Sustainabilty
While pulse-like releases of CO₂ to the atmosphere have been seen in past interglacial periods, as well, the anthropogenic rise in CO₂ that we’re seeing today is more than six times larger and nearly ten times faster than previous surges. This is the conclusion reached by a European research team led by the University of Bern.
A new measurement technology developed at the University of Bern provides unique insights into our climate’s past. High-resolution measurements of an Antarctic ice core have allowed scientists to reconstruct previous CO₂ concentrations in the atmosphere more accurately than ever before. The University of Bern study, which offered unprecedented insights into the composition of the Earth’s atmosphere between 330,000 and 450,000 years ago, was made possible by their researchers’ decades of experience in analyzing this unique repository of climate data. The results of the study were published in the August 2020 issue of Science.
Christoph Nehrbass-Ahles, the lead author of the study, as he operates the CO₂ measurement equipment that he helped develop at the University of Bern.
A detailed reconstruction of the climate during the eight successive glacial and interglacial periods of the past 800,000 years proved revealing. Bern’s ice core specialists were already able to show back in 2008 that the concentration of carbon dioxide in Earth's atmosphere during the last 800,000 years was consistently much lower than it is today. What had been unclear until now, however, was just how quickly natural centennial-scale carbon dioxide jumps can occur and how frequently events such as these even happen. The current study now shows that abrupt CO₂ rises are a pervasive feature of our climate system and that they can even occur during interglacial periods. “Until now, it had been assumed that the climate was very stable during previous interglacial periods and that there were no abrupt changes in the atmospheric CO₂ concentration,” explains Christoph Nehrbass-Ahles, lead author of the study, who earned his doctorate from the University of Bern and recently started conducting research at the University of Cambridge.
According to Nehrbass-Ahles, the abrupt increases were always evident when melting ice masses in Greenland or Antarctica caused massive disruptions to oceanic circulation. If atmospheric CO₂ concentrations rose quickly, simultaneous changes could also be detected in the Atlantic Ocean's circulation.
The fact that rapid CO₂ jumps could be detected not only during glacial periods but also during two previous interglacial periods surprised the researchers. “We remeasured these events in the ice several times and always came to the same conclusion,” explains Nehrbass-Ahles. The researchers cannot offer any conclusive explanations as to why the concentration of carbon dioxide in Earth’s atmosphere suddenly rose during previous interglacial periods. “We still don’t know why that happened,” explains Bernese climate researcher Thomas Stocker, co-author of the study: “This raises new research questions.”
However, the CO₂ jumps of previous interglacial periods are far exceeded by the present-day trend: “These natural jumps in the CO₂ concentration in the atmosphere happened nearly ten times more slowly than the human-driven increase seen over the last decade,” Nehrbass-Ahles points out.
“The atmospheric concentration of CO₂ is currently 35% higher than it ever was at any point in the past 800,000 years. As part of the EPICA project, Bernese researchers had already succeeded in 2008 in reconstructing the fluctuation range of CO₂ concentration in the atmosphere over that period of time by analyzing ice cores taken from the Antarctic – a world record.”
Another interesting insight is just how large past CO₂ jumps were compared to the current anthropogenic rise in CO₂ concentration. According to Stocker, the largest CO₂ jump in the past had been around 15 ppm (parts per million is the unit used to measure atmospheric CO₂ concentration), which is approximately equivalent to the increase caused by humankind over the last six years. “That might not seem significant at first glance,” says Stocker, “but considering the amount of CO₂ we’re still allowed to emit if we want to achieve the 1.5°C climate target agreed in Paris, increases like these are definitely relevant.” Because the fact is that if global warming triggers any further increase in greenhouse gas emissions, as has already happened in the past, this could put mankind under even greater pressure to protect the climate.
The Oeschger Centre for Climate Change Research (OCCR) is one of the strategic centers of the University of Bern. It brings together researchers from 14 institutes and four faculties. The OCCR conducts interdisciplinary research right on the frontline of climate science. The Oeschger Centre was founded in 2007 and bears the name of Hans Oeschger (1927-1998), a pioneer of modern climate research, who worked in Bern.