The carbon footprint and its reduction

What you'll learn

• What a carbon footprint means, including the idea of a full life cycle.
• Where carbon dioxide and methane emissions come from.
• Practical ways to reduce emissions of carbon dioxide and methane.
• Why some reduction actions are limited by cost, technology, behaviour, or trade-offs.

First: what are we trying to measure?

An emission is a substance released into the environment. In this topic, we mainly mean gases released into the atmosphere.

Some gases are greenhouse gases. They absorb infrared radiation from the Earth and help trap energy in the atmosphere. This contributes to global warming and climate change.

Carbon dioxide emissions

Carbon dioxide is produced when carbon-containing fuels burn. A fossil fuel is a fuel such as coal, oil or natural gas, formed over millions of years from the remains of living organisms.

Burning is also called combustion. For example, methane burns completely in oxygen:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

So, using petrol and diesel vehicles, gas boilers, coal power stations, and many industrial processes can all increase CO₂ emissions.

Methane emissions

Methane is another important greenhouse gas. It is the main gas in natural gas, so leaks during extraction, transport and use can release methane.

Methane is also produced when organic material decomposes anaerobically, which means without oxygen. This can happen in landfill sites, rice fields, and the digestive systems of cattle and sheep.

What is a carbon footprint?

A carbon footprint is not just the gas released at one moment. It includes emissions across the full life cycle of something.

A life cycle means all the stages a product, service or event goes through, from the beginning to the end. For a product, this could include raw materials, manufacture, transport, use, and disposal.

A product is a physical item, such as a phone, T-shirt or bottle. A service is an activity provided for someone, such as a train journey or food delivery. An event could be a concert, sports match or school trip.

You may see carbon footprints measured in kg CO₂e. This means “kilograms of carbon dioxide equivalent”. It allows different greenhouse gases, such as CO₂ and CH₄, to be compared using one unit.

The diagram shows how emissions can occur at different stages of a product’s life cycle.

Reducing carbon dioxide emissions

To reduce a carbon footprint, you can reduce the amount of CO₂ produced during the life cycle.

Use less energy

Many CO₂ emissions come from generating electricity or heating buildings using fossil fuels. Using less energy reduces the fuel burned.

Examples include:

• insulating homes so less heating is needed
• using more efficient appliances
• switching off unused devices
• designing factories to waste less energy

Energy efficiency means getting the same useful output while using less energy.

Use low-carbon energy sources

A low-carbon energy source produces little or no CO₂ while generating electricity. Examples include wind, solar, hydroelectric power and nuclear power.

These can replace electricity generated by burning fossil fuels.

Reduce fossil fuel transport

Transport often releases CO₂ because petrol, diesel and aviation fuel are burned.

Actions include:

• walking, cycling or using public transport
• sharing car journeys
• using electric vehicles, especially if the electricity is generated from low-carbon sources
• reducing unnecessary flights and long-distance transport

Reduce, reuse and recycle

Making new materials often needs lots of energy. Recycling metals, plastics and glass usually uses less energy than extracting and processing new raw materials.

Reusing a product can be even better, because it avoids making a replacement.

Reducing methane emissions

Methane matters because it is a greenhouse gas. Reducing methane emissions can therefore reduce the carbon footprint.

Capture methane from landfill

In landfill sites, buried food waste and other organic material can decay without oxygen and produce methane. Landfill sites can collect this gas instead of letting it escape.

The methane can then be burned to generate electricity. Burning methane still produces CO₂, but it prevents methane being released directly.

Reduce food waste

Less food waste means less organic material sent to landfill. This can reduce methane production.

It also reduces emissions from producing, transporting and storing food that would never be eaten.

Change farming methods

Cattle and sheep produce methane during digestion. Some farming changes can reduce methane emissions, such as improving animal feed or managing manure more carefully.

Eating less beef and lamb can also reduce demand for livestock farming, though this depends on people’s choices and food availability.

Reduce methane leaks

Natural gas is mostly methane. Better maintenance of pipelines, gas equipment and extraction sites can reduce leaks.

Why reduction actions may be limited

In exams, you are often asked not just to describe actions, but also to explain why they may be difficult to carry out.

Cost

Low-carbon technologies can be expensive to install. For example, solar panels, home insulation, electric vehicles, and methane capture systems all need money upfront.

A company or government may save money later, but the starting cost can still be a barrier.

Technology and infrastructure

Infrastructure means the support systems needed for something to work, such as charging points, public transport networks, recycling centres, or electricity grids.

For example, electric cars are less useful if there are not enough chargers. Recycling is harder if materials cannot be separated properly.

Reliability and availability

Some renewable energy sources are intermittent, meaning they do not produce power all the time. Solar panels depend on sunlight, and wind turbines depend on wind.

This does not mean they are bad, but it means energy storage and backup supplies may be needed.

Behaviour and lifestyle

Some actions need people to change habits, such as eating less meat, flying less, wasting less food, or using public transport. These changes may be unpopular, inconvenient or difficult for some people.

Life-cycle trade-offs

A change can reduce emissions in one stage but increase them in another. For example, an electric car has no exhaust emissions while being driven, but making its battery and generating its electricity may still produce CO₂.

How to write strong answers

When a question asks for actions to reduce emissions, do not just list random “green” ideas. Link each action to the gas it reduces.

Good answers often include:

• the source of the greenhouse gas
• the action taken
• the gas reduced, usually CO₂ or CH₄
• the reason the action may be limited

For example, “use renewable electricity” is better if you explain that it reduces the need to burn fossil fuels, so less CO₂ is produced.