The Greenland Ice Sheet (GIS) is the second-largest mass of ice on Earth, covering approximately 80% of Greenland’s landmass. This massive reservoir holds a colossal volume of water. Contemplating the hypothetical complete melting of this ice sheet illustrates the profound scale of potential climate change consequences. Such a scenario helps visualize the immense impact on coastlines worldwide and the future habitability of low-lying regions.
Defining the Global Sea Level Impact
If the entire Greenland Ice Sheet melted, the resulting influx of water would raise the global average sea level by approximately 23 to 24 feet (about 7.2 meters). However, the actual impact would not be uniformly distributed across the globe. Local sea level changes are influenced by complex factors, including the gravitational effect of the ice mass. As the ice sheet shrinks, its gravitational pull lessens, causing a slight drop in sea level near Greenland. Conversely, regions far from Greenland would experience a disproportionately larger rise than the global average.
Geographical Factors Determining Vulnerability
The threat posed by a 24-foot sea level rise is heavily dictated by the local geography of coastal areas. Cities built on low-lying coastal plains or expansive river deltas are inherently the most susceptible to complete inundation. These regions often have minimal natural elevation above the current sea line, making them unable to withstand a massive permanent water level increase.
Several critical factors compound this vulnerability. Land subsidence, the sinking of the ground beneath a city, is often caused by the excessive extraction of groundwater. When land is actively sinking, the effective sea level rise is compounded, drastically reducing the elevation buffer. Furthermore, cities built on soft sediments are less resilient than those on bedrock.
Major Cities Facing Complete Submergence
A 24-foot global rise would fundamentally redraw the map of human civilization, submerging vast swathes of densely populated coastal territory. The following major population centers would face complete inundation:
- Asian megacities built on low-elevation river deltas, including Shanghai (Yangtze River delta), Ho Chi Minh City (Saigon River), and Dhaka, Bangladesh.
- North American coastal cities along the eastern and Gulf coasts, such as Miami, which would vanish due to Florida’s low-lying nature.
- New Orleans, which is already largely below sea level and would be entirely submerged despite existing levee systems.
- New York City, where large portions of Manhattan and surrounding boroughs would be inundated.
- European cities, including Amsterdam, where existing defenses would be breached, and London, which would be permanently flooded via the Thames Estuary.
- Venice, the ancient, canal-dependent city, which would disappear entirely beneath the Adriatic Sea.
The Projected Timeline of Complete Melting
While the consequences of a fully melted Greenland Ice Sheet are catastrophic, this total loss is not expected to occur within the next few decades. Scientific projections indicate that complete melting would unfold over an extended geological timescale, spanning centuries to millennia. Under current climate trajectories, the full disappearance of the GIS is estimated to take between 1,000 and 10,000 years. The ice sheet is already losing mass at an accelerated rate, contributing measurably to current sea level rise each year. However, the sheer volume and thickness of the remaining ice mean that the process of total melt is necessarily slow, requiring sustained warming over many generations.