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Human Contributions to CO2 Levels

Since 1991, 97 percent of 4,000 peer-reviewed scientific papers on climate change agree that human activities are a leading cause of global warming, with carbon dioxide production accounting for much of the effect. Large-scale industrial processes and modern transportation have led to rising concentrations of atmospheric CO2. In addition, other actions such as deforestation have compromised natural means of removing CO2 from the air.

Electric Power Generation
- According to statistics from the Environmental Protection Agency for 2011, the US alone produced 6,700 million metric tons of CO2, with 33 percent of that coming from the generation of electric power. Although the US has significant amounts of nuclear power, which produces no CO2, coal and gas account for the majority of electric power production. In 2010, the world̵7;s output of CO2 from electric power was more than 12 billion tons out of a total of 30 billion tons emitted that year.
Industrial Processes
- To produce iron and steel, cement and other industrial commodities, manufacturers generate 6 billion of tons of CO2 each year -- about 20 percent of total CO2 emissions. Some industrial processes burn gas and coal to generate vast amounts of heat, such as to melt metals; other industrial sources of CO2 include the byproducts of chemical reactions.
Transportation Emissions
- Internal combustion engines burn gasoline, diesel and natural gas, powering vehicles and generating large amounts of CO2 in the process. In 2010, transportation accounted for 6.6 billion tons of CO2 worldwide, or 22 percent of 30 billion tons total. Although natural gas burns more cleanly than gasoline or diesel as it contains no sulfur or nitrogen, its advantage for carbon dioxide is slight; in terms of CO2 mass per energy produced, gas produces .23 kg per kilowatt-hour, diesel is .24 kg per kWh, and gasoline has .26 kg per kWh.
Land Clearing
- In developing nations, large areas that once held trees and other greenery have been cleared for human habitation, agriculture and other uses. Deforestation not only removes trees that once consumed large amounts of atmospheric CO2, it also releases large amounts of carbon dioxide back in the air when cut-down trees are burned and otherwise destroyed. If the land is reclaimed for agriculture, it reuses some of the released CO2 to grow plants. According to a 2012 Congressional Budget Office report, deforestation accounted for 12 percent of greenhouse gas emissions globally.

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