The Role of Snow and Ice in the Global Climate System: A Review

Global snow and ice cover (the “cryosphere”) plays a major role in global climate and hydrology through a range of complex interactions and feedbacks, the best known of which is the ice-albedo feedback. Snow and ice cover undergo marked seasonal and long-term changes in extent and thickness. In the Proterozoic era, for example, a long-lived “snowball” Earth has been proposed, while in the Pleistocene epoch, glacial and interglacial intervals alternated in a quasi-periodic manner, but with a smaller spatial extent. The perennial elements of the cryosphere—the major ice sheets and permafrost—play a role in present-day regional and local climate and hydrology, but the large seasonal variations in snow cover and sea ice are of importance on continental to hemispheric scales. The characteristics of these variations, especially in the Northern Hemisphere, and evidence for recent trends in snow and ice extent are discussed. The relative roles of natural variability in the climate-system forcing of such trends, versus possible anthropogenic influences, cannot yet be confidently separated. However, continued careful monitoring and assessment of the likely causes and their possible consequences of such changes is clearly a vital task for scientists studying climate-cryosphere processes. The World Climate Research Programme has recently established a new project focusing on Climate and the Cryosphere (CliC) that seeks to understand the role of the cryosphere in the climate system.