| Speaker: Jan Sieber Affiliation: University of Exeter Time: 2 pm Thursday, 1 March, 2018 Location: 303-257 |
| Palaeoclimate records show a curious transition from small-amplitude oscillations to large-amplitude oscillations in global ice extent and temperature around 1 million years ago. There is a debate whether this transition should be attributed to a change in forcing by the sun or mostly to internal dynamics of the Earth system. While highly credible data for the forcing is available, sophisticated climate models cannot be run this far into the past. We consider an extremely simple global mean model (originally proposed by Saltzman and Maasch) in a version with only a single variable and a delayed feedback loop and add the well-known very non-periodic forcing from the sun. We observe a sharp change in the behaviour of the model at a critical forcing strength (looking very much like the mid-pleistocene transition). This sharp change corresponds mathematically to a collision between a non-periodic attractor and a non-periodic saddle-type object. To properly observe this collision we tracked dynamically unstable non-periodic orbits over a long time in a system parameter. [joint work with Courtney Quinn, Tim Lenton (both Exeter), Anna von der Heydt (Utrecht)] |