Which gas is emitted in large amounts from swamps and flooded paddy fields?

Methane (CH4) is produced in large amounts in swamps, marshes and flooded rice (paddy) fields, where organic matter decomposes in the absence of oxygen. For this reason, methane is also called "marsh gas".

How methane is produced:

• In waterlogged soils, oxygen cannot reach the decaying plant material.
• Under these anaerobic (oxygen-free) conditions, microorganisms called methanogens (a group of archaea) break down organic matter and release methane.
• In paddy fields, methane escapes to the atmosphere mainly through the hollow stems of the rice plants, and also by bubbling through the water.

Major sources of methane:

Natural sources: wetlands and swamps (the largest natural source), termites and oceans.

Human (anthropogenic) sources:

• Agriculture: livestock (enteric fermentation in the stomachs of cattle, buffaloes, sheep and goats) and rice cultivation.
• Fossil fuels: leaks from natural gas pipelines, coal mines and oil wells.
• Waste: landfills, sewage and decaying organic waste.

Methane and climate change:

Methane is a powerful greenhouse gas. Over a 100-year period, it traps about 28 to 30 times more heat than carbon dioxide.

It stays in the atmosphere for a shorter time (about 12 years) than carbon dioxide, so cutting methane emissions can slow warming quickly.

The Global Methane Pledge, launched at COP26 in Glasgow (2021), aims to cut global methane emissions by 30 per cent from 2020 levels by 2030. India has not joined it, noting the importance of rice and livestock for small farmers.

Reducing methane from paddy fields:

• Alternate wetting and drying (AWD) of rice fields, instead of continuous flooding.
• Direct seeding of rice (DSR) instead of transplanting into flooded fields.
• The System of Rice Intensification (SRI), which uses less water.

Other uses:

Methane is the main component of natural gas (CNG) and biogas, used as fuel for cooking, vehicles and power.

Why not the other options?

• ✗Carbon dioxide is released mainly by burning fossil fuels and by respiration and decay in the presence of oxygen.
• ✗Ozone is formed in the atmosphere, not released from swamps.
• ✗Sulphur dioxide comes mainly from burning coal and from volcanoes.