A major interval of geologic time during which extensive ice sheets (continental glaciers) formed over many parts of the world. The best known ice ages are 1) the Huronian in Canada, occurring very ea
rly in the Proterozoic era (2700-1800 million years ago); 2) the pre-Cambrian and early Cambrian, which occurred in the early Paleozoic era (about 540 million years ago) and left traces widely scattered over the world; and 3) the Permo-Carboniferous, occurring during the late Paleozoic era (from 290 million years ago), which was extensively developed on Gondwana, a large continent comprising what is now India, South America, Australia, Antarctica, Africa, and portions of Asia and North America. The term ice age is also applied to advances and retreats of glaciers during the Quaternary era.
A cold period in Earth history when large ice sheets extend from the polar regions into temperate latitudes. The term is sometimes used synonymously with "glacial period" or "glacial period", or embra
ces several such periods to define a major phase of cold climate in Earth's climatic history.
A climate feedback involving changes in the Earth's surface albedo. Snow and ice have an albedo much higher (up to ~0.8) than the average planetary albedo (~0.3). With increasing temperatures, it is a
nticipated that snow and ice extent will decrease, the Earth's overall albedo will decrease and more solar radiation will be absorbed, warming the Earth further.
A positive feedback mechanism involving ice and snow cover, surface albedo, and temperature. For example, given an initial warming, a decrease in snow and ice cover occurs, lowering the surface albedo
. This causes an increase in the absorption of solar radiation, which amplifies the initial increase in temperature.
Steep, ice covered mountain faces; Hanging glaciers; Thin ice flanks; See longitudinal characteristics for further differentiation; Irregular, usually thin ice mass which adheres to a mountain slope o
r ridge; Includes ice fringes; Thin ice and snow covered mountain flank (ice flanks or steep ice fields)