Looking Into Surface Albedo
This hands-on inquiry activity allows students to explore how the color of materials that cover the Earth affects the amounts of sunlight it absorbs using a simple model.
- Students will explore how the color of materials at the Earth's surface affects warming.
- Students will collect and interpret data.
- Students will be able to explain why dark-colored materials cause hotter temperatures.
Materials for each group of 4 students:
- 2 thermometers (or more)
- Watch or stopwatch
- Outdoor sunshine or a small desk lamp with a 100-150 watt incandescent lightbulb
- Copies of:
- One per group:
- Ask students if they have ever noticed that wearing a black shirt on a warm sunny day will make you hotter. Ask them if they have noticed that they are hotter when standing on blacktop pavement/asphalt. Why is that the case? Discuss how light is absorbed and transformed into heat energy.
- Ask students what they think might happen if the Earth was wearing a white or black tee-shirt. Of course, the Earth can not wear a tee-shirt, but the color of the Earth's surface is not the same everywhere. Show students a picture of the Earth from space. What colors do they see? Which are the lightest colors? Which are the darkest? Where do they expect that most sunlight will be absorbed? Where do they expect that the least sunlight will be absorbed?
- Have each group of students look at the photo of the Bhutan glaciers. Explain that this picture was taken from a satellite high above the Earth. Ask students what they see in the picture. The dark reddish parts of the picture are land (rocks). The white sections are ice and snow. The ice and snow are in glaciers. Define glacier. Parts of the glaciers are light blue in color. These are made of blue ice, sand, and gravel. The very dark patches are lakes that form from the glacier meltwater.
- Ask students to make a hypothesis about which areas of the photograph they think would absorb the most solar energy and which would absorb the least. Write the hypothesis at the top of the Albedo Student Data Sheet.
- Instruct students to fix their thermometers to the back of the picture using tape. One thermometer bulb should be under a section of light-colored ice and the other thermometer bulb under a section of dark red land. Remember to place the thermometers so that when you lay the picture down on a table, the thermometers are right side up and can be read.
- Place the light (not turned on) directly above the picture, about a foot above. Do not turn it on yet!
- Ask students to decide who in their group is going to record the data, who is going to read the ice thermometer, who is going to read the land thermometer, and who is going to be the timekeeper.
- The two students read their thermometers before the light is turned on and give the numbers to the data collector. The thermometer readings should be approximately the same.
- Once they have the initial readings, groups should turn on their light and the timekeeper begins timing. Temperature readings will be taken every two minutes (for 6 or 8 minutes total). Advise students to read the thermometers without shading the light if possible.
Discuss results (or do a more throughout analysis as described in the Assessment section below). Point out how this model is different than the real world (For example, would either ice or the land surface ever get to those temperatures?) This model shows relative differences based on the color of the surface but does not take into account the type of material or its reflective abilities. Explain that ice is melting. How would less ice affect the system?
Have student groups create a PowerPoint slide of their results and present their findings to the class. Did all groups get the same result? If not, then discuss what factors may have affected the data.
While the Earth's temperature is dependent upon the greenhouse-like action of the atmosphere, the amount of energy retained by the Earth is strongly dependent on the albedo of Earth's surfaces.
Just as some clouds reflect solar energy into space, so do light-colored land surfaces. Scientists use the term albedo to define the percentage of solar energy reflected back by a surface. This surface albedo effect strongly influences the absorption of sunlight. Forests, grasslands, ocean surfaces, ice caps, deserts, and cities all absorb, reflect, and radiate solar energy differently. Sunlight falling on a white glacier surface strongly reflects back into space, resulting in minimal heating of the surface and lower atmosphere. Sunlight falling on a dark soil or rock is strongly absorbed and contributes to significant heating of the Earth's surface and lower atmosphere.
Understanding local, regional, and global albedo effects is critical to predicting global climate change. Light-colored ice and snow are very weakly absorptive, reflecting 80-90% of incoming solar energy. Dark-colored land surfaces, are strongly absorptive and contribute to warming, reflecting only 10-20% of the incoming solar energy. If global temperatures increase, snow and ice cover may shrink. The exposed darker surfaces underneath may absorb more solar radiation, causing further warming. The magnitude of the effect is currently a matter of serious scientific study and debate.
How Much Are Glaciers Melting?
Currently, glaciers cover about 10% of the Earth's land surface. In most areas of the world, mountain glaciers are melting. Between 1961 and 1998 small glaciers lost an average of 7 meters of ice thickness. Glaciers in mountainous areas near the equator have been particularly hard-hit. According to global climate models, all of the glaciers in Glacier National Park in Montana will be gone by the year 2030.
Snow and ice cover near the north pole is currently decreasing at approximately 0.4% per year. Arctic sea ice has been decreasing at about 2.9% per decade. Since 1974, seven ice shelves, most in Antarctica have retreated by a total of approximately 13,500 square kilometers.
About the Image
The image used in this activity is of retreating mountain glaciers in Bhutan. It is a satellite image taken by the ASTER instrument aboard NASA's Terra satellite. Visible in the image are several glaciers in the Himalayan mountains of Bhutan. The glaciers have been melting over the past few decades, and lakes have formed on the surfaces and near the termini of many of the glaciers. Some of the glaciers are white as the ice is covered with snowpack. Other parts are rocky and have the same color as the surrounding land.
This image and other satellite pictures can be found at the NASA Earth Observatory website https://earthobservatory.nasa.gov/.
Other pictures of glaciers and other varieties of snow and ice can be found at the National Snow and Ice Data Center website http://nsidc.org/.
Head outside and take a look at the colors of the surfaces at school. Ask students to make hypotheses about which surfaces would absorb more heat or less.
Follow this activity with the Feeling the Heat activity in which students use IR thermometers to collect data about the heat of surfaces on a sunny day.
This activity was developed for NESTA and NCAR Climate Discovery by Lisa Gardiner of the UCAR Center for Science Education.