Carbon dioxide has not been as high as current concentrations in 14 million years thanks to fossil fuel emissions now warming the planet.
Today, atmospheric carbon dioxide is at its highest level in at least several million years thanks to widespread burning of fossil fuels by humans over the past few centuries.
But where does 419 parts per million (ppm), the current concentration of the greenhouse gas in the atmosphere, fit into Earth’s history?
That’s a question that an international community of scientists, with key contributions from geologists at the University of Utah, is solving by examining a large number of markers in the geological record that offer clues to the contents of ancient atmospheres. Their initial study was recently published in the journal Sciencerebuilding CO2 concentrations dating back to the Cenozoic, the era that began with the disappearance of the dinosaurs and the rise of mammals 66 million years ago.
Glaciers contain air bubbles, providing scientists with direct evidence of CO2 levels dating back 800,000 years, according to University geology professor Gabe Bowen, one of the study’s corresponding authors. But this record does not extend very deep into the geological past.
“Once the ice cores are lost, the direct evidence is lost. You no longer have samples of atmospheric gas that you can analyze,” Bowen said. “Therefore, we have to rely on indirect evidence, what we call indicators. And it is difficult to work with these representatives because they are indirect.”
“Representatives” in the Geological Registry
These indicators include isotopes in minerals, the morphology of fossilized leaves, and other lines of geological evidence that reflect atmospheric chemistry. One substitute arises from the fundamental discoveries of Thure University geologist Cerling, co-author of the new study, whose previous research determined that carbon isotopes in ancient soils are indicative of CO in the past.2 levels.
But the strength of these indicators varies, and most cover small portions of the past. The research team, called Cenozoic CO22 Proxy integration projector CenCO2PIP, and organized by Columbia University Climate scientist Bärbel Hönisch set out to evaluate, categorize and integrate the available indicators to create a high-fidelity record of atmospheric CO.2.
“This represents some of the most inclusive and statistically refined approaches to interpreting CO2 over the past 66 million years,” said co-author Dustin Harper, a University postdoctoral researcher in Bowen’s lab. “Some of the new findings are that we can combine multiple indicators from different sediment archives, whether in the ocean or on land, and that hasn’t really been done at this scale.”
The new research is a community effort involving about 90 scientists from 16 countries. Funded by dozens of grants from multiple agencies, the group hopes to eventually rebuild the CO2 Go back 540 million years to the dawn of complex life.
At the beginning of the Industrial Revolution, when humans began burning coal, then oil and gas to fuel their economies, atmospheric CO2 It was around 280 ppm. Heat-trapping gas is released into the air when these fossil fuels are burned.
Looking ahead, concentrations are expected to increase between 600 and 1,000 ppm by 2100, depending on the rate of future emissions. It’s unclear exactly how these future levels will influence the climate.
But having a reliable map of past CO2 The levels could help scientists more accurately predict what future climates will be like, according to U. biology professor William Anderegg, provost of the U. Wilkes Center for Climate and Politics.
“This is an incredibly important synthesis and also has implications for future climate change, particularly the key processes and components of the Earth system that we need to understand to project the speed and magnitude of climate change,” Anderegg said.
The current 419 ppm is the highest CO2 in 14 million years
In times past, when the Earth was a much warmer place, CO levels2 They were much taller than now. Still, the 419 ppm recorded today represents a sharp and perhaps dangerous peak and is unprecedented in recent geological history.
“8 million years ago before the present, there was maybe a 5% chance that CO2 The levels were higher than today,” Bowen said, “but we actually have to go back 14 million years before we see levels that we think are like today.”
In other words, human activity has significantly altered the atmosphere in the span of a few generations. As a result, climate systems around the world are showing alarming signs of disruption, including powerful storms, prolonged droughts, deadly heat waves, and ocean acidification.
A solid understanding of atmospheric CO2 Variation through geological time is also essential for deciphering and learning from various features of Earth’s history. Changes in atmospheric CO2 and climate likely contributed to mass extinctions as well as evolutionary innovations.
During the Cenozoic, for example, long-term declines in CO2 and associated climate cooling may have driven changes in plant physiology, species competition and dominance, which in turn affected the evolution of mammals.
“A more refined understanding of past trends in CO2 “Therefore, it is critical to understanding how modern species and ecosystems emerged and how they will fare in the future,” the study states.
Reference: “Towards a Cenozoic history of atmospheric CO2”by the Cenozoic CO2 Proxy Integration Project (CenCO2PIP) Consortium*†, Bärbel Hönisch, Dana L. Royer, Daniel O. Breecker, Pratigya J. Polissar, Gabriel J. Bowen, Michael J. Henehan, Ying Cui, Margret Steinthorsdottir, Jennifer C. McElwain, Matthew J. Kohn, Ann Pearson, Samuel R. Phelps, Kevin T. Uno, Andy Ridgwell, Eleni Anagnostou, Jacqueline Austermann, Marcus PS Badger, Richard S. Barclay, Peter K. Bijl, Thomas B. Chalk, Christopher R. Scotese, Elwyn de la Vega, Robert M. DeConto, Kelsey A. Dyez, Vicki Ferrini, Peter J. Franks, Claudia F. Giulivi, Marcus Gutjahr, Dustin T. Harper, Laura L. Haynes, Matthew Huber, Kathryn E. Snell, Benjamin A. Keisling, Wilfried Konrad, Tim K. Lowenstein, Alberto Malinverno, Maxence Guillermic, Luz María Mejía, Joseph N. Milligan, John J. Morton, Lee Nordt, Ross Whiteford, Anita Roth- Nebelsick, Jeremy KC Rugenstein, Morgan F. Schaller, Nathan D. Sheldon, Sindia Sosdian, Elise B. Wilkes, Caitlyn R. Witkowski, Yi Ge Zhang, Lloyd Anderson, David J. Beerling, Clara Bolton, Thure E. Cerling, Jennifer M. Cotton, Jiawei Da, Douglas D. Ekart, Gavin L. Foster, David R. Greenwood, Ethan G. Hyland, Elliot A. Jagniecki, John P. Jasper, Jennifer B. Kowalczyk, Lutz Kunzmann, Wolfram M. Kürschner, Charles E. Lawrence, Caroline H. Lear, Miguel A. Martínez-Botí, Daniel P. Maxbauer, Paolo Montagna, B. David A. Naafs, James WB Rae, Markus Raitzsch, Gregory J. Retallack, Simon J. Ring, Osamu Seki, Julio Sepúlveda, Ashish Sinha, Tekie F. Tesfamichael, Aradhna Tripati, Johan van der Burgh, Jimin Yu, James C. Zachos and Laiming Zhang, December 8, 2023. Science.