by Olivia Berman ’14
Snow is one of the five components that make up the cryosphere; both winter snow and seasonally frozen ground fall under the category of snow. Winter snow forms in the atmosphere as water condenses into a droplet.[i] When more and more water vapor condenses onto the droplet’s surface, it grows; cold air then freezes this water into a snow crystal.[ii] Seasonally frozen ground is the ground that freezes in the winter and then thaws in the summer each year.[iii]
Snow is important for many reasons. The cryosphere depends on it because snow accumulation is the main source of glacier and ice cap growth. Firn snow, the snow that has remained from the last season throughout the summer, becomes the glacial ice that allows this growth. Globally, many different places depend on the snowpack, defined as the mass of snow on the ground that is hardened and compressed by its own weight, as a water supply. The snowpack can supply water for locations hundreds of miles away and thus it is crucial to the agriculture of many areas.
Snowfall follows a certain general pattern each year. Northern hemisphere snow cover first appears in northern Alaska and Siberia starting in early fall. By November, the snowpack has begun to grow thicker and spread down towards the South. From November on, the snow spreads through Russia, Europe, and the Northern United States and thickens even more. Spring marks the time when the snowpack begins to retreat. By the beginning of summer, the snowpack has diminished to being located around the Arctic Ocean and in high mountains.
The boundary between the snowy areas found on the top of mountains and the rest of the mountain is called the snowline. The snow that has remained through summer accumulates above the snowline and creates a constantly snowy area known as a snowfield. The amount of snow above this line changes from year to year, depending on the amount of winter snowfall and the range of temperatures during that summer.
Snow also has other less obvious but equally important effects on the globe. Its white, and thus highly reflective, surface reflects sunlight back into space, reducing surface air temperature. When snow melts, it is a major source of water for rivers and agricultural soils. California is currently suffering a drought because the Sierra Nevada snowpack is only half of its usual size this year; an important part of the water supply in the western United States is derived from runoff fed by mountain snowmelt.[iv] Reserves like the snowpack are particularly vulnerable to changes in climate.[v] Research has indicated recent trends toward increased winter temperatures and decreased streamflow; these findings indicate earlier annual snowmelt.[vi] This earlier snowmelt correlates with other global climate changes, such as the increase in carbon dioxide in the atmosphere and higher annual temperatures. The effects of these changes demonstrate the close connection between the cryos
[i] Weather: Ice and Snow. Annenberg Learner. http://www.learner.org/interactives/weather/iceandsnow.html
[ii]Weather: Ice and Snow. Annenberg Learner. http://www.learner.org/interactives/weather/iceandsnow.html
[iii] How Does Frozen Ground Form? National Snow and Ice Data Center. http://nsidc.org/cryosphere/frozenground/how_fg_forms.html
[iv] Cayan, Daniel R. Interannual Climate Variability and Snowpack in the Western United States. American Meteorological Society.
[v] Dozier, Jeff et al. Climate Change and the Sierra Nevada Snowpack. Interactions between the Cryosphere, Climate and Greenhouse Gases.
[vi] Dozier, Jeff et al. Climate Change and the Sierra Nevada Snowpack. Interactions between the Cryosphere, Climate and Greenhouse Gases.