Those regions of the globe, both land and sea that are permanently or seasonally covered by snow and ice are collectively known as the cryosphere. These include Antarctica, the Arctic Ocean, Greenland, Northern Canada, Northern Siberia and most of the high mountain ranges throughout the world, where sub-zero temperatures persist throughout the year. The cryosphere plays an important role in the regulation of the global climate.
Snow and ice reflect a lot of the sunlight they receive. Some parts of the Antarctic reflect as much as 90% of the incoming sunlight, compared to a global average of 31%. Without the cryosphere, this planetary average reflectivity would be considerably lower, and more energy would be absorbed at the Earths surface, raising its temperature and that of the atmosphere in contact with it. Scientists know that during the age of the dinosaurs 100 million years ago, little or no snow and ice covered the Earth, even at the poles, and the global average temperature was at least 8 to 10oC warmer than today.