State of the Cryosphere

Sea ice is frozen seawater that floats on the ocean surface. Blanketing millions of square kilometers, sea ice forms and melts with the polar seasons, affecting both human activity and biological habitat. In the Arctic, some sea ice persists year after year, whereas almost all Southern Ocean or Antarctic sea ice is "seasonal ice," meaning it melts away and reforms annually. While both Arctic and Antarctic ice are of vital importance to the marine mammals and birds for which they are habitats, sea ice in the Arctic appears to play a more crucial role in regulating climate.

Permafrost, or permanently frozen ground, is soil, sediment, or rock that remains at or below 0°C for at least two years. It occurs both on land and beneath offshore Arctic continental shelves, and its thickness ranges from less than 1 meter to greater than 1,000 meters. Seasonally frozen ground is near-surface soil that freezes for more than 15 days per year. Intermittently frozen ground is near-surface soil that freezes from one to 15 days per year.

Because they are so sensitive to temperature fluctuations, glaciers provide clues about the effects of global warming (Oerlemans, J. 2001). The 1991 discovery of the 5,000 year-old "ice man" preserved in a glacier in the European Alps fascinated the world, yet the discovery meant that this glacier had reached a 5,000-year minimum.

We all associate snowstorms with cold weather, but snow's influence on the weather and climate continues long after the storm ends. Because snow is highly reflective, a vast amount of sunlight that hits the snow is reflected back into space instead of warming the planet. Without snow cover, the ground absorbs about four to six times more of the Sun's energy. The presence or absence of snow controls patterns of heating and cooling over Earth's land surface more than any other single land surface feature.

In its Fifth Assessment Report, the Intergovernmental Panel on Climate Change reported that globally averaged combined land and sea surface temperature warmed between 0.65 and 1.06°C from 1880 to 2012 (IPCC 2013).

NSIDC's State of the Cryosphere provides an overview of the status of snow, ice, and permafrost as indicators of climate change. This site provides time-series data for Northern Hemisphere snow cover, mountain glacier fluctuations, sea ice extent and concentration, changes in ice shelves, and global sea level. It also provides a snapshot of current permafrost conditions.


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