FIGURE 14.62 Evidence of rapid climate changes at the start of the Holocene period ~11,600 years before the present (bp): (a) electrical conductivity; (b) rate of accumulation of snow; (c) calcium concentration. The depth of the ice cores is shown on the bottom axis and the corresponding age in years before the present on the top axis (adapted from Taylor et al„ 1997).

In short, ice core and other long-term records show that there have been dramatic climate changes in the past, some of them within or shorter than a typical human life span. Separating out such natural variability from anthropogenic perturbations remains a major challenge, particularly when it is possible that the anthropogenic emissions may act to hasten or "jolt" the climate system into a relatively rapid transition from one state to another.

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