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According to the Copernicus Climate Change Service, the last decade (2011 to 2020) was the warmest and 2020 was the year with the hottest summer on record. We also know that the average global temperature today is up to 1.2 degrees Celsius higher than at the end of the 19th century, mainly due to the emission of greenhouse gases, especially carbon dioxide (CO2). In 1896, the Swedish physicist and chemist and later Nobel Prize winner Svante Arrhenius predicted that CO2 would warm the Earth. In our interview, the young scientist and meteorologist Dr Leonore Jungandreas explains what exactly the Swede investigated and discovered back then, what role this plays in her own research, and why climate change depends on far more factors than how much CO2 there is in the atmosphere.

Ms Jungandreas, what was Arrhenius’ groundbreaking scientific work on CO2-induced global warming – something he accomplished 127 years ago?

Dr Leonore Jungandreas: Svante Arrhenius was the first to formulate mathematical formulae to determine the influence of CO2 on the Earth’s energy budget, after the British scientist John Tyndall (1820–1893) had discovered through experiments a few years earlier that thermal radiation is mainly absorbed by water vapour and carbon dioxide. Together with his colleague Arvid Högbom, Arrhenius calculated the mean temperature of the Earth under different CO2 levels. They concluded that doubling or halving CO2 levels – under the atmospheric conditions at the time – would result in a temperature change of five to six degrees Celsius. Based on these results, he stated in his famous paper On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground that humans would actively increase CO2 levels in the atmosphere – and thus also the temperature of the Earth system – by burning fossil fuels, a process that had already begun.

To what extent were his calculations correct – and independently of this, what significance do his insights still have for science today?

His calculations that a doubling of atmospheric CO2 would lead to an average temperature rise of five degrees Celsius overestimated the climate sensitivity calculated by today’s climate models. This was mainly because Arrhenius used simple linear equations for his calculations. Today’s climate models are much better at representing reality and include a variety of other factors and feedback mechanisms, which they use to arrive at an increase of about three degrees Celsius if CO2 levels double compared to pre-industrial levels.

Nevertheless, his emphasis on the human influence on climate, particularly the burning of coal, oil and gas, forms the basis for understanding how we affect the climate. Arrhenius thus started the debate on anthropogenic climate change, even though it was not until the mid-20th century that the first CO2 measurements and the first climate models provided increasing evidence of human influence on the climate.

What are you researching at the moment? And broadly speaking, does the Swedish Nobel laureate play any part in your work?

Broadly speaking, the work of Arrhenius matters to every climate scientist. It was he who laid one of the foundations for the study of anthropogenic climate change. The human impact on climate that is being studied today is highly complex and multifaceted, with many factors and interactions at play, studied separately and then brought together.

My work is mainly concerned with land-atmosphere interactions. The aim is to understand how changes to the land surface, such as agricultural land, affect atmospheric conditions, for example how much water evaporates or how much the Earth’s surface heats up. This affects processes such as cloud and precipitation formation, but can also contribute to the formation of stationary weather patterns. The atmosphere, in turn, influences how well plants grow, or how dry and hot it can get on the ground through rain, clouds and solar irradiation – to name just a few processes.

Everything is constantly interacting and interdependent. The fact that the climate is warming worldwide, as Arrhenius already pointed out, has an additional influence on all these processes, reinforcing them in one region and perhaps weakening them in another. At this point, however, no thought has been given to how economic and political interests influence events, how a farmer or forester decides how to manage fields and forests, or what chemical and ecological processes play a role. Arrhenius got the ball rolling on human influence on the climate – today we are trying to bring together a wide variety of interests and areas of research to inform our future actions in the best possible way.

If people have known for almost 130 years that CO2 is causing the earth to warm, why wasn’t action taken much sooner?

At the time, Arrhenius saw global warming as an opportunity and believed that his descendants would live in a more comfortable climate than he had. He calculated that it would take hundreds or thousands of years for the Earth’s temperature to rise by five degrees Celsius. He did not realise at the time that the Earth would warm much more quickly.
The first warning of the danger and possible irreversibility of human-induced climate change came in 1971. Since then, climate scientists and many others have been fighting for more attention and stronger action. I think it is important to say at this point that a lot has already happened: there is the Paris Climate Agreement, signed by almost every country in the world. Renewable energies are being researched and promoted more. There are major reforestation, land use and conservation projects to sequester more CO2, preserve original habitats and biotopes or create new ones, and preserve and promote biodiversity. New technologies are being developed to filter CO2 from the air. And there is so much more.
The fact that not everything happens and works as quickly and effectively as we would like is due to a rather complex interplay of many factors. Economic interests are often paramount, and it is politically challenging to coordinate international cooperation and balance the many interests of different countries and stakeholders. In addition, climate change occurs on longer time scales than economic and political processes. Individuals may simply feel helpless or be preoccupied with more pressing issues such as health, financial worries, stress and other everyday problems. It is understandably difficult to find the capacity to change to a more sustainable lifestyle. However, the more individuals are made aware and the earlier they are sensitised to environmental issues, the more motivation there will be to do more to combat climate change.

About Leonore Jungandreas

Climate scientist Dr Leonore Jungandreas lives in Leipzig. She works in the Theoretical Meteorology research group led by Professor Johannes Quaas at the Institute for Meteorology at Leipzig University as well as in the Biodiversity Economics research group led by Professor Martin Quaas at iDiv.

“I try to make sustainable choices in my daily life as much as possible,” she says. “Since I was a child, I have loved watching thunderstorms and staring at clouds, and I love animals – most of them, at least, and I accept the rest. I am convinced that everyone can make a difference to a more sustainable world, for example by fighting climate change out of conviction, because you want to keep the birds in your garden, because you like sitting on green grass in the park instead of brown, or because your head just tells you it is good for your health. At the same time, I think it is extremely important to treat other people and their feelings and opinions with respect, no matter how far their views may be from mine. Everyone wants the best for themselves and their loved ones. It is important to understand that we can only do well in the long term if our planet is doing well as a whole.”