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SUMMARY:Climate tipping as a noisy bifurcation: a predictive technique - T
 hompson\, M\, Sieber\, J (Cambridge and Portsmouth Universities)
DTSTART:20100825T090000Z
DTEND:20100825T100000Z
UID:TALK25886@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:In the first half of this contribution (speaker JMTT) we revie
 w the bifurcations of dissipative dynamical systems. The co-dimension-one 
 bifurcations\, namely those which can be typically encountered under slowl
 y evolving controls\, can be classified as safe\, explosive or dangerous. 
 Focusing on the dangerous events\, which could underlie climate tippings\,
  we examine the precursors (in particular the slowing of transients) and t
 he outcomes which can be indeterminate due to fractal basin boundaries.\n\
 n\nIt is often known\, from modelling studies\, that a certain mode of cli
 mate tipping is governed by an underlying bifurcation. For the case of a s
 o-called fold\, a commonly encountered bifurcation (of the oceanic thermoh
 aline circulation\, for example)\, we estimate (speaker JS) how likely it 
 is that the system escapes from its currently stable state due to noise be
 fore the tipping point is reached. Our analysis is based on simple normal 
 forms\, which makes it potentially useful whenever this type of tipping is
  identified (or suspected) in either climate models or measurements.\n\nDr
 awing on this\, we suggest a scheme of analysis that determines the best s
 tochastic fit to the existing data. This provides the evolution rate of th
 e effective control parameter\, the (parabolic) variation of the stability
  coefficient\, the path itself and its tipping point. By assessing the act
 ual effective level of noise in the available time series\, we are then ab
 le to make probability estimates of the time of tipping. In this vein\, we
  examine\, first\, the output of a computer simulation for the end of gree
 nhouse Earth about 34 million years ago when the climate tipped from a tro
 pical state into an icehouse state with ice caps. Second\, we use the algo
 rithms to give probabilistic tipping estimates for the end of the most rec
 ent glaciation of the Earth using actual archaeological ice-core data. \n\
 n\n\n\n
LOCATION:Seminar Room 1\, Newton Institute
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