Sources

Methane forms during decomposition of vegetation and organic waste under oxygen-limited conditions. It is also released as a waste gas from digestion in animals such as cattle.

Greenhouse role

Methane absorbs outgoing thermal energy and re-emits it, reducing the net loss of energy to space. Higher methane concentration therefore contributes to global warming and climate change.

Control strategies

Reducing livestock numbers or emissions per animal, capturing landfill gas and preventing leaks from fuel systems can lower methane emissions. Captured methane can be burned for energy, converting it mainly to CO2 and water.

Evaluation

A strategy may have food, economic and land-use consequences. Strong evaluation considers effectiveness, practicality and side effects.

High-value recall and connections

Essential recall: Name two methane sources. Decomposing vegetation/waste and digestion in animals. How does methane warm the climate? It absorbs and re-emits thermal energy, reducing loss to space. Give one control strategy. Capture landfill gas, reduce livestock emissions or prevent gas leaks. Practical connection: Interpret methane-emission data by source and calculate percentage contributions. Recommend a priority action using evidence. Examination connection: Methane’s adverse effect in this syllabus is increased global warming, not acid rain.

Review questions and suggested answers