Impacts on Snow

As we learned in Module 5: Snow, the atmosphere, water, snow, and ice work together to help keep the global temperature within a range that will support life. These factors keep temperatures fairly constant from year to year, thus preventing abrupt changes in local climates. Abrupt changes in local climate (which can cause events such as severe, prolonged drought) cause shifts in what food crops can grow, and what vegetation is available for food for animals. Abrupt changes in local climate can cause animal populations to die out if they are unable to move to more favorable locations, and seriously impact human populations, forcing populations to either move or die from starvation.

On the Northern Hemisphere continents, snow covers a maximum mean area of 45.2 million square kilometers, typically in January. The minimum snow-cover extent usually occurs in August and covers a mean area of 1.9 million square kilometers, most of which is snow on the Greenland ice sheet and on mountain glaciers. As a result, snow cover is the surface characteristic responsible for the largest annual and inter-annual differences in surface reflectivity (albedo) in the Northern Hemisphere. This has a direct affect on the amount of solar energy that is available for the Earth to absorb.

Figure 9.17: Mean snow-cover extent in the Northern Hemisphere 1966-2006. Snow occurs predominantly on the northern continents, on the sea ice of the Arctic Ocean and on Antarctica (not shown). Image from UNEP.

Figure 9.17: Mean snow-cover extent in the Northern Hemisphere 1966-2006. Snow occurs predominantly on the northern continents, on the sea ice of the Arctic Ocean and on Antarctica (not shown).
Image from UNEP.

Observations of snow-covered area for the Northern Hemisphere show a significant development in the later 20th century, with a reduction of the area covered by snow in the spring (March-April) from some 38 million square kilometers in the 1930’s to today’s 35 million square kilometers.

Large bodies of water (oceans and lakes) can store very large amounts of heat. Heat moves into and out of bodies of water on a daily and seasonal basis. There is a time lag between the warming and cooling of the air temperature and the warming and cooling of a water body because of their different heat capacities. As a consequence, areas adjacent to a large water body are cooler in early to mid-summer because energy is being used to warm the water. In the winter, the water body becomes a source of heat for the area.

Snow and ice impede the movement of energy between the atmosphere and a water body (or the ground). The density of the snow and the thickness of the ice are two factors that determine how effective these materials are as insulators. In addition to its insulating effects, ice is also important because it effectively holds in water (mass). In other words, because ice forms a cap on the liquid water, it prevents evaporation of water from the seas and lakes. If you prevent or slow down evaporation of water (matter or mass), you also slow down the rate of heat-loss, because the water (mass) is holding a lot of heat.

In recent years, increases in annual average air temperatures have been documented over most of the Earth. Warming is greater over land than over oceans, and the largest gains in temperatures for the planet are over the North American Arctic, north central Siberia, and on the Antarctic Peninsula. These recent increases in temperature are confirmed by changes in other features: loss of sea ice, shift of tundra to shrub vegetation, and migration of marine and terrestrial ecosystems to higher latitudes.

Ice and snow are important components of the Earth’s climate system and are particularly sensitive to global warming. Over the last few decades, the amount of ice and snow, especially in the Northern Hemisphere, has decreased substantially. Changes in volumes and extents of ice and snow have both global and local impacts on climate, ecosystems and human well-being.

By looking at patterns of change, scientists can examine the extent to which global climate change has already impacted the amount of snow and ice on the Earth. By comparing data from a wide variety of sources, scientists piece together the intricate balance between different Earth systems. Here are a few of the impacts that can occur (or, in some cases, already are occurring):

  • Rising seawater change shorelines.
  • Diminished ice caps are already opening up new shipping channels, which require new international agreements.
  • Reduction of polar ice increases the water temperature, which increases the melting of ice, which increases the water temperature, and so on, in a feedback loop.
  • Increased temperatures change the dynamics of agriculture worldwide, resulting in extended droughts that can reduce agricultural production in some areas of the world, and increased rainfall in other parts of the world, requiring shifts in what is grown in all parts of the world.

Recent significant declines in glacial ice and sea ice are well documented. In addition, river and lake ice, with their smaller areas and volumes, react relatively quickly to climate effects, influencing ecosystems and human activities on a local scale. Therefore, they are good indicators of climate change. Globally, scientists have documented changes in the dates that bodies of water freeze over in the winter and thaw out in the spring. Rising air temperatures are affecting river and lake ice. This is mainly seen as earlier spring break-up and, to a lesser extent, later autumn freeze-up. The trend to longer ice-free periods is projected to continue.

Visit the Forum: Impacts on Snow to discuss the impacts that changes in global snow and ice cover can have on the Earth.


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The MSP project is funded by an ESEA, Title II Part B Mathematics and Science Partnership Grant through the Montana Office of Public Instruction. MSP was developed by the Clark Fork Watershed Education Program and faculty from Montana Tech of The University of Montana and Montana State University, with support from other Montana University System Faculty.