The Suess effect is a change in the ratio of the atmospheric concentrations of heavy isotopes of carbon (C and C) by the admixture of large amounts of fossil-fuel derived CO, which contains no CO and is depleted in CO relative to CO in the atmosphere and carbon in the upper ocean and the terrestrial biosphere . It was discovered by and is named for the Austrian chemist Hans Suess, who noted the influence of this effect on the accuracy of radiocarbon dating. More recently, the Suess effect has been used in studies of climate change. The term originally referred only to dilution of atmospheric CO relative to CO. The concept was later extended to dilution of CO and to other reservoirs of carbon such as the oceans and soils, again relative to C.
Although the ratio of atmospheric CO to CO decreased over the industrial era (prior to atmospheric testing of nuclear weapons, commencing about 1950), because of the increase, due to fossil fuel emissions, in the amount of atmospheric CO over this period, roughly 1850 to 1950, the amount of atmospheric CO actually increased over this period.