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D3.5 · Identify greenhouse-gas sources and sinks

Learn to identify greenhouse-gas sources and sinks through clear examples and targeted practice.

Ontario Grade 10 Science

Earth and Space Science: Climate Change

Recognizing what adds greenhouse gases to the air and what removes them

A car that burns fuel releases gases into the air. A growing forest can take in carbon dioxide from the air. These processes have different roles: one is a source, and the other is a sink. In this lesson, you will learn to identify sources and sinks of greenhouse gases. A greenhouse gas is a gas in the atmosphere that helps keep Earth warm by absorbing and re-emitting some energy. The natural greenhouse effect helps make Earth warm enough for life. Human activities add extra greenhouse gases, strengthening this natural effect. Identifying sources and sinks helps us describe how gases enter and leave the atmosphere.

What you will learn

Explain what a greenhouse gas is and distinguish the natural greenhouse effect from its human-driven enhancement.
Identify examples of greenhouse-gas sources and sinks.
Use evidence about an activity or process to decide whether it adds greenhouse gases to the atmosphere or removes them.

1. A useful Grade 9 bridge: gases can move

Matter can move from one place to another. For example, a gas released from a vehicle moves into the surrounding air. A plant can take in a gas from the air. These examples show why it is useful to track where a gas goes.

The atmosphere is the layer of gases around Earth. Greenhouse gases include carbon dioxide, methane, and water vapour. They occur naturally. Human activities can also release greenhouse gases or increase their amount in the atmosphere.

The natural greenhouse effect is the warming that occurs because greenhouse gases are present naturally. The human-driven enhancement is the additional warming effect linked to human activities that add greenhouse gases. These are connected ideas, but they are not the same: the natural effect existed before modern human activities.

A greenhouse gas is a gas in the atmosphere that helps keep Earth warm.
The natural greenhouse effect is not the same as its human-driven enhancement.
To identify a source or sink, ask what happens to the gas in the atmosphere.

2. Sources and sinks: follow the gas

A source is a process or activity that releases a greenhouse gas into the atmosphere. Burning gasoline, diesel, coal, or natural gas releases carbon dioxide. Some farming activities release methane. The release of methane from farm animals and the handling of their waste are examples of human-related sources.

A sink is a process or place that takes a greenhouse gas out of the atmosphere and stores it. Plants take in carbon dioxide as they grow. Forests can act as carbon dioxide sinks when growing trees take in carbon dioxide and store carbon in their wood and other parts. Oceans also take in some carbon dioxide from the air.

A source adds gas to the atmosphere; a sink removes gas from it. The same kind of gas can have both sources and sinks. For example, carbon dioxide is released by burning fuel and taken in by growing plants. The word source or sink describes a process, not a permanent label for a gas.

This simple model summarizes the direction of movement. It is a way to organize ideas, not a complete account of every process.

change in atmospheric amount=

\text{gas added}

\text{gas removed}

Source: releases greenhouse gas into the atmosphere.
Sink: takes greenhouse gas out of the atmosphere and stores it.
Identify the gas and the direction it moves before naming a source or sink.

3. Use observations and evidence carefully

To classify a process, look for evidence about what happens to a gas. Does the process release it into the air, or take it from the air? For example, evidence that fuel is being burned supports identifying that activity as a carbon dioxide source. Evidence that plants are growing supports identifying plant growth as a carbon dioxide sink.

A place can contain both sources and sinks. A forest area may have growing trees that take in carbon dioxide, while vehicles or equipment in the area release it. Naming one sink does not prove that all emissions there are removed. Keep each process separate when describing it.

Changes in the amount of a gas in the atmosphere can reflect the combined action of sources and sinks. The simple model helps explain why identifying only one source or one sink is not enough to describe all movement.

Use safe, existing evidence such as a written description, a diagram, or a teacher-provided data set. Do not burn fuel or produce gases at home to test these ideas. The examples in this lesson do not report experimental measurements.

Classify a process by whether it adds a greenhouse gas to the air or removes it.
A location may have more than one process, including both sources and sinks.
Do not treat a possible sink as proof that emissions have been fully removed.

Examples of greenhouse-gas sources and sinks

Process	Gas and movement	Role
Burning gasoline in a vehicle	Releases carbon dioxide into the air	Source
Some farming activities	Can release methane into the air	Source
Growing trees	Takes in carbon dioxide from the air and stores carbon	Sink
Ocean taking in carbon dioxide	Moves some carbon dioxide from the air into the ocean	Sink

Worked example

A vehicle trip

A family drives a gasoline-powered car. The engine burns fuel and releases carbon dioxide. Identify the role of this activity for atmospheric carbon dioxide.

Name the gas
The description names carbon dioxide, a greenhouse gas.
Follow its direction
The engine releases carbon dioxide into the surrounding air. It adds the gas to the atmosphere.
Classify the activity
Because the activity releases carbon dioxide into the atmosphere, it is a source.

Answer: Burning gasoline in the car is a source of atmospheric carbon dioxide.

Check: The classification follows the stated release of gas; it does not claim that this is the only process affecting atmospheric carbon dioxide.

Worked example

A growing forest

In a hypothetical description, trees in a forest are growing and taking in carbon dioxide from the air. Identify the role of this process for atmospheric carbon dioxide.

Name the gas
The gas being taken in is carbon dioxide.
Follow its direction
The trees take the gas out of the air as they grow. The description says the carbon is stored in the trees.
Classify the process
Because this process removes carbon dioxide from the atmosphere and stores it, it is a sink.

Answer: The growing trees act as a carbon dioxide sink in this description.

Check: This answer describes the stated process. It does not mean that every forest always removes more carbon dioxide than all nearby sources release.

Worked example

A mixed example

A hypothetical community has buses that burn fuel and release carbon dioxide. It also has growing trees that take in carbon dioxide. Identify the source and sink, and explain why one does not erase the other.

Classify the bus activity
Burning fuel releases carbon dioxide into the atmosphere, so the buses are part of a source.
Classify the tree growth
The trees take in carbon dioxide from the atmosphere, so their growth is a sink.
Keep the processes distinct
The description gives no amounts for either process. We can identify their roles, but we cannot conclude that the trees remove all the carbon dioxide released by the buses.

Answer: The buses are a carbon dioxide source, and the growing trees are a carbon dioxide sink. The description does not provide enough information to compare their amounts.

Check: The answer identifies both directions of movement without making an unsupported claim about which process is larger.

Common mistakes and how to avoid them

Calling a greenhouse gas a source.

Correction: A gas is not itself a source. A source is a process or activity that releases that gas into the atmosphere.

Thinking that every greenhouse gas is only harmful or only human-made.

Correction: Greenhouse gases occur naturally. The natural greenhouse effect helps warm Earth. Human activities can add extra greenhouse gases and enhance that effect.

Assuming that a sink cancels every source in the same area.

Correction: A sink removes some gas, but its presence alone does not show how much it removes or whether it balances a source.

Calling any forest a sink without describing a process.

Correction: Connect the label to evidence, such as growing trees taking in carbon dioxide and storing carbon.

Lesson summary

A greenhouse gas is a gas in the atmosphere that helps keep Earth warm.
The natural greenhouse effect and the additional human-driven enhancement are distinct.
A source releases a greenhouse gas into the atmosphere.
A sink takes a greenhouse gas out of the atmosphere and stores it.
To identify a source or sink, name the gas and follow its movement.

Check your understanding

Question 1

A description says that fuel burning releases carbon dioxide into the air. What role does fuel burning have?

A source of carbon dioxide
A sink for carbon dioxide
Neither a source nor a sink because carbon dioxide is natural
correctIndex: 0

Show answer and explanation

A source of carbon dioxide

Fuel burning releases carbon dioxide into the atmosphere, so it is a source. Carbon dioxide can occur naturally and still be released by a source.

Question 2

Growing plants take in carbon dioxide from the air and store carbon. What role does this process have?

A source of carbon dioxide
A sink for carbon dioxide
Neither, because plants are not part of the atmosphere
correctIndex: 1

Show answer and explanation

A sink for carbon dioxide

The described process removes carbon dioxide from the air and stores carbon, so it is a sink.

Question 3

A town has both fuel-burning vehicles and growing trees. The description gives no amounts. What can you conclude?

The trees definitely remove all carbon dioxide released by vehicles.
The vehicles are a source and the trees are a sink, but their relative amounts are unknown.
The town has only a sink because trees are present.
correctIndex: 1

Show answer and explanation

The vehicles are a source and the trees are a sink, but their relative amounts are unknown.

The roles follow from the directions of gas movement. Without amounts, it is not possible to say whether the sink balances the source.

Key terms

Atmosphere: The layer of gases around Earth.
Greenhouse gas: A gas in the atmosphere that helps keep Earth warm by absorbing and re-emitting some energy.
Natural greenhouse effect: Warming that occurs because greenhouse gases are naturally present in the atmosphere.
Source: A process or activity that releases a greenhouse gas into the atmosphere.
Sink: A process or place that takes a greenhouse gas out of the atmosphere and stores it.

Continue through SNC2D

View the complete SNC2D Ontario Grade 10 Science curriculum and lessons

About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 10 Science (SNC2D), expectation D3.5. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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