Snow is much more than an opportunity to participate in winter recreation or a hassle that means shoveling and challenging road conditions for those who live in places where it snows in the wintertime. Snow affects people everywhere by cooling the Earth, supplying water for a variety of human uses, and sustaining healthy ecosystems, including fish and wildlife populations. Who would think that a tiny snowflake drifting down from the clouds could end up having such a big impact on our planet?
Cooling the planet
If you have ever forgotten your sunglasses on a sunny, snow-covered winter day, you know that the reflection of the sun off of the bright white carpet of snow can be so strong that it’s hard to keep your eyes open. Snow’s white color affects the Earth on a much bigger scale, too.
Heat and light energy from the sun is called radiation. Radiation that is coming to the Earth from the Sun is called incoming solar radiation. Incoming radiation can be absorbed by the Earth, or it can be reflected back to the atmosphere. The more radiation that the Earth absorbs, the warmer it becomes. When the Earth’s surface reflects solar radiation instead of absorbing it, it helps to keep the planet cool.
The amount of radiation that a material reflects is called albedo. The word albedo comes from the Latin word that means “white.” Guess what substance on the Earth’s surface has the greatest albedo? Snow! New snow on the ground can reflect up to 90% of incoming radiation from the Sun back to the atmosphere. In comparison, sea ice reflects about 60% of incoming solar radiation, land typically reflects 10-20%, and open ocean reflects only about 6% of incoming solar radiation. Older, dirtier snow reflects less radiation than pure white new snow. The overall albedo of the Earth depends on how much of the Earth’s surface is covered with light and dark substances over time.
Whatever radiation is not reflected back to the atmosphere is absorbed by the Earth. Because it doesn’t absorb much heat from the sun, snow helps keep the Earth cool.
Learn more about albedo and snow here.
One of the reasons that snow can affect people directly is that it melts into water! Although this might be an obvious fact, most people are not aware that snow that falls hundreds of miles away from their homes might provide the water that comes out of their taps, produces the food they eat and the things that they buy, and even supplies the electricity that they use. For example, if you live in the western United States, there is a good chance that the water you used to brush your teeth today started off as millions of tiny snowflakes that fell in the mountains during the winter.
In the eastern United States, there is enough precipitation throughout the year to provide a reliable source of water. Water that falls in the form of snow or rain seeps into the soil and supplies the aquifer, the area below the ground surface that acts like a storage tank for water. Most places in the western United States receive less precipitation; the climate is drier. When other sources of water are not available, people can pump water out of aquifers. In dry climates and with high demand for water use, water stored in the aquifer can be used up more quickly than it is replenished by rain and snowmelt, though.
Melting snow is the source of up to 75% of the water supply in some western states (USGS, n.d.-c). Snowmelt is especially important in areas that receive relatively little precipitation during the warm summer months, because melting in the high mountains takes place gradually during the spring, flowing into rivers that supply water to humans and other living things downstream. Because snow melts gradually, it can provide a steady stream of water. If it melted all at once, it would cause flooding in the short term and be gone before the dry summer months.
The ability of humans to use water from snow melt depends in part on dams and canals that allow people to control the amount of water that is released to the places that need it when they need it. Dams block river flow and create above-ground reservoirs where water can be stored until it is needed. The construction of dams and the management of water flow by humans can be very helpful for human activities, but it can also have negative impacts on ecosystems.
Snow in a changing climate
As the Earth’s climate warms, snow patterns are changing. Scientists have observed changes in how much of the planet is covered by snow each year, the total amount of snow that it receives, the timing of spring snowmelt, and how much winter precipitation falls as rain versus snow in some areas (Sturm, et al., 2015).
Some scientists study snow by observing and recording the depth, density, and other characteristics of snow on the ground by digging snow pits. Automated weather stations also provide information about snow. Because snow covers such a large area and varies greatly from place to place and year to year, the study of snow is often conducted by remote sensing, which collects data from a distance using satellites or aircraft. Remote sensing can be especially helpful in observing the total amount of the Earth’s surface that is covered by snow each year. Ground-based study of snow is important for understanding local characteristics of snow such as temperature, grain size, layering, and density and for detecting variation in snow conditions from place to place and over time.
Select a photo to read more about what scientists are learning about Earth’s changing snow patterns.