The entire Earth will not flood in the way depicted in disaster movies, where water covers every continent. There simply isn’t enough ice and water on the planet to submerge all land. But large-scale flooding of coastal regions is already happening and will intensify significantly over the coming decades. The real question isn’t whether water will cover the globe, but how much of the world’s coastlines, cities, and low-lying countries will be swallowed by rising seas.
Why a Total Global Flood Is Physically Impossible
If every glacier, ice cap, and ice sheet on Earth melted completely, global sea levels would rise by about 195 feet (60 meters). That’s an enormous amount of water, enough to redraw the map of every continent and displace billions of people. But Earth’s highest point sits at over 29,000 feet, and the average elevation of land is roughly 2,750 feet above sea level. Even in the most extreme scenario imaginable, more than 80% of current land area would remain above water.
It also matters what kind of ice melts. Ice that’s already floating in the ocean, like Arctic sea ice and icebergs, barely changes sea level when it melts. This works the same way an ice cube in a glass doesn’t cause the water to overflow as it melts: the ice was already displacing its weight in water. The ice that drives sea level rise sits on land, primarily in Greenland and Antarctica, where gravity pulls meltwater downhill into the ocean, adding new volume.
How Fast Seas Are Actually Rising
Satellite measurements since 1993 show that global sea levels have risen by about 111 millimeters (roughly 4.4 inches) over three decades. That sounds small, but the pace is accelerating. In 1993, seas were rising at about 2.1 millimeters per year. By 2023, that rate had more than doubled to approximately 4.5 millimeters per year. The trend line is curving upward, not holding steady.
Two main forces drive this rise. Ice sheet melt and thermal expansion (the ocean physically expanding as it warms) together account for about two-thirds of the total. Mountain glaciers melting add another 20%, and changes in how water is stored on land, through groundwater pumping and reservoir management, contribute the remaining 10%.
What the Projections Say for 2100
The latest international climate projections estimate sea levels will rise somewhere between about 0.3 meters (1 foot) and 1 meter (3.3 feet) by the year 2100, depending on how aggressively the world cuts emissions. Under the most extreme warming scenario, the upper range stretches to 1.6 meters (5.2 feet) when accounting for less likely but possible outcomes like rapid ice sheet collapse.
One or two meters may not sound catastrophic on a planetary scale, but it’s devastating at ground level. Coastal flooding that used to happen once a century starts happening every few years. Storm surges push farther inland. Saltwater infiltrates freshwater supplies. Cities like Miami, New Orleans, and New York all have neighborhoods sitting at or just above sea level. Globally, hundreds of millions of people live in coastal zones below 10 meters of elevation. For them, even a fraction of a meter changes daily life.
The Tipping Points That Could Make It Worse
The scariest scenarios involve ice sheets crossing thresholds where their collapse becomes self-sustaining, meaning it continues even if warming stops. The West Antarctic Ice Sheet is the most closely watched. Research suggests that only a small amount of additional ocean warming beyond present-day temperatures could trigger its collapse, which would eventually add over 4 meters (13 feet) to global sea levels over the following centuries. Once that tipping point is crossed, it appears very unlikely to be reversed.
Greenland’s ice sheet holds enough frozen water to raise seas by 7.4 meters (24 feet) if it melted entirely. That won’t happen overnight. Complete melting would take centuries to millennia. But Greenland is already losing ice at an accelerating rate, and every fraction of a degree of warming locks in more loss.
Earth Has Done This Before
During the last interglacial period, roughly 125,000 years ago, global temperatures were only slightly warmer than today. Sea levels stood at least 3 meters higher than current levels, and probably more than 5 meters higher. Most of that extra water likely came from a significantly smaller Greenland ice sheet, which may have contributed 4 to 5.5 meters on its own. This matters because it shows the planet doesn’t need dramatic warming to produce dramatic sea level changes. The ice responds to sustained warmth over time, not just peak temperatures.
What This Means in Practical Terms
The Earth won’t be swallowed by an ocean. The continents aren’t going anywhere. But the coastline you see on a map today will not be the coastline your grandchildren know. Over the next century, rising seas will permanently flood low-lying islands, reshape river deltas, and force the relocation of coastal infrastructure worldwide. Over longer timescales of several centuries, if major ice sheets destabilize, the changes become far more severe.
The degree of flooding depends almost entirely on how much warming occurs in the coming decades. At lower warming levels, humanity faces manageable but costly adaptation. At higher levels, the loss of the West Antarctic and Greenland ice sheets becomes increasingly likely, committing the planet to meters of sea level rise that will play out over hundreds of years. The flooding won’t look like a single catastrophic wave. It will look like shorelines creeping inland, year after year, in a process that has already begun.