CLIMATIC TRENDS FROM ISOTOPIC RECORDS OF TREE-RINGS - THE PAST 100-200 YEARS

There has been a great deal of discussion about global warming from ac cumulation of anthropogenic greenhouse gases in the atmosphere (Hought on et al., 1990). Relatively less attention has been paid to spatial a nd/or temporal climatic variations that may be associated with a warme r climate (Rind et al., 1989) or with anthropogenic activities (Schnei der, 1994). In this article; we show that an increase in climatic vari ability may have started. Fourteen isotopic time series of tree rings are presented. These trees were randomly collected from world-wide loc ations and cover time periods of 120 to over 200 years. The isotopic r ecords show increasing delta D values that suggest a consistent and pr ogressive warming occurred in the 19th century in all locations where the trees were sampled. The rate of warming is greater at relatively c old locations than at warm locations with two exceptions. The records also suggest greater climatic variations both temporally and spatially in the 20th century than in the 19th century.