What exactly do the winners of the 2021 Nobel Prize in Physics do?

The Nobel Prize in Physics of the year 2021 has awarded two pioneers in modeling the complexity of the planet. Accustomed to the fact that these awards went to fields such as particle physics, astronomy, and materials science, it is a joy that it has gone to the hands of those who study Earth physics, Syukuro Manabe and Klaus Hasselmann . It is a field that presents formidable theoretical and practical difficulties, including geophysics, meteorology and oceanography.

The other half of the Nobel Prize went to Giorgio Parisi, whose contribution to complex systems and random processes has also been a pioneer, especially in the study of magnetic systems known as spin glasses.

The functioning of the planet is very complex, but that does not mean that we cannot study it. On the contrary, it is an incentive to do so. The inert elements of the atmosphere and the ocean behave in a very complex way, to which we must add that the Earth is alive and both plants and animals exert a measurable influence on the climate. That complicates the task a lot: it is not the same to try to study inert balls than those balls packed with a prodigy of biodiversity.

To model this complexity, understand it and make predictions, you have to start step by step. Start with the basics.

There is a famous joke among physicists in which a rancher asks a physicist to calculate the volume of his cow. The physicist thinks about it, and after a few seconds he replies: “Suppose the cow is spherical and of radius R”.

The joke is funny because it picks up very well the standard procedure for tackling problems in this science: abstracting the most important elements, obviating the accessory at first glance, and analyzing the fundamentals, the essence of the matter, with very powerful tools.

The Earth is not a spherical ball with radius R. There are mountains, an ocean of varying depth, forests, animals, buildings, and a mosaic of surfaces. The planet, in fact, is not even spherical: if we measure well, it is shaped like an ellipsoid. But you have to start somewhere. The beginning is to simplify, keeping the essentials, and then adding details.

Syukuro Manabe found a way to tackle this seemingly endless task. It was he who laid the foundations and foundations of the climate models that today are the basis of our knowledge of climate change. He developed the first viable model, a very simple and elegant one, which has become more detailed over the years. Thanks to him it was possible to study for the first time the crucial role of the water cycle in the atmosphere.

Klaus Hasselmann’s contribution, on the other hand, was to elucidate in a technical way the difference between weather and climate. That is, to explain why we can know what the climate of the future will be like even though we cannot know if it will rain in Toledo next Tuesday. His work on ocean models has also been fundamental because it laid the foundations for the developments that have followed.

Thanks to the contributions of Manabe and Hasselmann, today we can know for sure that greenhouse gas emissions from humans warm the planet. We know this because they provided a physical, mechanical explanation of the processes that operate. This is done through those essential computer programs that are climate models, which are like the laboratories of climatologists.

These models allow us to study the climate in a quantitative way, testing hypotheses and making it possible to reliably predict what will happen if a series of conditions are met. Its results are the basis for the reports of the Intergovernmental Panel on Climate Change (IPCC).

The current models, inherited from those who have won the Nobel Prize, are quite complex and include intricate details that account for the enormous complexity of the natural world, and the challenges that physics faces when applied to the study of our planet. .

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What exactly do the winners of the 2021 Nobel Prize in Physics do?