Earth still holds more than five million cubic miles of ice. If every bit of it on land melted, the oceans would climb by roughly 65 to 70 metres (216 to 230 feet), enough to redraw every coastline on the planet. National Geographic mapped that ice-free world in its September 2013 issue, and the maps still get passed around today.
The video below walks through the same scenario, continent by continent. Here is what the numbers mean, where the ice is, and how fast the sea is actually rising.
How much would sea level rise if all the ice melted?
National Geographic’s maps assume a rise of about 216 feet (66 m). The U.S. Geological Survey gives a figure of approximately 70 metres (230 feet), “flooding every coastal city on the planet”, and adds that the total volume of the world’s glaciers and ice caps is still somewhat uncertain. The small gap between the two figures comes from different estimates of that volume.
Almost all of the water sits in two places. According to the National Snow and Ice Data Center, the two great ice sheets hold more than 99 percent of Earth’s land ice and over 68 percent of its fresh water:
- Antarctic Ice Sheet: about 14 million km², up to 4.9 km thick, around 30 million km³ of ice. Melted, it would raise the sea by about 58 m (190 ft).
- Greenland Ice Sheet: about 1.7 million km², over 3 km thick, around 2.9 million km³ of ice, worth about 7.4 m (24 ft) of sea-level rise.
Mountain glaciers in the Alps, the Himalaya, the Andes and Alaska add comparatively little to the total, though they matter enormously for the rivers and towns below them.
What the ice-free maps show, continent by continent
National Geographic’s maps paint a very different world:
- North America: the entire Atlantic seaboard, Florida and the Gulf Coast disappear. San Francisco’s hills become islands and California’s Central Valley turns into a huge bay.
- South America: the Amazon and Paraguay river basins become Atlantic inlets, wiping out Buenos Aires, coastal Uruguay and most of Paraguay.
- Europe: London and Venice are lost, the Netherlands is under water and most of Denmark is gone.
- Africa: the Mediterranean swamps Alexandria and Cairo, yet Africa loses less land than the other continents.
- Asia: land now home to 600 million Chinese floods, along with all of Bangladesh and much of coastal India.
- Australia: it gains an inland sea but loses much of the narrow coastal strip where most Australians live.
How long would it take for all the ice to melt?
This is a far-future scenario. National Geographic notes that some scientists estimate it would take more than 5,000 years to melt all the ice on Earth. In such an ice-free world, the magazine adds, the planet’s average temperature would be about 80°F (27°C), against roughly 58°F (14°C) today.
The ice sheets respond slowly, but once they start losing mass the process can continue for centuries. That is why scientists speak of sea-level rise as a long commitment: what happens this century sets the course for many centuries after.
How fast the sea is rising today
The real-world rise is measured in centimetres, and it is speeding up. The IPCC’s Sixth Assessment Synthesis Report finds that global mean sea level rose about 0.20 m between 1901 and 2018. The average rate was 1.3 mm a year from 1901 to 1971, 1.9 mm from 1971 to 2006 and 3.7 mm from 2006 to 2018, and human influence was very likely the main driver since at least 1971.
Two processes do most of the work: water expands as it warms, and melting land ice adds new water. Floating sea ice in the Arctic and around Antarctica plays almost no direct part, because it already displaces its own weight of seawater, just as a melting ice cube leaves the water level in a glass unchanged.
Even small rises matter. A few tens of centimetres make storm surges and high tides reach further inland, which is why coastal cities plan for them long before any map looks different.
For a closer view of retreating ice, explore the Svalbard glacier comparison. For ice moving on a much shorter timescale, see the King’s Point rollover video.
Related reading
- Nine Glacier Comparisons from Montana: Reading the Historic and Repeat Views
- Antarctic Sea Ice: Understanding an Older Growth Story
- Lake Hodgson: Microbial Evidence from Antarctic Sediments
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