imagine a world where you can sail right up to the north pole. where the largest ice sheet in the northern hemisphere is simply melting away. >> the melt is winning this game. >> we've now broken all time records for three consecative years. >> as oceans continue to rise flooding the streets of american cities half a world away. >> what happens in the arctic doesn't stay in the arctic. >> imagine a world where hurricanes and heat waves wreak havoc. >> breaking news as hurricane irma continues to show no mercy.

>> just a held storm. >> politicians deny the problem as temperatures continue to rise. >> it's a hoax. a money-making industry. >> greenland is an epicenter for climate change. >> what if i told you this is already happening? right here, right now. we are the primary cause and that only we have the power to stop it. this is greenland. though you will find very little greenery here. home to some of the most stunning wildlife on the planet, the world's largest island is more than 80% made up of pure ice. it's only from the air that you really get a sense of the scale and enormity of this ice sheet and what's just staggering to imagine is that in the center of

the island, this ice is two miles thick. it looks as though time has stood still for thousands of years, but this environment reflects the big changes in our world's atmosphere. as the planet gets warmer, the arctic is heating up at double the rate and greenland in particular is warming even faster. >> jason box is an american climate scientist who has been coming to this corner of the world for more than 20 years. >> the amount of water produced all across this landscape has increased, doubled in the last 50 years. >> doubled in the last 50 years. everywhere you go in greenland you can see and hear the ice sheet melting. sometimes a drip, sometimes a roar. its surface is etched with fast-flowing rivers that carry

the melt water deep down to the bed. >> this water cascades down thousands of feet and eventually makes its way to the bed, and it is heating the bed of the ice sheet. everything's kind of stacking up that the ice is going faster than forecast. >> no sign of slowing down. >> the melt is winning this game. >> and the more greenland melts, the more it speeds up the melting process. take the large melt lakes that are forming on top of the ice sheet. stunning to look at, but bad news for the ice. these lakes are deceptively beautiful because where is the white of the ice actually reflects the sun light, the piercing blue of the lakes actively absorbs them, heating them up and accelerating the rate of melt. perhaps the clearest example of this vicious melt cycle can be

seen in greenland's many glaciers. it is a mass of thick ice that moves under the force of its own weight. like a slow river into the sea. but as melt water moves through the ice, it softens it, draining to the bed where it then lubricates the movement of the glacier. we got a rare close-up view of one of greenland's fastest moving glaciers, named hel heim after a viking, it is fast and unforgiving. >> this is one of the most productive glaciers in greenland. it's about three golden gate bridges wide. it graidrains almost an astronol amount of water in is delivering from high on the ice sheets down into the sea. >> between august of last year and august of this year, new york university scientists

say it retreated a whopping two miles, the furthest retreat inland they have seen in a du decade. you can see vast chunks of it crashing into the water. a process called caving. >> what does that mean for the sea? >> there's hundreds of glaciers like this in greenland and many have doubled in speed. t it has really gone up in ways that surprise the science community. >> it's not only scientists who have been surprised. 56-year-old toe bias has been hunting with his dogs in greenland his whole life just like his father and grandfather before him. only these days there's far less ice for dogsledding. >> 15 years ago, all maybe from here to 500 meter and more is glacier. so we can start from down from

sea. >> is that something you have seen with your own eyes? >> yeah. i can see it. now we cannot hunt. only boat. >> this year, he has to take his dogs off the ice and back to town for the summer. he doesn't know if his grandsons will become hunters. but if the recent past is anything to go by, the future looks bleak. warming in the last century has been faster than at any time in the past several million years. how concerned are you by the scientific data that you've collected, by the changes you've seen here? >> what concerns me most is this concept of committed loss, so the amount of co 2 excess in the atmosphere due to humans burning fossil fuels mainly, that commits us to more than one

meter of sea level rise. >> that's roughly three feet. the and this is where the rest of the world comes in. greenland doesn't play by las vegas rules. what happens here doesn't stay here. as temperatures increase and melt accelerates, greenland has become the largest source of sea level rise globally. this year, after decades of decline, the amount of ice lost in greenland was roughly equal to the amount gained, but, box says this is an anomaly and that even drastic cuts in carbon dioxide emissions won't be enough to stop the continued melting. some have said if greenland is the ca nairry in the coal mine the canary is dead. >> it's time to get out of the mine. in other words, we have a problem. now's the time to start developing that response. >> he says he is frustrated by the white house's lack of

commitment to climate change studies and its decision to with draw from the paris accord. >> some people will say listen, look back over the history of the planet. there have been ice ages, huge heat waves. there's a natural extreme fluctuation in temperatures and that's just part of living on plan planet earth. what do you say? >> what's happening now is human activity has become the dominant agent of change for about the last 150 years. the climate change we observe today is at least 80% due to human activity. we are now a force of nature. >> when we come back. >> it's one of the biggest risks. >> the u.s. is feeling the impact of what's happening in the arctic. >> the a analogy i'd like to use is we're stepping out on to a

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they're great for us. the right care. right at home. . it's been a year of hurricanes, pummeling, floods rising and wildfires raging. so what exactly is going on? in part 1, we traveled all the way to the arctic, which scientists call the world's refrigerator.

we found that as temperatures rise due to carbon emissions in the atmosphere, the greenland ice sheet, the largest in the northern hemisphere, is melting at an unprecedented rate, causing oceans to rise. this is one of the most unique and surreal environments on earth. to many people it probably looks like another planet. but make no mistake, what is happening to the ice beneath my feet here is already having an impact on coastal cities all around the world. now we've come back to the united states to see that impact up close. starting in miami beach. ♪ >> this buzzle city in the sunshine state feels a long way from the icy glaciers of greenland but as the ice sheet has melted global sea levels have climbed 8 inches since the

beginning of the last century. miami has become known as ground zero in the u.s. with nearly a foot of sea level rise. former miami beach mayor phil levine likes to joke he floated into office by making this the main plank of his campaign. >> about five or six years ago we would notice that during sunny days the water would come up, and the roads would become flooded in the western parts of the city which are the lowest lying areas. >> was unnerving for everybody. >> the city is spending a whopping $500 million building up sea walls and raising roads. measures levine says helped protect miami during the ferocious hurricane irma. >> i actually believe these, we call them these abnormal unusual once in a century storms, that's not the case. this is the new normal. we were very fortunate in miami

beach. the areas we had invested in, raised roads and put in pumps. during the hurricane, they were as dry as the sahara. >> houston was not so lucky. more than 80 people were killed after hurricane harvey dumped a mind boggling 50 inches of rain on the city. the same amount normally expected in a year. scientists say some of that water should have been frozen in the greenland ice sheet. >> there's a saying that goes what happens in the arctic doesn't stay in the arctic. and it's absolutely true. >> michael mann is one of the country's top scientists, he has testified before congress about the threat posed by climate change. >> is there a direct connection between the intensity of the hurricanes we're seeing and climate change? >> there is a direct connection. too often we hear the problem framed as did climate change

cause this storm. did it cause this hurricane. that's not the right way to think about it. the question is is climate change amplifying the impacts of these hurricanes. it absolutely is. >> mann explains that as arctic ice, the world's refridge rater has melted, that has accelerated the overall warming of the planet. the world's oceans have warmed by more than 1 degree farren heig height. it allows more moisture into the atmosphere making hurricanes stronger with more potential to flood. the vast majority of climate scientists agree that without significant cuts to carbon admissions temperatures will continue to climb and problem only continue to get work. >> i like to use the analogy we're stepping out on to a mine

field. >> in norfolk virginia knows that better than most. since 2003 enough ice has melted off glereenland to fill chesapee bay. 14 inches of sea level rise here in the last century. >> it may be fun for the kids but it is a real concern for residents like this. so how high does the water get here? >> so far, the water has come to just here, which is eight feet. we're talking like a few more inches. >> exactly. exactly. that's our worry. >> that must be a big worry. the. >> huge. >> flooding now consumes her neighborhood, up to ten times a year during high tides or after a big storm. >> we move the iron outside furniture indoors and put the sofa up on them and move

everything soft up to the second floor and take the books out of the bookcases and get them upstairs. >> you've devised a drill by now. >> exactly. >> she bought her dream home here 35 years a ago. but since then the water ant flood insurance prices have soared. >> i gave my husband weighaders christmas. >> very practical. >> does he get good use? >> he sure does. >> let me ask you this. if you had known when you bought this house everything that would come with it in terms of the tides, floods, the power outages, would you have maybe looked for somewhere else to live? >> maybe, but it really was my dream house, and it always has been. so, i can certainly see it becoming unlivable. and that does worry me. >> for norfolk, the problem has added significance.

it hosts the largest naval base in the country. sailors are coming home from long deployments to a base threatened by encroaching seas. made worse by natural phenomena that caused the land here to sink. >> this base is uniquely vulnerable to sea level rise. that potentially makes it a very expensive headache for the military. to replace just one of these piers would cost roughly $100 million. may mavis is the former secretary of the navy. >> if we don't arrest sea level rise. if we don't reverse this or slow it down, norfolk is going to disappear. that nail base will go under water. i represented the navy. our bases tend to be on the ocean. and so you're going to see these bases being more and more at

risk. >> so it sounds like you're saying that climate change does not only have an impact on national security, that it's vitally important to national security. >> it's one of the biggest risks we have in national security. it's one of the things we've got to plan for the most in national security. >> but america has been slow to wake up to the threat posed by climate change. in part because it has become a politically charged issue. wp issue -- trump administration actively dismantling legislation by president obama to curb the use of fossil fuels. >> does it frus trait you this has become a political issue. >> in notion that climate change is a party san issue is just nuts. you can see it happening. you can see it out there. and when the military is telling you in unequivocal terms this is

it happening, it's having an impact on us as a military but having an impact on this country in security terms, to not listen to that, is just foolishness in the highest order. >> it's a sentiment phil levine shares. >> can you imagine debating gravity and the theory of relatively and all the other proven scientific theories. the ocean is not republican and democrat. it just knows how to rise. >> when we come back, have we reached a tipping point? we take a look at where we are headed and what we can do about it.

up in the arctic, we visited a beautiful strange and distant world. and we saw for ourselves how life up there is changing for creatures great and small as a result of -- connected to ours than eever could have imagined. and as it changes, we humans are living that change too. as the earth gets hotter, the arctic ice is melting, global sea levels are rising, and the whole delicate interconnected balance that underpins our weather systems is getting thrown off. heat waves are common occurre e occurrenc occurrences. this year carbon emissions are

projected to spike to record highs. if things don't change we're on course to heat the planet by more than 5 degrees farenheit but end of the century. scientists agree that humans are the main drivers of climate change. in the weeks since we filmed our report 15,000 scientists from around the world issued a warning to mhumanity. they say we're heading down a path to substantial and ir versable harm to the planet. there is no silver bullet. we spoke to dozens of scientists for this program and all of them agree there is still time but not much. the only question is what will we do about it. when food is god and clean and real, it's ok to crave. and with panera catering, there's more to go around. panera. food as it should be.

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-- captions by vitac -- www.vitac.com you are in the cnn news room. breaking news. the an enormous revelation from president trump that really changes the conversation about who knew what in the first weeks of this presidency. president trump now saying in a tweet he knew michael flynn lied to the fbi. and that is partly the reason he fired him as national security adviser. now this is huge. because as you know, flynn pleaded guilty just yesterday to the federal crime of lying to the fbi. if the president's words are true, and he knew about this crime, the felony back in feb and it would mean that he knew this when he asked comey,