Coal forms from plant remains buried and compressed for hundreds of millions of years, but a mine can strip a seam in about fifty years. How should coal be classified, and why?

Turbines on a plain turn whenever the Sun's uneven heating of Earth's surface stirs the air, which happens somewhere on the plain almost every day. How should wind be classified, and why?

An Icelandic town pipes steam from wells drilled two kilometers into hot rock, where heat flows up continually from Earth's interior. How should this energy source be classified, and why?

Natural gas is pumped from shale that formed as marine organisms were buried and heated over roughly 300 million years. Which statement best explains why it is classified as nonrenewable?

A power plant burns wood chips from a tree farm that is replanted after every harvest and regrows in about twenty years. How should this fuel be classified, and why?

Sunlight is classified as a renewable resource because the Sun resupplies it continuously on a human timescale.

A reactor is fueled with uranium mined from ore bodies that formed with Earth itself. How should uranium be classified, and why?

A reservoir behind a dam is refilled each spring by rain and snowmelt, about as fast as the dam releases water through the year. How should this source be classified, and why?

A student says petroleum is renewable because new oil is forming inside Earth right now. What is the main problem with that claim?

A barrage across a bay generates electricity as the Moon's gravitational pull drives water in and out twice a day, every day. How should tidal energy be classified, and why?

In a desert facility, thousands of flat mirrors slowly turn through the day, all aimed at the top of a tall tower, where water boils into steam that spins a turbine. Which primary energy source drives this station?

A plant draws steam up from wells sunk two kilometers into hot volcanic rock. The steam spins the turbines, then condenses and is injected back underground. Which primary energy source is this?

A small station beside a landfill collects the methane rising from decaying food and yard waste and burns it to spin a turbine. Which primary energy source is it using?

Blades tens of meters long turn on towers strung along a ridge, each rotor linked through a gearbox to a generator. No fuel is ever delivered to the site. Which primary energy source is this?

Trains deliver crushed black rock daily. It is burned in a boiler, the steam spins turbines, ash is trucked away, and a tall stack releases carbon dioxide. Which primary energy source is this?

A shielded core heats water by splitting atoms of a heavy metal fuel, and the steam drives turbines. The reactor itself releases no carbon dioxide. Which primary energy source is this?

Water held in a reservoir is released down large pipes, and its motion spins the turbines that drive the generators at the base of a dam. Which primary energy source is this?

Panels of dark silicon cells cover a warehouse roof and feed current straight to an inverter. There is no turbine, no fuel and no moving part. Which primary energy source is this?

A town retires its natural gas plant and builds a solar farm with the same peak output. Which pair of consequences should the planners expect?

A district heating utility compares a geothermal system with a coal boiler over fifty years of operation. Which long-term difference should it expect?

Burning wood chips and burning coal both release carbon dioxide, but only the wood can be regrown within a human lifetime.

A country dams a wide river valley for electricity. Besides low-carbon power it can schedule, which long-term consequence should it plan for?

A nation is building nuclear plants to get low-carbon electricity. Which long-term tradeoff must it plan for?

Two countries have equal populations, but one burns three times as much fossil fuel per person. What long-term difference follows from that?

A company burns wood chips for power and wants the supply to last indefinitely. Which harvesting rule keeps the resource renewable?

Solar and wind farms supply most of a region's electricity. Which long-term investment best keeps power available through a calm, cloudy night?

A region keeps burning fossil fuels at its current rate for another hundred years. Which pair of long-term outcomes does the evidence support?

A utility replaces its coal units with natural gas units of the same output. Which long-term result should it expect?

A country clears large areas of forest for cropland and burns the felled timber. What long-term effect on atmospheric carbon dioxide should be expected?

A wind farm delivers the same amount of electricity in every hour of the day and night, all year round.

Use the table of three electricity sources. Which conclusion does the data best support?

Use the table of fuel reserves. Which conclusion does the data best support?

Use the table showing the share of full output each plant delivers over a year. Which conclusion does it best support?

Use the bar chart of carbon dioxide released per kilowatt-hour. Which source releases the least, and what does that suggest?

Use the line chart of one town's electricity from renewable sources. Which conclusion does it best support?

Use the bar graph of energy used per person in four countries. Which conclusion about their energy use does it support?

Use the table comparing a solar farm and a gas plant of equal output. Which conclusion does the data best support over 25 years?

Use the table showing how deep each region must drill to reach rock at 150 degrees Celsius. Which conclusion does it best support?

Use the table showing how long each source takes to be replenished. Which conclusion does the data best support?

Use the table of one home's solar output by season. Which conclusion does the data best support?