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Physicists have been trying for 200 years to understand why the Earth is not a huge ice cube: the answer (and everything it brought with it) has deserved a Nobel

Around 1820 the French physicist Joseph Fourier realized that we should be dead. Frozen, to be more exact. According to his calculations and taking into account the distance at which we are from the Sun, an object the size of the Earth would have to be much colder than, in reality, it is. What was happening? How was it possible? What mechanism was capable of heating a planet of this size?

Throughout that decade, Fourier carried out numerous investigations to verify all the ideas that occurred to him, no matter how pilgrims they were. Eventually, he came to the conclusion that the only thing that matched was that the atmosphere was functioning like the huge lid of a pressure cooker called Earth. Fourier was discovering what we now know as the “greenhouse effect” and, incidentally, was raising one of the most complex scientific puzzles in history. The one who just won the 2021 Nobel Prize in Physics.

The hurricane, the butterfly and the weather puzzle

And it is that the climate of our planet is the paradigmatic example of the dreaded ‘complex systems’. Enternos in which millions of different elements interact in such complex ways that describing their behavior is tremendously difficult. As if that weren’t enough, the climate is not only complex, it is also chaotic. That is, small initial changes can result in colossal changes at a later stage.

Do you remember that “a butterfly flapping its wings in Brazil ends up causing a typhoon in the China Sea”? Well, behind that well-known metaphor, lies one of the most important intellectual challenges of modern science. A challenge that, in the end, has helped us look at a phenomenon that will mark the future (and is already marking the present) of humanity: climate change.

Who is who of the 2021 Nobel Prize in Physics?

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Although I will now go into more detail about how scientists have managed to begin to understand the climate, perhaps it would be convenient to place the three protagonists of the 2021 Nobel Prize in Physics to have a more precise idea of ​​what we are talking about:

  • Thank you Manabe (Japan, 1931) was the first to demonstrate how increased concentrations of carbon dioxide in the atmosphere lead to increased temperatures on the Earth’s surface. During the 1960s, he played a key role in the development of the first physical models of the Earth’s climate capable of capturing the interaction between radiation balance and air mass dynamics. It is, without a doubt, one of the fathers of climate models.

  • Klaus Hasselmann (Germany, 1931) entered this story a decade later by answering a key question: how can we trust climate models if, in short, the weather has proven to be a chaotic and changing animal. For this, he not only created the first models capable of linking time and climate, but was also able to identify the “fingerprints” of the activity of human beings in the atmosphere.

  • Giorgio Parisi (Italy, 1948) made its appearance another decade later, in the 1980s. It was then that he discovered that messy complex materials could have hidden patterns. That is to say, and without half measures, “his discoveries are among the most important contributions to the theory of complex systems.” Without them we would not be able to understand the seemingly random phenomena that arise in physics, but also in mathematics, biology, neuroscience or machine learning.

Understand the weather, understand the chaos

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However, these are not the only Nobels working on the impact of carbon dioxide in the atmosphere. The first piece we find to solve this puzzle has names and surnames: the Swedish Svante Arrhenius, Nobel Prize in Chemistry in 1903. It was he who understood the physics behind Fourier’s discovery and, in fact, put figures to his intuition : Without the atmosphere, the Earth’s temperature would barely exceed -18 ° C. Furthermore, it concluded that it was enough that atmospheric CO2 levels fell by half, to cause a new ice age.

Eleven GIFs that explain, once and for all, what is causing global warming

It was not until the 1950s that Syukuru Manabe came to the United States from a Japan that was still recovering from the wounds of the war. 70 years later, Manabe took Arrhenius’s research back and brought it up to date by incorporating things like the latent heat of water vapor. That is, he began to create dynamic models capable of also accounting for internal differences within the atmosphere. That allowed him to discover that while oxygen and nitrogen had minimal effects in the temperature of the Earth’s surface, carbon dioxide variations had a huge impact.

The problem is that at that time our computational capacity was very very small. That required the Manabe model to be very simple. So much that, Although he found the correct elements to understand the climate, he was not able to account for the chaotic behavior of the world climate. It was like having a general sketch that, despite being correct and invaluable, was unable to capture the complexity of the real world. That was where Klaus Hasselmann tried to shed some light.

How could we pretend what would happen in 200 years if we didn’t know if it was going to rain this afternoon? Hasselmann realized that behind the noise caused by changing weather there was a clear melody that allowed us to predict the next steps the weather would take. But even with these it was not possible to create theories that worked well until they developed the first long-term stochastic models: that is, until they integrated chance into our own vision of the weather.

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From that moment on, Hasselmann dedicated himself to finding methodologies that would allow him to identify the traces of human activity in the atmosphere. It was the only way to answer the most basic questions about climate change. and it was successful. Today, we can safely say that human activity is what drives current climate change. And it is thanks to them.

However, that was not the end of the road. Our understanding of the climate (of chaotic systems in general) had only taken its first steps. And this was especially problematic in a context where physical determinism was crumbling. The work of Giorgio Parisi and his obsession to understand the complexity of apparently disordered systems is the best example of this. It’s just the beginning, but a really exciting start.

Image | Elena Mozhvilo