What Is The Cryosphere?

The cryosphere is Earth’s frozen water. It includes snow cover, sea ice, glaciers, ice caps, ice sheets and permafrost. We examine the stability of these ice stores and explain how the cryosphere influences Earth's climate.
Cryosphere Ice Berg
Image Credit: Alto Crew /Unsplash

The cryosphere is a critical component of the water cycle and the global carbon cycle, and therefore an essential part of Earth’s climate system.

Most areas of frozen water can be found either at the North Pole (an expanse of sea ice surrounded by land), or the South Pole (a continent covered with ice sheets, surrounded by water), or in high altitude mountainous locations (Alps, Himalayas, Andes etc).

More widespread is permafrost, which covers approximately 22.8 million square kilometers (8.8 million square miles) in the Northern Hemisphere. Most of it is located within or around the Arctic Circle, but it is also found on the Qinghai–Tibet Plateau in China, or in the Khangai and Altai Mountain ranges in Mongolia.

The static nature of deep ice provides an ideal research platform for paleoclimatologists and cryologists, who obtain valuable data about historical climates from ice cores taken from drillings in Greenland and Antarctica, some of which reach depths of 3200 metres (2 mi) or more. The cores are able to retrieve ice and other materials (trapped gases, particles of dust, and water molecules) that have collected over millions of years. 1

The Cryosphere And Climate

The cryosphere is one of the five main sub-systems that interact to shape the climate and environment of the Planet. The others are: the atmosphere (air), the hydrosphere (all liquid water), the lithosphere (Earth’s solid outer layer of rock), the pedosphere (Earth’s soil layer), and the biosphere (all living things).

The cryosphere’s main contribution to Earth’s climate system is locking up large quantities of water in the form of ice and snow. This frozen reserve exerts a significant cooling effect on the planet (through air and sea currents), while its albedo effect is responsible for reflecting back into space roughly 80 percent of the sunlight it receives, thus limiting global warming in polar regions.

What Is Sea Ice?

Sea ice forms when ocean water reaches sub-zero temperatures. Sea ice covers roughly 7 percent of the Earth’s surface and some 12 percent of the world’s oceans. 2 Most of the world’s sea ice is found in the polar ice packs of the Arctic and Southern Oceans.

Polar sea ice increases in surface size during the winter and retreats in the summer, creating a seasonal movement and habitat which is relied upon by birds, mammals (polar bears, seals, Emperor penguins) and other members of the polar ecosystem.

Winds, ocean currents and temperature fluctuations combine to create a variety of ice types. These include ice floes, typically a flat piece of floating sea ice; drift ice, a larger expanse of ice consisting of several ice floes; and icebergs – chunks of ice that break off ice shelves or glaciers and drift out into the ocean. Ice that floats on the ocean like icebergs and ice floes, does not raise sea levels when it melts, because the volume of water it displaces as ice, is pretty much the same as the volume it adds to the ocean when it melts.

What Are Ice Shelves?

Ice shelves are platforms of ice that extend out into the sea as land-based ice sheets and glaciers cross the coastline. They are found chiefly in Antarctica, or in the Arctic along the Canadian and Alaskan coasts. Ice shelves constitute an important foraging ground for Antarctic krill (small shrimp-like fish preyed on by larger fish, penguins, seals, whales, and sea birds) because they graze on algae and other micro-organisms who live on the underside of the ice. Without an abundant supply of krill, the marine food web would almost certainly collapse.

Unfortunately, ice shelves can become unstable and collapse very quickly. For example, between January 31 and April 13, 2002, scientists monitoring the east coast of the Antarctic Peninsula watched the entire Larsen B Ice Shelf disintegrate and fall into the sea in less than 6 weeks. The ice shelf occupied roughly 3,250 sq km (1,254 sq mi).

Nor was this the first ice shelf to suffer an abrupt collapse. About 1,500 sq km (579 sq mi) of ice suddenly broke off Larsen A, the northern part of the Larsen Ice Shelf Complex, in January 1995. Following these collapses, the Larsen A and B glaciers began to lose ice at a rate ten times faster than before. A few years later, in the southern part of the peninsula, the Wilkins Ice Shelf disintegrated completely between February 2008 and April 2009. This was the tenth major ice shelf to disintegrate in recent years. 3

What Are Ice Sheets?

An ice sheet is an expanse of land ice larger than 50,000 square km (31,000 sq mi). 4 During the last Ice Age, enormous polar ice sheets extended southwards to cover all of New England, and much of the upper Midwestern United States, as well as most of Canada, Alaska, Greenland, Iceland, White Russia, Scandinavia, and most of Great Britain and Ireland. Today, the two biggest ice sheets are those covering Antarctica and most of Greenland, which between them contain more than 99 percent of the freshwater ice on Earth.

The Antarctic Ice Sheet covers an area roughly 14 million square kilometers (5.4 million square miles) in size, roughly the equivalent of the contiguous United States and Mexico combined. The Greenland Ice Sheet is about 1.7 million square kilometers (656,000 square miles), which is roughly three times the size of Texas. Cryologists calculate that if the Greenland Ice Sheet melted, sea level would rise about 7.2 metres (24 feet). 5

How Do Ice Sheets Evolve?

Ice sheets begin to form in areas where winter snow fall does not melt entirely during the following summer. Over thousands of years, layers of snow build up into dense masses of ice, growing thicker and denser under the weight of new layers of ice and snow. Ice sheets move continuously, flowing downhill under their own weight. (Note: Unlike a glacier, which usually flows in one single direction, an ice field may flow outward in all directions from the center.)

As the main bulk of the glacier gets closer to the coast, a large proportion of the ice is channelled through faster-moving ice streams and glaciers. Although these streams and glaciers empty into the sea, the ice sheet will remain quite stable as long as it accumulates a similar amount of new snow to compensate for its losses. 6

What Are Glaciers?

Like an ice sheet, glaciers consist of fallen snow that slowly (over centuries) becomes compressed into an airless and dense mass of snow, known as névé. Under further pressure this névé forms an even denser type of granular ice, known as firn, and later turns into glacial ice. 

Certain climatic conditions must be present for glaciers to evolve. For example, they are usually found above the snow line in regions that experience heavy snowfall in winter, and cool temperatures in summer. In this way, the glacier gains more snow in the winter than it loses in the summer. This is why most glaciers are located either in polar or mountainous areas. Above all, the amount of snowfall a glacier receives is critical: one reason why somewhere like Siberia has almost no glaciation – there’s not enough snow.

A glacier usually forms in an upland area, often in a small depression between mountains enclosed by narrow ridges. When the glacier reaches a certain mass, it begins to move down the incline under the influence of gravity. The surface area of a glacier varies enormously. Some glaciers are no bigger than a football pitch; others can be hundreds of kilometers in length.

Glaciers will flow down mountain valleys, spread out across plains, or onto the sea. Movement along the bottom of a glacier is much slower than movement along the top due to the friction caused by contact with the ground, and by the weight of the glacier itself.

Glaciers may retreat or advance, depending on the accumulation or ablation that occurs. But even as it retreats, it still moves downslope, like an escalator that descends and then loops back under itself. Whether retreating or advancing, glaciers typically move with exceptional slowness. On rare occasions, however, glaciers will retreat rapidly, and movement will be visible over a period of weeks or months. In recent years, glaciers in Alaska, the Himalayas and Greenland have surprised glaciologists with their speed of retreat due to the effects of global warming.

As of 2019, glaciers occupy roughly 10 percent of the world’s land surface, mostly in Greenland and Antarctica, although they are found on every continent, even Africa. In Antarctica, glaciers have an average thickness of 2,100 metres (1.3 mi). 7

How Does The Cryosphere Influence Earth’s Climate?

The cryosphere plays an important role in Earth’s climate system.

  • By maintaining a substantial amount of water in the form of ice, the cryosphere exerts an important cooling effect on both the atmosphere and hydrosphere, through their air and ocean currents, respectively. The thermohaline circulation, in particular, is entirely dependent on frigid, high-salinity polar water to achieve the density required for downwelling in the polar oceans.
  • Ice and snow both have a bright reflective surface with a high “albedo”. As a result, almost 80 percent of the sunlight that falls on polar ice is immediately reflected back into space. This keeps the polar regions cool, and helps to keep global temperatures stable.
  • However, as sea ice melts in the summer, it is replaced by the much darker surface of the ocean, which instead of reflecting 80 percent of the sunlight, now absorbs 90 percent of it. Which means the ocean gets warmer, and more ice melts, and so on. This is one of the Planet’s climate feedbacks that boosts global warming. In a nutshell, the loss of ice caused by global warming causes even more warming. Which is very bad news for the planet.
  • The polar ecosystem also assists the thermohaline circulation – sometimes called the ocean conveyor belt – in its function of absorbing CO2 from the atmosphere and storing it in the ocean depths for centuries before recycling it into the atmosphere.
  • The global cryosphere, with its 198,000 glaciers scattered around the world’s uplands, maintains a huge store of freshwater in a solid state. This has two important benefits for the global environment. First, it provides a vital store of freshwater for local communities, farmers and animals in mountainous regions, during the hot summer months when rainfall is low. Second, it prevents the glaciers and the ice sheets from liquifying and thus helps to maintain stable sea levels. It’s worth remembering that the Antarctic Ice Sheet contains enough ice to cause a sea level rise of up to 60 meters (200 feet). If even 2 percent of it melted, it would raise levels by 4 feet: enough to swamp half the houses in Miami.

What’s Happening To Arctic Sea Ice?

According to scientists at the U.S. National Snow & Ice Data Center, Arctic sea ice reached its annual low on 18 September 2019, when sea ice extent averaged 4.15 million square km (1.60 million sq mi) – the second lowest in the satellite record, equalled only by 2007 and 2016.

What’s Happening To Antarctic Ice?

On average, only about 15 percent of sea ice in the Southern Ocean remains at the summer minimum, whereas in the Arctic the figure is around 40 percent. Because only a small amount of sea ice persists around Antarctica, the majority of it is only one winter old at most. Because of this, Antarctic sea ice is comparatively often averaging 1 meter/3 feet or less. In the Arctic, ice that remains throughout at least one complete year is typically 3-4 meters thick.

Since the late 20th century, the Antarctic ice sheet has experienced increased warming and increased melting, although these effects are not spread equally across the continent. In a nutshell, West Antarctica has been losing ice, while East Antarctica may have experienced modest gains.

Since the late 20th century, West Antarctica has been experiencing ice losses, while East Antarctica has been experiencing modest gains. That was what most climatologists – though not all 8 – believed until 2019, when a new study led by Eric Rignot used a newly adjusted ice-accumulation climate model that proved East Antarctica had actually been losing ice from 1979 right up to 2017. 9

The study also uncovered increasing losses across Antarctica each decade: 40 ± 9 gigatons per year during the period 1979-1990, 50 ± 14 gigatons per year during the period 1989-2000, 166 ± 18 gigatons per year during the period 1999-2009, and 252 ± 26 gigatons per year during the period 2009-2017. These findings await corroboration by satellite observations. 10

In West Antarctica, well-documented worries about the stability of the ice sheet have centered on the Amundsen Sea Embayment, where the Thwaites, Pine Island, Smith, Kohler, Pope, and Haynes glaciers drain into the sea. Since the 1980s, for example, the Thwaites glacier alone has suffered a net loss of over 600 billion tons of ice. 11

Several studies (Alley et al. 2015, Pollard et al. 2015, Feldmann and Levermann 2015) highlighted the vulnerability of the West Antarctic Ice Sheet to a rapid collapse which, studies showed, could happen in a matter of decades once it started. It was suggested that the climate tipping point for such a collapse might have already been reached, even though rapid changes might not actually happen for centuries.

Unfortunately, more recent research by DeConto and Pollard suggests that collapse could happen much sooner. Certain glaciological processes such as ice cliff failure and hydro fracture, omitted from most ice-flow models, might trigger a collapse of the Thwaites Glacier within a matter of decades. 12 13

What’s Happening To The Permafrost?

Because satellite sensors cannot identify the precise state of the region’s huge permafrost deposit, and predictions by climate models have yet to overcome the inherent difficulties in simulating cold-region processes, it is difficult to forecast the future prospects of this gigantic carbon reservoir.

That said, there is a growing number of reports from all over the tundra and taiga biomes that temperatures are rising fast and the permafrost is thawing much faster than expected. How do people know that the permafrost is thawing? Easy. Their ice cellars are flooding, forcing them to store fish and meat outside.

And their houses and stores are subsiding. In one area of Canada, alone, scientists have recorded a 60-fold increase in massive ground slumps from 1984 to 2013.

In most areas of the main permafrost zone around the Arctic circle, the permanently frozen layer is topped by a few feet of dirt and humus. Known as the “active layer”, this soil usually thaws every summer and refreezes again during the winter, protecting the permafrost from rising heat above. But recently, scientists and locals have started reporting wintertime thawing – hitherto unheard of.

The causes are not hard to find. Rising temperatures have become the norm throughout the region. Arctic fires have warmed the land further – in fact, in some areas of Siberia the soil itself is still burning. Then there’s the snow. Recent heavy winter snowfalls have blanketed Siberia, trapping summer heat in the earth. At a scientific research site near Cherskiy on the Kolyma River, biogeochemists found that snow depth had doubled since 2014. In 2018 temperatures in the active layer were found to have risen by 10 degrees Fahrenheit.

No one expects all or even most of the permafrost in the cryosphere to thaw. But when the active layer stops freezing in winter, it’s time to wake up. If the decomposers and other microbes start munching on thawing carbon-rich material in the soil and giving off methane (CH4) and carbon dioxide (CO2) all year round, we could be in for a nasty surprise when our satellite sensors finally start working. 14

IPCC Special Report On The Ocean And Cryosphere (2019)

The Intergovernmental Panel on Climate Change published its long awaited Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) in September 2019. It told us much of what we already know, so there were no great surprises. Here are some of its main points.

  • Arctic sea ice extent in September (traditionally its minimum extent) has declined by about 13 percent per decade (during the period of satellite observation from 1979 to 2018), producing changes that are unprecedented in at least 1,000 years. The Arctic’s older, thicker sea ice, which slows down the melting of other ice, has almost completely disappeared. Only about 10 percent of sea ice is more than five years old.
  • During the period 2006-2015, Greenland’s Ice Sheet lost 278 billion tons of mass each year. Antarctica’s Ice Sheet lost 155 billion tons per year, while other glaciers around the world lost 220 billion tons a year. All told, the ice loss between Greenland, Antarctica and other glaciers not part of ice sheets was 653 billion tons per year.
  • All mountainous regions in the cryosphere have seen their snow cover decline in depth, extent and duration. During the period 1967-2018, For example, June snow cover in the Arctic declined by 13 percent per decade.
  • Due to climate change, Arctic temperature rises are more than double the global average since 2000. In fact, during winter 2016 and winter 2018, temperatures in the central Arctic region were 6°C (10.8°F) above the 1981-2010 average.
  • During the period 2007-2016, permafrost temperatures increased by about 0.3°C (0.5°F), a record amount of warming for permafrost.
  • The report also confirmed that global mean sea level is expected to rise by 0.43 meters (1.4 feet) under a low emissions scenario, and 0.84 meters (2.8 feet) under a high emissions scenario during this century. Significantly, this report revises the IPCC’s previous estimate upwards, no doubt as a result of newer projections indicating a larger loss of ice from the Antarctic ice sheet. However, the IPCC’s estimate is quite conservative compared to other projections.


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  2. “On Sea Ice.” Willy F. Weeks. University of Alaska Press. p.2 (2010). []
  3. World of Change: Collapse of the Larsen-B Ice Shelf.” 2010. NASA. []
  4. “Glacial Geology: Ice Sheets and Landforms.” Matthew Bennett, Neil Glasser. (1996) Chichester, England: John Wiley and Sons Ltd. ISBN 0-471-96345-3. []
  5. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881pp. []
  6. U.S. National Snow & Ice Data Center. State of the Cryosphere. 2019. []
  7. National Geographic Almanac of Geography, 2005, ISBN 0-7922-3877-X, p. 149.[]
  8. “Stable’ region of Antarctica is melting.” Radar data from Cryosat-2 probe show sudden ice loss on southern Antarctic Peninsula. Jeff Tollefson. Nature. May 21, 2015. []
  9.  “Four decades of Antarctic Ice Sheet mass balance from 1979–2017.” Eric Rignot, Jeremie Mouginot, Bernd Scheuch, Michiel van den Broeke, Melchior J. van Wessem, Mathieu Morlighem. PNAS January 22, 2019 116 (4) 1095-1103. []
  10. U.S. National Snow & Ice Data Center. State of the Cryosphere. Arctic. 2019. []
  11. Patel, Jugal K. (October 26, 2017). “In Antarctica, Two Crucial Glaciers Accelerate Toward the Sea”. The New York Times. []
  12. Contribution of Antarctica to past and future sea-level rise.” Robert M. DeConto & David Pollard. Nature. Vol 531, p.591. March 2016. []
  13. Evolving Understanding of Antarctic Ice-Sheet Physics and Ambiguity in Probabilistic Sea-Level Projections.” Robert E. Kopp, Robert M. DeConto, Daniel A. Bader, Carling C. Hay, Radley M. Horton, Scott Kulp, Michael Oppenheimer, David Pollard, Benjamin H. Strauss. Earth’s Future. 13 December 2017. []
  14. “Arctic permafrost is thawing fast. That affects us all.” Craig Welch. National Geographic Magazine. Sept 2019. []
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