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

The Runaway Greenhouse Effect in Earth-like Climates

Typically when we think of tipping points, scenarios that may come to mind include the collapse of the AMOC, melting of the Greenland ice sheet, or dieback of the Amazon. We know from past evidence and model simulations that each of these would significantly disrupt the climate system, having a detrimental impact on human society and the biosphere. Ultimately whether any—or many (I hope not)—of these tipping points are passed or not is within our control as a species, but what about tipping points we have no control over? What if such a tipping point leads to Earth becoming completely and irreversibly inhospitable? Welcome to the cheery world of the runaway greenhouse scenario and hot-house climates. I will aim to give an introduction to the runaway greenhouse effect and how climates can tip into a runaway state, with comparisons to analogues in our own solar system and beyond. I will then present a series of model analyses that demonstrate how the runaway tipping point can be modified by changing the moisture budget and orbital configuration of an Earth-like planet; including demonstrating why on Earth we are safe from such a fate (for now at least).

How do you even quantify tipping in a realistic & complex system? Application in clouds?

In this talk I will introduce my recent research on transitions (tipping) between alternative climate states, and highlight the relevance it has for the broader climate and Earth system. The research is based on a conceptual model, that itself however is both complex and highly realistic. Its behaviour is governed by 50+ equations and 10+ parameters, all of which have direct and meaningful impact over when or how the system may transition to an alternative state. Things become even worse when we face the uncertainty in the equations themselves: some equations may be represented by different versions. The question is, how do we even quantify tipping in such a system? The traditional way of incrementing a parameter and recording when a bifurcation occurs is neither scalable nor meaningful in such a system: in reality all system parameters change in partially correlated and partially noisy manner. I’ll showcase my approach on estimating tipping probabilities, and welcome thoughts on how to better approach the problem!

Global Tipping Points Report 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)