The climate defenders

Measured against the pace of social debates, the Nobel Prize in Physics is rather slow. Current events rarely play a role in the award. Different this year. With the highest honor in the subject of physics, the committee directs the view to the advancing climate change and the realization that this is clearly due to greenhouse gas emissions of mankind. It is thus also a political statement.

“It is encouraging to see that the Nobel Prize in Physics recognizes the work of scientists who have contributed so much to our understanding of climate change,” says the Chair of the Intergovernmental Panel on Climate Change Hoesung Lee. Syukuro Manabe and Klaus Hasselmann have also contributed as authors to earlier reports of the IPCC.

Syukuro Manabe, Klaus Hasselmann and Giorgio Parisi receive the award “for their groundbreaking contributions to our understanding of complex physical systems” . Weather and climate are essential. The parameters are quickly compiled: temperature, humidity, wind, plus clouds and sunshine.

And yet it is a science in itself to understand the interplay of these parameters and to make predictions of what the weather will be like in the next few days, or in the next few decades if the emissions continue to rise.

Klaus Hasselmann wurde am Dienstag am Max Planck Institut in Hamburg von vielen Kolleginnen und Kollegen beglückwünscht.

Klaus Hasselmann was congratulated by many colleagues on Tuesday at the Max Planck Institute in Hamburg. Photo: REUTERS / Fabian Bimmer

Today’s models can do this well – measured by their ability to depict the known climatic past. But in the early days of modeling, on the one hand, the computers were terribly slow and, on the other hand, the algorithms were not very sophisticated. But that wasn’t necessarily a weakness. “You have to simplify things,” was Manabe’s credo. “You cannot take on the complexity of nature; so much physics is already in a single raindrop that it will never be possible to calculate everything. “

Simplify the complex

Manabe managed the simplification very well. Already in the 1960 he developed, at that time for the US weather service active, computer models that could map climate changes. He was the first scientist to research how the earth’s radiation balance – how much solar radiation reaches us and how much is released back into space – and vertical air movements in the earth’s atmosphere interact.

[Lesen Sie hier ein Kurzporträt von Klaus Hasselmann, Physik-Nobelpreisträger 2021]

middle of 1970 years the researcher used a simple computer model for a basic climate projection. He calculated that the average temperature on the earth’s surface increases by 2.4 degrees Celsius if the carbon dioxide content of the earth’s atmosphere is 280 ppm (parts per million parts) on 560 ppm is doubled. This indicator, known as climate sensitivity, is the guide value for the effect of released greenhouse gases on the earth’s climate.

Graphic: Tsp / Bartel, Source AFP / Nasa / UNO Environment Program

Later model calculations resulted in higher values ​​of 3.5 to 3.9 degrees Celsius. It is remarkable how right Manabe was so early. The range of expected values ​​widened in the following decades, the more factors were recognized and taken into account in the complex climate system. Only with the latest report by the Intergovernmental Panel on Climate Change are three degrees Celsius accepted as the central estimate and a probable range of 2.5 to four degrees Celsius as the state of research. Manabe is a pioneer of this realization.

Mankind is far advanced on the way to doubling the carbon dioxide content of the atmosphere. Today it is over 410 ppm – the highest value since 800 000 years.

Climate is weather averaged over decades and millennia

“A Nobel Prize for reliably predicting global warming is one great news for all climate researchers, ”said Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research to Tagesspiegel. But climate researchers would rather see their forecasts come true than politicians finally act accordingly. Rahmstorf is reminiscent of Sherwood Rowland, who 1995 received the Nobel Prize for discovering the ozone hole and then said: “What is the use of developing a science that is able to make predictions, if in the end we are just willing to stand around and wait for them to come true?”

Syukuro Manabe von der Princeton University in den USA hat die Grundlagen für die Modellierung des Erdklimas und damit des Klimawandels gelegt.

Syukuro Manabe from Princeton University in the USA has the basics for modeling the earth’s climate and thus the … Photo: Seth Wenig / AP / dpa

The climate modeling shows more and more clearly how the increasing CO2 content will affect the earth’s climate. The equally excellent Klaus Hasselmann played a major role in this. He linked weather and climate, which at first glance hardly fit together. The weather is the current state of the atmosphere, with 15 Degree and drizzle in Berlin or 28 Degrees and clouds in Singapore. This can change noticeably in just half an hour, especially over days and weeks. Large air masses can literally bring “different weather” with sudden drops in temperature and thunderstorms. Climate, on the other hand, is the long-term average of all weather parameters over 20 or 30 years.

A frequent question to climate researchers is therefore: How do you want to make long-term statements when it is impossible to predict the weather for more than two weeks? Despite all the data from satellites and measuring stations, complex algorithms and the knowledge that small deviations in individual parameters lead to significantly different results?

Fluten, wie sie an der Ahr in Rheinland-Pfalz seit Jahrhunderten nicht vorkamen, werden im Klimawandel häufiger werden. Wo genau sie auftreten werden, können jedoch die besten Modellierungen nicht vorhersagen.

Floods, which have not occurred on the Ahr in Rhineland-Palatinate for centuries, will become more frequent with climate change. Where exactly … Photo: Boris Roessler / dpa

On the Dog come

The answer is inextricably linked with Klaus Hasselmann. To 1970 he showed that the unsteady weather as a “rapidly changing noise” can be described and integrated into climate models. To do this, imagine a walk with your dog. The animal is excitedly jumping around its legs, scurrying back and forth, jumping to the side. Its trail with the abrupt changes resembles the weather. Predicting them is difficult. But the course and the speed of your master – symbolic of the climate – can be recognized and you can say with relative certainty in which direction he will move in the future. This “random walk” theory is decisive for Hasselmann’s work.

Der Italienische Physiker Giorgio Parisi feiert am Dienstag seinen Nobelpreis.

The Italian physicist Giorgio Parisi celebrates his on Tuesday Nobel Prize. Photo: Cecilia Fabiano / LaPresse via ZUMA Press / dpa

By bringing together models, observations and expectations from theory, he was also able to make human fingerprints visible in the climate system. Here, for example, solar activity leaves clear traces or volcanism. For decades, however, the temperature development of the earth can no longer be explained without the human activities that release large amounts of greenhouse gases. “We can no longer say that we did not know,” announced the Nobel Prize Committee. “The climate models are clear.”

The third winner, Giorgio Parisi, has little to do with climate research. In the opinion of the committee, he should not be missing in the Nobel Prize for the research of complex systems.

In the 1970 years he researched spin glass. The name goes back to the spin: a magnetic moment that iron atoms have. You can think of them like tiny compass needles. Ideally, they are all aligned in the same way. But there are also chaotic arrangements where the needles point in all imaginable directions. As disordered as the atoms in a glass, hence “spin glass”.

Parisi discovered hidden patterns in such disordered materials. The jury stated that it made a decisive contribution to the theory of complex systems. This makes it possible to understand and describe a wide variety of apparently random materials and processes, in physics as well as in biology, neuroscience and machine learning.

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