Given its particular importance for the climatic regulation of the Earth system, the solid portion of the hydrosphere (ice in form of glaciers, ice caps, snow cover sea ice, permafrost etc.) has received special attention and is sometimes considered as a single sub-system: the Cryosphere.
Its unique property of reflecting most solar radiation back to space, its high albedo, acts as a natural cooler of the Earth. With the gradual decrease in planetary snow cover due to climate change, along with pollution of the ice surfaces, the global albedo is decreasing, which means less solar radiation reflected, thus, more energy absorbed by the system, raising its temperature. This causes a positive feedback loop, contributing to the rising of the global average temperature and, consequently, to more climate warming and more melting of ice surfaces.
The Cryosphere is potentially the most threatened sphere, with alarming rates of yearly loss of mass and area worldwide.