On the stochastic nature of the rapid climate shifts during the last ice age

The rapid climate shifts observed in the glacial climate are analysed. The transitions into the warm interstadial states, the onsets, are easy identifiable in the record. The distribution of waiting times between consecutive onsets is well fitted assuming the remaining residence time in each state to be independent on the past. That implies that it has a simple no memory exponential waiting time distribution, but with mean waiting time depending on the climate state. The mean waiting time from one onset to the next is around 2400 y. The most likely (maximum likelihood) distribution derived solely from the onset sequence is rather insensitive to the mean waiting time in the warm interstadials in the range 400-1200 y. When extending the analysis to include the transitions from the warm interstadials to the cold stadials observed with a larger uncertainty, the distributions in the two states are well fitted to exponential distributions with mean waiting times of around 800 y in the warm state and around 1600 y in the cold state. This observation is an important piece in the climate puzzle, since the fact that the climate is a no memory process indicates that the transitions are noise induced and the mean residence time in one state indicates how stable that climate state is to perturbations. The possibility of a hidden periodic driver is also investigated. The existence of such a driver cannot be ruled out by the relatively sparse data series (containing only 21 onsets). However, since the record is fitted just as well by the much simpler random model, this should be preferred from the point of view of simplicity.