The main sources of carbon dioxide in the atmosphere are decaying plants, waste products as a result of the respiration of animals and volcanic eruptions. Human activity also releases carbon dioxide into the air. The main source of this carbon dioxide is the burning of fossil fuels.
The carbon dioxide that is released into the air from natural sources is removed in equal measures by other natural occurrences. This includes photosynthesis in plants and dissolution in water, primarily the world's oceans. Therefore, the natural production and removal of carbon dioxide is well balanced. As a result, human activity is the main cause of carbon dioxide in the air.
The main sources of carbon dioxide in the air from human activity come from the burning of fossil fuels. The production of electricity, transportation and industry are the three areas that produce the most carbon dioxide through the burning of fossil fuels. Electricity production accounts for 38 percent of the total carbon dioxide emissions produced by the United States, according to the Environmental Protection Agency. Transportation of people and goods accounts for 32 percent, while industry accounts for 14 percent.
Humans have contributed to carbon dioxide in the atmosphere since the start of the industrial revolution in 1750, as stated by the EPA.