Cryosphere

The term cryosphere comes from the Greek root kryos and means “cold” or “frost.” In physical geography, cryosphere is a general term referring to the worldwide occurrence of frozen water in its snow and ice forms. These cold landscapes and seascapes are important on their own but also help to regulate temperatures for the planet as a whole. The high reflectivities of snow and ice are considerable greater than liquid water and land surfaces, so they redirect solar energy back toward space preventing part of that energy from warming the surface via absorption. Snow and ice are also direct determinants of sea level. Three-quarters of Earth’s freshwater is locked in ice, which covers about 10 percent of the land surface.

Cold temperatures allow water to freeze and this phase change is caused by energy loss from strings of liquid water molecules to rigid crystalline configurations. Pure water freezes at 0°C but seawater of average salinity does not freeze until it reaches −2°C. Over much of the world, precipitation starts in clouds as snow. If temperatures below the clouds are below freezing the precipitation is received as snow on the surface. There are several major forms that snow and ice can take on Earth’s surface.

Snow cover is present in some places year round and seasonally in many places, including middle latitude lowlands and tropical mountains. The ground surface is blanketed and, ironically, this greatly moderates ground temperatures so that life can survive underneath. Snow can be considered to be a reservoir of fresh water. For instance, human activities in the U.S. Southwest are dependent on stream flow that emanates from the summer melt of the snowpack in the mountains.

Glaciers are large bodies of ice that have formed because season after season of snowfall has been greater than the melting and sublimation subtracting from the mass. The snow becomes denser over time, translating into glacial ice. Ice is interesting because it seems so brittle in our common experience, but it is capable of bending and flowing when subjected to slow, steady pressure. Once ice is more than a few tens of meters thick it will move under its own weight and gouges and deposits materials on a grand scale.