What is the cryosphere?
The cryosphere is the sum of frozen water around the globe. By volume, the perennial ice-containing cold regions of the world are dominated by the continental ice sheets of Greenland and Antarctica. Sea ice and snow, have much less volume but are large in areal extent. Ice sheets, snow, and sea ice play a critical role in the Earth's climate. The reflectivity or albedo of these vast areas of the Earth's surface are a key component of the Earth's energy balance.
Large swings in the volume of water trapped as ice occur during the glacial-interglacial cycles. During periods of warming, large volumes of fresh water flow into the ocean and affect ocean salinity and currents. Ice age cycles radically alter sea level by roughly 100 meters, dramatically changing coastlines. Permafrost covers large high latitude areas and hosts its own unique ecosystems. Many forms of life from polar bears to humans of the circumpolar region have adapted to life in and near the cryosphere. As the permafrost melts with higher temperatures, scientists are concerned that organic material now locked in ice will decompose releasing carbon dioxide and methane exacerbating global warming.
How does the cryosphere change?
The state of the cryosphere – from change in mountain glaciers to the annual extent of sea ice – serves as a readily observable marker of change in climate, both historically and currently. Today, most mountain glaciers around the world are retreating. Summer sea ice extent in the Arctic is diminishing as is the thickness of old sea ice. Melting sea ice does not affect sea level rise directly but is critical as part of the Earth's energy balance. Loss of sea ice exposes the dark ocean surface enabling it to absorb solar radiation and warm more than it would if covered in ice. However, the melting of the great ice sheets and mountain glaciers on land do contribute to sea level rise as the melt waters make it to the ocean. During the last glaciation, sea level is estimated to be about 120m lower than today enlarging significantly the area of continents and allowing for organisms to cross land bridges now underwater.
Human interactions with the cryosphere
In the mountainous regions of the world, snowpack serves as a frozen reservoir. As temperatures in the spring warm, the snowpack begins to melt, metering out water over the months of summer and fall. The recent widespread reductions in mountain snowpack around the globe affects summer stream flows critical for hundreds of millions of people for food production and other uses. La Paz faces this crisis today as glaciers high in the Andes retreat. City planers in the Bolivian capital are developing plans to relocate a percentage of its population as a possible adaptation to a reduced freshwater supply.
Glacier Bay, Alaska: 1941-2004 comparison. On the left, Muir and Riggs Glaciers in Glacier Bay National Park Alaska as photographed in 1941. At right, Riggs Glacier (and absense of Muir Glacier) in 2004. (Photos: William field/USGS, Bruce Molnia)
South Cascade Glacier: 1928-2000 comparison. These photos of the South Cascade Glacier in the Washington Cascade Mountains show dramatic retreat between 1928 and 2000. (Photos: USGS)