The specific type of CO2 that is increasing in earth's atmosphere can be directly connected to human activity. CO2 produced by burning fossil fuels such as oil and coal [18] can be differentiated in the atmosphere from natural CO2 due to its specific isotopic ratio. [101] According to the Intergovernmental Panel on Climate Change (IPCC), 20th century measurements of CO2 isotope ratios in the atmosphere confirm that rising CO2 levels are the result of human activity, not natural processes such as ocean outgassing, volcanic activity, or release from other "carbon sinks." [102] US greenhouse gas emissions from human activities in 2012 totaled 6.5 million metric tons, [19] which is equivalent to about 78.3 billion shipping containers filled with greenhouse gases.