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Evidence from north-west Canada for an early Holocene Milankovitch thermal maximum


According to the Milankovitch theory of global climatic change, maximum summer solar radiation at high latitudes of the Northern Hemisphere occurred at 10,000 yr BP (refs 1, 2). In particular, it predicts summer solstice radiation greater by 9–10%. Preliminary climate simulation experiments with these increased values of radiation confirm that high-latitude land surfaces received maximal insolation at 10,000 yr (refs 3, 4). Paradoxically, however, the large volume of fossil pollen and other evidence from North America indicates a maximum of Holocene warmth at 7,000–6,000 yr (ref. 5), and a recent review of the evidence from New England suggests that the warming began at 9,000 and ended at 5,000 yr, but also stresses the difficulties of interpretation in terms of climate change6. We summarize here data from sites in the north-west corner of mainland Canada (Fig. 1) that directly support the Milankovitch hypothesis.

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Ritchie, J., Cwynar, L. & Spear, R. Evidence from north-west Canada for an early Holocene Milankovitch thermal maximum. Nature 305, 126–128 (1983).

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