- The last time we had the same level of carbon dioxide in our atmosphere.

Our oceans looked very different.

But how different?

I asked one of the leading experts on the subject and what I learned was pretty shocking.

The sea level was a lot higher then compared to today.

That's because it takes a long time for sea levels to adjust as Earth's temperatures change.

As the planet warms all that new heat energy slowly melts ice caps and glaciers, and eventually, once the Earth stops warming, the oceans find equilibrium at a new level.

So if we stop emitting carbon dioxide today, how much higher would our sea levels rise?

Well, we have a pretty good idea of what things looked like thousands of years ago when atmospheric CO2 levels matched ours today.

In this episode, we're going to use some amazing new imagery to simulate what places we know and care about would look like in a few different warming scenarios in our lifetime and just beyond.

It turns out we don't have to project far into the future to start seeing major impacts on our coastal regions and that will impact millions of people.

Carbon dioxide levels are currently rising faster than at any time since the last ice age.

I know that because I went and held 50,000 year old ice from Antarctica that has tiny bubbles of ancient atmosphere trapped inside of it.

Scientists use those bubbles to compare our current atmospheric carbon to the distant past.

I was holding that ice while filming a very exciting broadcast season called Weathered: Earth's Extremes, which you can stream right now.

Scientists at Oregon State University found that we're currently emitting CO2 10 times faster than at any time in the last 100,000 years.

Coastal communities are already feeling the impacts of sea level rise, but so far what we've experienced is tiny compared to what we'll see in the future because the rate of rise is speeding up.

In the last 30 years, we've had about four inches of rise, but we're projected to see a foot in the next 30.

There are a lot of unknowns when it comes to sea level rise, but paleoclimate records show the potential for a startling future - 125,000 years ago and and 3 million years ago, or some some last high stands of of sea level that are comparable to when temperatures and carbon dioxide levels were about the same as they are now.

And back then, we know that sea levels were five meters, maybe 10 meters higher than they are today.

So we still probably have a lot of melt left to occur.

- Here's what 10 meters of sea level rise will look like in the U.S. according to the data model, visualization tools created by Climate Central and powered by NOAA data.

If or maybe when that happens, much of New York, Long Island and Newark would be underwater.

The White House would become waterfront property along with all of Norfolk, Virginia, Savannah, Georgia, and so many more.

But the most impressive change is southern Florida, where major coastal cities would be submerged.

In southern Florida alone, more than 10 million people will become displaced.

Even in mountainous states like California, much of San Francisco and even Sacramento would be covered.

Worldwide, around 1 billion people or about one eighth of the world's population live less than 10 meters above current high tide lines.

Most of the country of Bangladesh would be underwater, all of Bangkok, Shanghai, and most of Hanoi would be covered as well as much of Singapore, Buenos Aires, and of course nearly all of the Gulf Coast.

Without a meaningful reduction in Earth's average temperature, this is very likely to play out, eventually.

And that's just at current CO2 levels.

As we continue to emit greenhouse gases, the projections rise even higher, but it'll take centuries for sea levels to catch up with current temperature.

But what exactly is causing sea level rise?

- The dominant signals causing global sea levels to rise are about two parts land-based ice melt: Antarctica, Greenland, mountain glaciers, and about one part thermal expansion.

So roughly two to one.

- When water warms, it takes up more space and there's so much water getting warmer in our oceans that thermal expansion used to be equal to ice melt, but that's changed.

- The ice sheets are really starting to lose mass and that the rate of which they're losing mass is accelerating.

And now it's overtaken the thermal expansion part.

And that's the real elephant in the room, is how much are these ice sheets going to melt, and what will that look like at the end of the century?

- Projections for the next 30 years are more dependable than looking further into the future.

So we'll start at 2050.

Over the last 100 years, oceans have risen about a foot, but that rate of change is increasing, - So history will repeat itself and fast forward.

We're set for a foot of sea level rise in the next 30 years relative to 2020.

- One foot may not sound like a lot compared to 10 meters or 30 feet, but low-lying coastal communities around the world will absolutely feel the impacts and that one foot of additional water pushes floods higher as well.

So on our US map, we're adding the ground covered by a 10 year or 10% chance flood to our map, meaning the likelihood of this flood happening this year is one in 10.

Many low-lying coastal communities have levees and sea walls.

But on our maps, we're showing areas that are potentially protected as flooded to give a sense of the risk.

But what will these sea levels look like on the ground?

Enter Climate Central, they're undertaking an ambitious project driving the East and Gulf Coasts of the U.S. collecting images and elevation data to create realistic, scientific based flood model visualizations.

We talked to Max, who is out collecting data for this project.

- Right now I'm in beautiful Daytona Beach, just woke up.

This is Climate Central's Edge of America Flood Rover 2, the vehicle.

It's a fully electric Ford F-150 Lightning.

Up on top, we have mounted on both sides, two cinema cameras, and in between those two cinema cameras is the silver cylinder.

This is a LiDAR unit, which sprays basically a laser cloud similar to what they use in augmented reality.

And then the other two units up there are GPS units.

- With that data, they can create scientifically accurate images of future sea level.

- Our interface allows us to zoom in on a particular city or town or road like Charleston.

So what you're seeing is just based on three feet of ground level water.

This is what the, the downtown Charleston market might look like with three feet of water.

- We'll look at our most likely warming and sea level rise scenarios in a bit.

But first we're gonna look at four to five degrees of warming and it's not the most likely path, but if renewable energy transition takes longer than we currently project, it is possible.

- If we start talking about four, five degrees C, you know, we're talking perhaps more certainty in saying yes, we're gonna hit three, possibly four feet, even more.

- Four feet would put large parts of the East Coast, underwater and populous global cities like Shanghai and Bangkok would no longer exist the way we know them today, but there are a lot more unknowns the further out we project.

And by 2100 melt could speed up.

The potential collapse of large ice sheets could be a major catalyst for faster melt.

- What will be some of the triggers that might create some collapsing, some rapid discharge?

These processes aren't very well modeled.

They're not very well observed.

Is it plausible by 2100 for global sea levels to rise two meters?

And what would that look like along the United States?

Well, that two meters would actually look like 2.2 meters.

So that would really be like seven feet, eight feet.

Now that's a very low likelihood, but what if these glaciers really start becoming unhinged?

These ice sheets really start to melt.

- 2.2 meters of rise along the East Coast would be devastating.

In Florida, popular cities like Miami and Cape Coral would be flooded.

Cities along the East Coast would be completely changed from Savannah, Georgia, Charleston, South Carolina, and all the way to Philadelphia, New York, and Boston.

As we model out to 2150, there are even more uncertainties - If some of these known unknowns start kicking in at higher temperatures, four to five degrees C, the numbers just become a bit scary, right?

We're talking about upwards of four meters of sea level rise.

12, 13 feet, very unlikely, but we can't take it off the table.

- But for now, some good news.

Our most likely emissions and warming path shows very significant cuts in greenhouse gas emissions by 2100, hitting somewhere around three degrees, hopefully just under.

- On the trajectory that we are on, let's say two and a half, three degrees C rise by the end of the century, we're looking at somewhere about probably three feet of rise on average along the United States coastline.

- And that extra foot is meaningful compared to the four or five degree warming scenario with four feet of rise.

And by 2150, well, it's important to understand that we're not currently on track to fully stop warming by 2100.

The more we warm in that extra 50 years, the faster seas will rise.

- The coastal environment is going to look very different regardless of what we do.

We're on a trajectory now of six to seven feet by 2150 under the commitments at hand.

It could be a lot larger, probably not going to be too much smaller.

- So by 2150, our grandchildren and great-grandchildren are very likely to witness the evacuation of large parts of New York City, most of Miami and the already below sea level city of New Orleans, plus dozens of smaller towns and coastal communities, just to name a few.

And that's in a relatively optimistic scenario.

I want to talk about Louisiana for a second.

Much of the area is already below sea level.

There are over 3000 miles of levees protecting large parts of the area, including New Orleans.

So will all cities just build walls instead of relocating as our seas rise?

Probably not, but it's hard to say.

Levees are only protective up to a certain point, and as seas get higher, the risk of failure becomes catastrophic.

We have already seen government relocation projects for communities in Louisiana, where the government pays to move an entire community often because it's cheaper and extending a levee or constant rebuilding.

Isle De Jean Charles is a community we visited while producing Weathered: Earth's Extremes.

It was relocated after it was excluded from a levee project, but the choice to leave was still incredibly difficult.

And even with effective levees, eventually communities will be living in a very risky fishbowl.

- The Texas spine, this idea of of big gates in Boston, New York City, that's not going to combat sea level rise.

I'm sorry to say, - But we have the technology to reach net zero.

And that's the point when we have reduced human greenhouse gas emissions to a point so low, that we can capture the rest and put that carbon in long-term storage.

And we can reach that point far earlier than 2150.

If we really move quickly and support the energy transition, we could reach net zero well before 2100.

That will mean a lot more support for speeding up the transition to low carbon energy like solar, wind, batteries, electric vehicles, and even our food systems.

See you next time on Weathered.