Answered by John Hinsberger Meteorologist, National Weather Service-Pocatello, ID Office
The amount of incoming radiation from the sun that gets reflected back into space is known as albedo. Higher albedo means more of that radiation gets reflected back. Thus, less radiation can be absorbed by the surface, so temperature is affected. One of the highest albedo conditions is a fresh snowpack. In fact, 80-90% of incoming solar radiation is reflected by fresh snow cover, meaning that solar energy is not available to warm the temperature near the ground. Some of the remaining energy also goes toward melting the snow, rather than warming the temperature.
One additional factor is that snow acts as a blanket for the surface, so that heat from the Earth’s surface is trapped below the snow layer, allowing nighttime temperatures to plummet.
Thus, where there is snow cover, both daytime and nighttime temperatures tend to be cooler than areas without snow. In fact, the graph below shows definitively how snow cover affects high and low temperature for the Pocatello area. You will see a similar trend wherever you go.
The cryosphere is the frozen water part of the Earth system. Frozen water is found in many different places on Earth.
- Snow cover during winter.
- Frozen parts of the ocean, such as waters surrounding Antarctica and the Arctic. It also includes frozen rivers and lakes.
- Glaciers and larger ice sheets.
- The soils of polar regions, called permafrost.
Approximately three-quarters of the world’s fresh water is frozen in the cryosphere.
Some parts of the cryosphere are only around during winter months. Other parts of the cryosphere, such as glaciers and ice sheets, stay frozen year-round and, in fact, can stay that way for tens of thousands or even hundreds of thousands of years. Some of the ice in the ice sheet that covers most of the continent of Antarctica has been there for nearly a million years.
Permafrost is any ground that remains completely frozen, 32°or colder, for at least two years straight. These permanently frozen grounds are most common in regions with high mountains and near the North and South Poles.
A layer of soil on top of permafrost does not stay frozen all year. This layer, called the active layer, thaws during the warm summer months and freezes again in the fall. In colder regions, the ground rarely thaws, even in the summer. There, the active layer is very thin, only 4 to 6 inches. In warmer permafrost regions, the active layer can be several yards thick.
Let’s make a permafrost model to understand how it works.
Materials: Clear container approximately 9”x13”, 12 ice cubes, sand or soil (enough to fill the container half-way), 2 cups water, 1 cup Sphagnum moss
- Pour 2/3 of the soil into the container
- Add water until moist. Mix.
- Freeze overnight (several hours).
- Place ice cubes on top (to mimic ice wedges).
- Mix the last 1/3 of moist soil and the Sphagnum moss together.
- Cover the top of the permafrost model with the Sphagnum moss/soil mixture.
- Freeze for minimum 3 hours.
- Observe your model as it slowly melts.
What happened to the surface of the ground when the permafrost thawed? How would this affect the tundra, plants, and animals?
Thawing permafrost can make the ground collapse and disturb and deepen the active layer. Sometimes, tree roots become so weak that trees tilt and fall over. Wetland ecosystems also change as water sinks further underground without a frozen buffer to keep it in place.