The ocean supermodeller

© © SNF

Combining his enjoyment of maths with his love for nature, Thomas Frölicher develops climate models to calculate the impact of greenhouse gases on the ocean.

Why is there a poster featuring the children’s book Globi und die Energie on Thomas Frölicher's office door? “The authors asked me to check some of the facts. And of course I said yes.” Although a professor of climate and environmental physics and the lead author of UN climate reports, he evidently doesn't consider editing children’s books to be beneath him. His outward appearance might indicate as much: wearing a t-shirt and trainers, he looks more like a dad who would rather go for a walk in the forest with his kids than someone attending high-level conferences.

Frölicher’s main working tool is the computer. However, the ordinary PC on his desk wouldn't be up to the modelling. For that he needs powerful supercomputers like those at the Swiss National Computing Centre (CSCS) in Lugano. That’s where he installs the climate models that his group is co-developing. Such calculations can often take between two and three months. Afterwards the researchers load the data back onto their PCs in the office and evaluate them there. That process can easily take another few months.

A sense of curiosity and a flair for maths

As a child, Frölicher often went down to the basement workshop with his father – an electrical engineer who also enjoyed doing physics experiments. That’s where he developed his own sense of scientific curiosity, while at school his impressive flair for complex calculations also came to the fore. At the same time, he developed a profound love of nature. He spent many a summer holiday in the mountains. Later on, he organised youth camps for up to 50 youngsters at a time. “That shaped my mindset” says Frölicher. “I learnt how to assume responsibility and keep a group together – something I benefit from to this day.” In spring this year he took his team cycling at Lake Bienne, and last year he took them for a hike at Oeschinensee. He lunches with his six-strong group at least once a week, usually on Tuesdays.

Frölicher studied environmental sciences at ETH Zurich. “That’s where I saw a good opportunity to combine my interest in maths with my fascination for nature.” In his studies he specialised in atmospheric physics, and for his doctorate at the University of Bern he expanded his horizon to the entire earth system, including the ocean. He took a particular interest in the oxygen content of the sea and how this varies over time. “Those were early days for that area of research, and there were a lot of imponderables,” Frölicher remembers. “We didn't know exactly which fluctuations were natural and which changes were due to human influences.” Today it’s clear that the oxygen content of the ocean has declined by between one and three per cent since 1960. That has major implications both for the ecosystems and for fisheries. Fish avoid poorly oxygenated waters – they swim on to other areas and fishermen’s nets remain empty.

Between 2010 and 2013 Thomas Frölicher worked as a postdoctoral fellow at Princeton University, near New York. It was there, in the 1960s and 70s, where the first atmosphere and ocean models were developed. Syukuro Manabe also researched and taught there, and in 2021 he was awarded the Nobel Prize in Physics for his pioneering climate modelling. “We often lunched together. He was very interested in the research his younger colleagues were doing.” At Princeton, Frölicher focused on modelling the changes in heat and carbon fluxes in the Southern Ocean around the Antarctic. The data available back then were mainly obtained from expeditions by ship. But due to rough seas and the harsh climate such expeditions are confined to the summer, thus leaving a gap in the data. The group in which Frölicher did his research at the time was the first to release “drifters” – yellow buoys the size of people – that would continually gather data on the acidity and oxygen content of the water as well as temperatures, salinity and pressure, and send them to the lab. It is due in large measure to this research work that we now know that 75 per cent of the ocean uptake of excess heat stemming from human-made greenhouse gases and 15 per cent of human-made CO2 emissions are absorbed by the Southern Ocean.

Warm-water "blob” 1,600 kilometres across

In 2018 Frölicher, who by that time was an SNSF Assistant Professor at the University of Bern, published a study in the journal Nature. He had calculated that heatwaves in the ocean caused by climate change have doubled in frequency since the beginning of satellite measurements in 1982. Moreover, Frölicher and his team showed that this probability would increase with each additional tenth of a degree Celsius of global warming. The relevance of these marine heatwaves only entered the public consciousness ten years ago: between winter 2013/2014 and the end of 2015, an unusually long-lasting mass of warm water nicknamed the “Blob” was detected on the surface of the northern Pacific. At times, the Blob measured up to 1,600 kilometres across, and water temperatures were more than three degrees Celsius above the long-term average. Also, the dissolved oxygen content during the Blob was extremely low while acidity was high, which negatively impacted ecosystems and fish populations. “Such compound events in the ocean will likely become more frequent in future. Currently, we are trying to model their drivers and impacts.”

Frölicher admits that, despite his daily encounters with the ocean on the computer, he has little marine experience in practice. He has never actually been on an expedition. And the sailing boat he shares with friends is not on the Atlantic or the Pacific but on Lake Bienne. That’s where he goes to relax, or to take part in one of the cross-lake swimming contests. While he would relish the opportunity to go on an Antarctic expedition or a sailing adventure on the high seas, he simply doesn't have time for it. If Frölicher doesn’t happen to be poring over a mathematical model, his two kids will certainly be keeping him busy.