Snow and Ice Cover

Introduction

Snow and ice are both the reflective covers that turn away the sun’s warming rays and the thermal blanket under which much biological activity takes place. While plants and animals struggle to adapt to extreme cold, snow and ice cover protects them. In the summer, snow and ice again protect plants and animals by melting into water that nourishes them in times of drought. Climate change as a result of global warming has had an impact on Earth’s snow and ice cover.

Historical Background and Scientific Foundations

The snow and ice cover involves much more than snowflakes that have accumulated on the ground. As snowflakes fall to the earth, they are tumbled in the wind, fractured and compacted, then often melted and refrozen. This initial deterioration results in the formation of ice crystals. These grains of ice may then coalesce with others, until all are nearly the same size. Throughout this process, air spaces within the snowpack are reduced in size as individual ice grains pack together and bond at their points of contact. Both the snowpack density and the mechanical strength of the snow increase substantially through this process. Water vapor then moves upward, reducing the size of the ice crystals at the bottom of the snowpack. The subsequent formation of depth hoar facilitates the movement of small animals as they forage under the snow during the winter. Under typical winter conditions, the snowpack is warmest at the bottom and coldest at the top.

As the temperature of the planet warms, the snow-pack diminishes. The shrinking snowpack in the Arctic and Antarctic has received much attention as concern about global warming rises. However, climate chang has already begun to leave a dramatic mark on more inhabited regions of the planet. In the 1990s, the inhabitants of Shishmaref, a Native American village on the Alaskan island of Sarichef, noticed that sea ice was forming later and melting earlier. The change meant that a protective skirt of ice no longer buffered the small settlement from destructive storm waves.

Numerous mountain systems, including the Canadian Rockies, have also experienced a reduction in snow and ice cover. The loss may disturb the sensitive ecosystem of the areas. The survival of many plants and animals depends on an annual snow cover.

Impacts and Issues

Global warming has clearly already begun to influence the amount of snow and ice cover. Scripps Institution of Oceanography researchers studied climate changes in the American West between 1950 and 1999. They found that winter precipitation fell increasingly as rain rather than snow and that snow melted faster over the years. The scientists concluded that up to 60% of changes in the snow-pack could be attributed to human activities that release emissions including carbon dioxide into the atmosphere.

Scientists have developed scenarios that indicate air temperature will increase in high latitude regions in coming decades, causing the period of snow cover to shorten, the growing season to lengthen, and soil temperatures to change during the winter, spring, and early summer. A 2006 Swedish study concluded that a warmer climate by the end of the twenty-first century will increase the growing season by 30 to 43 days and shorten the duration of a consistent snowpack by 73 to 93 days. Although a longer growing season is a benefit, the food chain is likely to be disrupted since variable soil temperatures will adversely affect insects as well as all the plants and animals that depend on insects for their survival.

WORDS TO KNOW

DEPTH HOAR: Brittle, loosely arranged crystals at the base of a snowpack.

ICE CRYSTALS: An arrangement of water molecules in which motion among the molecules slows and the structure takes on a rigid shape, as a consequence of temperatures near freezing. Crystals often form around particulate matter (dust, pollutants, etc.).

See Also Antarctic Issues and Challenges; Arctic Darkening and Pack-Ice Melting; Glacial Retreat; Glaciation; Human Impacts; Ice Cores

BIBLIOGRAPHY

Books

Doesken, Nolan J. The Snow Booklet: A Guide to the Science, Climatology, and Measurement of Snow in the U.S… Fort Collins: Colorado State University, 1997.

Kolbert, Elizabeth. Field Notes from a Catastrophe: Man, Nature, and Climate Change. New York: Bloomsbury USA, 2006.

Marchand, Peter J. Life in the Cold: An Introduction to Winter Ecology. Hanover, NH: University Press of New England, 1987.

Web Sites

Rutgers University. “Global Snow Lab.” April 9, 2008. http://climate.rutgers.edu/snowcover/ (accessed on April 9, 2008).

IN CONTEXT: CLIMATE CHANGE IMPACTS ON SNOW AND ICE

According to the Intergovernmental Panel on Climate Change (IPCC): “With regard to changes in snow, ice and frozen ground (including permafrost), there is high confidence that natural systems are affected. Examples are:”

• “enlargement and increased numbers of glacial lakes;”
• “increasing ground instability in permafrost regions, and rock avalanches in mountain regions;”
• “changes in some Arctic and Antarctic ecosystems, including those in sea-ice biomes, and also predators high in the food chain.”

Source: Parry, M. L., et al. IPCC, 2007: Summary for Policymakers. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.