Generating a kWh emits 0.8 pounds of CO2 on average (source: https://www.eia.gov/tools/faqs/faq.php?id=74&t=11); burning a gallon of gasoline in a car emits about 20 pounds of CO2. That means that 800 kWh (= 640 pounds of CO2 emitted) is as bad as using 32 gallons in a year.
