Greenland Interstadials and the Younger Dryas-Preboreal Transition: Early-Warning Signals for the Onsets

Australia: The Land Where Time Began

Greenland Interstadials and the Younger Dryas-Preboreal Transition: Early-Warning Signals for the Onsets

If the prevailing climate state loses stability the climate system approaches a tipping point. The reduced stability in the vicinity of a tipping point, a result from the theory of randomly driven dynamical systems, is accompanied by increasing fluctuation levels and longer correlation times (critical slowing down) and can serve in principle as early-warning signals of an upcoming tipping point. It is demonstrated by this study that the high-frequency band of the variations in the concentrations of ¹⁸O in the North Greenland Ice Core Project displays increasing fluctuation levels as the onset of an interstadial (warm) period is approached. For the locally estimated Hurst exponent for the high-frequency fluctuations similar results are found, signalling longer correlation times. In the Younger Dryas the slowing that is observed is even stronger, which suggests that both the Younger Dryas-Preboreal transition and the Greenland Interstadials onsets are preceded by a climate state of decreasing stability. Rypdal also verified that during the stadial periods the temperature variations can be modelled approximately as a scale-invariant persistent noise, which can be approximated as an aggregation of processes that respond to perturbations on certain characteristic time scales. According to Rypdal the results are consistent with the hypothesis that the onsets of the Greenland Interstadials, as well as the Younger Dryas-Preboreal transition, are caused by tipping points in dynamical processes that have characteristic time scales on the order of decades and that the variability of other processes on longer time scales masks the early-warning signatures in the ¹⁸O concentration signal.

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