ANDREA DUTTON: Our research shows that with just the amount of warming we've seen today, the seas could rise much higher, up to 20 to 30 feet higher than today.
NARRATOR: This enormous increase is due, in part, because warmer water has a greater volume, but it also means that, at that time, some of the world's great ice sheets must have collapsed.
WALEED ABDALATI: The big question is how fast? Does it take us 500 years to get there? Well that's one thing. Or does it take us 100 years to get there. That's three feet in a decade. That's a lot.
KATHARINE HAYHOE: In Antarctica, we see massive glaciers breaking off, adding to the amount that sea level is rising. Two thirds of the world's biggest cities are within just a few feet of sea level. And you can't pick up a city and move it.
NARRATOR: So, when will we start to feel the impact of sea level rise? Some people already are.
The Marshall Islands are a nation of low-lying islands in the Pacific. They are home to 50,000 people and a vibrant culture. Today, they face becoming a new kind of refugee: a climate refugee.
KATHY JETNIL-KIJINER (Marshall Islands Resident): We are only, like, two meters above sea level, so every time that there is a high tide, all this water gushes over and crashes into our homes and washes away graves. You feel really small. These floodings are going to continue to the point where we can't live there anymore.
NARRATOR: Kathy Jetnil-Kijiner is a poet from the Marshall Islands. For her family, it is their homes and their very way of life that is at stake.
KATHY JETNIL-KIJINER: What's going to happen to our culture, our traditions? We're hoping to not become nomads. We're hoping to not become lost, There are songs and chants that you can't hear anywhere else. What will happen to those stories that have survived for thousands of years? There's just things that you can't find anywhere else on Earth that you can only find in the Marshalls.
UNITED NATIONS ANNOUNCER: From the Marshall Islands, please welcome Kathy Jetnil-Kijiner.
NARRATOR: Kathy has become the voice of the Marshalls, addressing the United Nations with a poem to her daughter about the world she will face.
"dear matafele peinem,
i want to tell you about that lagoon
that lazy lounging lagoon lounging against the sunrise
men say that one day
that lagoon will devour you
they say it will gnaw at the shoreline
chew at the roots of your breadfruit trees
gulp down rows of your seawalls
and crunch your island's shattered bones"
NARRATOR: Her words are an attempt to bring the realities of climate change to people who believe it will not affect them.
KATHY JETNIL-KIJINER: "with only a passport to call home"
It's kind of hard to connect to an issue that you don't see outside of your own front door, you know? I understand that. It doesn't stop it from being a reality though. If our island goes down, who do you think will be next? It's going to be the rest of the world, it's just going to start with us.
NARRATOR: The results of climate change are, in fact, already striking the rest of the world, and much closer to home.
SKIP STILES (Wetlands Watch, Norfolk, Virginia): For those people who don't believe that sea level rise is happening, all you've got to do is come to Norfolk, or Charleston, or Miami, or New Orleans or San Diego, because you could see evidence of this in every one of those cities. This walkway, that was once supposed to allow people to walk and enjoy the water, is now under water.
REAR ADMIRAL ANN PHILLIPS (United States Navy, Retired): Sea level rise means there is just that much more flooding and that means that there's just that much more impact to roads, logistics infrastructure, moving cargo back and forth. And so that just makes it that much harder for you to prepare that ship to go and for the crew to prepare themselves to go.
NARRATOR: According to retired admiral Ann Phillips, climate change is a national security issue.
ANN PHILLIPS: It's about readiness. The Navy does see climate as an impact to its readiness and its ability to be resilient. From a national security perspective, sea level rise is a threat multiplier or a threat magnifier.
NARRATOR: But to the people who live here, coastal flooding has an enormous personal cost.
DONNA WOODWARD (Norfolk Resident): This house has flooded three times. I just don't know. I don't know how we'd be able to sell the house. Honestly, I really don't.
NARRATOR: Donna Woodward and Jim Schultz doubted they could sell their house and so decided to raise it up.
DONNA WOODWARD: It came down to deciding whether we wanted to go ahead and move out of the area or put all the money into elevating the house and staying.
JIM SCHULTZ (Norfolk Resident): It's happening now, not in the future, today. It's happening as we stand here. So, anyone who doubts it, we invite them to buy all of this property here and to come live and see for themselves.
DONNA WOODWARD: Sea level rise affects me in ways I had not thought of, you know? I need to be able to get to work. I bought a truck that has a snorkel.
ANN PHILLIPS: Sea level rise affects everyone here personally, and that is going to continue to accelerate. We have no time to waste, the situation is urgent.
NARRATOR: For the people of Norfolk, climate change is already affecting their lives. And across all of America, the costs are mounting.
On a single day in 2017, a satellite recorded three megastorms bearing down on the Americas. Meteorologist Paul Douglas' weather team has never seen anything like it.
PAUL DOUGLAS: Wow.
METEOROLOGIST: Look at that. It's terrifying.
PAUL DOUGLAS: This is easily going to be a three-hundred-billion-dollar year for hurricanes.
NARRATOR: Two-thousand-seventeen was the costliest hurricane season on record. Harvey alone caused catastrophic flooding in southeastern Texas, with financial damages that rival Katrina, and Puerto Rico was devastated by Hurricane Maria.
PAUL DOUGLAS: Warmer oceans don't trigger hurricanes, but the hurricanes that do spin up naturally have a greater potential to become extreme.
MARSHALL SHEPHERD: You can think of warm ocean water as the fuel supply for these big heat engines in these hurricanes. In a warmer climate, system hurricanes will have more octane gasoline to draw from in the ocean, and that drives these large powerful storms.
NARRATOR: Wildfires in the western United States have quadrupled since the 1980s, exacerbated by drought.
KATHARINE HAYHOE: We're seeing wildfires burning greater and greater areas, the hotter and drier it gets.
NARRATOR: Effects like these are being felt across the planet, and some are even accelerating the warming itself.