Physics Nobel awarded for work on chaotic systems such as the climate

The 2021 Nobel prize for physics has been awarded to three researchers for two discoveries that together represent “groundbreaking contributions to our understanding of complex physical systems” such as weather and, on a longer time scale, climate change.

One half of the Nobel was awarded jointly to Syukuro Manabe at Princeton University and Klaus Hasselmann, formerly at the Max Planck Institute for Meteorology in Hamburg, Germany, for their work developing physical models of Earth’s climate that helped to reliably predict global warming and prove that human actions have an impact on the climate system.

The other half was awarded to Giorgio Parisi at Sapienza University of Rome, Italy, for his discoveries on chaotic systems such as how disorder and tiny fluctuations interplay on atomic to planetary scales.

Both discoveries relate to chaotic systems that can be difficult to describe mathematically due to enormous numbers of variables or large deviations in results from small changes to input. The winners have all contributed to gaining greater knowledge of such systems and their long-term development, said the Nobel Committee for Physics.

Thors Hans Hansson, chair of the committee, said that although the two prizes were separate, there was a common theme “that has to do with disorder, that has to do with fluctuations, and how disorder and fluctuations together, if you understand it properly, can give rise to something we can understand”.

Manabe led the development of physical models of Earth’s climate in the 1960s, particularly investigating the interaction between the heat coming into our atmosphere from the sun and that leaving via reflected radiation. His work laid the foundation for the development of climate models used subsequently to predict the extent of climate change under various scenarios.

A decade later, Hasselmann created a model building on that work, which linked together weather and climate. His methods have been used to show that the increased temperature in the atmosphere is due to human emissions of carbon dioxide.

The other half of the prize, awarded to Parisi, relates to his work on spin glass. This unusual material is any metal alloy in which the magnetic field of one element is constantly changing in a chaotic manner, such as iron in copper. His work understanding these complex systems has been useful in the study of many other systems, including weather and climate.

Parisi said that ahead of next month’s COP26 summit, it was clear that nations need to work at a “strong pace” to mitigate the effects of climate change. “It’s clear for the future generations we have to act now, in a very fast way,” he said. “We are in a situation where we could have positive feedback and that may accelerate the increase of temperature.”