Climatic implications of stable carbon isotopes in tree rings

STABLE carbon isotope variations in tree rings are normally attributed to either a direct temperature dependent fractionation process in the tree 1 , or alternatively to variations in atmospheric composition 2,3 . To clarify this apparent conflict we have begun measurements of ratios in rings of Southern Hemisphere trees. In spite of some obvious differences between the two trees studied so far, both show a positive correlation with regional temperature trends over the past 75 yr. This result is discussed in terms of the alternatives above, and with the view of extracting palaeoclimatic information. Verification of such influences could provide > 2,000 yr of data on the climate of the region.