The cryosphere is the collective term for every part of Earth’s surface where water exists in frozen form. That includes glaciers, ice sheets, sea ice, snow cover, permafrost, and ice shelves. Together, these frozen regions store about 69% of the world’s fresh water and play an outsized role in regulating global climate, ocean currents, and sea levels. Far from being static, the cryosphere is one of the most rapidly changing systems on the planet.
The Major Components
The cryosphere isn’t a single place. It spans both poles, every major mountain range, and a surprising amount of the Northern Hemisphere’s land surface. Each component behaves differently and responds to warming on its own timeline.
Ice sheets are the giants. Only two exist today: one covering Greenland and one covering Antarctica. They hold enough frozen water to raise global sea levels by more than 60 meters if they melted entirely. Ice sheets spread across vast areas of land in broad domes, and their sheer mass depresses the bedrock beneath them.
Glaciers are smaller rivers and fields of ice found on every continent except Australia. Alpine glaciers form in mountain valleys and flow slowly downhill under their own weight. Himalayan glaciers alone provide water to roughly 1.4 billion people. Across the Andes, large populations depend on glacial meltwater for both agriculture and drinking water, especially during dry seasons.
Sea ice forms when ocean water freezes. Because saltwater has a lower freezing point than fresh water, this requires especially cold conditions. Sea ice expands and contracts with the seasons, reaching its minimum extent each September in the Arctic. In 2024, that minimum measured 1.65 million square miles, roughly 749,000 square miles below the 1981–2010 average.
Permafrost is ground that remains frozen for at least two consecutive years, though much of it has been frozen for thousands. About a quarter of all Northern Hemisphere land sits on a permanently frozen underground layer. More than half of Northern Hemisphere land freezes and thaws seasonally at the surface, but permafrost beneath stays locked in place, or at least it did until recently.
Snow cover and ice shelves round out the system. Seasonal snow blankets huge areas of land each winter, and ice shelves are extensions of land ice that float out over cold ocean waters, acting as buttresses that slow the flow of glaciers behind them.
How the Cryosphere Regulates Climate
Frozen surfaces are among the most reflective on Earth, and this reflectivity, called albedo, is the cryosphere’s most powerful climate function. Fresh snow and snow-covered sea ice bounce more than 80% of incoming solar radiation back into space. Even melting summer sea ice still reflects more than 50%. Open ocean water, by contrast, reflects only about 7% and absorbs the remaining 93%.
This difference creates a feedback loop. As ice melts, it exposes darker ocean or land surfaces that absorb far more heat, which accelerates further warming, which melts more ice. The Arctic is warming roughly two to four times faster than the global average, and this albedo feedback is a major reason why. It’s a self-reinforcing cycle: less ice means more heat absorption, which means still less ice.
Permafrost and Stored Carbon
Permafrost holds an estimated 1,500 gigatons of carbon, roughly twice what the entire atmosphere currently contains. This carbon comes from plants and animals that died thousands of years ago but never fully decomposed because the ground stayed frozen. As permafrost thaws, bacteria begin breaking down that ancient organic material, releasing carbon dioxide and methane into the atmosphere. Methane is a particularly potent greenhouse gas, trapping far more heat per molecule than carbon dioxide over shorter timescales.
This creates another feedback loop. Warming thaws permafrost, which releases greenhouse gases, which drives more warming, which thaws more permafrost. Unlike burning fossil fuels, this process is largely outside human control once it begins. The speed and scale of permafrost thaw will shape how much additional warming the planet experiences in coming decades.
Ice Melt and Rising Seas
The Greenland and Antarctic ice sheets are the largest contributors to sea level rise from ice loss. Between 2012 and 2016, Greenland added about 0.68 millimeters per year to global sea levels, while Antarctica contributed roughly 0.55 millimeters per year. Combined, that’s about 1.23 millimeters annually from ice sheets alone. That may sound small, but both rates have been accelerating. Antarctica’s contribution during that period was roughly four times higher than it was in the 1990s.
Sea level rise isn’t just about volume. Glaciers and ice sheets also shift water from land into the ocean, altering coastlines, increasing flooding risks, and threatening low-lying island nations. The effects compound over time: even modest annual increases translate into significant coastal changes over decades.
Disruption of Ocean Currents
When ice sheets melt, they release enormous volumes of fresh water into the ocean. Fresh water is less dense and less salty than seawater, and this matters because the ocean’s major circulation systems depend on differences in water density to drive deep currents. In the North Atlantic, cold, salty water sinks to great depths and flows southward, pulling warm tropical water northward at the surface. This conveyor belt, known as the Atlantic Meridional Overturning Circulation (AMOC), distributes heat across the planet and shapes weather patterns on multiple continents.
Greenland’s meltwater is already slowing this system. The influx of lighter fresh water interferes with the sinking process that drives the circulation. Modeling studies show the AMOC declines gradually as Greenland melt rates increase, but at very high melt rates it can collapse entirely. A weakened or collapsed AMOC would cool northern Europe, shift tropical rainfall patterns, and alter marine ecosystems across the Atlantic.
Effects on Wildlife and Ecosystems
Sea ice is not just frozen water. It’s a habitat. Ice algae that grow on the underside of sea ice form the base of the Arctic food web, supporting everything from tiny crustaceans to fish, seals, and polar bears. As ice cover shrinks and its seasonal patterns shift, the balance between ice algae and open-water plankton changes, sending ripple effects through the entire food chain.
Warming is compressing the habitat range for species adapted to cold conditions. At the same time, less-specialized species from southern regions are moving northward into territory that was previously too cold. This shift changes competitive dynamics and can displace native Arctic species. The pattern holds on land as well: permafrost thaw destabilizes the ground beneath forests, infrastructure, and tundra ecosystems that evolved on stable frozen soil.
How Scientists Track Changes
Monitoring the cryosphere requires satellites because much of it covers remote, inaccessible terrain. NASA’s ICESat-2, launched in September 2018, carries a laser altimeter that splits into six beams and measures the elevation of ice sheets, glaciers, and sea ice in detailed 3-D. It fires photon-counting laser pulses at Earth’s surface and times how long they take to bounce back, generating precise elevation maps that reveal how ice thickness is changing year to year.
Gravity-measuring satellites track changes in ice mass by detecting tiny shifts in Earth’s gravitational field as ice is gained or lost. Together, these tools give scientists a continuous, global picture of how much ice exists, how quickly it’s changing, and where the most significant losses are occurring. The satellite record for Arctic sea ice now extends back to 1978, providing more than four decades of data to measure long-term trends against.
Water Supply for Billions
Beyond climate regulation, the cryosphere directly sustains human life. Glacier-fed rivers supply water for farming, energy production, drinking water, and tourism across Asia, South America, and parts of Europe. In the Himalayas, glacial meltwater supports roughly 1.4 billion people. Across the Andes, entire communities depend on seasonal glacier runoff during dry months when rain is scarce.
As glaciers shrink, they initially release more meltwater, which can temporarily increase river flows. But once a glacier retreats past a tipping point, flows decline permanently. Communities that depend on that water face growing shortages, particularly during the dry seasons when they need it most. The timeline varies by region, but many glacier-fed river systems are already showing signs of peak water having passed or approaching within the next few decades.