Ice caps are thick, dome-shaped masses of glacial ice that cover less than 50,000 square kilometers of land. They form over thousands of years as snow accumulates, compresses, and slowly transforms into dense ice. Found primarily in polar and subpolar regions, ice caps sit on top of mountains and highland areas, spreading outward under their own weight much like a drop of thick batter on a countertop. They are smaller relatives of the massive ice sheets covering Greenland and Antarctica, but they play an outsized role in storing freshwater, reflecting sunlight, and influencing sea levels worldwide.
How Ice Caps Differ From Ice Sheets
The dividing line between an ice cap and an ice sheet is surface area. Any dome-shaped body of glacial ice smaller than 50,000 square kilometers qualifies as an ice cap. Only two ice sheets exist on Earth today: the Greenland Ice Sheet and the Antarctic Ice Sheet, both far exceeding that threshold. The National Snow and Ice Data Center describes ice caps as “essentially miniature ice sheets” because they share the same dome-like shape and outward-flowing movement.
One key difference is how the underlying landscape affects each one. Ice sheets are so massive and thick that they overwhelm the terrain beneath them, flowing outward from their centers regardless of what the ground looks like underneath. Ice caps, being thinner and smaller, tend to follow the contours of the mountains and highlands they sit on. The shape of the bedrock beneath an ice cap has a much stronger influence on where and how fast the ice moves.
How Ice Caps Form
Ice caps begin as snowfields in regions where more snow falls each winter than melts each summer. When a layer of snow survives an entire melt season, it compresses into a denser material called firn. Each new year of snowfall buries and further compacts the layers below. Over time, the snow grains merge into larger ice crystals, and the air spaces between them shrink.
As the weight of overlying snow increases, the remaining air gets squeezed into tiny, isolated bubbles. At depths of hundreds of meters, even those bubbles disappear into the crystal structure of the ice itself. The result is dense glacial ice that still contains traces of trapped ancient air, which is why scientists can drill ice cores to study atmospheric conditions from thousands of years ago. Once enough ice accumulates, gravity causes it to spread outward from its thickest point, forming the characteristic dome shape.
Where Ice Caps Are Found
The world’s ice caps cluster in high-latitude and high-altitude regions. The Canadian Arctic archipelago hosts several large ice caps, including the Devon Ice Cap, one of the most studied in the world. Iceland is home to Vatnajökull, the largest ice cap in Europe, covering roughly 8,100 square kilometers with ice up to 900 meters thick. Norway’s Svalbard archipelago, situated between mainland Norway and the North Pole, contains numerous ice caps and glaciers. Arctic Russia and Alaska also hold significant ice masses, though many of Alaska’s are classified as ice fields rather than true dome-shaped ice caps.
Outside the Arctic, smaller ice caps exist on high mountain plateaus in places like Patagonia and parts of Central Asia. But the vast majority of the world’s ice cap volume sits in polar regions, where cold temperatures and consistent snowfall sustain them year-round.
Freshwater Storage and Water Supply
About three-quarters of Earth’s freshwater is locked in glacial ice, making glaciers and ice caps the planet’s largest freshwater reservoir. Roughly 2.1% of all water on Earth, including saltwater, exists in frozen form. If every glacier and ice cap on the planet melted completely, global sea levels would rise approximately 70 meters, or about 230 feet.
Beyond that dramatic scenario, ice caps serve a quieter but critical role as seasonal water sources. As surface ice melts during warmer months, meltwater feeds rivers, lakes, and coastal fjords. Communities in Iceland, Norway, and parts of South America depend on glacial meltwater for drinking water, agriculture, and hydroelectric power. The steady, predictable release of meltwater through spring and summer acts like a natural reservoir, supplementing rainfall during drier periods.
How Ice Caps Regulate Climate
Ice caps help cool the planet through a process called the albedo effect. Their bright white surfaces reflect a large portion of incoming sunlight back into space, preventing that energy from being absorbed by the Earth’s surface. It works the same way a white shirt keeps you cooler on a sunny day compared to a black one.
When ice caps shrink, they expose darker land or ocean surfaces underneath, which absorb more heat instead of reflecting it. That additional heat causes more warming, which melts more ice, which exposes more dark surface, creating a feedback loop that accelerates warming. Soot and dust landing on ice surfaces can also lower reflectivity, causing the ice to absorb more heat and melt faster even before the ice disappears entirely.
Ecosystems Tied to Ice Caps
The meltwater flowing from ice caps shapes biological communities downstream. In polar fjords, glacial meltwater carries nutrients and minerals that influence which species of phytoplankton thrive at the base of the food web. These microscopic organisms support everything from zooplankton to fish to seabirds and marine mammals. Researchers at the Scripps Polar Center have found that the presence or absence of glacial meltwater directly changes the composition of phytoplankton communities in surrounding waters.
On land, the edges of ice caps create unique habitats where cold-adapted plants and insects colonize freshly exposed ground as ice retreats. Polar organisms have evolved their life cycles around the seasonal rhythm of freezing and melting, making them especially vulnerable when that rhythm shifts. High-latitude regions support surprisingly rich biological activity and high rates of productivity, much of it closely tied to ice dynamics.
Ice Loss and Sea Level Rise
Ice caps around the world are losing mass at an accelerating rate. Between 2000 and 2023, the world’s glaciers and ice caps (excluding the Greenland and Antarctic ice sheets) lost a combined 6,542 billion metric tons of ice. That contributed roughly 18 millimeters to global sea level rise over those 23 years, averaging about 0.75 millimeters per year. While that sounds small, glacier melt accounts for about 20% of observed sea level rise, a larger share than even the Greenland Ice Sheet contributes.
The rate is getting worse. Mass loss increased by 36% between the first half of the record (2000 to 2011) and the second half (2012 to 2023). The 2024 hydrological year saw 450 billion tons of ice loss globally, the fourth most negative year on record and the third consecutive year in which every glacier region on the planet lost ice. Alaska and Arctic Canada are the hardest-hit regions, losing roughly 66 and 63 billion tons per year respectively. Iceland, Arctic Russia, and Svalbard each lose between 9 and 14 billion tons annually.
For coastal communities, these numbers translate into real consequences: higher storm surges, more frequent flooding, and gradual inundation of low-lying areas. For inland communities that depend on glacial meltwater, the short-term effect is actually increased water flow as ice melts faster. But once an ice cap shrinks past a critical point, that water supply diminishes permanently.