🏭 Industry
Factories burn fuels to power machines and make heat. Some industrial processes also release carbon dioxide themselves. Making cement and steel are two examples. The more goods the world makes, the more gas is released.
Fragile Environments Under Threat » The Enhanced Greenhouse Effect
What you'll learn this session
Study time: 30 minutes
Edexcel spec: 7.1 Fragile environments are under threat from desertification, deforestation and global climate change (c)
- How the greenhouse effect works and why it is natural and useful
- How industry, transport, energy and farming add extra greenhouse gases
- What the enhanced greenhouse effect is and how it leads to warming
- How to read graphs and maps that show the human causes of climate change
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Unlock This CourseThe greenhouse effect and the enhanced greenhouse effect
The last lesson, Natural Causes of Climate Change, showed that the climate has always changed without any help from people. This lesson looks at the part people play. The spec says human activities (industry, transport, energy and farming) can cause the enhanced greenhouse effect.
First, the natural greenhouse effect. The Sun's energy reaches the Earth and warms the land and sea. The warm surface sends some of that heat back up towards space. Certain gases in the air, such as carbon dioxide, methane and nitrous oxide, trap some of this heat and send it back down. Without this, the Earth would be far too cold for most life. So the natural greenhouse effect is a good thing.
The problem starts when people add extra greenhouse gases. More gas means more heat is trapped, so the planet warms up more than it would naturally. That extra warming is the enhanced greenhouse effect.
Key terms:
- Greenhouse effect: the natural trapping of heat in the atmosphere by greenhouse gases, which keeps the Earth warm enough for life.
- Greenhouse gas: a gas in the air that traps heat, such as carbon dioxide, methane and nitrous oxide.
- Enhanced greenhouse effect: extra warming caused by human activities adding more greenhouse gases to the air.
- Emissions: gases released into the air.
Four human causes
The spec names four human activities. Each one puts extra greenhouse gases into the air.
🚗 Transport
Cars, lorries, ships and planes mostly burn petrol, diesel or aviation fuel. Burning these fuels releases carbon dioxide from their engines. More people and goods travelling means more emissions.
⚡ Energy
Many power stations burn coal, oil or natural gas to make electricity. Homes also burn gas and oil for heating and cooking. Burning a fossil fuel releases carbon dioxide that was locked underground for millions of years.
🐄 Farming
Cattle and sheep release methane when they digest grass. Flooded rice fields also release methane. Fertilisers put on fields can release nitrous oxide. Farm machines burn fuel too, which adds carbon dioxide.
Notice the pattern. Burning fossil fuels is behind industry, transport and energy, and it releases carbon dioxide. Farming is different because its main gases are methane and nitrous oxide. Methane traps more heat than carbon dioxide does, molecule for molecule, but there is much less of it in the air.
From emissions to warming
You can explain the enhanced greenhouse effect as a chain of steps. This is how you earn marks in an "explain" question.
- Humans burn fossil fuels and farm animals and crops on a huge scale.
- This releases extra carbon dioxide, methane and nitrous oxide.
- The extra gases trap more of the heat that the Earth sends back towards space.
- The atmosphere and surface warm up, so average global temperatures rise.
Since the Industrial Revolution, which began in the 1700s, people have burned more and more fossil fuels. The amount of carbon dioxide in the air has risen from about 280 parts per million to well over 400 parts per million today. That is why scientists link the recent warming to human activities, even though natural causes are still at work.
Skill: graphs and maps of human causes
The spec asks you to use and interpret graphs and maps showing human causes of climate change. The figures below are imaginary. They are not real data and are only here to practise the skill.
📈 Imaginary graph: emissions by source
A bar chart shows a country's carbon dioxide emissions in one year: energy 40 million tonnes, transport 25, industry 20, farming 10, other 5. Energy has the tallest bar. Together, energy and transport make 65 of the 100 million tonnes.
🗺️ Imaginary map: emissions per person
A shaded map uses dark colours for high emissions per person and pale colours for low. Countries with many power stations and cars are dark. The key tells you what each shade means, so always read it first.
Worked example
Question: Using the imaginary bar chart, what percentage of emissions came from transport?
Read the value for transport (25 million tonnes) and the total (100 million tonnes). Divide: 25 ÷ 100 = 0.25, which is 25 per cent.
To describe the chart, name the biggest source and quote numbers: "Energy is the largest source, at 40 million tonnes, which is more than farming (10) and industry (20) put together."
For a map, give the pattern and use the key: "The darkest shades, meaning the highest emissions per person, are in the countries with the most industry and the most cars."
Common mistakes
- Mixing up the greenhouse effect and the enhanced greenhouse effect. The first is natural and needed for life. The second is extra warming caused by people.
- Saying the greenhouse effect is a hole in the air. Greenhouse gases trap heat. They do not make a hole.
- Writing only "pollution" or "fumes". Name the gas, such as carbon dioxide or methane, and the activity that releases it.
- Forgetting that farming is a cause. Its main gases are methane and nitrous oxide.
- On graphs and maps, giving a pattern with no numbers or no use of the key.
Exam-style question
(a) State what is meant by the enhanced greenhouse effect. [2 marks]
(b) Explain how farming can add to the enhanced greenhouse effect. [3 marks]
(c) Using the imaginary bar chart, state which human activity produced the most emissions and give the figure. [2 marks]
Model answer
(a) Extra warming of the Earth (1) caused by human activities adding more greenhouse gases to the air (1).
(b) Cattle and rice fields release methane (1). Fertilisers release nitrous oxide (1). These are greenhouse gases that trap more heat, so the atmosphere warms (1).
(c) Energy (1), at 40 million tonnes (1).
Exam tip
When a question mentions an activity, always name the gas it releases and say what that gas does. "Cattle release methane, which traps heat" earns more than "cattle cause pollution".