What if all ice on Earth melted: sea level rise and what it would mean

01How much ice is on Earth and where it is

Earth holds approximately 30 million cubic kilometers of ice, distributed across two massive ice sheets and thousands of smaller glaciers and ice caps. The two currently existing ice sheets are the Antarctic ice sheet and the Greenland ice sheet. The Antarctic ice sheet alone contains roughly 26.5 million cubic kilometers of ice, accounting for about 61 percent of all fresh water on Earth. If it melted entirely, it would raise global sea levels by approximately 58 meters.

The Greenland ice sheet contains roughly 2.9 million cubic kilometers of ice, which would contribute about 7.4 meters to sea level rise if it melted completely. Though smaller than Antarctica, Greenland is melting faster relative to its size, and its contribution to current sea level rise is already significant. Greenland is losing ice at an accelerating rate, with mass loss doubling approximately every decade since the 1990s.

Mountain glaciers and ice caps, though much smaller in total volume than the two ice sheets, contribute roughly 0.4 meters of potential sea level rise. While their contribution to total sea level rise is modest, these glaciers are critical for regional water supplies and ecosystems. The loss of mountain glaciers affects communities from the Andes to the Himalayas, where glacial meltwater provides drinking water, irrigation, and hydroelectric power.

02What sea level rise would look like

If all ice on Earth melted, global sea levels would rise by approximately 70 meters. This would not happen overnight, but the result would be transformative. Every coastline on Earth would shift inland by tens to hundreds of kilometers, depending on the slope of the continental shelf. Low-lying regions like Florida, Bangladesh, the Netherlands, and most of the world's major river deltas would be submerged entirely.

The sea level has generally been rising since the end of the Last Glacial Maximum, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by 15 to 25 centimeters, with an increase of 2.3 millimeters per year since the 1970s. This was faster than the sea level had ever risen over the preceding several thousand years. Current projections suggest sea levels could rise by 0.3 to 1.0 meters by 2100, depending on emissions scenarios.

A 70-meter sea level rise would redraw the world map. The Mediterranean Sea would expand into North Africa, creating a vast inland sea across what is now the Sahara. The Amazon basin would become a shallow sea. Most of northern Europe would vanish beneath the waves, and Australia would be split into multiple islands. The loss of coastal infrastructure, including ports, power plants, and desalination facilities, would trigger a global economic crisis.

03Which cities would be submerged first

Coastal cities are the most immediately vulnerable to sea level rise. At just 1 meter of rise, cities like Miami, New Orleans, Venice, and Jakarta would face chronic flooding. At 3 meters, large portions of Miami, Mumbai, and Shanghai would be underwater at high tide. By 10 meters, most of Florida, the Netherlands, Bangladesh, and the Nile Delta would be submerged.

The horizontal bar chart below shows the sea level rise threshold at which major coastal cities would be significantly affected. Cities at lower elevations are at risk sooner, while those with higher ground have more time to adapt. The data underscores that even modest sea level rise poses existential threats to some of the world's most populous urban areas.

The displacement of populations would dwarf any migration in human history. Bangladesh, with a population of over 170 million, lies mostly at elevations below 10 meters. The mass migration of coastal populations to higher ground would strain the resources of inland regions and could destabilize entire countries. The economic cost of relocating or abandoning coastal cities would run into the tens of trillions of dollars.

04The timeline for ice melt under current projections

Complete melting of all ice on Earth would take thousands of years under even the most extreme warming scenarios. However, the rate of ice loss is accelerating, and the threshold for irreversible ice sheet collapse may be much closer than the timeline for complete melt. Research suggests that the Greenland ice sheet could reach a tipping point at approximately 1.5 to 3 degrees Celsius of warming, beyond which it would continue melting regardless of future emissions.

Present-day climate change includes both global warming, the ongoing increase in global average temperature, and its wider effects on Earth's climate system. Even if warming is limited to the Paris Agreement target of 1.5 degrees Celsius, some ice loss is already locked in. The question is not whether sea levels will rise, but how fast and how much.

Under current emissions trajectories, sea levels are projected to rise by 0.3 to 1.0 meters by 2100. Higher estimates, accounting for potential ice sheet instability, suggest rises of up to 2 meters are possible. Beyond 2100, sea levels would continue rising for centuries, even if emissions are halted, due to the thermal inertia of the oceans and the slow response of ice sheets to warming.

05How ocean currents would change

Melting all ice on Earth would not just raise sea levels. It would fundamentally alter ocean circulation. The influx of fresh water from melting ice sheets would reduce the density of surface waters in the North Atlantic, potentially weakening or shutting down the Atlantic Meridional Overturning Circulation, or AMOC. This current transports warm water from the tropics to the North Atlantic, and its disruption would dramatically cool Europe while altering weather patterns worldwide.

A complete shutdown of the AMOC would shift the global climate in ways that are difficult to fully predict. The North Atlantic region, including Western Europe, would experience significant cooling, even as the rest of the planet warms. The monsoon systems of Africa and Asia could be disrupted, affecting food production for billions of people. The Southern Ocean would also see changes in circulation as Antarctic meltwater alters deep water formation.

The ocean absorbs about a quarter of the carbon dioxide emitted by human activity, and changes in circulation would affect this absorption. A weakened AMOC could reduce the ocean's capacity to absorb carbon, accelerating atmospheric warming. The combined effects of sea level rise, circulation changes, and altered carbon uptake would create a feedback loop that could amplify the warming that caused the ice melt in the first place.

06The impact on weather patterns

A world without ice would have fundamentally different weather patterns. Without the bright, reflective surface of polar ice and snow, Earth would absorb more solar energy, raising global temperatures further. This albedo feedback is one of the most powerful amplifiers in the climate system. The loss of Arctic sea ice, which is already accelerating, is reducing the planet's reflectivity and contributing to Arctic warming at roughly four times the global average rate.

The disappearance of ice sheets would also affect regional climates. The Antarctic and Greenland ice sheets are cold, high-altitude features that influence atmospheric circulation. Their removal would alter the position of jet streams, the tracks of storm systems, and the distribution of rainfall. Some regions would become wetter while others would experience drought.

The loss of mountain glaciers would also have immediate weather and hydrological impacts. Many regions depend on glacial meltwater for dry-season water supplies. Without glaciers, these regions would face water scarcity during the summer and autumn, affecting agriculture, hydropower, and drinking water availability. The transition from glacial to non-glacial hydrology would reshape water management for billions of people.

07What the worst case scenario actually means

The worst case scenario, in which all ice on Earth melts, is not a prediction. It is an exploration of the maximum possible sea level rise and its consequences. Under any realistic emissions pathway, this would take thousands of years. But the path we choose in the coming decades determines how much ice is ultimately lost and how quickly the oceans rise.

What makes the worst case concerning is not its immediacy but its irreversibility. Once an ice sheet collapses past its tipping point, the process becomes self-sustaining, and even returning to pre-industrial temperatures may not stop it. This is why scientists are focused on identifying tipping points and understanding the thresholds beyond which ice loss becomes unstoppable.

The practical implication is that every fraction of a degree of warming matters. The difference between 1.5 and 2 degrees of warming may determine whether the Greenland ice sheet reaches its tipping point. The difference between 2 and 3 degrees may determine the fate of the West Antarctic ice sheet. The choices made in the next few decades will shape coastlines for thousands of years.