What is carbon intensity?

• A. The total CO2 in the atmosphere
• B. The CO2 emitted per hour of operation
• C. The CO2 emitted per unit of energy produced (e.g., g CO2 per kWh)
• D. The energy produced per unit CO2 emitted

Answer: (C)

Carbon intensity is a measure of how much CO2 is released for each unit of energy produced. It answers the question: how much carbon is emitted per unit of energy we generate? It’s typically written as grams of CO2 per kilowatt-hour of electricity.

To find it, you divide the total CO2 emitted by the total energy produced over the same period. This creates a rate that lets you compare different energy sources on a per-unit-energy basis—so a plant or fuel with a lower carbon intensity is cleaner per unit of energy, even if total emissions differ.

This is different from the total amount of CO2 in the atmosphere, which isn’t tied to a specific amount of energy produced, and from CO2 emitted per hour, which is just a rate of emissions without normalizing for how much energy is generated. It’s also the inverse of energy produced per CO2 emitted, which is useful in other contexts but not the standard definition of carbon intensity.

Using carbon intensity helps you compare coal, natural gas, nuclear, and renewables on an equal footing, and it’s essential when evaluating the environmental impact of electricity generation and planning decarbonization.