12.2Chapter 12: The Carbon Cycle and Climate Change

People and the carbon cycle — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

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12.2 People and the carbon cycle — Fossil Fuels and Deforestation — Alhussan International Academy — Biology (Stages 7–9) notes: Explain how burning fossil fuels and deforestation add carbon dioxide to the atmosphere and strengthen the greenhouse effect.Greenhouse gases — carbon …

Effect of more carbon dioxide
Before the industrial revolution
Carbon sinks
Electricity
Less removal
Other effects

Section 1 of 8The greenhouse effect

1Greenhouse gases

Greenhouse gases carbon dioxide and other gases trap energy from the Sun, like the glass in a greenhouse.
They trap enough to keep the Earth's surface warm, but not so much that it overheats.

2Effect of more carbon dioxide

Effect of more carbon dioxide more energy is trapped and temperatures at the surface rise.
Many ecosystems are finely balanced, so a change in temperature may decide whether a type of organism lives or dies.

Section 2 of 8The balance of the carbon cycle

1Before the industrial revolution

Before the industrial revolution carbon dioxide in the atmosphere was fairly stable because photosynthesis and dissolving in the oceans balanced respiration, decay and combustion.

2Now

Now human activity adds carbon dioxide faster than natural processes can remove it, so the concentration is rising.

3Carbon sinks

Carbon sinks places such as forests, coral reefs and oceans that naturally absorb and store carbon.

Some human activities add carbon dioxide and others interfere with carbon sinks.

Section 3 of 8Burning fossil fuels

Formation

Formation coal, oil and natural gas formed over millions of years from the remains of plants and microscopic organisms that were buried and compressed.
They are stores of carbon taken from the air long ago and are non-renewable.

Burning

Burning hydrocarbon + oxygen → carbon dioxide + water, which releases the carbon in a short time.

Transport

Transport cars, lorries, boats and planes burn fuels made from oil and release about 6.7 gigatonnes (Gt) of carbon dioxide each year.
One gigatonne is one thousand million tonnes.

Electricity

Electricity generation by burning coal, oil or gas adds around 33 Gt each year.

Total

Total about 36.2 billion tonnes of carbon dioxide were produced worldwide in 2017.

Section 4 of 8Deforestation

Deforestation

Deforestation clearing forests for farmland, timber, cattle grazing, roads and housing.

Less removal

Less removal trees take in carbon dioxide in photosynthesis, so fewer trees mean less is removed from the air.
Globally, forests absorb 33% less carbon dioxide than they did 30 years ago.

Release

Release when cleared trees are burned or left to rot, the stored carbon is released by combustion and by decomposers respiring.
Soil carbon can also be lost.

Other effects

Other effects forests help keep water in the soil, so their loss can cause soil erosion and floods.

Section 5 of 8Who produces most

1Emissions by region in 2017

Asia produced 53% of global emissions, North America 18%, Europe 17%, Africa 3.7%, South America 3.2% and Oceania 1.3%.
International aviation and shipping added 3.2%.

2Historical emissions 1751-2017

Europe produced 33%, Asia 29%, North America 29%, Africa 3%, South America 3% and Oceania 1.2%.

3Why patterns change

Why patterns change the use of science and technology changes in different countries.

4Wealth

Wealth as people get richer they use more transport and more electricity for clean water, lighting, refrigeration, heating and air conditioning.

Section 6 of 8Other human effects and solutions

Activity	Effect on carbon cycle	Possible solution
Burning fossil fuels	Adds carbon dioxide	Use renewable energy; save energy
Deforestation	Removes a carbon dioxide sink; releases stored carbon	Protect forests; replant trees
Farming livestock	Adds methane	Change diet; improve feed

Planting

Planting reforestation and afforestation increase carbon dioxide uptake.

Carbon capture

Carbon capture it traps carbon dioxide from power stations and stores it underground.

Agreements

Agreements international agreements try to limit emissions but must balance climate goals with the energy needs of poorer countries.

Section 7 of 8Key terms

Term	Meaning
Greenhouse effect	Warming of the Earth because gases trap energy from the Sun.
Carbon sink	A store, such as a forest or ocean, that absorbs carbon.
Deforestation	Clearing forests.
Fossil fuel	A non-renewable fuel formed from ancient buried organisms.
Gigatonne	One thousand million tonnes.
Reforestation	Replanting trees where forest was cleared.