beautiful, dangerous, hard to get to and even harder to study." "Also, like volcanoes, a lot of the action goes on where you can't see it." "In the case of a glacier, it goes on underneath hundreds of metres of ice right where it meets solid rock, which is why I'm in this tunnel, and I'm heading in that direction for another kilometre and a half." "In a chamber at the end of the tunnel we come face to face with ice." "It takes scientists two days of hard graft using hot water to melt a cave in the bottom of the glacier" "big enough to get inside and see exactly what happens when ice meets rock." "Here's the ice tunnel." "Watch your head!" "Miriam Jackson's a glaciologist." "She spends up to three weeks at a time down here." "Look at that!" "STEWART:" "It's beautiful!" "It's amazing, isn't it?" "It's absolutely beautiful." "This is like a piece of art." "It is, isn't it?" "Wow!" "You've got to remember there's 200 metres of ice over us now." "200 metres?" "JACKSON:" "Yes, we're at the bottom of the glacier and the ice is over us." "It's also closing in on us." "As we speak, it's contracting in?" "Yeah." "We couldn't stand here for 48 hours, the ice would close in on us." "We'd be stuck fossilised in the ice, like a big ice cube." "It's down here, right at the very bottom of the glacier, that you can see how it carves out great landscapes and can slice through solid rock." "JACKSON:" "This is the bottom two metres of the whole ice, of the whole glacier, and this is what's doing all the erosion." "And there's a lot of sediment in it, a lot of rocks in it, and these are being carried along all the time." "They're being scraped up off the bottom." "And all those particles are wearing away for years and years." "So the beautiful glacial valleys that you have where glaciers used to be were carved out by this kind of thing." "STEWART:" "It's not the ice itself that does all the damage." "It's the debris that it picks up along the way that makes glaciers act like giant sandpaper." "In effect, the ice uses the rock against itself." "There's a little rock here." "That's been travelling in the ice now for perhaps the past thousand years." "That is amazing." "It's amazing to think that when that first fell in, what was happening on the planet." "Genghis Khan sweeping across Europe or something like that." "Yeah, you can get really big ones, you know, a metre across, but they've found rocks being carried by glaciers as big as a house." "Really?" "They can be huge." "STEWART:" "But the ice cave has another surprise, one that offers a clue as to why something as apparently solid as ice can also bend and flow." "Have you seen this?" "It's an air bubble, is it?" "It's not an air bubble, this is water here." "Oh, look at that!" "So, we opened this up when we were melting, but before then, it was totally enclosed in the ice." "The interesting thing about these is when they're melting, sometimes they might drain on us all of a sudden." "And these can be a decent size, 20 litres or more, and suddenly you find a gush of water coming down on you." "It's a bit hard to see just because of the effects of melting, but the ice is full of these near the base and they're making the ice softer." "These water pockets may help explain how ice can flow." "The glacier is not the solid mass that it first appears." "Seeing it from the inside has given me a completely different perspective." "Really what I'm looking at here isn't solid ice at all." "It's almost spongy." "Yes, it feels very hard but it can flow." "It's weird stuff, isn't it?" "I thought I knew it but this is weird." "It seems almost alive." "As if to prove the point, the ice invades the space we've left behind." "In just three days, our magical ice cave disappears." "From space you can really see how fluid ice is." "On the west coast of Greenland, glaciers flow around the contours of a landscape hidden beneath the ice." "A false colour image reveals the blue ice of the Malaspina Glacier in Alaska." "It flows through a gap in the mountains and spreads out like syrup for more than 50 kilometres." "This is part of the Lambert Glacier in Antarctica." "It's one of the longest glaciers on Earth." "You can follow its flow lines as it bends and twists on its slow motion descent." "Ice is soft and bendy, yet it's also powerful enough to destroy almost everything in its path." "But while glaciers usually take tens of thousands of years to sculpt the landscape, occasionally, they can trigger a devastating change that happens in just a few hours." "You can see the aftermath of one such event in the northwest corner of the United States." "It's a land of gorges, canyons and barren rock covering 40,000 square kilometres." "It's known as the Scablands." "Vic Baker is a geologist who has spent 40 years trying to discover exactly what took place here." "The landscape creates this impression of something fantastic that happened, and as you drive through it, you can have a sense that you're following the path of that great catastrophe." "STEWART:" "In fact, it was a catastrophe waiting to happen." "Sixteen thousand years ago, a giant lake formed, Lake Missoula, that was held back by nothing more than a wall of ice, a part of what's known as the northern ice sheet." "Behind me would be the ice dam that was holding in glacial Lake Missoula, and it was holding back a phenomenal amount of water." "STEWART:" "As the huge mass of water built up behind the dam year after year, the dam began to weaken" "until the ice gave way in a catastrophic failure." "A mass of water the volume of the Irish Sea had nothing holding it back." "The force of water rushing forward was like releasing a bomb." "It generated a shockwave of air." "First thing, you'd see dust and wind, and you'd feel rumbling." "STEWART:" "An enormous flood quickly followed." "Lake Missoula's water had begun a fast and furious journey across the American continent." "BAKER:" "It would be moving very fast." "We're driving at just about the same speed as the water, and going along what would have been the bottom of the flood water." "STEWART:" "It would have torn through the landscape with the energy equivalent of 60 Amazon Rivers." "The water would be curling and crashing down in front as it moved along in this giant roller with horrible noise." "STEWART:" "It would have ripped up everything in its path." "You can imagine water a hundred metres above your head, all dark, filled with sediment and all kinds of debris, large rocks, trees, woolly mammoths, anything." "I think it would be absolutely terrifying." "STEWART:" "The water cut into the land up to 200 metres deep, excavating billions of tons of solid rock in just a few hours." "It would probably be described as a kind of giant monster." "STEWART:" "In just 1 0 hours the flood smashed a path from source to ocean, a distance the length of Great Britain," "leaving behind a colossal canyon." "And when the flood reached the sea, it sent sediment shooting out across the ocean floor" "for 2,000 kilometres." "The ice age flood had left behind extraordinary scars on the landscape." "This was once a waterfall five times the size of Niagara." "These are giant ripples formed by the turbulent flood water." "And huge potholes were created by whirlpools that drilled straight down into the rock." "The flood was so vast that nothing that happens on the planet today comes close to the scale of this catastrophe." "But we now know that as the ice advanced and retreated during the ice age, there were lots of floods on this scale in many parts of the world." "Since humans evolved, it is ice, through glaciers, ice sheets and floods, that has been the dominant force shaping our planet." "But the greatest influence of ice relies on far more than brute force," "and that's because ice has some unusual properties that have a profound effect on the Earth's climate." "I am on the west coast of Greenland in what's known as Iceberg Alley." "This is the biggest iceberg factory in the world." "I've never been up this close to icebergs before." "I know they're chunks of glacier that fall off the front of the ice sheet and they float here, but when you get this close, they're like majestic beautiful ships flowing silently by." "Geologists use the word calving to describe the formation of bergs, calving as in a cow giving birth to a calf, and this is known as an iceberg nursery." "The most bizarre property about ice is something so obvious that we just don't give it a second thought." "These shouldn't be floating at all." "Most substances are denser when solid than when liquid which means they sink." "Ice is an exception." "Because it expands when it freezes, it becomes less dense and so it floats." "It's also dazzlingly bright, which makes it highly reflective, and this combination has a dramatic effect on the Earth's climate." "These two qualities, floating and reflecting, make ice uniquely powerful on Earth." "Ice turns these polar regions into two giant reflectors, and they don't just reflect light but heat." "Land and sea are dark so they absorb the Sun's warmth, but ice reflects it straight back out to space." "It's called the albedo effect." "Filmed for a year from a satellite above the North Pole, you can see how the Arctic sea ice grows and shrinks with the seasons." "This changes the amount of energy absorbed by the Earth, and this in turn can influence the climate right across the planet." "The effects are even greater when ice spreads beyond the poles during an ice age." "Then increasingly large amounts of the Sun's energy are reflected into space." "Climate and ice are intimately linked." "Ice doesn't just respond to climate changes, it can amplify and accelerate them." "Ice can take a small change in temperature and make it much bigger, big enough to affect everything on the planet, including us." "Climatic upheaval generated by the ice even affected the path of our own evolution." "Fossils found all over East Africa show how in the last three million years there appear to have been two great evolutionary leaps forward." "The first was the appearance of an ape man with a brain 60% larger than anything that had gone before." "Then later came the evolution of Homo erectus, who was the first of our ancestors to make sophisticated stone tools." "What might have caused these rapid changes has always remained a bit of a mystery." "It now appears that they tie in with the two greatest advances of the northern ice sheet." "Each time the ice extended further south, more of the Sun's energy was reflected from the planet." "This destabilised the climate and led to extreme conditions in many regions of the world." "In East Africa, home to our ancestors, the climate became chaotic and unpredictable." "In this fast-changing world, only those who adapted best survived." "Both big brains and new weapons gave our ancestors an edge." "Eventually, out of the climatic turmoil modern humans began to emerge." "If it wasn't for the ice age driving climate change in East Africa, we might not be here at all." "Ice has been a crucial part of the human story." "For us, the ice has always been here." "We've never known a world without it." "Throughout our past we've always had a close relationship with ice." "So what's the future of that ice, and what might it mean for Earth and for us?" "Greenland is covered in the second largest ice sheet on the planet." "On the west coast is the massive Jakobshavn Glacier." "It has become the front line in our attempts to understand what's happening to the world's ice as global temperatures rise." "I'm just the latest in a long tradition of scientists who have come here to poke, probe and measure the glacier in the name of science." "The first was a Dane, Henrik Rink." "Now, he was the first to realise that the glacier came from snow that accumulated high up on the top of Greenland's vast ice cap." "Now, ever since our Mr Rink, scientists have come here to monitor the state of the glacier, and as a result, we've got a pretty good record of what's been happening here for the last 1 50 years." "Until as recently as 1 99 7, the glacier was relatively stable." "But in the last 1 0 years, it's changed dramatically." "Seen from space, the glacier is on the right and the fjord which it flows into is on the left." "And you can see that it's retreated massively, by 1 0 kilometres." "But the reason it's retreated is not simply because it's melting in the increased temperatures, it's because the glacier has speeded up." "It's now moving at 40 metres a day, and this has made it much thinner." "The result, the front of the glacier keeps breaking off into the fjord leaving it jam-packed with icebergs that are floating towards the sea." "Filmed over three months, you can see just how much of Jakobshavn's ice is floating away." "These are worrying signs and they're completely changing our understanding of Greenland's ice." "It may not be only Jakobshavn Glacier that's disappearing so fast." "There's other glaciers along this coast that are also accelerating." "The problem is if glaciers continue to retreat at this rate, it could lead to the eventual disappearance of all Greenland's ice." "That's 1 0% of the world's total." "That would raise sea levels by at least seven metres, which would flood many of the most highly populated regions of the world." "Florida would be one of the worst places to suffer." "The northern coast of Europe would be barely recognisable and much of London would disappear beneath the waves." "So, not surprisingly, scientists are eager to find out what's going to happen to Greenland's ice as global temperatures continue to rise." "KONRAD STEFFEN:" "Well, the landscape is very special, as you can see, and on top of it, it never gets dark." "STEWART:" "Yeah, the Sun, it's fantastic." "I've joined up with Konnie Steffen." "We're on a part of the ice sheet that's connected to the Jakobshavn Glacier." "Konnie's trying to understand what's causing the ice to speed up and break off into the sea, and whether it's related to climate change." "The ice moved fast, at first by 1 0%, then by 2002, 30-40% and it produced more water, like this river." "And this water is probably the explanation why the ice here starts to move faster." "STEWART:" "Each summer, as a result of rising temperatures, more and more melt water is forming lakes and rivers on the surface of the ice." "And this is where all the water flows, into deep shafts called moulins." "No one knows for sure where the water ends up when it disappears into the moulins, but Konnie believes it flows straight to the base of the glacier." "If he's right, this could explain why the glacier is moving so fast." "Water is heavier than ice so it will push itself under the ice and lift up the entire ice sheet." "So this water here dives down to the bottom of the ice sheet, lifts it up, lubricates it and allows it to move really fast?" "If we have a water column that goes all the way down." "STEWART:" "So far no one has been able to prove if the melt water actually does reach the bedrock and lubricate the ice sheet, or if it simply flows through the ice, never reaching the bottom at all." "Now Konnie and his team hope to solve this mystery." "They're going to drop a camera deep into the ice to trace the route the water takes." "It's the first time anyone's attempted this." "Is it heavy?" "STEFFEN:" "Very heavy, yes." "STEWART:" "They're using a camera built by NASA, designed to withstand freezing temperatures." "It could finally answer the question of whether the increased amount of water is actually speeding up the flow of ice." "If it is, then he will have made a direct connection between climate change and the disappearing glacier." "The moulins are full of tight twists and turns, so to help the camera get through, they've chosen the biggest moulin they could find." "There's no water running into it at surface level but they know there's plenty down there because they can hear it." "It's a precarious business." "For a start, I'm not sure how thick this overhang of ice is." "But it looks as if this is all undercut here?" "It is undercut, that's why we are on the rope." "Right, okay." "We go down, we hang on the rope" "and our colleagues take us out again." "All right." "All right, okay, I trust you!" "Don't worry, Iain, don't worry." "This is the first time it's gone down a natural moulin?" "This is the first, and maybe the last." "STEWART:" "They've got 1,000 metres of cable which Konnie believes is long enough to lower the camera all the way to the bedrock." "Sixty metres." "This is amazing." "Seventy metres." "Seventy metres." "(RUMBLING)" "STEWART:" "Whoa, what was that sound?" "These are walls falling down and the cave collapses." "That's what I was fearing, yeah." "This is pretty safe, right?" "I think so." "Okay." "STEWART:" "There we go." "Now we're submerged." "Look at that!" "Finally, 90 metres down and we've reached melt water." "Now it's a lot, yeah." "It's a good sign that the camera's on the right track." "But if this water does reach the very bottom of the ice, there's still a long way to go." "MAN:" "I think it's stuck." "STEWART:" "I think it's stuck." "It's stuck on a wall." "STEWART:" "Is it getting snagged, do you think?" "STEWART:" "The camera seems to have reached a bend in the moulin and it's not moving." "It's hit a ledge." "STEFFEN:" "We have to pull it back." "Right now the camera is where the water flows horizontal away." "Yeah." "But our camera's kind of stuck there?" "It's either not enough water to drag it," "or the camera is too heavy." "Yeah." "STEWART:" "It could be just a kink in the moulin or it could be the water never reaches the bedrock." "For the moment, it will have to remain a mystery." "Konnie and his team will have to redesign the camera and return next summer." "But wherever this water ends up, it's clear that more surface ice is melting." "Scientists have mapped the area of the Greenland ice sheet that experiences surface melting in summer." "As recently as 1 992, it was a relatively small area around the edges of the ice sheet." "But by 2005, the melt zone had massively expanded." "This would be bad enough on its own but if the melt water is also causing the glaciers to accelerate into the sea, it could have very serious consequences." "There seems to be no doubt that Greenland's ice is moving and changing faster than we ever conceived of even five years ago." "What's more, because this process continues every summer, the whole ice cap loses elevation, which means it'll be sitting in warmer temperatures and that, of course, means more melting, more of these moulins and so an even faster demise." "And it isn't only Greenland's ice that's under threat." "Around the world, it's the same story." "This is the Columbia Glacier in Alaska." "Like Jakobshavn, this is a fast moving glacier that ends up in the sea." "It's three kilometres wide and 500 metres thick." "But 20 years ago, it was nearly twice as thick." "You can see the line around the valley where the ice used to reach." "It's like a high tide mark." "This change has had a devastating effect." "Where the glacier meets the ocean, you can see the result." "Chunks of ice are falling into the sea 30 times faster than before." "As more and more ice breaks off, the whole process accelerates." "Now ice is disintegrating too fast for the glacier to replace it." "Since 1 980, the Columbia has retreated 1 5 kilometres." "In fact, in the past 50 years, glaciers have been shrinking all over the world." "The floating ice shelves that surround Antarctica are also disintegrating." "This one collapsed in just five weeks, destroying an area of ice the size of Cornwall." "There is now no doubt that the world's ice is in retreat." "It's still not possible to say for certain how much ice on the planet will vanish or how fast." "But in the long term, if global warming continues, then it will have a huge effect on the planet's ice and on us." "The world's ice is melting at a phenomenal rate, and it's a rate that's likely to accelerate over the next few years." "For the planet, being without ice is nothing new." "But for us humans, it'll be the start of a new era." "The disappearance of ice will transform the appearance of our planet." "It'll be the most visible change on Earth since the dawn of civilisation." "Next time, the oceans." "Far more than just a vast reservoir of water, they are bound together by a complex network of currents so vital to life on Earth that when it fails, the result is catastrophic."