What If All the Ice on Earth Melted?

If every bit of ice on Earth melted, global sea level would rise about 70 meters, or roughly 230 feet. That's enough water to drown most of the world's coastal cities. The good news is a full melt would take thousands of years; the catch is that even a partial melt is already reshaping coastlines this century.

Where all that ice actually is

Most of Earth's frozen water isn't floating sea ice, it's locked away on land in two giant sheets. Antarctica holds the lion's share, with Greenland a distant but still enormous second.

Melting floating ice barely nudges sea level, the same way a melting ice cube doesn't make your glass overflow. It's the land ice sliding into the ocean that adds the 70 meters, because that water wasn't in the sea to begin with.

The numbers are staggering. Antarctica's ice alone is over a mile thick in places and holds enough water to raise the oceans by around 58 meters by itself, with Greenland good for roughly another 7. Everything else, every mountain glacier on the planet, makes up only the small remainder.

Which cities go under

A 70-meter rise redraws the map. Coastlines retreat inland by miles, and the low, flat places where billions of people live disappear first.

These aren't fringe towns. They're some of the most populated, economically critical places on the planet, and a lot of them sit just a few meters above today's sea level.

• New York, London, Shanghai, and Mumbai: largely submerged.
• The entire state of Florida: gone.
• Bangladesh and most of the Netherlands: underwater.
• Venice, Miami, and New Orleans: among the first to vanish.

The slow version is the real story

A complete melt would unfold over millennia, not headlines. Ice sheets that big take a very long time to disappear entirely, even under heavy warming.

But you don't need all of it gone to feel it. Even a few feet of rise this century floods subway tunnels, salts farmland, and pushes storm surges deeper into cities that were never built for it.

We won't wake up underwater. We'll wade in slowly, one high tide at a time.

What it would do to the rest of the planet

Sea level is only part of it. Dumping that much freshwater into the oceans would scramble the currents that move heat around the globe, shifting weather patterns far inland from any coast.

Reflective white ice also bounces sunlight back to space. Lose it, and darker land and water soak up more heat, which speeds up the warming that started the melt in the first place. That feedback loop is part of why scientists watch the ice so closely.

Could we ever reverse it?

Once an ice sheet collapses, it doesn't snap back. Regrowing ice on that scale needs thousands of years of sustained cold, which the planet isn't trending toward.

That's the uncomfortable part of the thought experiment. The melt is slow on a human timescale but effectively permanent on a civilizational one, so the coastlines we draw now are closer to a one-way door than a dial we can turn back.

What it would look like from space

The planet would change color. The bright white caps at the poles that you can spot from orbit would be gone, replaced by the dark blue of open ocean and newly exposed rock.

The familiar shapes of the continents would soften and shrink, with bays pushing far inland and chains of islands swallowed entirely. Maps drawn today would be useless, the way ancient coastlines no longer match the modern ones.

It's a striking way to grasp the scale. We're not talking about a beach losing a few feet of sand; we're talking about a different-looking world, one whose outline a future astronaut wouldn't recognize from our photos.

Even the land that stayed dry would feel the change. Forests and farmland near the new coast would slowly turn to salt marsh, deserts would shift as rainfall patterns moved, and the places that stay livable might sit hundreds of miles from where the biggest cities are today.

Try It Yourself

Want to mess around with the ideas above? On whatifs.fun, Carbon Footprint, Ocean Depth and Weather Maker all let you do exactly that — free, in your browser, no download.

Keep reading: how to shrink your carbon footprint and how much water is on Earth. Both go deeper on the same rabbit hole.