Snow Cover
 
 
 
 
Climate Change Indicators: Snow Cover

This indicator measures the amount of land in North America that is covered by snow.

Key Points

When averaged over the entire year, snow covered an average of 3.24 million square miles of North America during the period from 1972 to 2015 (see Figure 1).

The extent of snow cover has varied from year to year. The average area covered by snow has ranged from 3.0 million to 3.6 million square miles, with the minimum value occurring in 1998 and the maximum in 1978 (see Figure 1).

Between 1972 and 2015, the average extent of North American snow cover decreased at a rate of about 3,300 square miles per year. The average area covered by snow during the most recent decade (2006–2015) was 3.21 million square miles, which is about 4 percent smaller than the average extent during the first 10 years of measurement (1972–1981)—a difference of 122,000 square miles, or approximately an area the size of New Mexico (see Figure 1).

Decreases in snow cover have largely occurred in spring and summer, whereas fall and winter snow cover have remained fairly steady over the time period studied (see Figure 2). Spring and summer snow cover can have a particularly important influence on water supplies.

Since 1972, the U.S. snow cover season has become shorter by nearly two weeks, on average (see Figure 3). By far the largest change has taken place in the spring, with the last day of snow shifting earlier by 19 days since 1972. In contrast, the first date of snow cover in the fall has remained relatively unchanged.
Background

Snow cover refers to the amount of land covered by snow at any given time. Naturally, it is influenced by the amount of precipitation that falls as snow. Air temperature also plays a role because it determines whether precipitation falls as snow or rain, and it affects the rate at which snow on the ground melts. As temperature and precipitation patterns change, so can the overall area covered by snow.

Snow cover is not just something that is affected by climate change; it also exerts an influence on climate. Because snow is white, it absorbs only a small portion of the sunlight that hits it (10 to 20 percent in the case of fresh snow), and it reflects the rest back to space. In contrast, darker surfaces such as bare ground and open water absorb the majority of the energy they receive and heat up more quickly. In this way, the overall amount of snow cover affects patterns of heating and cooling over the Earth’s surface. More snow means more energy reflects back to space, resulting in cooling, while less snow cover means more energy is absorbed at the Earth’s surface, resulting in warming.

On a more local scale, snow cover is important for many plants and animals. For example, some plants and animals rely on a protective blanket of snow to insulate them from sub-freezing winter temperatures. Humans and ecosystems also rely on snowmelt to replenish streams and groundwater. Snow cover also keeps the soil moist, so if the snow melts away earlier in the spring, the soil may dry out sooner, which can stress plants and increase the risk of wildfire.
About the Indicator

This indicator tracks the area covered by snow since 1972, based on maps generated by analyzing satellite images collected by the National Oceanic and Atmospheric Administration. Figure 1 was created by analyzing weekly maps to determine the total extent of snow cover, then averaging the weekly observations together to get a value for each year. Figure 2 uses the same method, but with average snow cover calculated for each season: spring (defined as March–May), summer (June–August), fall (September–November), and winter (December–February). These two figures cover all of North America, not including Greenland. Figure 3 focuses on the contiguous 48 states plus Alaska. It shows the average date when snow first starts to cover the ground in the fall, the average last date of snow cover in the spring, and the length of time between them. These snow cover season dates have been averaged over all parts of the country that regularly receive snow.

Indicator Notes

Although satellite-based snow cover maps are available starting in the mid-1960s, some of the early years are missing data from several weeks during the summer, which would lead to an inaccurate annual average. Thus, the indicator is restricted to 1972 and later, with all years having a full set of data.

Data Sources

The data for this indicator were provided by the Rutgers University Global Snow Lab, which posts data online at: http://climate.rutgers.edu/snowcover, and the National Oceanic and Atmospheric Administration’s National Environmental Satellite, Data, and Information Service, which collects satellite measurements and compiles maps at: www.nesdis.noaa.gov.

Technical Documentation

Download related technical information PDF
Figure 1. Snow-Covered Area in North America, 1972–2015
This graph shows the average area covered by snow in a given calendar year, based on an analysis of weekly maps. The area is measured in square miles. These data cover all of North America (not including Greenland).
Data source: Rutgers University Global Snow Lab, 20162
Figure 2. Snow-Covered Area in North America by Season, 1972–2015
This graph shows the average area covered by snow during spring (March–May), summer (June–August), fall (September–November), and winter (December–February), based on an analysis of weekly maps. The area is measured in square miles. These data cover all of North America (not including Greenland).
Data source: Rutgers University Global Snow Lab, 20163
Figure 3. Snow Cover Season in the United States, 1972–2013
This figure shows the timing of each year’s snow cover season in the contiguous 48 states and Alaska, based on an average of all parts of the country that receive snow every year. The shaded band spans from the first date of snow cover until the last date of snow cover.
Data source: NOAA, 20154
 
EPA Page
This is the EPA page for this topic. To see if the Trump administration has changed the EPA page, simply click the link and compare the information with this page. If you notice changes were made to the EPA page, please post a comment. Thanks.
 
 
Additional Climate Change Information
Climate Change and Carbon Dioxide
(Beginner - Listening, reading)

A video lesson to help with your understanding of climate change and carbon dioxide.
The English is spoken at 75% of normal speed.
Great English listening and reading practice.
Carbon Dioxide and Climate Change
(Beginner - Listening, reading)

A video lesson to help with your understanding of carbon dioxide and climate change.
The English is spoken at 75% of normal speed.
Great English listening and reading practice.
Environmental Group Warns Earth's Health at Risk
(Beginner - Listening, reading)

A video lesson to help with your understanding of climate change.
The English is spoken at 75% of normal speed.
Great English listening and reading practice.

A report by the World Wildlife Fund looked at thousands of animal populations and found they have dropped significantly in 40 years.
Sea Levels Rising at Fastest Rate in 3,000 years
(Beginner - Listening, reading)

A video lesson to help with your understanding of climate change.
The English is spoken at 75% of normal speed.
Great English listening and reading practice.

A group of scientists say sea levels are rising at record rates. Another group found that January temperatures in the Arctic reached a record high.
Capturing CO2 Gas Is Not Easy
(Beginner - Listening, reading)

A video lesson to help with your understanding of climate change.
The English is spoken at 75% of normal speed.
Great English listening and reading practice.

Most scientists agree that carbon-dioxide gas is partly to blame for climate change: rising global temperatures. But capturing the CO2 gas released by power stations is costly and difficult.
Growth, Climate Change Threaten African Plants and Animals
(Beginner - Listening, reading)

A video lesson to help with your understanding of climate change.
The English is spoken at 75% of normal speed.
Great English listening and reading practice.

Researchers believe Africa may lose as much as 30 percent of its animal and plant species by the end of this century.
Cool Stuff
Online Reference
Dictionary, Encyclopedia & more
Word:
by:
Confused?

Found a word you do not know?
1. Type the word
2. Click Look it up
Top Hits

Listen to American music while you study.
1. Click The ► button
2. Enjoy some great music
       
  Resources

These links contain many English learning resources. Some are for students, some are for teachers. If you find information not on Fun Easy English, please post a comment below, and I will make every effort to add it to the site. Thanks.
 
 
 
 
 
Site Links Site Content Contact My Other Sites
About
Site Map
Copyright
Classroom
Activities
Idioms
Alphabet
Surveys
About America
Pronunciation
Conversation
Slang
Alphabet Kids
Tests
Citizen America
Reductions
Videos
Vocabulary
Environment
Acronyms
Drive America
Grammar
Reading
Listening
Study
Portmanteau
Travel America
Email
Facebook
Twitter
Google
Howie Hayman
English Global Group
San Diego California Events
Tanegashima Japan
Japanese Language Culture Food
Akikos Kitchen
Shai Hayman