Consider the following: Which of the above are sources of methane, a major greenhouse gas?

Answer: (d) 1, 2, 3 and 4

All four release methane.

Statement by statement

1. ✓ YES Flooded paddy soils lack oxygen — methanogens release methane.

2. ✓ YES Coal seams hold methane that escapes during mining.

3. ✓ YES Cattle and other ruminants belch methane (enteric fermentation).

4. ✓ YES Wetlands are the largest natural methane source.

The idea

Methane is made wherever organic matter rots without oxygen. A group of microbes called methanogens do this. The four sources look different but three of them are the same process in different places; coal mines release methane that was trapped when the coal formed.

Wetland mud: no oxygen → methanogens → Flooded rice field: no oxygen → methanogens → Stomach of cattle: no oxygen → methanogens → belched out → Coal seam: old trapped methane escapes on mining

Also know

Other sources: landfills, leaking gas pipelines, termites. Methane stays in the air about 12 years and is about 28 times as strong as carbon dioxide over a century. India has the world’s largest bovine population (cattle + buffaloes); ICAR has developed a feed supplement, Harit Dhara, that cuts methane from cattle.