If all the ice on Greenland and Antarctica melted, global sea levels would rise an estimated 67 meters (about 223 feet), enough to submerge every coastal city on Earth. A full melt like that would take centuries or millennia, but the process is already underway, and even partial melting triggers a cascade of consequences for weather, ecosystems, economies, and hundreds of millions of people.
How Much Ice Exists and How Fast It’s Disappearing
The Greenland and Antarctic ice sheets hold more than 99 percent of Earth’s freshwater ice. Greenland alone lost an average of 219 billion metric tons of ice per year between 2003 and 2024. The 2025 measurement came in at 129 billion metric tons, less than the recent average but still continuing decades of net loss. Antarctica follows a similar pattern, shedding mass at an accelerating rate.
These numbers sound abstract, but each lost gigaton becomes meltwater flowing into the ocean. The ice sheets are enormous, so even at current rates a full collapse would take a very long time. The danger is that warming doesn’t have to melt all the ice to cause serious problems. Every fraction of a meter of sea level rise reshapes coastlines, and the melting itself triggers feedback loops that speed up further warming.
The Tipping Point Problem
Ice sheets don’t melt in a straight line. They can reach tipping points where the loss becomes self-sustaining and irreversible, even if temperatures stop climbing. For the Greenland ice sheet, early model simulations place that critical threshold somewhere between 0.8°C and 3.2°C of warming above preindustrial levels, with a best estimate around 1.6°C. The planet has already warmed roughly 1.2°C, which means the margin before crossing that line is uncomfortably thin.
Once a tipping point is crossed, the ice sheet’s own geometry works against it. As the surface drops to lower, warmer altitudes, melting accelerates even without additional warming from the atmosphere. This is why scientists track these thresholds so closely: they represent a point of no return for ice that took tens of thousands of years to accumulate.
Why Losing Ice Makes Warming Worse
Ice and snow reflect up to 90 percent of incoming solar radiation back into space. Open ocean, by contrast, absorbs about 95 percent of that energy. So when ice melts and exposes dark water, the ocean soaks up far more heat, which melts more ice, which exposes more water. This is called the ice-albedo feedback, and it’s one of the most powerful accelerators of climate change.
A second feedback loop sits in the ground beneath the ice. Arctic permafrost holds an estimated 1,024 billion metric tons of carbon in just the top three meters of soil, with hundreds of billions more in deeper frozen sediments. As ice cover disappears and permafrost thaws, microbes begin breaking down that ancient organic material, releasing carbon dioxide and methane. Modeling suggests this process could release between 25 and 85 billion metric tons of carbon over the 21st century, depending on how much warming occurs. Methane emissions from high-latitude regions are projected to roughly double, jumping from 34 to as high as 70 million metric tons per year. This released carbon then drives more warming, which thaws more permafrost.
What Happens to Ocean Currents
The Atlantic Ocean has a massive circulation system that works like a conveyor belt, carrying warm water northward near the surface and cold, dense water back south along the ocean floor. This system depends on water in the North Atlantic becoming cold and salty enough to sink. Freshwater pouring off the Greenland ice sheet dilutes that salinity, making the water lighter and less likely to sink. The result is a slowdown, or potentially a collapse, of this circulation pattern.
This has happened before. At the end of the last ice age, a massive pulse of meltwater flooded the North Atlantic, disrupting the current. The Northern Hemisphere cooled dramatically while the Southern Hemisphere warmed, all within a matter of decades. A modern disruption could cool parts of Europe, shift tropical rain belts southward, cause droughts across Africa’s Sahel region, and even flip the wet and dry seasons in the Amazon. Sea levels along the U.S. East Coast would rise faster than the global average because the current normally pulls water away from the coastline. Storms would intensify.
Sea Level Rise and Human Displacement
You don’t need 67 meters of sea level rise to displace millions of people. Research modeling a range of scenarios through 2100 estimates that between 4 million and 72 million people will be forced to migrate inland as coastal flooding makes their homes uninhabitable. That range depends on how much emissions continue and how much coastal protection is built. Without any new flood defenses, the number jumps to between 49 and 250 million people.
The areas most vulnerable include low-lying island nations in the Pacific, river deltas in Bangladesh and Vietnam, and densely populated coastal cities worldwide. Land loss projections range from 2,800 to 490,000 square kilometers, an area that at its upper end approaches the size of Spain. The economic toll is staggering: under a high-emissions scenario with no new defenses, coastal flooding could threaten up to $14.2 trillion in buildings, roads, and infrastructure, equivalent to roughly 20 percent of projected global GDP in 2100.
Arctic Wildlife Losing Its Platform
For species that depend on sea ice, melting doesn’t just change the scenery. It removes the foundation of their survival. Polar bears hunt seals from ice platforms. Ringed seals need early-forming ice with enough accumulated snow to build the dens where they raise their pups. Bearded seals depend on ice positioned over shallow waters where they can reach food on the ocean floor. Walruses haul out on ice to rest between feeding dives.
These are classified as ice-obligate species, meaning ice isn’t just helpful for them but essential. The statistical relationship between polar bear population numbers and the duration of sea ice cover has been strong enough to forecast the species’ decline. As ice seasons shorten, mothers have less time to hunt, pups face longer swims between ice floes, and the entire food web built around the ice edge unravels. Some seasonally migrating species may benefit from more open water, but for ice-dependent animals, there is no substitute habitat.
A Slower Spin for the Planet
One consequence most people never consider: melting ice actually changes how fast the Earth rotates. When ice sitting at the poles melts and the water redistributes toward the equator, it’s like a spinning ice skater lowering their arms. The planet’s rotation slows. NASA-funded research found that since 2000, days have been getting longer at a rate of about 1.33 milliseconds per century, faster than at any point in the previous hundred years.
That’s not enough to notice in daily life, but it matters for precision technologies like GPS satellites and global communication networks that rely on exact timekeeping. It’s also a measurable fingerprint of just how much mass is shifting across the planet’s surface as ice disappears.