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If the ice caps melted, would our world really look like Waterworld?

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Jul 29, 2020, 11:00 AM EDT

Years before Bear Grylls got meme'd for drinking his own urine, Kevin Costner did it aboard a trimaran as the nameless Mariner in 1995’s Waterworld. The film received mixed reviews and almost failed to recover its nearly $200 million budget (the largest of any movie ever made, at the time) at the box office.

Despite lackluster ticket sales, however, it found its place in the memories of moviegoers and is still remembered (and occasionally celebrated) 25 years later.

Perhaps that’s because it so perfectly encapsulates, like so much dirt in a jar, the time in which it was made. The '90s were the peak of pop environmentalism, and Waterworld offered a possible vision of what might await us at the far end of climate change, when the ice caps have melted and the seas have claimed the Earth.

The only problem is, it’s super wrong!

The post-apocalyptic survivors of Waterworld populate an endless global ocean, living on floating cities called atolls and telling stories of fabled remnants of dry land. The notion of land is so precious, and the water so ubiquitous, that dirt is valued as currency.

The question, then, is how much water is locked inside ice caps and glaciers? And how would the world be changed if it all melted and joined the world’s oceans?


The rotation speed of the Earth changes over time as a natural consequence of lunar pressure. That the Earth rotates at all is a leftover effect of the initial angular momentum of the solar system forming, and the planetary collision that resulted in the Moon.

The Sun and all its planets were, collectively, a vast top, set to spinning, and which still hasn't stopped. That’s great news for us. The rotation of the Earth spreads energy from the Sun over the whole of the planet, rather than concentrating it on one side, as it would if the planet didn’t spin.

The difference in the rotational period from any given year to the next is nearly negligible, but it adds up. The length of a day in the Precambrian period was only 21 hours. The lengthening of the day is partially a result of lunar pressure, but is also hypothesized to have been impacted by a sudden change in global temperatures.

The rotation of the planet would also be impacted by the continued melting of ice caps and glaciers. One factor of a body’s rotation is the distribution of mass. A body with centralized mass spins more quickly than one with its mass spread out.

With ice concentrated at the poles, that mass is held closely to the center of the Earth’s axis. As it melts, and that mass is distributed across the world’s oceans, the world will spin more slowly. While the change would be measured in milliseconds, the change in global temperature might have a significant impact in diurnal cycles, particularly when extrapolated over long time periods.


While the rising tides will most directly impact humanity by submerging large population centers (more on that later), perhaps the largest global impact of melting ice is the way it would change the world’s oceans.

The most immediately obvious impact is a change to overall ocean salinity. On the surface, this isn’t a complex problem to wrap one’s mind around. The introduction of a large amount of fresh water to a salinated environment results in the desalinization of that environment. In short, melt a bunch of freshwater ice into the oceans, and they become less salty.

This could have a drastic impact on the species that live in the ocean as that environment changes. But it isn’t that simple. Much like the rest of the world, the oceans have an overall climate that is distinct from local phenomena.

If all the world’s ice melted into the oceans, it wouldn’t distribute evenly. Instead, local areas would be most heavily impacted by the influx of fresh water. Those areas would then go on to impact neighboring areas in a global domino effect.

The world’s oceans aren’t static things; they move and flow, like the wind, based on temperature, salinity, density, and subsurface geography. The flow and exchange of water across the globe is an integral part of the health of oceanic environments.

A drastic change in salinity and temperature could change the way global waters interact in ways we don’t fully understand.

Salinity isn’t the only factor to consider, either. Adding fresh water changes the acidity of oceans and the mix of nutrients like carbonates, which some oceanic animals use to build shells.

The impact of a global ice melt could be sufficient to arrest some ocean currents entirely, eliminating the exchange of nutrients and oxygen in some parts of the ocean and further changing the global climate by reducing temperature circulation.


Of all the world’s fresh water, nearly 68.7 percent of it exists as ice. A further 30.1 percent is groundwater. Only 1.2 percent of the world’s fresh water exists as surface water.

Take all of the lakes, rivers, and streams, all of the rain you’ve ever seen, every bit of water that ever came out of your tap or went down your drain. Take all of the fresh water you’ve encountered in your life and extrapolate that throughout the rest of the world. Then multiply it by 70 and you’ve got an idea of the ice. Of course, the water you experience in your day-to-day is recycled. It isn’t all different water. Still, there’s a lot of ice in the world.

If you took the world’s ice and pressed it into cubes a mile on each side, you’d need almost six million of them to trap it all.

If you lined those cubes up between the Earth and the Moon, you could build a road a mile wide with only 4 percent of them. To use them all, that road would need to be 24 miles wide. You could circle the globe with that ice 230 times and still have some left over.

All of which is to say, the world has a lot of ice. So much ice it boggles the mind. But it’s nothing compared to the total water on Earth.

All of that ice, all of the groundwater, and all of the fresh water we use to survive accounts for only 2.5 percent of the water on Earth. Almost all the rest of it is in the oceans.

If all of the ice melted, it would certainly raise sea levels, but not as much as you might think. Some of the ice is already in the ocean. The weight of that ice displaces the same amount of water it would displace were it to melt and intermix.

This is an experiment you can confirm at home by watching ice cubes melt in a glass of water. There’s zero net change in water levels there.

The real trouble is landlocked ice. Were it to melt, that water would add to the world’s oceans and cause levels to rise.

Current estimates indicate that global sea levels would rise between 60 and 70 meters (approximately 197 to 230 feet) if every glacier and ice sheet melted, a far cry from the 25,000 feet of Waterworld. Still, it’s also important to note that as temperatures rise, water expands and takes up more space.

Even if we take the extreme end of that scale, roughly 230 feet, how would it reshape the world’s landmasses?

Jeffrey Linn, a Seattle-based cartographer, has created a series of maps looking at different locales after 200 feet of sea level rise. What’s clear in looking at these maps is that land masses still exist. The continents won’t be covered over. But that doesn’t mean rising oceans won’t wreak havoc on global populations.

Today, nearly a billion people — one seventh of the global population — occupy locales less than 10 meters above sea level. Even if we’re conservative in our estimates, those people’s homes are gone long before all of the ice is melted.

It’s likely, if we don’t combat climate change in a serious way, that large swaths of the world’s water ice will melt, change the behavior of the oceans, and swallow coastal lands. Dry land won’t be fabled or difficult to find, and the post-climate-change world won’t look much like Waterworld at all. But it won’t look like home, either.