IB Environmental systems and societies 2.3D Methane Notes

Methane: A Short-Lived but Powerful Greenhouse Gas

1. Methane (CH₄) is a potent greenhouse gas, with a global warming potential over 80 times that of carbon dioxide (CO₂) across a 20-year period.
2. It plays a critical role in both the carbon cycle and climate change.

Methane Forms Where Oxygen Is Scarce

1. When dead organic material decomposes under anaerobic (oxygen-poor) conditions, carbon is converted into methane by methanogenic microbes.
2. This process, called methanogenesis, is part of the carbon cycle: it temporarily stores carbon as methane before it is oxidised back to CO₂.

1. The methane can later escape into the atmosphere or accumulate underground in natural gas deposits.

Organic matter → simple organic acids → CO₂ + H₂ → CH₄ (methane)

Conditions for Methane Production

1. Methane forms where oxygen is extremely low and organic matter piles up.
2. These conditions block complete aerobic decomposition, letting methanogens thrive.
3. Key environments include:
   1. Swamps and wetlands: submerged plant material creates ideal anaerobic conditions.
   2. Rice paddies: flooded fields restrict oxygen, so residues decompose to methane.
   3. Landfills: buried organic waste decomposes anaerobically.
   4. Digestive tracts of ruminants: methanogens live in the stomachs of cows, sheep, and goats.
   5. Permafrost and peat bogs: frozen organic matter traps methane that is released on thawing.

Anthropogenic Methane Sources

1. Human activities have sharply increased methane emissions.
   1. Agriculture: rice cultivation and livestock farming are major sources.
   2. Landfills and sewage treatment: decomposing waste releases methane.
   3. Fossil fuel extraction: methane leaks from coal mining, oil drilling, and gas pipelines.

In the Atmosphere, Methane Traps Heat Then Breaks Down

Atmospheric Presence and Fate of Methane

1. Once released, methane absorbs long-wave infrared radiation from Earth's surface, trapping heat in the troposphere.
2. But methane's residence time is short, about 10 years on average.

Oxidation of Methane

1. Methane is eventually oxidised to carbon dioxide and water vapour by hydroxyl radicals (OH•) in the atmosphere.
2. This removal regulates atmospheric methane, but it converts methane into longer-lived CO₂.

CH₄ + OH• → CH₃• + H₂O → CO₂ + H₂O

Methane's Role as a Greenhouse Gas

1. Methane is the second most significant greenhouse gas after carbon dioxide.
2. Its global warming potential (GWP) is about 28 times that of CO₂ over a 100-year period.
3. Over 20 years its GWP exceeds 80 times that of CO₂, making it especially dangerous for short-term warming.

Climate Implications and Mitigation

1. Methane accounts for roughly 30% of the rise in global temperatures since the Industrial Revolution.
2. Because it is short-lived, cutting methane emissions brings measurable climate benefits within decades.

Mitigation Strategies

1. Agriculture
   1. Use alternate wetting and drying in rice fields, and feed additives that inhibit methane-producing microbes in livestock.
2. Waste management
   1. Capture landfill gas and use it for biogas energy.
3. Energy sector
   1. Repair leaking pipelines and capture fugitive emissions.