Seminars

This page contains a collection of titles from recent and upcoming seminars.

Please contact Isobel Parry if you have a suggestion for a seminar speaker.

Autumn 2025

Thresholds of the Antarctic Ice Sheet and high impact future sea level scenarios.

What’s up with Betelgeuse?

In late 2019, the red supergiant Betelgeuse—one of the brightest stars in the night sky—suddenly dimmed to a record low brightness, an unprecedented event discernible by the naked eye. Explanations have ranged from an impending supernova, dust clouds expelled by the star, internal convective outbursts, to speculation about a stellar companion. What remains uncertain is whether this event marked a lasting change in the star’s dynamics. In this work, we examine Betelgeuse’s long-term brightness variation (light curve) and find statistical patterns resembling the early warning signals (EWS) commonly associated with critical transitions in complex systems. 
We suggest that the dimming was associated with a shift in the star’s dominant mode of pulsation, consistent with a tipping-like event. Remarkably, five years later, this new oscillation pattern has persisted. We present Betelgeuse as a case study for how ideas from dynamical systems theory, particularly those related to tipping points, can be applied to astrophysical systems.(George, S.V., Kachhara, S., Misra, R. and Ambika, G.: https://doi.org/10.1051/0004-6361/202038785)

Early warning skill, extrapolation and tipping for accelerating cascades.

We investigate how nonlinear behaviour (both of forcing in time and of the system itself) can affect the skill of early warning signals (EWS) to predict tipping in (directionally) coupled bistable systems when using measures based on critical slowing down (CSD) due to the breakdown of extrapolation. We quantify the skill of early warnings with a time horizon using a receiver–operator methodology for ensembles where noise realizations and parameters are varied to explore the role of extrapolation and how it can break down. We highlight cases where this can occur in an accelerating cascade of tipping elements, where very slow forcing of a slowly evolving ‘upstream’ system forces a more rapidly evolving ‘downstream’ system. If the upstream system crosses a tipping point, this can shorten the time scale of valid extrapolation. In particular, ‘downstream-within-upstream’ tipping will typically have warnings only on a time scale comparable to the duration of the upstream tipping process, rather than the time scale of the original forcing. (joint work with R Bastiaansen, A von der Heydt and P Ritchie: https://doi.org/10.1098/rspa.2025.0405)