Abstract
13C/12C data for the past 500 years are reported on two sets of European oak forest trees from the German Spessart and on free‐standing Scots pine trees from Muddus National Park, Sweden. While the forest trees show large nonsystematic variations in the 13C/12C ratio over the 500 years, the free‐standing trees show smaller fluctuations, which can be correlated to climatic changes. Since industrialization of these areas in 1850 A.D., the 13C/12C record for the free‐standing trees has been dominated by a systematic decrease of about 2‰, which is comparable with other mean 13C/12C tree ring data. The calculated Northern Hemisphere 13C/12C record derived from a total of about 50 trees reflects the recent 13C/12C change in atmospheric CO2 observed from 1956 to 1980 A.D.