Burning fossil fuels affects atmospheric CO2 by which of the following?

• A. Decreasing CO2 levels
• B. No effect on CO2 levels
• C. CO2 is converted to oxygen directly
• D. Increasing CO2 levels

Answer: (D)

When fossil fuels are burned, carbon stored underground is released as carbon dioxide. The combustion reaction uses oxygen to form CO2, which goes into the atmosphere. CO2 is a greenhouse gas, so higher atmospheric CO2 concentrations trap more heat and contribute to warming. The idea that CO2 would be converted into oxygen directly isn’t how burning works—oxygen is consumed and CO2 is produced. Some CO2 is absorbed by oceans and plants, but the net effect of burning fossil fuels is an increase in atmospheric CO2.