APES Unit 6 Nonrenewable Energy: How We Power Society and the Tradeoffs We Make

Renewable and Nonrenewable Resources

What “renewable” and “nonrenewable” really mean

In AP Environmental Science, an energy resource is any natural resource that can be used to do work (move cars, run factories, heat buildings, generate electricity). The first big idea you need is that not all resources replace themselves on the same time scale that humans use them.

A renewable resource is replenished naturally on a human time scale (years to decades, sometimes a bit longer) if it’s managed sustainably. Examples include biomass (when harvested at or below regrowth rates), solar radiation, wind, moving water (hydropower), and geothermal heat.

A nonrenewable resource forms so slowly (typically over geologic time) that once you use it, it is not replaced within a human lifetime. Most nonrenewable energy in this unit refers to fossil fuels (coal, petroleum, natural gas) and uranium for nuclear fission.

A useful way to think about it is “speed of refilling the tank.” A renewable resource has a refilling rate that can keep up with your withdrawals (at least in principle). A nonrenewable resource has a refilling rate so slow that you are essentially emptying a one-time savings account.

Why the distinction matters: sustainability, pollution, and risk

The renewable vs nonrenewable label is not just vocabulary. It shapes three major environmental questions you’ll repeatedly answer on AP-style prompts:

1. Depletion and energy security: Nonrenewables eventually run out economically (even if small amounts remain). As high-quality deposits are depleted, extraction tends to become more expensive and more environmentally disruptive.
2. Environmental impacts and externalities: Energy systems create externalities—costs not included in the market price (health impacts from air pollution, ecosystem damage from mining, climate impacts from greenhouse gases). Different resources have very different externalities.
3. Time scale of consequences: Burning fossil fuels adds carbon dioxide to the atmosphere faster than natural processes can remove it, causing long-lasting climate change. Nuclear power produces long-lived radioactive waste that must be isolated for very long periods.

A common misconception is that “renewable” automatically means “no environmental impact.” Renewable energy can still cause habitat loss, water impacts, or pollution (for example, dams altering river ecosystems, or poorly managed biomass harvest reducing soil carbon). “Renewable” describes replenishment rate, not total environmental harmlessness.

How energy resources become useful energy

Energy resources are converted into forms society can use:

• Primary energy is energy in its raw form in nature (coal, crude oil, sunlight).
• Secondary energy is produced by converting primary energy into a more convenient form (electricity, gasoline).

Most modern societies rely heavily on electricity because it is versatile and clean at the point of use. But electricity is not a resource; it’s an energy carrier. You generate it using a resource (coal, natural gas, uranium, wind, etc.).

A second misconception: students often treat “electricity” like a fuel type. On AP questions, you usually need to name the underlying resource and process (for example, “natural gas in a combined-cycle plant” rather than “electricity”).

“Resource” vs “reserve” (a frequent exam trap)

Two terms that look similar but mean different things:

• Resource: the total amount of a material that exists (known and unknown).
• Reserve: the portion that can be extracted economically with current technology at current prices.

Reserves can grow or shrink as technology changes (like improved drilling) or as prices change, even though the total resource in Earth’s crust does not change much.

Exam Focus

• Typical question patterns
  • Classify an energy source as renewable vs nonrenewable and justify using formation/replenishment time scales.
  • Explain why “electricity” is not an energy resource and identify primary resources used to generate it.
  • Distinguish “resource” from “reserve” in the context of fossil fuels or uranium.
• Common mistakes
  • Claiming renewables have “no impact” instead of comparing types of impacts (habitat, emissions, water use).
  • Mixing up reserves with total resources, or implying reserves are fixed forever.
  • Calling electricity a “fuel” without naming the primary energy source.

Global Energy Consumption

What global energy consumption describes

Energy consumption is the amount of energy used over time by individuals, cities, or the entire world. AP Environmental Science emphasizes that energy use is tied to:

• Population size (more people generally means more energy demand)
• Economic activity and standard of living (more goods and services typically require more energy)
• Technology choices (efficiency, fuel type, infrastructure)

A helpful organizing idea is that energy demand is not just “how many people,” but also “how energy-intensive their lifestyles and economies are.”

Why global patterns matter: climate, equity, and development

Global energy consumption patterns matter because they connect directly to:

• Greenhouse gas emissions: Burning fossil fuels is a major source of carbon dioxide; energy choices therefore drive climate outcomes.
• Air pollution and health: Coal and petroleum combustion can release particulate matter, sulfur dioxide, nitrogen oxides, and toxic metals.
• Environmental justice and equity: Per-capita energy use is much higher in some countries than others. At the same time, many lower-income regions are still expanding access to electricity and clean cooking fuels.
• Resource geopolitics: Concentrated fossil fuel reserves and uranium supply chains can influence international relations and energy security.

A common misconception is that “the biggest population always emits the most.” Total emissions depend on both population and per-person consumption patterns, as well as the carbon intensity of the energy supply.

How energy is used: major sectors and end uses

Energy consumption is often broken down by sector. While the exact percentages vary by country and year, the main sectors you should be able to reason about are:

• Transportation: mainly depends on petroleum-based fuels (gasoline, diesel, jet fuel) because liquid fuels have high energy density and are easy to store and transport.
• Industry: uses electricity and fuels for process heat (steel, cement, chemicals) and for running machinery.
• Residential and commercial buildings: use energy for heating/cooling, lighting, appliances, and electronics.
• Electric power sector: converts primary fuels (coal, natural gas, uranium) into electricity used by homes, businesses, and industry.

You should also separate energy from electricity in your thinking. Transportation can consume a large share of energy while using relatively little electricity (depending on electric vehicle adoption). Conversely, buildings may be electricity-heavy.

Energy transitions: why societies shift fuels over time

Historically, many economies move through “energy transitions,” often from solid fuels (like coal or biomass) to more energy-dense and flexible fuels (like oil and natural gas), and then toward lower-emission electricity generation as technology and policy change.

These shifts happen because of:

• Energy density and convenience (liquids for transport)
• Cost and availability (new discoveries or new extraction technologies)
• Infrastructure lock-in (pipelines, refineries, power plants last decades)
• Environmental regulation (limits on pollutants can push a shift from coal to natural gas or to non-combustion sources)

A misconception to avoid: thinking the world can “switch overnight.” Energy systems are built infrastructure systems; replacing them takes time, investment, and policy.

Conservation vs efficiency (and the rebound idea)

Two strategies to reduce energy demand are related but not identical:

• Energy conservation: using less energy by changing behavior (turning off lights, reducing driving).
• Energy efficiency: delivering the same service with less energy (LED bulbs, better insulation, efficient motors).

Efficiency improvements sometimes lead to a rebound effect: as energy services get cheaper, people may use more of them (for example, driving more because fuel costs less per mile with a more efficient car). On AP-style questions, you can mention rebound as a reason efficiency does not always reduce total energy use as much as expected.

Exam Focus

• Typical question patterns
  • Interpret a graph of energy use by sector and explain which fuels dominate which sectors (especially transportation vs electricity generation).
  • Compare per-capita energy use and environmental impacts between developed and developing regions.
  • Propose strategies to reduce emissions using efficiency, conservation, and fuel switching, and justify tradeoffs.
• Common mistakes
  • Treating electricity and energy as the same thing, or assuming reducing electricity demand automatically reduces transportation fuel use.
  • Overgeneralizing: “more people = more emissions” without discussing per-capita consumption and fuel mix.
  • Ignoring infrastructure constraints and time scales when proposing energy transitions.

Fuel Types and Uses

What a “fuel” is in environmental science

A fuel is a material you can convert into usable energy, usually by combustion (a chemical reaction with oxygen) or, in the case of nuclear fuel, by fission. Most nonrenewable fuels are fossil fuels formed from ancient organic matter altered by heat and pressure over long periods.

Fossil fuels are widely used because they are energy dense, easy to store, and compatible with existing infrastructure. Their biggest downside is that combustion produces carbon dioxide and other pollutants.

Fossil fuels: formation in one idea

Fossil fuels store chemical energy originally captured by photosynthesis. Over millions of years:

• Organic material is buried (often in low-oxygen environments that slow decomposition).
• Heat and pressure transform it.
• Different conditions create different fuels:
  • Coal: mostly from ancient plant material in swampy environments.
  • Petroleum (crude oil) and natural gas: often from marine microorganisms buried in sediments.

A misconception: “Fossil fuels come from dinosaurs.” In reality, much petroleum and natural gas formed from microscopic marine organisms; coal formed largely from plants.

Coal

Coal is a solid fossil fuel used primarily for electricity generation and some industrial processes.

Why coal has been used so much: It is abundant in many regions, historically cheap, and easy to store.

How coal is extracted:

• Surface mining (including strip mining and mountaintop removal) removes overburden to access shallow seams. This can cause major habitat loss, erosion, and water pollution.
• Subsurface mining accesses deeper seams and poses worker safety risks; it can also cause land subsidence.

How coal is used to generate electricity (step-by-step):

1. Coal is burned in a boiler.
2. Heat converts water to steam.
3. Steam spins a turbine.
4. The turbine drives a generator, producing electricity.
5. Waste heat is released (often into water bodies via cooling systems), causing thermal pollution.

Major pollutants from coal combustion:

• Carbon dioxide (climate change)
• Sulfur dioxide (acid deposition; can be reduced with scrubbers and low-sulfur coal)
• Nitrogen oxides (smog and acid deposition; can be reduced with catalytic reduction technologies)
• Particulate matter (respiratory and cardiovascular impacts)
• Mercury and other trace metals

Coal is often the fossil fuel with the highest air pollution and carbon emissions per unit of electricity, especially in older, less efficient plants.

Petroleum (crude oil) and refined products

Petroleum is a liquid mixture of hydrocarbons that is refined into many fuels and products.

Why petroleum matters: It dominates the transportation sector because liquid fuels are convenient and energy dense.

How it’s used (and why it’s not just “gasoline”):
Crude oil is refined into:

• Gasoline (cars)
• Diesel (trucks, ships, some cars)
• Jet fuel (aviation)
• Heating oil
• Petrochemical feedstocks (plastics, synthetic fibers, solvents)

Environmental risks beyond combustion:

• Oil spills during extraction and transport (pipelines, tankers)
• Habitat disruption from drilling infrastructure
• Refining emissions and localized air pollution

A misconception to avoid: “Oil is only for cars.” On AP questions, it’s common to be asked about non-fuel uses (plastics and chemicals), or to recognize that transportation is difficult to electrify quickly because of existing vehicle fleets and fueling infrastructure.

Natural gas

Natural gas is a fossil fuel composed mostly of methane.

Why it has expanded: Natural gas burns more cleanly than coal in terms of many air pollutants, and modern combined-cycle power plants can be very efficient.

How natural gas generates electricity:

• In a simple gas turbine plant, burning gas spins a turbine directly.
• In a combined-cycle plant, hot exhaust is used to make steam for a second turbine, producing more electricity from the same fuel.

Key environmental tradeoff: Natural gas combustion emits carbon dioxide, but generally less per unit energy than coal. However, methane itself is a potent greenhouse gas, so methane leakage during drilling, processing, and transport can significantly affect the overall climate impact.

Extraction methods to know:

• Conventional drilling
• Hydraulic fracturing (fracking) for shale gas: high-pressure fluid fractures rock to release gas. Concerns include groundwater contamination risks (often related to well integrity), high water use, wastewater disposal, and induced seismicity from deep wastewater injection.

A common mistake is to say “natural gas is renewable” because it can be produced from biological sources in small amounts (biogas). Fossil natural gas is nonrenewable.

Unconventional fossil fuels

As conventional reserves are depleted or become harder to access, extraction increasingly includes unconventional sources such as:

• Oil sands (tar sands): a mixture of sand/clay, water, and bitumen. Extraction and processing tend to be energy- and water-intensive and can cause major land disturbance.
• Oil shale and other tight formations: require advanced drilling and sometimes heating or chemical processing.

For APES, the key idea is that unconventional sources often increase environmental impacts per unit of usable fuel because they require more processing and disturbance.

Comparing fuels: what AP questions usually want you to weigh

AP Environmental Science often asks you to compare fuels across several dimensions: availability, cost, emissions, and environmental damage from extraction.

“Show it in action” examples

Example 1: Choosing a fuel for electricity generation
Imagine a region deciding whether to replace an old coal plant. If the goal is to reduce smog-forming pollution quickly, switching to natural gas can reduce sulfur dioxide and particulate emissions substantially. But if the goal is deep long-term climate mitigation, the region must also consider methane leakage and the fact that natural gas still emits carbon dioxide when burned. This kind of tradeoff explanation (air quality benefits vs climate goals) is exactly what AP free-response questions reward.

Example 2: Why transportation is different
If a city wants to cut transportation emissions, switching from coal to wind does not directly reduce gasoline use unless vehicles become electric (or people drive less). This helps you avoid a common AP pitfall: proposing an electricity-sector solution for a transportation-sector problem without explaining the link.

Exam Focus

• Typical question patterns
  • Compare coal, oil, and natural gas on emissions, extraction impacts, and primary uses (especially electricity vs transportation).
  • Explain how a specific technology reduces pollution (scrubbers for SO2, catalytic converters for NOx, combined-cycle plants for efficiency).
  • Evaluate an energy proposal by identifying at least one environmental benefit and one environmental cost.
• Common mistakes
  • Saying “natural gas has no emissions” instead of distinguishing lower air pollutants from still-significant greenhouse impacts.
  • Confusing extraction impacts with combustion impacts (for example, mixing up oil spills with smokestack pollution).
  • Ignoring methane leakage when comparing coal and natural gas for climate impacts.

Nuclear Power

What nuclear power is (in APES terms)

Nuclear power is electricity generated using energy released from nuclear fission, where the nucleus of a heavy atom (commonly uranium) splits into smaller nuclei, releasing heat and additional neutrons.

Nuclear power is nonrenewable in typical APES classification because the fuel (uranium ore) is finite and must be mined. However, it is not a fossil fuel and does not involve combustion.

Why it matters: low air pollution, high-stakes risks

Nuclear power is important to understand because it sits in a unique tradeoff space:

• Very low air pollution during operation: No smokestack carbon dioxide, sulfur dioxide, or particulate matter from the fission process itself.
• High energy density: A small mass of fuel can produce a large amount of electricity.
• Challenges: radioactive waste, accident risk (low probability but potentially high consequences), high construction costs, and concerns about weapons proliferation.

A misconception: “Nuclear power releases greenhouse gases.” The fission reaction does not emit carbon dioxide, but the full life cycle (mining, processing, construction) does involve emissions. On AP questions, it’s strongest to say “low operational emissions” and then note life-cycle impacts.

How a nuclear power plant works (step-by-step)

Even though the energy source is different, the electricity-generation pathway is similar to many fossil fuel plants: heat makes steam; steam spins a turbine.

1. Fuel and fission: Uranium fuel (often in ceramic pellets inside fuel rods) undergoes fission in the reactor core.
2. Chain reaction control: Neutrons released by fission can trigger more fissions. Control rods absorb neutrons to slow or stop the reaction.
3. Heat transfer: The reactor heats a working fluid (water in many designs). A coolant carries heat away to prevent overheating.
4. Steam and turbine: Heat ultimately produces steam (directly or in a secondary loop), which spins a turbine connected to a generator.
5. Cooling and thermal pollution: Used steam is condensed back to water. Cooling water drawn from rivers, lakes, or oceans can warm the receiving water, affecting dissolved oxygen and aquatic life.

A common mistake is to describe nuclear electricity generation as fundamentally different from other thermal power plants. The core difference is the heat source (fission vs combustion), not the turbine-generator part.

The nuclear fuel cycle: where impacts happen

Understanding nuclear power requires thinking beyond the reactor.

• Mining and processing: Uranium ore must be mined and milled, which can disturb land and create waste rock and tailings. Improperly managed tailings can pose radiation and contamination risks.
• Enrichment and fabrication: Many reactors require uranium enriched in the fissionable isotope. This step is energy-intensive and raises proliferation concerns because enrichment technology can potentially be used for weapons-grade material.
• Operation: Produces electricity with low air pollution, but requires strict safety systems.
• Waste management: Spent fuel remains radioactive and hot. It must be cooled (often in pools initially) and then stored securely (for example, in dry casks) while long-term disposal solutions are developed and implemented.
• Decommissioning: Retiring a plant involves dismantling and managing contaminated materials, which is expensive and time-consuming.

Radioactive waste: what “half-life” implies (conceptually)

Radioactive isotopes decay at predictable rates described by half-life, the time required for half of a given amount to decay. The key APES takeaway is conceptual: long half-lives mean some wastes remain hazardous for very long periods, requiring secure isolation.

A misconception is that “after one half-life, it’s safe.” After one half-life, 50% remains; after two half-lives, 25% remains, and so on. Hazard depends on both remaining quantity and radiation type, so long-term management is necessary.

Accidents, safety, and risk perception

Major nuclear accidents are rare, but they shape public perception because consequences can be severe and long-lasting (radiation exposure, land contamination, evacuation, economic disruption). AP questions may ask you to describe safety concerns without sensationalism.

A strong AP-style explanation distinguishes:

• Probability of failure (designed to be low with multiple redundant systems)
• Magnitude of consequence (potentially high)

This “low probability, high consequence” framing helps you analyze risk clearly.

Nuclear power’s role in climate and energy planning

Because nuclear plants provide steady baseload electricity with low operational greenhouse emissions, they are sometimes proposed as part of climate mitigation. However, long construction timelines, high upfront costs, waste challenges, and political opposition can limit deployment.

The exam often rewards answers that avoid extreme claims (“nuclear is perfect” or “nuclear is always unacceptable”) and instead weigh competing priorities: climate mitigation, air quality, cost, safety, and waste.

“Show it in action” examples

Example 1: Tracing energy conversions
In a nuclear plant, nuclear potential energy in uranium is converted to thermal energy in the reactor, then to kinetic energy in steam, then to mechanical energy in the turbine, and finally to electrical energy in the generator. If you can narrate this chain clearly, you can handle many FRQ explanations.

Example 2: A policy tradeoff response
If a state closes a nuclear plant and replaces it with natural gas, it may reduce radioactive waste concerns but increase carbon dioxide emissions (and possibly methane leakage impacts). If it replaces it with wind and solar plus storage and grid upgrades, it may reduce both CO2 and waste but must address intermittency and land use. AP questions frequently ask you to justify which tradeoff you would accept and why.

Exam Focus

• Typical question patterns
  • Describe how nuclear fission produces electricity, including the role of control rods, coolant, and turbines.
  • Compare nuclear power to fossil fuels in terms of air pollutants, greenhouse gas emissions, and waste.
  • Analyze a scenario involving nuclear waste storage, thermal pollution, or accident risk and propose mitigation strategies.
• Common mistakes
  • Confusing nuclear fission with fusion, or implying nuclear plants burn fuel via combustion.
  • Claiming nuclear power has “zero” environmental impact rather than noting mining, waste, and thermal pollution.
  • Treating half-life as a “time until safe” without explaining what fraction remains after each half-life and why isolation is still needed.