Warming of the Earth’s surface poses a particular threat for the Earth’s ice systems including ice sheets, sea ice, permafrost (frozen ground), and glaciers. An ice sheet is a mass of glacial land ice that covers more than 50,000 square kilometers. Antarctica and Greenland hold the Earth’s two ice sheets, and both lose hundreds of gigatonnes (109 tonnes) of ice mass each year to melting (Fig 220.127.116.11).
In addition to persistent melting, the patterns of ice loss in Figure 3.3.1 lead to instability in portions of the ice sheets that can also result in major catastrophic events. A series of such events have occurred in the Larsen Ice Shelf on the Antarctic Peninsula. In ice shelf is a mass of ice that is anchored to land, but which juts out over the ocean, like a shelf. The Larsen A portion of the ice shelf collapsed and melted into the ocean in 1995. The Larsen B portion collapsed in 2002, dropping a sheet of ice the size of the US state of Rhode Island into the Southern Ocean, where it melted (Fig 18.104.22.168). In 2015, the Larsen C portion developed a 120-mile long crack from which, in 2017, a sheet of ice the size of the US state of Delaware collapsed into the Southern Ocean and melted.
Recently, both Greenland and Antarctica have experienced short intense heat waves which have significantly increased localized melting. In July 2012, NASA’s Earth Observatory documented surface melting across 97% of the Greenland ice sheet in response to a week-long heat wave. On June 18th 2019, Greenland experienced a 40℉ temperature increase which led to massive surface warming and an estimated loss of 11 billion tons of surface ice in a single day. Similarly, Antarctica set its highest temperature record of 65℉ on February 7th, 2020, leading to significant ice loss along the Antarctic peninsula, and associated islands, such as Eagle Island.