A continental glacier, also known as an ice sheet, is a massive body of glacial ice that covers an expansive area of land, flowing outward under its own weight. To qualify as a true continental glacier, the ice mass must cover more than 50,000 square kilometers, completely obscuring the underlying topography. This distinguishes them from smaller alpine or mountain glaciers, which are confined by mountain valleys. Continental glaciers are the largest single masses of ice on Earth and hold the vast majority of the planet’s freshwater. Today, only two such bodies of ice remain.
The Antarctic Ice Mass
The Antarctic Ice Sheet covers approximately 14 million square kilometers, nearly 98% of the continent. It is estimated to contain about 61% of all the planet’s fresh water, with an average ice thickness exceeding two kilometers.
The Antarctic Ice Sheet is divided into two major sections separated by the Transantarctic Mountains: the East Antarctic Ice Sheet (EAIS) and the West Antarctic Ice Sheet (WAIS). The EAIS is the larger and more stable, grounded mostly on bedrock above sea level. This eastern section holds enough water to raise global sea levels by over 50 meters.
The WAIS is a marine-based ice sheet, meaning much of its base rests on bedrock far below sea level. This grounding makes the West Antarctic portion more dynamic and vulnerable to warming ocean currents. The WAIS is currently losing mass rapidly from major outlet glaciers like Thwaites and Pine Island, and its total melt would result in a global sea level rise of approximately 3.3 meters.
The Greenland Ice Giant
The Greenland Ice Sheet is the second-largest ice mass globally. It blankets about 1.7 million square kilometers, covering roughly 80% of Greenland’s landmass. The ice forms a vast, high dome, with the thickest parts exceeding three kilometers in depth.
Though smaller than its Antarctic counterpart, the Greenland Ice Sheet is a major feature of the northern hemisphere. The weight of the ice depresses the central landmass far below sea level. It is the primary source of freshwater flowing into the North Atlantic, influencing ocean currents across the globe.
Its location in the Arctic makes it highly sensitive to atmospheric warming, and it has been losing mass at an accelerating rate. If the Greenland Ice Sheet were to melt completely, it would contribute an estimated seven meters to global sea level rise. The ice flows outward through fast-moving outlet glaciers that calve icebergs directly into the surrounding fjords and ocean.
Why These Glaciers Matter Globally
The continental ice sheets in Antarctica and Greenland regulate the planet’s climate and ocean systems. Their enormous white surfaces reflect a significant portion of the sun’s energy back into space, known as the albedo effect, helping to keep global temperatures lower. The introduction of cold freshwater from melting glaciers also affects ocean density and salinity.
Meltwater from the Greenland Ice Sheet can impact the Atlantic Meridional Overturning Circulation (AMOC), a major system of ocean currents that transfers heat northward. A slowdown of the AMOC could lead to significant shifts in weather patterns in the North Atlantic region. The most immediate global concern is the potential for sea level rise.
The combined volume of ice stored in these two ice sheets is enough to raise the global mean sea level by over 70 meters. These glaciers are also invaluable natural archives. Ice cores drilled deep into the sheets contain trapped air bubbles and layers that record hundreds of thousands of years of past atmospheric composition, providing scientists with a long-term record of Earth’s climate history.