Recent research shows that the current rate of increase in atmospheric CO2 is unprecedented, being ten times faster than any period in the past 50,000 years, highlighting significant implications for global climate dynamics and the future CO2 absorption capacity of the Southern Ocean.
Researchers carrying out a detailed chemical analysis of ancient Antarctic ice have found that the current rate of increase in atmospheric carbon dioxide is 10 times faster than at any time in the last 50,000 years.
The findings, just published in Proceedings of the National Academy of Sciencesprovide important new understanding of periods of abrupt climate change in Earth’s past and offer new insight into the potential impacts of climate change today.
“Studying the past teaches us how today is different. The rate of CO2 today’s change is truly unprecedented,” said Kathleen Wendt, an assistant professor in Oregon State University’s College of Earth, Ocean and Atmospheric Sciences and lead author of the study.
“Our research identifies the fastest rates of natural CO2 increase in the past ever observed, and the rate seen today, largely driven by human emissions, is 10 times higher.”
Carbon dioxide or CO2 is a greenhouse gas that occurs naturally in the atmosphere. When carbon dioxide enters the atmosphere, it contributes to climate warming due to the greenhouse effect. In the past, levels have fluctuated due to ice age cycles and other natural causes, but today they are rising due to human emissions.
Antarctic ice core analysis
Ice accumulated in Antarctica over hundreds of thousands of years contains ancient atmospheric gases trapped in air bubbles. Scientists use samples of this ice, collected by drilling cores up to 2 miles (3.2 kilometers) deep, to analyze traces of chemicals and create records of past climates. The US National Science Foundation supported the ice core drilling and chemical analysis used in the study.
Previous research has shown that during the last ice age, which ended about 10,000 years ago, there were several periods when carbon dioxide levels jumped much higher than average. But those measurements weren’t detailed enough to reveal the full nature of the rapid changes, limiting scientists’ ability to understand what was happening, Wendt said.
A piece of an Antarctic ice core. Researchers study chemicals trapped in old ice to learn about past climates. Credit: Katherine Stelling, Oregon State University
“You probably wouldn’t expect to see this at the end of the last ice age,” she said. “But our interest was piqued and we wanted to go back to those periods and make measurements in greater detail to understand what was going on.”
Using ice core samples from the West Antarctic Ice Sheet, Wendt and his colleagues investigated what happens during these periods. They identified a pattern showing that these spikes in carbon dioxide occurred alongside cold intervals in the North Atlantic, known as Heinrich events, which are associated with drastic climate changes around the world.
“These Heinrich events are truly remarkable,” said Christo Buizert, associate professor in the College of Earth, Ocean and Atmospheric Sciences and co-author of the study. “We think they were caused by a dramatic collapse of the North American ice sheet.” This sets off a chain reaction that includes changes in the tropical monsoons, westerly winds in the Southern Hemisphere, and these large bursts of CO2 emerging from the oceans.”
Comparison of natural and current CO2 increases
During the largest natural increases, carbon dioxide increased by about 14 parts per million over 55 years. And the jumps happened once every 7000 years or so. At today’s rates, this rate of increase only takes 5 to 6 years.
Evidence suggests that during past periods of natural increase in carbon dioxide, westerly winds, which play an important role in deep ocean circulation, also strengthened, leading to a rapid release of CO2 from the Southern Ocean.
Other research shows that these westerly winds will increase over the next century due to climate change. The new findings suggest that if this happens, it will reduce the capacity of the Southern Ocean to absorb human-generated carbon dioxide, the researchers note.
“We rely on the Southern Ocean to absorb some of the carbon dioxide we emit, but rapidly strengthening southerly winds are weakening its ability to do so,” Wendt said.
Reference: “Southern Ocean Leads to Multidecadal Atmospheric CO2 uplift during the Heinrich Stadials’ by Kathleen A. Wendt, Christoph Nehrbas-Alles, Kyle Niezgoda, David Nunn, Michael Kalk, Laurie Menviel, Julia Gottschalk, James W.B. Ray, Jochen Schmidt, Hubertus Fischer, Thomas F. Stoker , Juan Muglia, David Ferreira, Sean A. Marcotte, Edward Brooke, and Christo Buizert, 13 May 2024, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2319652121
Additional co-authors include Ed Brooke, Kyle Niezgoda and Michael Kalk of Oregon State; Christophe Nerbas-Alles of University of Bern in Switzerland and the National Physical Laboratory in the United Kingdom; Thomas Stoker, Jochen Schmidt and Hubertus Fischer of the University of Bern; Laurie Menviel of the University of New South Wales in Australia; James Ray of the University of St. Andrews in the United Kingdom; Juan Mulia of Argentina; David Ferreira of the University of Reading in the United Kingdom and Sean Marcotte of the University of Wisconsin-Madison.
The study was funded by the US National Science Foundation.
