evidence: Carbon dioxide [edit]Carbon dioxide (CO2) has a large warming effect on global temperatures through the greenhouse effect. Although individual CO2 molecules have a short residence time in the atmosphere, it takes an extremely long time for carbon dioxide levels to sink after sudden rises, due to e.g. volcanic eruptions or human activity[17] and among the many long-lasting greenhouse gases, it is the most important because it makes up the largest fraction of the atmosphere.[10] Since the Industrial Revolution, the CO2 concentration in the atmosphere has risen from about 280 ppm to almost 400 ppm.[7] Although the amount of CO2 introduced makes up only a small portion of the global carbon cycle, carbon dioxide's long residence time makes these emissions relevant for the total carbon balance. The increased carbon dioxide concentration strengthens the greenhouse effect, causing changes to the global climate. Of the increased amounts of carbon dioxide that are introduced to the atmosphere each year, approximately 80% are from the combustion of fossil fuels and cement production.