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 variation 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 stematic 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.