AP® Environmental Science review sheet from Aim for Five (aimforfive.com/enviro/units/6/6-1)
Unit 6 · Topic 6.1
6.1 Renewable and Nonrenewable Resources
Every energy source is either nonrenewable (a fixed supply that forms far more slowly than you use it) or renewable (refilled by nature on a human timescale). The label matters because it tells you whether a source can last, and some renewable sources only stay renewable if you manage them carefully.
Key terms
- renewable resource
- nonrenewable resource
- fossil fuel
- nuclear fuel
- sustainable use
Nonrenewable resources
A nonrenewable resource exists in a fixed amount on human timescales. It may still be forming somewhere, but so slowly (over millions of years) that every barrel or ton you use is effectively gone for good.
The nonrenewable energy sources in this course are the fossil fuels and nuclear fuel. Fossil fuels (coal, oil and natural gas) are the remains of ancient plants, algae and plankton that were buried and slowly changed by heat and pressure. Nuclear fuel is mostly uranium, a metal mined from rock. Nuclear power releases no CO₂ while it runs, but it is still nonrenewable, because the uranium in the ground is finite.
Renewable resources
A renewable resource is replaced by natural processes at about the rate you use it, or faster. Sunlight, wind, moving water, tides and the earth's internal heat keep coming no matter how much you use today.
Some renewable resources can run out if you overuse them. Wood, other biomass and groundwater are renewable only when you harvest them no faster than they regrow or refill. Cut a forest faster than it grows back and, for practical purposes, it has become a nonrenewable resource. That idea, using a resource at a rate that lets it keep supplying you indefinitely, is called sustainable use.
Sorting the energy sources
You should be able to place every source from this unit in the right column, and explain why. The key question is always the same: does nature replace it about as fast as you use it?
| Source | Category | Why |
|---|---|---|
| Coal, oil, natural gas | Nonrenewable | Take millions of years to form |
| Uranium (nuclear) | Nonrenewable | A finite ore that is mined |
| Solar, wind | Renewable | Keeps arriving no matter how much you use, though output varies with weather |
| Hydroelectric, tidal | Renewable | The water cycle and the moon keep refilling them |
| Geothermal | Renewable | Earth's heat is constant, though one site can cool if overused |
| Wood and other biomass | Renewable if managed | Only while regrowth keeps up with harvest |
Why the label is not the whole story
Renewable does not mean harmless. Dams flood valleys, wind turbines kill some birds and bats, and solar panels need mined metals. Nonrenewable does not mean useless either: fossil fuels are dense, easy to store and available on demand, which is why they still supply most of the world's energy.
When you compare sources later in this unit, look at three things: where the energy comes from, how it is turned into electricity or heat, and what it costs the environment at each step, from extraction to waste.
Worked examples
Try each one yourself first, then open the solution.
- Example 1Calculator allowed
When a renewable resource stops being renewable
A town owns 50,000 hectares of forest. After a patch is clear-cut, it takes 40 years for the trees to grow back to harvestable size. (a) What is the largest area the town can cut each year and still have mature trees to cut forever? (b) The town actually cuts 2,000 hectares a year. Is that sustainable? Explain.
Show the solutionHide the solution
- Step 1: For the forest to supply wood forever, each patch must get its full 40 years to regrow before it is cut again. So the whole forest can be harvested at most once every 40 years.
- Step 2: Largest sustainable harvest = 50,000 ha ÷ 40 years = 1,250 hectares per year.
- Step 3: At 2,000 hectares a year, the town cuts through the whole forest in 50,000 ÷ 2,000 = 25 years.
- Step 4: In year 26 the patches cut in year 1 are only 25 years old, 15 years short of harvest size. The town runs out of mature trees, so the wood is being used faster than it is replaced.
Answer: (a) 1,250 hectares per year. (b) No. At 2,000 ha per year the mature forest is gone in 25 years, before the first cut patches have regrown, so the wood is being treated like a nonrenewable resource.
- Example 2
Classic trap: nuclear power
A student writes: 'Nuclear power is renewable because it doesn't release greenhouse gases.' Identify the error.
Show the solutionHide the solution
- Step 1: Renewable versus nonrenewable is about whether the fuel supply is replaced, not about pollution.
- Step 2: Nuclear plants run on uranium, which is mined from a limited supply in the earth's crust and is not replaced on a human timescale.
- Step 3: Low carbon emissions while running is a real advantage, but it is a separate idea from being renewable.
Answer: The student confused 'low-carbon' with 'renewable'. Nuclear power is nonrenewable because uranium is a finite, mined resource.
Common mistakes
- Calling nuclear power renewable because it is low-carbon. Renewability is about whether the fuel is replaced; uranium is finite.
- Saying wood or biomass is always renewable. It is renewable only when harvest is no faster than regrowth.
- Thinking 'renewable' means 'no environmental impact'. Every source has trade-offs, so name them when an answer asks for a disadvantage.
On the exam
- Multiple-choice questions often list several sources and ask which one is nonrenewable or which one is renewable only under certain conditions. Check each against the 'replaced as fast as used' test.
- In free response, a strong answer names the source, classifies it, and gives the reason in one sentence, for example 'Coal is nonrenewable because it takes millions of years to form.'
Connected topics
Videos
Check yourself
4 questions on 6.1 Renewable and Nonrenewable Resources. Pick an answer to see if you got it, and why.
Which energy resource is nonrenewable?
Under which condition is firewood from a forest a renewable resource?
Natural gas is still forming slowly today from organic matter buried deep underground. Why is it still classified as a nonrenewable resource?
At a geothermal power field, steam output fell steadily for years as more wells pulled hot water and steam from underground. Output leveled off after operators began piping treated wastewater back down into the hot rock. Which conclusion is best supported?
0 of 4 answered