Climate and the Cryosphere

The cryosphere includes those regions, both land and ocean, that are covered by snow and ice. It includes the great ice sheets of Antarctica and Greenland; the sea ice of the Arctic and Southern Oceans; frozen stretches of Canada, Siberia, and other lands within the Arctic Circle; and mountain glaciers.

Snow and ice, along with frozen ground or permafrost, have far-reaching effects on Earth’s climate. The white crystals have a high albedo, meaning they reflect most of the sunlight they receive. Freshly fallen snow, for example, has an albedo of 75–95%, considerably higher than the average albedo for Earth and its atmosphere overall, which is about 30%.

By reflecting most solar radiation back into space, snow and ice have a significant cooling effect on the atmosphere. This is an important research area because global warming could reduce the size of the cryosphere, potentially allowing more solar radiation to stay in the atmosphere and further warm the planet. If northern forests encroach on areas that are now covered by tundra or ice, the dark trees will tend to absorb solar radiation, thereby accelerating the warming cycle.

The cryosphere has varied greatly over time. In the past 600 million years, Earth was sometimes so warm that the poles provided subtropical habitat for alligators; at other times, ice sheets buried much of the present-day United States.

The cryosphere has other important effects on climate. Ice that forms on the ocean reduces the movement of moisture and energy into the air, thereby affecting climate patterns and atmospheric circulation. When openings, called leads, appear in melting sea ice, more water can evaporate to form more clouds and precipitation. The freezing over of sea ice and the melting of ice sheets and glaciers also influence the global circulation of oceans by affecting the ratio of fresh water to salt.

Climate scientists view the drastic retreat of mountain glaciers and the thinning of ice sheets as possible signs of global climate change. At NCAR, researchers have used a computer climate model to study Arctic climate and the reasons behind thinning summertime sea ice and thawing permafrost. The research suggests that human-related greenhouse gas emissions, rather than natural variability, are behind the warmer temperatures.

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