HES Lesson 5 Background Information

In Lessons 3 and 4 students studied the fluxes that affect CO₂ concentrations in the atmosphere, including the key role that human-caused emissions play as an unbalanced flux. In Lesson 5 students study the nature of the unbalanced CO₂ flux. Most students will see that some activities, such as driving cars, cause CO₂ to go into the atmosphere because they depend on combustion of fossil fuels. But what about other activities? Does driving a “zero emissions” electric car contribute to the CO₂ flux? What about making the car? Paving a road? Eating a hamburger?

Each of these activities also contributes to the CO₂ flux, but in more indirect ways. In Lesson 5 students study the consequences of our lifestyles and the technologies that support them. In particular, they learn that it is important to trace matter and energy through human technological systems in order to understand how combustion of fossil fuels often drives the transformations and movements of matter and energy. In this way they come to appreciate the many ways in which our daily activities and the technological systems that support those activities contribute to the unbalanced CO₂ flux.

In this lesson, students explore in greater depth how we rely on combustion of fossil fuels for our lifestyles and daily activities. They explain how we use energy in four important sectors of our economy—electricity, housing, food, and transportation—and how our energy use is related to both direct and indirect emissions of carbon dioxide.

This Lesson focuses on the many ways that our lifestyles depend on carbon-transforming processes that oxidize organic carbon and therefore increase the amount of carbon dioxide in the atmosphere. Again, we can use the Large-scale Four Questions to organize the key points.

• The Carbon Pools Question: Most students are aware of the foods and fuels that we use directly; we oxidize food when we need energy for body functions, and we oxidize fuels when we drive cars, burn wood, etc. Many students are less aware of the fossil fuels we use indirectly, when we build and heat buildings, buy food and other goods that have been manufactured and transported, or use electricity from fossil fuel power plants.
• The Carbon Cycling Question: In order to understand the many ways that our lifestyles and activities lead to CO₂ emissions, students need to learn how to engage in “life cycle analysis,” becoming aware of the many ways that producing goods and services for our economy requires combustion of fossil fuels.
• The Energy Flow Question: Chemical energy stored in biomass and fossil fuels is transformed into the energy we use for our lifestyles. This is radiated into the atmosphere, where some of it is trapped in greenhouse gases, warming the planet. Ultimately this heat is radiated out into space. Note that the heat energy is radiated into space in the form of infrared light. This is also the process that cools off our planet at night. Greenhouse gases cause global warming by absorbing some of the infrared light that the Earth radiates into space.
• The Stability and Change Question: The CO₂ emissions associated with our lifestyles are increasing the concentration of CO₂ in the atmosphere. Through the Greenhouse Effect, this causes global climate change, including changes in global temperatures, Arctic sea ice, and sea levels.

Major lifestyle choices within the sectors of transportation, food, housing and electricity use contribute greatly to carbon emissions. Average lifestyles for individuals in different countries vary greatly; per capita carbon emissions are particularly high in developed countries --- especially the United States.

You may notice that Activity 5.4 is similar to many of the carbon footprint calculators that are available online. This Activity is offered here as an alternative for a few reasons. For one, many of the online calculators focus on individual consumer choices without considering how our geographical locations can influence how we use carbon (e.g., political systems, energy infrastructures, access to public transportation, agriculture, etc.). Second, individual carbon footprint calculators often give students a result that is reflective of their socioeconomic status and/or the lifestyles of their parents. Having a lower carbon footprint can be a sign of poverty, while having a high carbon footprint can be a sign of wealth. Subsequently, low socio-economic communities and developing countries are the most affected groups by the consequences of high carbon emissions. Instead of asking students to reveal this information to the class, this Activity focuses on how average citizens of different countries use carbon, which reduces the risk of stigmatizing students based on choices that are largely out of their control. Third, online carbon footprint calculators often mask the mechanisms they use to calculate the results. Having students calculate the pounds of carbon dioxide associated with the lifestyle choices of these various countries is designed to make this calculation more visible to students.

Key Carbon-Transforming Processes: Combustion, Photosynthesis, Fossil Fuel Formation, Cellular Respiration