What is the Cryosphere?
What is the cryosphere?
The cryosphere refers to the regions on Earth where water freezes into snow or ice. The term comes from the Greek word for icy cold—krios. Features of the cryosphere include:
- frozen ground and permafrost
- glaciers, which include alpine glaciers, ice caps, and the ice sheets that cover Greenland and Antarctica
- ice shelves and icebergs
- sea ice
The cryosphere spreads out all around the world. In some areas, it exists seasonally in the form of snowfall and frozen rivers, lakes, or ground. In the Arctic and Antarctic, sea ice shrinks in spring and summer and expands in fall and winter. Still, parts of the cryosphere have not thawed for hundreds of thousands of years.
Snow is precipitation made up of ice crystals. When low temperatures and high humidity levels combine in the atmosphere, ice crystals grow—typically in clouds. These tiny crystals often stick together. When the crystals get heavy enough, they fall as snowflakes.
- Snow falls all over the world, even near the equator at high elevations.
- Snow’s bright white color reflects sunlight, cooling the planet, and affecting climate.
- Snow provides an insulating layer during winter, under which plants and animals can survive the coldest months.
- Snow provides water for agriculture, people, plants, and animals.
- Where it is cold enough for year-to-year snow accumulation, a glacier may form.
Ice forms when temperatures drop below the freezing point and liquid water becomes a solid, creating a tightly bonded substance. Ice is the key component of glaciers, sea ice, ice shelves, icebergs, and frozen ground.
- Naturally occurring ice exists all over the world, but mostly forms in the high latitudes, at high elevations, or at night when temperatures drop below freezing.
- Ice is less dense than liquid water, allowing it to float in oceans, lakes, and rivers. As global temperatures increase, however, many of these water bodies may lose their ice cover.
- Ice provides water for people, animals, and plants.
- Where snow has accumulated for hundreds, even thousands of years, it compresses into glacial ice. Scientists drill into this ice and recover cores to get information about Earth’s past climate.
Frozen ground & permafrost
When water turns into ice in soil, it becomes frozen ground. Permafrost is ground that has been below 32 °C (0 °F) for at least two years—perennially frozen ground. It consists of soil, gravel, and sand, usually bound together by ice. If the ground freezes seasonally, thawing at least once within a two-year period, it is not considered permafrost. Instead, it is simply called frozen ground.
- More than half of all the land in the Northern Hemisphere freezes and thaws every year. Frozen ground can be found in high elevations, as well as parts of the Arctic and Antarctic.
- Permafrost can be found on land and below the ocean floor.
- Permafrost is found in areas where temperatures rarely rise above freezing, like the Arctic or Antarctic. In the Arctic, regions like Greenland, the US state of Alaska, Russia, China, and Eastern Europe contain permafrost.
- Permafrost has an active layer near the surface, where plants can live because the soil is thawed for at least part of the year.
- Many roads, buildings, dams, or other structures have been built on top of permafrost. As the Earth warms, permafrost thaws, causing the ground to deform—sometimes causing considerable damage to these structures.
There are two types of glaciers: alpine glaciers and ice sheets.
Alpine glaciers are frozen rivers of ice, slowly flowing under their own weight down mountainsides and into valleys. Glaciers form when fallen snow compresses over many years into thick ice masses. The force of gravity on the ice mass causes glaciers to move.
- Glaciers cover about 10 percent of the world's land.
- Thawing glaciers are major contributors to sea level rise.
- Glaciers store about 69 percent of the world's fresh water and provide water for many people around the world.
- Glaciers carve landscapes by eroding mountain valleys and shaping underlying sediments as they flow.
An ice sheet is a type of glacier, defined as a mass of glacial land that extends more than 50,000 square kilometers (19,300 square miles) across a land. Unlike Alpine glaciers, ice sheets are not limited to mountainous regions. Ice sheets spread out in broad domes.
- There are only two ice sheets on Earth today, covering most of Greenland and Antarctica. During the last ice age, which ended 11,700 years ago, ice sheets also covered much of North America and Scandinavia. During the peak of the last ice age, glaciers and ice sheets covered about 32 percent of Earth’s total land area.
- Ice sheets contain enormous quantities of frozen water. Together, the Antarctic and Greenland Ice Sheets contain more than 99 percent of the freshwater ice on Earth.
- At its thickest, the Greenland Ice Sheet is over 3 kilometers (1.9 miles) thick, or roughly 3,200 meters (10,500 feet). The Antarctic Ice Sheet measures nearly 4.9 kilometers (3 miles), or 4,900 meters (16,100 miles), at its thickest point on the Astrolabe Subglacial Basin.
- On average, the ice on both the Greenland and Antarctic Ice Sheets, which has accumulated over millions of years, is more than 2 kilometers (1.2 miles) thick. The colossal weight of both ice sheets has pushed down the land under them.
- Surface mass balance is a term used to characterize the mass gain or loss at the surface of an ice sheet. Ice sheets grow if the amount of snow falling on them exceeds the melt runoff, evaporation, and loss at the edges. However, ice sheets lose mass if melt, evaporation, and ice flow are more than the snowfall input. Both ice sheets are currently losing ice and increasing sea level.
- Data from 2020 show that if the entire Greenland Ice Sheet melted, sea levels would rise about 7.4 meters (24 feet); if the entire Antarctic Ice Sheet melted, sea levels would rise about 60 meters (200 feet).
- The Greenland and Antarctic Ice Sheets also influence weather and climate through their significant influence on ocean circulation and their effect on winds in the polar regions.
- Ice sheets are constantly in motion, slowly flowing downhill under their own weight. As long as an ice sheet accumulates the same mass of snow as it loses to the sea, it remains in balance.
Ice caps are miniature ice sheets. An ice cap is a type of glacier, covering less than 50,000 square kilometers (19,300 square miles) and comprises several merged glaciers. Like ice sheets, ice caps tend to spread out in dome-like shapes as opposed to occupying a single valley or set of connected valleys.
- Ice caps form primarily in the high-altitude polar and subpolar mountain regions.
- Northern Europe is home to many ice caps, such as the Vatnajökull ice cap in Iceland and the Austfonna ice cap in the Svalbard archipelago of Norway, the latter of which is the largest ice cap (in area) in Scandinavia.
- The largest ice cap in the world is the Severny Island ice cap, part of the Novaya Zemlya archipelago in the Russian Arctic.
- Ice caps are also found in mountain ranges like the Himalayas, Rockies, Andes, and the Southern Alps of New Zealand.
Ice shelves & icebergs
As ice sheets and alpine glaciers extend out to the ocean, they form thick plates of ice that float on the ocean called ice shelves. These extensions of ice connect to a landmass. Ice shelves exist mostly in Antarctica and Greenland, as well as in far northern Canada. Icebergs are chunks of ice that break off alpine glaciers or ice shelves and drift in the oceans.
- Both ice shelves and icebergs raise sea level, but only when they first leave land and push into the water. Once present in the water, they do not raise sea levels even as they melt because they are already afloat.
- Iceberg calving under warming climate conditions can reach catastrophic proportions. In 2002, a total of 3,250 square kilometers (1,255 square miles) of Antarctica's Larsen B Ice Shelf disintegrated; larger than the size of Rhode Island, the mass shattered in only a few weeks, sending thousands of icebergs into the ocean.
- Icebergs carry sediments and dust into the ocean, which offer nutrients for algae and plankton growth. These plankton blooms provide food for krill, small shrimplike creatures eaten by larger animals like penguins, seals, whales, and seabirds.
- Biologists, climatologists, and glaciologists study ice shelves and icebergs to understand their impact and significance for wildlife, climate, and Earth as a whole.
Sea ice forms when water temperature in the ocean drops below the freezing point of saltwater, about -1.8 °C (28.8 °F). Most sea ice forms in the Arctic Ocean and the Southern Ocean, the ocean surrounding Antarctica.
- Sea ice does not raise sea level when it melts because it is already floating in ocean water.
- Sea ice reflects between 50 and 70 percent of the sun’s rays hitting its surface.
- Snow typically covers sea ice. Snow is even more reflective than the ice, reflecting up to 90 percent of the sun’s energy. The open ocean, by contrast, only reflects up to 10 percent of the sun’s energy. Thus, Arctic and Antarctic sea ice keeps the polar regions cool and helps moderate global climate.
- Sea ice fills a central role in the lives and customs of native Arctic people. Indigenous Peoples use sea ice for hunting and traveling. Sea ice also protects coastal areas from erosion by damping ocean waves. In areas with less sea ice, storms on the Arctic Ocean can generate much larger waves, damaging shorelines and Arctic communities.
- Sea ice creates a platform for algae to thrive, sustaining krill—shrimp-like crustaceans—and other animals.
- Scientists and local experts observe sea ice to study the effects of climate change.