AP Environmental Science

## Learning Outcomes

- Define a **nonrenewable energy source** and explain why formation timescale matters
- Distinguish between **fossil fuels** and **nuclear energy**
- Identify the main features, uses, and extraction methods of coal, petroleum, natural gas, and uranium fuel
- Explain the major environmental impacts linked to each nonrenewable source
- Use **proved reserves** and **resource vs. reserve** correctly in exam answers
- Apply quantitative reasoning to basic energy calculations and efficiency questions
- Compare trade-offs among nonrenewable energy sources in AP-style questions

## AP Environmental Science Syllabus

For the AP Environmental Science, you are expected to understand nonrenewable energy sources, with a focus on the following syllabus points:

- Know that nonrenewable energy sources are limited and are not replenished on a human timescale
- Identify the major nonrenewable energy sources: **coal**, **petroleum**, **natural gas**, and **nuclear energy**
- Explain the difference between a **fossil fuel** and **nuclear energy**
- Understand how coal, petroleum, and natural gas form from ancient organic matter over geologic time
- Know that nuclear energy is nonrenewable because it depends on finite **uranium fuel**
- Compare the environmental impacts of coal mining, oil drilling, fracking, and uranium mining
- Explain major pollution issues, including **acid mine drainage**, **methane leakage**, **radioactive waste**, and **thermal pollution**
- Use **proved reserves** accurately as the economically recoverable portion of a broader resource base

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. What makes an energy source nonrenewable?
2. What is the difference between a fossil fuel and nuclear energy?
3. Why is natural gas often described as cleaner than coal, and why can that still be misleading?
4. Name one major environmental impact of coal, petroleum, natural gas, and nuclear energy.
5. What is the difference between a resource and a reserve?

## Introduction

Nonrenewable energy sources are a core part of Unit 6 because they still supply most of the world's energy. On the AP Environmental Science exam, you are not just expected to name them. You need to explain where they come from, how humans extract and use them, and why each one creates a different set of environmental problems.

A common exam trap is to define nonrenewable energy by saying it is "dirty" or "polluting." That is not enough. A source is nonrenewable because humans use it much faster than nature replaces it, or because the usable fuel supply is finite. Some nonrenewable sources create severe air pollution, while others create less during operation but still bring major risks.

> **Key Term: nonrenewable energy source**
> An energy source that is used faster than it is naturally replaced, or that exists in a finite supply that cannot be replenished on a human timescale.

## Introduction to the main nonrenewable sources

### What counts as nonrenewable, and why

The main nonrenewable energy sources in AP Environmental Science are **coal**, **petroleum**, **natural gas**, and **nuclear energy**. The first three are fossil fuels. Nuclear energy is not a fossil fuel, but it is still nonrenewable because uranium fuel is limited.

This distinction matters. If an exam question asks for a nonrenewable source, nuclear energy is a valid answer. If it asks specifically for a fossil fuel, nuclear is wrong.

> **Key Term: fossil fuel**
> An energy source formed from ancient organic matter over geologic time, including coal, petroleum, and natural gas.
>
> **Key Term: nuclear energy**
> Energy generated from nuclear reactions, usually the fission of uranium in power plants; it is nonrenewable but not a fossil fuel.

The reason formation timescale matters is simple. Coal, oil, and natural gas formed over millions of years from buried organic matter under heat and pressure. Humans extract and burn them in decades or centuries. That mismatch is what makes them nonrenewable.

Nuclear energy works differently. Uranium was not formed from ancient biomass, so it is not a fossil fuel. But the ore that can be mined and enriched into reactor fuel is finite, so it also falls into the nonrenewable category.

> **Test Tip:** If a question asks why a source is nonrenewable, mention **finite supply** or **geologic formation time**. Do not just say it causes pollution.

### Resource, reserve, and proved reserves

Students often blur together "resource" and "reserve." AP questions may reward precise wording here.

A **resource** is the total amount of a material that exists in the Earth, whether or not we can find it, reach it, or afford to use it. A **reserve** is the part of that resource that is identified and usable. A **proved reserve** is narrower still: it is the portion that can be recovered with reasonable certainty under current economic and technological conditions.

> **Key Term: proved reserves**
> Known quantities of an energy resource that can be economically extracted with current technology and under current operating conditions.

This means reserves can change even when the actual geology does not. If extraction technology improves, or if prices rise enough to make difficult drilling profitable, proved reserves may increase. That is why reserves are not fixed forever.

This also explains why a country can have a large resource base but a smaller reserve base. The energy may exist, but that does not mean it is currently practical to extract.

## Fossil fuel nonrenewables

### Coal: formation, use, and environmental costs

Coal is a **solid fossil fuel** formed mainly from ancient plant material. Over geologic time, dead vegetation accumulated in swampy environments, was buried, compressed, and altered by heat and pressure.

Coal has long been important for electricity generation because it is abundant and relatively energy-dense. It is especially associated with power plants rather than transportation.

Coal extraction happens through several methods. **Surface mining** removes overburden to access shallow deposits. **Subsurface mining** digs underground to reach deeper seams. **Mountaintop removal** is an extreme form of surface mining in which the summit is blasted away to expose coal seams.

The key APES point is that coal creates major impacts at both the extraction stage and the combustion stage. Students often remember one and forget the other.

Mining impacts include habitat destruction, erosion, stream burial, and land disturbance. One major problem is **acid mine drainage**, which happens when water reacts with exposed sulfur-bearing minerals in rock, producing acidic runoff that can mobilize metals and damage aquatic systems.

> **Key Term: acid mine drainage**
> Acidic, often metal-rich water formed when water reacts with sulfur-containing minerals exposed during mining.

Combustion impacts include high **carbon dioxide** emissions plus major air pollutants: **sulfur dioxide**, **nitrogen oxides**, **particulate matter**, and **mercury**. Coal also produces **coal ash**, including fly ash, which must be managed as waste.

Coal is often the strongest example of a nonrenewable source with both severe land impacts and severe air-pollution impacts. That is why coal is frequently used in compare-and-contrast questions.

> **Test Tip:** In FRQs, separate **mining impacts** from **burning impacts**. For coal, acid mine drainage is an extraction impact; sulfur dioxide and mercury are combustion impacts.

### Petroleum: why it matters and why spills are not the whole story

Petroleum, or crude oil, is a **liquid fossil fuel** formed mainly from buried marine organic matter. It is extracted by drilling and then refined into products such as gasoline, diesel, jet fuel, heating oil, asphalt, and petrochemical feedstocks.

> **Key Term: crude oil**
> Unrefined liquid petroleum as it is extracted from the ground.

Petroleum is especially important in transportation. That is a distinction AP questions sometimes test. Coal and nuclear are mainly tied to electricity; petroleum is heavily tied to vehicles and liquid fuels.

Its benefits are linked to high energy density and ease of transport. Liquids can be pumped, shipped, and refined into many useful products. That makes petroleum central to modern economies.

Its environmental harms happen across the whole chain: extraction, transport, refining, and combustion.

Extraction can disrupt habitats and pose risks to groundwater and nearby natural areass. Transport creates the famous risk of oil spills from tankers and pipelines. Spills can coat wildlife, damage coastal habitats, and contaminate food webs. But spills are not the only problem.

Combustion of petroleum products releases carbon dioxide and air pollutants. Refining also has environmental costs. So if an exam answer says petroleum is harmful only because of spills, it is incomplete.

Another common APES angle is the distinction between conventional petroleum and heavier unconventional sources such as tar sands or oil shale. These generally require more energy and cause greater land and water damage, but the main petroleum concept you need first is that it is nonrenewable because it formed over geologic time.

### Natural gas: lower combustion emissions, but not impact-free

Natural gas is a **gaseous fossil fuel** composed mostly of **methane**.

> **Key Term: methane**
> A simple hydrocarbon gas, CH₄, that is the main component of natural gas and a powerful greenhouse gas.

Natural gas often forms in the same general regions as petroleum and is extracted by drilling. In many regions, extraction now includes **hydraulic fracturing**, or **fracking**, in which high-pressure fluid is injected into rock to release trapped oil or gas.

> **Key Term: hydraulic fracturing (fracking)**
> A method of extracting oil or natural gas by injecting water, sand, and chemicals under high pressure to fracture rock.

Natural gas burns more cleanly than coal in relative terms. When combusted, it generally releases less carbon dioxide per unit of energy, and much smaller amounts of sulfur dioxide, particulates, and mercury. That is why it is often described as a "cleaner" fossil fuel.

But "cleaner" does not mean clean. It still emits carbon dioxide. More importantly, methane leakage during production, processing, storage, and transport can greatly increase its climate impact. Methane is a strong greenhouse gas, so even leaks before combustion matter.

This is the key trade-off. If you compare only smokestack emissions, natural gas looks much better than coal. If you include methane leakage across the full system, the climate benefit may shrink.

Fracking also creates added concerns: large water use, chemical spills, wastewater disposal issues, habitat fragmentation, and induced earthquakes linked especially to wastewater injection.

Students often overcorrect and say natural gas is either harmless or just as bad as coal. Neither is accurate. APES wants the trade-off: lower conventional air pollution than coal, but still nonrenewable and still environmentally damaging.

## Nuclear energy as a nonrenewable source

### Why nuclear is nonrenewable but not fossil fuel

Nuclear power relies on **uranium fuel**, usually uranium-235 in APES discussion. In a nuclear reactor, **nuclear fission** splits a heavy atomic nucleus, releasing heat. That heat is used to produce steam, which turns turbines and generates electricity.

> **Key Term: nuclear fission**
> The splitting of a heavy atomic nucleus, such as uranium, releasing energy used to generate electricity.

Nuclear energy is often grouped with fossil fuels in compare questions because all are nonrenewable, but the environmental profile is very different.

Nuclear plants do not burn fuel, so during operation they produce very low direct air-pollutant emissions and very low direct greenhouse-gas emissions compared with coal or oil power plants. This makes nuclear attractive in arguments about reducing climate change or air pollution.

However, nuclear still has major costs and risks. Uranium must be mined, processed, and enriched. That creates land disturbance and waste. Spent fuel remains radioactive for very long periods and requires secure storage. Plants also involve high construction costs and long-term decommissioning concerns.

Students sometimes think "low carbon" means renewable. That is incorrect. Low operational emissions do not change the fact that uranium is finite.

### Radioactive waste, thermal pollution, and reactor trade-offs

Radioactive waste is one of the central APES concerns with nuclear energy. Not all nuclear waste is the same. The most serious is spent fuel, often called high-level waste. There is also lower-level radioactive waste such as contaminated equipment or protective clothing.

The exam may also test **thermal pollution** in connection with nuclear plants. Like other thermoelectric plants, nuclear facilities often use large amounts of water for cooling. When warmer water is discharged back to rivers, lakes, or coastal areas, the temperature increase can lower dissolved oxygen and stress aquatic organisms.

> **Key Term: thermal pollution**
> The release of heated water into the environment, which raises water temperature and can reduce dissolved oxygen and harm aquatic life.

This matters because students often answer that nuclear produces "no pollution." That is too broad. It produces very little direct air pollution during operation, but it does create radioactive waste and thermal pollution.

A good APES comparison is this:

- **Coal**: high air pollution, high carbon dioxide, severe mining damage
- **Petroleum**: major transport fuel, spill risks, combustion emissions
- **Natural gas**: lower combustion pollution than coal, but methane leakage and fracking impacts
- **Nuclear**: low direct operational air emissions, but radioactive waste, uranium mining impacts, and thermal pollution

That comparison shows why APES prefers trade-off thinking over simple rankings.

## Comparing nonrenewable sources and applying them on the exam

### Side-by-side comparison of major trade-offs

A strong exam answer often compares sources directly rather than describing them in isolation.

**Coal** is usually the best example of a source with severe extraction damage and severe combustion pollution. If a prompt asks for the largest air-pollution burden among major nonrenewables, coal is often the safest answer.

**Petroleum** is the clearest example of a nonrenewable source tied to transportation and to spill risks. If a question asks about fuels for cars, gasoline and diesel point toward petroleum.

**Natural gas** is the main example of "cleaner combustion" that still has hidden climate costs. A good answer includes both lower sulfur dioxide and particulate emissions than coal and the warning about methane leakage.

**Nuclear** is the key contrast source: low direct operational carbon emissions, but long-term waste and cooling-water issues.

A common APES skill is explaining why no source is simply "best." That depends on what criterion matters most: climate, air quality, land disruption, waste, reliability, or water use.

### Worked calculation and exam application

APES also expects simple quantitative reasoning. Here is a common style of energy problem.

A coal-fired plant uses fuel energy to generate electricity at **40% efficiency**. If the fuel input is **1,000 units of energy**, how much useful electrical energy is produced?

Step 1: Write the formula.

$$
\text{Efficiency} = \frac{\text{useful energy output}}{\text{total energy input}} \times 100
$$

Step 2: Rearrange to solve for useful output.

$$
\text{useful energy output} = \frac{\text{Efficiency}}{100} \times \text{total energy input}
$$

Step 3: Substitute values.

$$
\text{useful energy output} = \frac{40}{100} \times 1000
$$

$$
= 0.40 \times 1000 = 400
$$

So the plant produces **400 units of useful electrical energy**.

The remaining **600 units** are not destroyed. They are mostly degraded into less useful heat, which links directly to the **Second Law of Thermodynamics**.

Students often make three errors here:

- forgetting to divide the percentage by 100
- giving 40 instead of 400
- saying the remaining energy is "lost" instead of converted to lower-quality heat
  > **Test Tip:** If a calculation uses a percentage, convert it into a decimal before multiplying. And if energy is "lost," say it is degraded into **heat**, not destroyed.

### Common misconceptions to avoid

Several mistakes appear again and again in APES responses:

- Saying nonrenewable means polluting rather than slow to replace
- Calling nuclear a fossil fuel
- Calling natural gas renewable because it burns cleaner than coal
- Using resource and reserve as if they mean the same thing
- Saying nuclear causes no pollution at all
- Mentioning only oil spills when discussing petroleum
- Forgetting that coal impacts happen at both mining and combustion stages

The best way to avoid these errors is to answer with specific mechanisms. For example, do not write "coal is bad for the environment." Write that coal mining can cause habitat destruction and acid mine drainage, while coal combustion releases carbon dioxide, sulfur dioxide, nitrogen oxides, particulates, and mercury.

That kind of answer earns more credit because it shows applied understanding rather than memorized labels.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Nonrenewable energy sources are not replenished on a human timescale or exist in finite usable supplies
- The major nonrenewable sources in APES are coal, petroleum, natural gas, and nuclear energy
- Coal, petroleum, and natural gas are fossil fuels formed from ancient organic matter over geologic time
- Nuclear energy is nonrenewable because uranium is finite, but it is not a fossil fuel
- Coal causes major environmental damage through both mining and combustion
- Petroleum is especially important for transportation and creates impacts through drilling, refining, combustion, and spills
- Natural gas burns more cleanly than coal but still emits carbon dioxide and can have serious methane leakage and fracking impacts
- Nuclear power produces low direct operational air emissions but creates radioactive waste and thermal pollution
- Proved reserves are the economically recoverable part of a broader resource base under current conditions
- Acid mine drainage is linked to mining, while sulfur dioxide, particulates, and mercury are linked to fossil fuel combustion
- Thermal pollution from power plants can reduce dissolved oxygen and harm aquatic life
- Efficiency calculations use useful energy output divided by total energy input times 100

## Key Terms and Concepts

- nonrenewable energy source
- fossil fuel
- nuclear energy
- proved reserves
- acid mine drainage
- crude oil
- methane
- hydraulic fracturing (fracking)
- nuclear fission
- thermal pollution


Renewable and Nonrenewable Resources - Nonrenewable energy sources