Tree Ring Data
By studying the width of tree rings (dendrochronology) history of annual tree growth can be determined. Individual rings represent individual years while the width of each ring shows the growth rate during that year. The width of rings from trees found at higher altitudes and higher latitudes is generally a function of temperature where wide rings indicate warm years and narrow rings indicate cool years (Lamb, 1995.) Because the pattern of rings is similar to a fingerprint, dendrochronologists are able to construct a chronology by matching similar ring patterns found in living trees, construction timbers, and fossil trees. Fig. 3 shows how a fossil timber in a river bed is dated by noting matching ring patterns found in building timbers and in living trees. LaMarche (1974), Lamb (1995), and Baillie (1982) have cited various tree-ring data that indicate warmer temperatures during the MWP and cooler temperatures during the LIA. Fig. 4 shows tree-ring widths of bristle cone pines in California during the end of the MWP [Medieval Warm Period] and through the LIA [Little Ice Age] that suggest warm and cool climates during the MWP and LIA, respectively.
Figure 4: Tree-ring widths vs. time from California Bristle Cone Pine trees. (Source: Tkachuk, 1983)
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