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Methane, carbon dioxide and climate change

Human influences on ecosystems · Pollution · note 3 of 3

Spec 20.3.3Download all Pollution notes (PDF)Download all notes (PDF)5 pages

Methane, carbon dioxide and climate changeSpec 20.3.3

In short

The enhanced greenhouse effect is the extra heating caused when human activities increase the concentrations of carbon dioxide and methane, so more infrared radiation is trapped in the atmosphere. Carbon dioxide comes from burning fossil fuels and forests; methane comes from cattle, rice paddy fields and landfill. This causes global warming and climate change, such as rising sea level.

Sources of methane and carbon dioxide
GasSources
Carbon dioxideBurning fossil fuels (in vehicles, power stations and homes); burning forests; respiration of decomposers when trees decay
MethaneCattle and other livestock (from digestion); rice paddy fields; decomposition of waste in landfill sites

The enhanced greenhouse effect

  1. Short-wave radiation from the Sun passes through the atmosphere and warms the Earth's surface.
  2. The Earth re-radiates this energy as infrared (heat) radiation.
  3. Greenhouse gases such as carbon dioxide and methane trap some of this infrared radiation in the atmosphere, which keeps the Earth warm. This is the natural greenhouse effect.
  4. Human activities have increased the concentrations of carbon dioxide and methane, so more heat is trapped. This is the enhanced greenhouse effect.

The average temperature of the Earth rises (global warming). This leads to climate change. Effects include melting ice caps and rising sea level, changes to rainfall and weather, and loss of habitats, so some species may become endangered or extinct.

Greenhouse effect: short-wave radiation from the Sun reaches the Earth's surface; infrared radiation leaves the surface, some escaping to space and some trapped by a layer of greenhouse gases (CO₂ and methane), which warms the Earth. (opens full size in a new tab)
Greenhouse gases such as carbon dioxide and methane trap infrared radiation. More of these gases traps more heat.
Common mistake:

The greenhouse effect is not caused by a hole in the ozone layer. These are separate issues.

Quick check

  1. Why does excess fertiliser harm rivers and lakes?

    Show answer

    Nitrates cause rapid growth of algae and water plants, which can lead to eutrophication and the death of other organisms.

  2. Why do non-biodegradable plastics last so long?

    Show answer

    Microorganisms cannot break them down.

  3. Name two sources of methane.

    Show answer

    Cattle (livestock); rice paddy fields; landfill sites.

  4. What is the enhanced greenhouse effect?

    Show answer

    Extra heat trapped in the atmosphere because human activity has raised carbon dioxide and methane levels.

Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026

Frequently asked questions

What is eutrophication and what causes it?

Supplement Eutrophication is caused by extra nitrate and other ions entering water from excess fertiliser or untreated sewage. Algae and water plants grow faster, forming an algal bloom that blocks light. Producers deeper in the water die, and decomposers increase. Their aerobic respiration uses up dissolved oxygen, so fish and other organisms that need oxygen die.

How does plastic pollution affect marine life?

Plastic pollution harms marine life because plastics are non-biodegradable, so they last a very long time. Turtles, seabirds and fish swallow plastic, which can block their digestive system so they starve. Animals become tangled in plastic and drown or cannot move. Plastic also breaks into tiny pieces that enter food chains.

What causes the enhanced greenhouse effect?

The enhanced greenhouse effect is caused by human activities increasing the concentrations of carbon dioxide and methane in the atmosphere. Burning fossil fuels and forests releases carbon dioxide, while cattle, rice paddy fields and landfill sites release methane. These gases trap more infrared radiation, so the Earth's average temperature rises, causing climate change.

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