Which greenhouse gas is produced from livestock manure and used on some farms to generate electricity?

• A. Carbon dioxide
• B. Methane
• C. Nitrous oxide
• D. Ozone

Answer: (B)

Methane is produced when manure is broken down by microbes in oxygen-free conditions (anaerobic digestion). On some farms, this methane-rich gas is captured as biogas and burned to generate electricity. This not only provides a source of energy but also reduces methane emissions, since burning converts methane (a potent greenhouse gas) into carbon dioxide and water, which have a lower warming potential. Other gases like carbon dioxide, nitrous oxide, or ozone aren’t typically produced in this specific manure-digestion-to-electricity process in the same notable way, so methane is the correct gas in this context.