Climate change and the butterfly effect: can a chaotic system be truly predicted?

This talk will be at the intersection of fluid mechanics, climatology and dynamical system theory. It will be delivered in the framework of the course Fluid mechanics II (LMECA2322).

Everyone is welcome to attend.

Abstract

Two centuries ago, French mathematician and physicist Joseph Fourier (well known for his famous « series » but also for his theory of heat conduction) was the first person to suggest the existence of the greenhouse effect on planet Earth. Yet, in 2025, despite overwhelming scientific evidence linking the buildup of long-lived greenhouse gases in the atmosphere to extreme climate events, high scepticism persists. A common belief feeding that scepticism is that climate predictability cannot extend beyond 15 days due to the inherent limits of weather forecasts. In this lecture, I will use elements of computational fluid dynamics, dynamical systems theory, and physical climatology to provide the keys for resolving this issue. Starting from the Navier–Stokes equations, I will illustrate how large-scale atmospheric motions give rise to Rossby waves—the building blocks of midlatitude weather. I will then discuss how the chaotic nature of the atmospheric motion was first discovered (in fact, by accident) and why chaos does not preclude predictability of the atmosphere. Finally, I will revisit the earliest climate projections made in the 1970s which proved to be a spectacular success, as recently recognized with a Nobel Prize in Physics.

On the speaker

François Massonnet is a Civil Engineer in Applied Mathematics from UCLouvain (2009) and holds a PhD in Sciences from the same university (2014). He is a F.R.S.-FNRS Research Associate and part-time Lecturer at Earth and Life Institute, UCLouvain where he leads several national and international projects, including a European Starting Grant (ERC) research focusing on the prediction of rapid Arctic sea ice loss events. He is author or co-author of 86 papers published in the international peer-reviewed literature, and teaches several courses on climate dynamics, modelling, and forecasting.