“A butterfly can flap its wings in Peking, and in Central Park you get rain instead of sunshine”—at least according to Jeff Goldblum in Jurassic Park. But the reality is actually not far off: the “butterfly effect”, formally known as Chaos theory, holds that miniscule changes in a chaotic system could have large, unpredictable effects. Our climate is a chaotic system, a consequence of an unending list of interconnected events from solar radiation and the motion of air, to methane leaks and deforestation. To imagine reliably predicting Earth’s climate from this entangled jumble of factors seems impossible—no wonder, then, why the 2021 Nobel Prize in Physics was awarded to three pioneering scientists who discovered patterns in this complex system. 

              Without a DeLorean time machine, our next best alternative is a computer simulation of our climate, which applies mathematical equations to predict how this system evolves. Laureate Dr. Manabe was a pioneer in climate modelling. In the 1960s, his simple simulations showed the critical connection between increased greenhouse gases, namely carbon dioxide and water vapour, and warming in the atmosphere. Later on, he developed sophisticated 3D models of the coupled atmosphere-ocean-land system which predicted global warming. 

Dr. Hasselmann built upon this work by answering why we can reliably predict long-term shifts in climate despite rapidly varying weather patterns. Inspired by Brownian motion—the motion of pollen grains’ displacement in water due to tiny, random collisions with the water molecules—he showed how weather patterns are similar to the water molecules or random “noise”, which can be integrated into larger forces like atmospheric patterns that modulate the climate. By introducing chaos into a model, he also discovered statistical methods to distinguish between the background noise of the natural climate variability and signals from human activities, proving global warming is humanity’s fault. 

Interestingly, Dr. Parisi, the third Laureate, was working in a field seemingly unrelated to environmental sciences. By investigating a strange material known as “spin glass”, which behaves as a complex system, he discovered a mathematical technique to find “hidden rules” that govern the chaotic movement of its particles. This technique has extended far beyond spin glass, and has allowed climate scientists to construct more accurate models. “A (complex) system that looks hopelessly random, if analysed the right way, can yield a robust prediction for a collective behaviour,” commented David Yllanes—a researcher in spin glass—on Parisi’s revolutionary work. 

A famous tragedy in Greek Mythology is that of Cassandra, a princess granted with the gift of prophecy but cursed to remain ignored and dismissed, eventually causing the destruction of Troy. In this modern age, climate scientists empathise with Cassandra’s situation—these projections, which “rest on a solid scientific foundation based on a rigorous analysis of observations”, have become equivalent to her divine power of prophecy, yet most of the world acts as if global warming is still a hypothesis. Dr. Parisi sums up the message of their research with the simple phrase: “We have to act now.” 

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