Inside This Unit: The Full Breakdown
Energy Resources and Consumption examines the sources of energy that power human societies, including fossil fuels, nuclear energy, and renewable alternatives. This unit evaluates the environmental impacts and sustainability of each energy source.
Why it matters
Energy questions are a major part of the AP Environmental Science exam. You must compare the advantages and disadvantages of different energy sources, understand energy efficiency concepts, and evaluate proposals for transitioning to cleaner energy.
Key concepts
- Fossil fuels (coal, oil, natural gas) are nonrenewable, energy-dense, and currently supply most of the world's energy. Their combustion produces CO₂ and other pollutants.
- Nuclear energy produces no direct CO₂ emissions but generates radioactive waste and carries risks of meltdown. Fission splits heavy atoms; fusion combines light atoms.
- Renewable energy sources (solar, wind, hydroelectric, geothermal, biomass) are replenished naturally but have lower energy density and intermittency challenges.
- Energy efficiency and conservation reduce total demand. The first and second laws of thermodynamics limit how efficiently energy can be converted and used.
Fossil Fuels
Fossil fuels — coal, petroleum (oil), and natural gas — formed from ancient organisms buried and transformed by heat and pressure over millions of years. They are nonrenewable on human timescales. Coal is burned primarily for electricity generation and is the most carbon-intensive fossil fuel. Oil is refined into gasoline, diesel, and jet fuel for transportation. Natural gas (primarily methane) burns cleaner than coal or oil, producing less CO₂ per unit of energy, but methane leaks during extraction are a potent greenhouse gas concern. Hydraulic fracturing (fracking) has expanded natural gas production but raises concerns about groundwater contamination and induced seismicity. All fossil fuel combustion releases CO₂ (driving climate change), SO₂ and NOₓ (causing acid rain), and particulate matter (harming respiratory health).
Nuclear and Renewable Energy
Nuclear fission splits uranium-235 atoms, releasing enormous energy used to generate electricity. Nuclear plants produce no direct greenhouse gas emissions during operation, but uranium mining, waste disposal, and the risk of accidents (Chernobyl, Fukushima) are significant concerns. Radioactive waste remains hazardous for thousands of years. Solar energy (photovoltaic cells and concentrated solar power) is abundant and clean but intermittent and requires energy storage or backup. Wind energy is one of the fastest-growing renewable sources; turbines convert kinetic energy of wind to electricity but face siting challenges and wildlife impacts (bird and bat mortality). Hydroelectric power is reliable and emission-free during operation, but dams alter river ecosystems. Geothermal energy taps Earth's internal heat and is highly reliable but geographically limited.
Energy Efficiency and Conservation
The most cost-effective way to reduce environmental impacts from energy use is to improve efficiency and reduce consumption. The first law of thermodynamics states that energy cannot be created or destroyed, only transformed. The second law states that every energy transformation increases entropy — some energy is always lost as waste heat, limiting efficiency. Cogeneration (combined heat and power) captures waste heat from electricity generation for heating, improving overall efficiency from about 35% to over 80%. LED lighting, high-efficiency appliances, building insulation, and fuel-efficient vehicles all reduce energy demand. Transportation accounts for about 28% of U.S. energy consumption, making vehicle efficiency standards and public transit important policy levers. Reducing energy waste is typically cheaper and faster than building new energy supply.
AP exam tip
For AP Environmental Science, be prepared to compare any two energy sources by listing advantages and disadvantages of each. Always include environmental impacts, economic factors, and reliability. Practice calculating energy efficiency and comparing the carbon intensity of different fuels.
Connections to other units
- Unit 7 (Atmospheric Pollution): Fossil fuel combustion is the primary source of air pollutants including CO₂, SO₂, NOₓ, and particulates.
- Unit 9 (Global Change): Energy choices directly determine greenhouse gas emissions and the trajectory of climate change.
- Unit 4 (Earth Systems): Fossil fuels are geological resources formed over millions of years; their extraction alters landscapes and water systems.
