Beginning in the 18th century, human activities has increased the amount of greenhouse gases (such as carbon dioxide) through burning of fossil fuels, electricity and heat production, agriculture,
manufacturing, and engines used for transportation. These activities amplify the natural "greenhouse
effect" and cause the average temperature on Earth to increase. This gradual increase in average
temperatures on Earth is known as

a) global warming

b) weather

c) carbon footprint

d) Earth heating