Getting to Know the Cryosphere
Part B: Why We Study the Cryosphere
Earth's radiation budgetradiation budget: the relationship between how much energy the Earth gets from the Sun and how much energy the Earth-system radiates back into space. helps us understand the net energy flow between the sun and the Earth system. The sun's energy provides the fuel and warmth needed to support and sustain life on Earth. Sunlight also provides the energy that powers Earth's climate system. If you've ever worn a dark-colored t-shirt outside on a sunny day or tried to walk across a black tar driveway on a summer afternoon, you probably already know that darker colors absorb more light and heat up more easily than lighter colors that largely reflect incoming light. Similarly, the colors of Earth play a large part in how much light from the sun is absorbed and how much is reflected. White clouds, snow, and ice are highly reflective and help regulate the planet's temperature by bouncing sunlight back into space.
Scientists use a measurement called albedoalbedo: a measure of the reflectivity of a surface ranging from 0 to 1; albedo is calculated by taking the ratio of reflected radiation to incoming radiation, such that a surface that reflects 100% of light hitting it has an albedo of 1, and a surface that absorbs 100% of the light hitting it has an albedo of 0. to describe how reflective a surface is. An object's albedo is the ratio of reflected radiation to incoming radiation. It has no units and ranges from 0-1, such that a perfect absorber has an albedo of 0 and a perfect reflector has an albedo of 1.
If Earth was completely covered in ice like a giant snowball, its albedo would be about 0.84, meaning it would reflect 84 percent of incoming sunlight and absorb just 16 percent. On the other hand, if Earth was completely covered by a dark green forest canopy, its albedo would be about 0.14, meaning 86% of incoming sunlight would get absorbed and our world would be significantly warmer than it is today. Satellite measurements made since the late 1970s estimate Earth's average albedo to be about 0.30. In other words, about 30 percent of incoming solar radiation is reflected back into space, and 70 percent is absorbed. Earth's radiation budget is balanced when the amount of incoming radiation is equal to the amount of outgoing radiation. If the budget is out of balance, Earth may experience net warming or cooling. Therefore, it's extremely important for scientists to monitor the cryosphere and keep track of how much snow and ice there is at any given time on Earth.
In this part of the lab, you will model different surface conditions to explore how snow and ice help regulate Earth's temperature and climate.
- Cover the bottoms of four plastic containers with different surface materials found on Earth: snow (or shaved ice), soil, gravel, and sand.
- Turn on your light meter or probe and set it to measure in units of lux (the SI unit for light intensity).
- If you are able to conduct this experiment outside, use the sun as your light source. If you are indoors, use overhead lights or a desk lamp. Make sure that all four containers are receiving the same amount of incident light.
- Point the sensor at the light source and measure the incident illuminance (I). Record the value on your data table.
- Hold the light meter sensor 1-2 inches above the first sample with the sensor pointing directly at the material in the container. Avoid shadows from your hand.
- Record the reflected illuminance (R) on your data table.
- Repeat for the remaining materials.
- Calculate the albedo (A) for each material (A = R/I), and record the values in your data table.
Stop and Think
1: What albedo did you find for the:
2: How much more reflective is the snow/ice than the soil (i.e., what is the ratio of the ice's albedo to the soil's albedo)?
- Look at the printed image of Antarctic sea ice.
- Tape two thermometers to the back of the image so that the bulb of one thermometer is directly beneath a section of the image with bright white ice and the bulb of the other thermometer is directly beneath a section of the image with dark open ocean. Make sure you will be able to read both thermometers easily when the image is lying face up on the table.
- Position the desk lamp so that it will shine directly over the image, but DO NOT turn it on yet.
- On your data table, record the starting temperature (time = 0 minutes) showing on each thermometer.
- Turn on the lamp. Record the temperature shown on each thermometer every 2 minutes for 10 minutes. Be careful not to cast any shadows over the image or thermometers when taking your measurements.
- (Optional) Try repeating this exercise with different regions of the image. For example, you might compare the upper right quadrant of the image (scattered ice floes in open water) or the blue melt pond to solid ice and open ocean.
- Using graph paper or a spreadsheet program such as Excel, make a plot of temperature as a function of time for the ice-covered and ocean regions of the image.
Stop and Think
3: How did the temperatures of the two regions compare over time?
With a partner, in a small group, or as a whole class, discuss the following:
- What do you think would happen to the temperature of the planet if the albedo decreases? What evidence do you have to support your hypothesis?
- Snow Cover;
- Sea Ice Concentration & Snow Extent;
- Average Land Surface Temperature (Day); and
- Other Land Data