Climate Fact: Earth’s Ice and Tipping Points
Ice masses maintain their own local climate through several mechanisms. One mechanism is known as the ice-albedo feedback mechanism: ice is more reflective than surrounding rock or ocean and the more reflective a surface is, the less sunlight it absorbs and the less it warms. Highly reflective ice surfaces promote the cold conditions that allow the ice to exist in the first place. A second mechanism has to do with a glacier’s height. Higher elevations are cooler and for every 340 feet of elevation gain or loss on a glacier, the temperature at the glacier’s surface will rise or fall by between one and 1.8 degrees Fahrenheit. These two phenomena are types of “positive feedback mechanisms” – an initial loss or gain in an ice mass triggers further losses or further gains. Ice masses are also influenced by what are known as “negative feedback mechanisms” – an initial loss or gain in an ice mass triggers effects that make further losses or further gains less likely. A retreat of the Arctic Sea ice, for example, exposes more ocean water. While this increased exposure allows more sunlight to be absorbed (a positive feedback mechanism) it also means that more heat can leave the ocean, thus cooling the waters (a negative feedback mechanism). Another example of a negative feedback mechanism is glacial retreat causing warming, but that warming leading to increased moisture transport to the glacier, greater snow accumulation and glacial growth. Better understanding of these feedbacks and their interactions with other feedbacks will enable better prediction of future trends in Earth’s ice masses.
Seasons: Winter, Spring, Summer, Fall
Source: Notz, D. “The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss.” Proceedings of the National Academy of Sciences 106 (2009): 20590-20595.
