Japanese-born American Syukuro Manabe, German Klaus Hasselmann and Italian Giorgio Parisi: awarded the 2021 Nobel Prize in Physics

By Nehru Odeh

Three scientists, Japanese-born American Syukuro Manabe, German Klaus Hasselmann and Italian Giorgio Parisi, have been awarded the 2021 Nobel Prize in Physics for their work on understanding complex systems, such as the Earth’s climate. The winners will share the prize money of 10 million krona (£842,611).

One half of the prize goes in equal parts to Manabe, who is 90, and Hasselmann for modelling earth’s climate and reliably predicting global warming. The other half goes to Parisi for discovering “hidden rules” behind seemingly random movements and swirls in gases or liquids.

Their works are important because they help us understand complex systems that are difficult to predict because of their randomness and disorder. It will also help us predict global warming in spite of the fluctuations of the weather.

Hasselmann, for instance, created a separate model that linked together weather and climate, helping to answer the question of why climate models can be reliable despite the weather being changeable and chaotic.

Thors Hans Hansson, the chair of the Nobel committee for physics, said: “Although the prize is divided into two parts, there is the common theme that has to do with how disorder and fluctuations together – if you understand it properly – can give rise to something that we can understand and predict.

“The discoveries being recognised this year demonstrate that our knowledge about the climate rests on a solid scientific foundation, based on a rigorous analysis of observations. This year’s laureates have all contributed to us gaining deeper insight into the properties and evolution of complex physical systems.”

Asked about the timing of the award, Parisi, a professor at Sapienza University of Rome, Italy, said: “We are in a situation where we can have a positive feedback that may accelerate the increase of temperature. It is clear that for the future generations, we have to act now in a very fast way and not with a strong delay.”

This award is significant because it has come at a time the globe is battling with climate change and world leaders are preparing for a critical UN climate conference, known as COP26, to be held in Glasgow this November

“Complex systems are characterised by randomness and disorder and are difficult to understand,” the Swedish Academy of Sciences said in a statement. “This year’s Prize recognises new methods for describing them and predicting their long-term behaviour.”

Paul Hardaker, the chief executive of the Institute of Physics, said: “Whilst complex systems are difficult to deal with mathematically they are all around us and affect our lives in many different ways, not least through the way they affect the nature of our weather and climate.

“Their work has laid the foundations for our understanding of the Earth system and the impact of our interactions with it. Never has this been more important than in what we are doing now to tackle the challenges of our changing climate and move toward a new green economy.”

Manabe, a senior meteorologist at Princeton University, demonstrated how increased levels of carbon dioxide in the atmosphere can lead to increased temperatures at the Earth’s surface. During the 1960s he also led the development of physical models of the Earth’s climate, laying the foundations for the climate models in use today.

About 10 years later, Hasselmann, a professor at the Max Planck Institute for Meteorology in Hamburg, Germany, created a separate model that linked together weather and climate, helping to answer the question of why climate models can be reliable despite the weather being changeable and chaotic.

He also developed methods for identifying specific signals that natural phenomena and human activities imprint in the climate, demonstrating that increased atmospheric temperatures can be linked to human carbon dioxide emissions.

Parisi’s groundbreaking work focused on identifying hidden patterns in disordered complex materials called spin glasses, making it possible to understand and describe many different and apparently entirely random materials and phenomena.

“[He] tamed this complicated landscape by building a deep physical and mathematical model which was so broad that it has impacted a vast range of fields far beyond spin glasses, from how granular materials pack, to neuroscience, to how we compute to random lasers, and to emergent phenomenon far beyond what he envisioned in the 1970s when he started this work,” said the Nobel committee member John Wettlaufer, a professor of earth and planetary sciences at Yale University in the US.

On a superficial level, Prof Parisi’s original work seems to bear little relation to climate change. It was concerned with a metal alloy called spin glass, in which iron atoms were randomly mixed into a grid of copper atoms. Even though there are only a few iron atoms, they change the material’s magnetic properties in a radical and very puzzling manner.

But the Nobel Committee saw the behaviour of atoms in spin glass as a microcosm for the complex functioning of the Earth’s climate.

Prof John Wettlaufer, a physicist at Yale University in New Haven, US, explained: “What emerged from the committee’s work was the duality between the study of Earth’s climate – which is complex on scales from millimetres to the size of the planet – and Giorgio Parisi’s work.

“[Parisi is] building from the disorder and fluctuations of complex systems at their microscopic constituents… whereas the work of Syukuro Manabe is taking the components of individual processes and knitting them together to predict the behaviour of a complex physical system.

“Even though we’ve divided the prize between the climate part and the disorder part, they really are linked,” Wettlaufer said.