How does the burning of fossil fuels influence atmospheric CO2 levels?

• A. It converts CO2 into methane, lowering atmospheric CO2.
• B. It removes CO2 from the atmosphere through chemical weathering.
• C. It stores CO2 in soil as organic matter, reducing atmospheric CO2 immediately.
• D. Combustion releases CO2 from carbon stored in fuels, increasing atmospheric CO2 and contributing to greenhouse effect.

Answer: (D)

Burning fossil fuels releases CO2 because the carbon stored in those fuels reacts with oxygen to form carbon dioxide. This carbon was locked away underground for millions of years, and combustion returns it to the atmosphere as CO2. Since CO2 is a greenhouse gas, this additional CO2 traps more infrared radiation and strengthens the greenhouse effect, leading to warming.

Think of it as the direct result of oxidation: C + O2 → CO2. The other ideas don’t fit the process of combustion—they describe different mechanisms or different timescales (weathering removing CO2 slowly, soil storing carbon, or CO2 being transformed into methane)—whereas burning fuels immediately adds CO2 to the atmosphere.