Changing Planet: Black Carbon - a Dusty Situation
Students investigate the climate effects of increasing amounts of black carbon on the absorption of solar radiation on the Earth's surface.
For each team of 3-4 students
Adapted by NESTA/Windows to the Universe team members Missy Holzer, Jennifer Bergman, and Roberta Johnson from the Looking into Surface Albedo activity on Windows to the Universe.
Student Learning Outcomes:
Inquiry-based and hands-on laboratory investigation
- For background information on the origin and impacts of black carbon watch Changing Planet: Black Carbon. Also, explore these topics on the Windows to the Universe website at the links listed below.
- Gather materials and print out the student worksheet. Cut the pages with dots into quarters and provide each student team with a quarter sheet of the 10, 50, and 80 percent paper as well as a quarter sheet of white paper.
- This lesson can be done as a follow-up to the Looking into Surface Albedo activity on Windows to the Universe. Preview the lesson by reviewing the concept of surface albedo and what surfaces have high albedos versus low albedos. Next, brainstorm a list of ways that surface albedo can be altered leading students into examples of how the percent reflectivity can be increased or decreased. Have students read Black and White: Soot on Ice or one of the articles listed below to introduce them to the concept of black carbon. If you have discussed local and global winds, this would be a good time to discuss the global distribution of black carbon caused by global winds.
- Ask them to create a hypothesis for this question: how does an increase in black carbon impact surface warming? Ask them to place their hypothesis on their lab sheet, and then ask them to read the procedure before beginning their investigation. Point out that they will be assessed on their lab skills since this investigation requires a number of controls to ensure they collect quality data. Also tell students that each team will share their lab results with the rest of the class.
- Inspect each lab set-up to make sure that the lamp bulb is an equal distance from each thermometer, and about 30 cm off the lab table. Remind students to take care not to move the thermometers while taking their readings. Continue to monitor student progress during data collection.
- After students have collected the data, assist them in creating a multi-line graph that includes all 4 sets of data. Since the data was collected over two stages (heat-up and cool-down) have students draw a vertical line to delineate the two stages on their graph. If a computer-based graphing program is available, coach students in how to create a graph using the program which can then be projected during the class discussion portion of the lab.
- Once all students are finished created their graphs, ask each team to share their results with the class. Discuss their results in reference to the topic of black carbon and whether or not their results support what is taking place on a global scale. This is a good time to tie in experimental design and limitations of classroom models. Probe students about their data collection techniques and whether they would change anything if they were to do the lab over again. Ask them what other data might be useful in order to study the impact of black carbon on the absorption of solar radiation.
- Wrap-up the lesson with a discussion on how to limit black carbon emissions. Have students research the feasibility of their ideas, and report their findings to the class.
Assess students in their ability to control an experiment, collect data, display data, analyze data, and work as a team. They can also be assessed in their abilities to articulate their results to the class, including their use of correct terminology in articulating their conclusions.
Always use safe laboratory practices.
Store materials for future use.
- Create a mock global summit to discuss methods of reducing black carbon emissions. Be sure to have representatives from countries with differing perspectives on this issue, so students become more aware that there are different ideas of how to resolve these issues.
BACKGROUND INFORMATION:Little particles in the atmosphere called aerosols may be small but they have the ability to change climate. These tiny particles are a natural part of the atmosphere, coming from erupting volcanoes, sea salt, and wildfires. However, since the start of the Industrial Revolution additional aerosols have been added to the atmosphere as fossil fuels are burned. Black carbon is the term that has been given to the product of the incomplete combustion of fossil fuels, biofuel, and biomass. It is commonly known as soot.
Black carbon stays in the atmosphere for several days to weeks and then settles out onto the ground. Sources of black carbon are open biomass burning (forests and savannah burning that can start from natural causes like lightning or human-induced causes like slash and burn methods for clearing land), biofuel burning, diesel engines, industrial processes and residential coal burning. Black carbon is produced around the world and the type of soot emissions vary by region.
Black carbon contributes to global warming in two ways. First, when soot enters the atmosphere, it absorbs sunlight and generates heat, warming the air. Secondly, when soot is deposited on snow and ice, it changes the albedo of that surface, absorbing sunlight and generating heat. This warming causes snow and ice to melt, and darker colored Earth surface and ocean are exposed and less solar energy is reflected out to space causing even more warming. This is known as the ice-albedo feedback.
Just what is albedo? The amount of energy reflected by a surface is called albedo. Albedo is measured on a scale from zero to one (or sometimes as a percent).
- Very dark colors have an albedo close to zero (or close to 0%).
- Very light colors have an albedo close to one (or close to 100%).
Because much of the land surface and oceans on Earth are dark in color, they have a lower albedo and absorb a large amount of the solar energy that gets to them, reflecting only a small fraction of the Sun's energy. Forests have low albedo, near 0.15. Snow and ice, on the other hand, are very light in color. They have very high albedo, as high as 0.8 or 0.9, so they reflect most of the solar energy that gets to them, absorbing very little.The amount and type of aerosols in the atmosphere has an impact on the albedo of our planet. Earth’s planetary albedo is about 0.31. That means that about a third of the solar radiation that gets to Earth is reflected out to space and about two thirds is absorbed. Aerosols like black carbon have a low albedo and reflect very little solar energy. This air pollution is having an impact on Earth’s climate.
Scientists Ramanathan and Carmichael estimate that black carbon emissions are the second largest contributor to global warming, after carbon dioxide emissions. Reducing black carbon emissions is one of the fastest strategies for slowing global warming. Luckily, many policies have been put in place to reduce the production of black carbon around the world, and the technology necessary to lessen black carbon emissions already exists. To improve further, we need to better regulate the industrial processes that produce black carbon, and individuals need affordable and available technology to be able to make shifts from practices like biofuel cooking and residential coal combustion that are still used in much of the world today. The importance of black carbon's role in global warming has come to the forefront of the minds of many concerned citizens and exciting steps are already being taken to address issues like making cleaner burning cookstoves available in developing nations. These reductions of black carbon around the world will not only aid in reducing global warming, but will improve human health and environmental aesthetics.
RELATED SECTIONS OF THE WINDOWS TO THE UNIVERSE WEBSITE:
- Global Warming: Scientists Say Earth Is Heating Up
- What Controls the Climate?
- Aerosols and Climate Change
- Air Pollution
- Aerosols: Tiny Particulates in the Air
- Aerosols in the Atmosphere: They Are the Same All Around the World - News story originally written on December 10, 2009
- Black Carbon Deposits on Himalayan Ice Threaten Earth's "Third Pole" a NASA news release
- Third-World Stove Soot is Target in Climate Fight from New York Times
- Carbon's Other Warming Role from GeoTimes
- Climate Wire: Public-Private Partnership Forms to Push Cleaner-Burning Cookstoves
- Global Clean Cookstoves Alliance Aims to Save Millions of Lives