The role of extreme noise in tipping between stable states

<p>Paleoclimatic records show that under glacial boundary conditions the climate has jumped irregularly between two different climate states. These are the stadial and interstadial climates characterized by extremely abrupt climate change, the Dansgaard-Oeschger events. The irregularity and the fact that no known external triggering is present indicate that these are induced by internal noise, so-called n-tipping. The high resolution record of dust from Greenland icecores, which is a proxy of the state of the atmosphere, can be well fitted by a non-linear 1D stochastic process. But in order to do so the noise process needs to be an alpha-stable process, which is characterized by heavy tails violating the central limit theorem.  I will discus how extreme events can influence the transition from one climate state to the other.</p>

Is there evidence for a 4.2 ka BP event in the northern North Atlantic region?

We review paleoceanographic and paleoclimatic records from the northern North Atlantic to assess the nature of climatic conditions at 4.2 ka BP, which has been identified as a time of exceptional climatic anomalies in many parts of the world. The northern North Atlantic region experienced relatively warm conditions from 6 to 8 ka BP, followed by a general decline in temperatures after ∼5 ka BP, which led to the onset of neoglaciation. Over the last 5000 years, a series of multi-decadal- to century-scale fluctuations occurred, superimposed on an overall decline in temperature. Although a few records do show a glacial advance around 4.2 ka BP, because they are not widespread we interpret them as local events – simply one glacial advance of many that occurred in response to the overall climatic deterioration that characterized the late Holocene.

Is there evidence for a 4.2 ka BP event in the northern North Atlantic region?

We review paleoceanographic and paleoclimatic records from the northern North Atlantic to assess the nature of climatic conditions at 4.2 ka BP, which has been identified as a time of exceptional climatic anomalies in many parts of the world. The northern North Atlantic region experienced relatively warm conditions in the early Holocene (6–8 ka BP) followed by a general decline in temperatures after ~ 5 ka BP, which led to the onset of Neoglaciation. Although a few records do show a distinct anomaly around 4.2 ka BP (associated with a glacial advance), this is not widespread and we interpret it as a local manifestation of the overall climatic deterioration that characterizes the late Holocene.

On Bifurcations Inducing Glacial Cycle Lengthening During Pliocene/Pleistocene Epoch

In the Pliocene (about two–five million years ago) global climate fluctuated with a period corresponding well to the 41-thousand-year cycle of changes in the Earth's axis obliquity. Then, this period disappeared, despite the fact that the obliquity cycle even slightly increased its swing and, therefore, the climatic response to this external climate forcing would have only strengthened. By analyzing paleoclimatic records covering the whole Pliocene and Pleistocene epoch, we show that the climatic response to the obliquity cycle simply became unstable, and therefore unobservable. At the same time, through the period-doubling bifurcation, which is well-known in dynamical system theory, new stable, and so observable, climatic fluctuations have been excited with an approximately doubled period. Further, these fluctuations experienced several secondary bifurcations, and, as a result, their periods increased even more.