Throughout the year, various forms of ice, including glaciers, ice sheets, and sea ice, cover approximately 10% of the Earth’s land and water surfaces. This widespread ice presence plays a crucial role in Earth’s global climate, especially in light of the harsh realities of climate change. In the following exploration, we delve into the unique roles played by these major forms of ice.
Defining Ice Forms
Glaciers, ice sheets, sea ice, and icebergs collectively make up the Earth’s cryosphere, where water exists in its solid form. Glaciers are expansive fields of land ice that form over centuries as accumulated snow compresses into massive layers of ice. These behemoths are so substantial that they flow downhill under their immense weight, resembling a slow-moving river. Despite their massive size, most glaciers creep along at such a slow pace that their movement is imperceptible to the naked eye.
While today’s glaciers date back to the last ice age (the Pleistocene Epoch), when ice covered a substantial portion of the Earth, they have significantly diminished since then. Currently, they are mainly confined to regions with high snowfall in winter and cool temperatures in summer, such as Alaska, the Canadian Arctic, Antarctica, and Greenland.
Glaciers not only attract millions of visitors to these locations every year, as exemplified by Montana’s Glacier National Park, but they also serve as a vital source of freshwater. The meltwater from glaciers feeds into streams and lakes, which, in turn, support crop irrigation and provide drinking water for people in arid mountainous regions. For instance, Bolivia’s Tuni glacier supplies at least 20% of La Paz’s annual water supply.
An extensive snow-covered expanse qualifies as an ice sheet if it blankets an area of land exceeding 20,000 square miles (50,000 square kilometers). Ice sheets are not formed from a single layer of snow; instead, they consist of numerous layers of snow and ice that accumulate over thousands of years. During the last glacial period, ice sheets covered North America, northern Europe, and the tip of South America. Today, however, only two significant ice sheets remain: the Greenland and Antarctic Ice Sheets, which together contain 99% of Earth’s freshwater ice.
Ice sheets also act as substantial reservoirs for carbon dioxide and methane, preventing these greenhouse gases from entering the atmosphere, where they would contribute to global warming. The Antarctic ice sheet, for instance, stores around 20,000 billion tons of carbon.
Sea ice, unlike glaciers and ice sheets that form on land, comprises frozen ocean water. It forms, grows, and melts in the ocean, with its extent changing annually, expanding during winter and receding somewhat each summer. Beyond providing a critical habitat for Arctic animals like polar bears, seals, and walruses, sea ice plays a significant role in regulating our global climate. Its highly reflective surface (high albedo) bounces back approximately 80% of the sunlight that strikes it, helping maintain the cooler temperatures of the polar regions where it resides.
An iceberg is essentially a chunk of ice that has broken off from a glacier or an ice shelf and has floated into open water. These icebergs are primarily composed of densely packed snow that has accumulated over extended periods. As evidenced by events like the Titanic’s fateful encounter, the visible portion of an iceberg above the water’s surface represents only a fraction of its total size, with the majority of the iceberg hidden beneath the water’s surface. Ultimately, icebergs melt in the ocean.
Impact of Climate Change on These Ice Forms
Much like ice cubes melting under the summer sun, the world’s ice is retreating in response to global warming.