Changing carbon: Human fingerprints
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Measurements show that the levels of carbon dioxide (CO2) in the atmosphere are rising and that the rate of the rise is accelerating. Scientists have demonstrated that this increase is mostly being caused by human activities, particularly the burning of fossil fuels. The carbon contained in fossil fuels has a slightly different mix of carbon isotopes (different types of the same element) than the carbon originally in the atmosphere. By releasing fossil-fuel carbon which combines with oxygen to form CO2 in the atmosphere, humans have changed the ratio of atmospheric carbon isotopes. Scientists have measured this change, enabling them to link the CO2 increase directly to fossil fuels.