A deep dive into 66 million years of carbon dioxide data

Carbon dioxide has not been as high as its current concentrations for 14 million years, thanks to fossil fuel emissions that are now warming the planet.

Today, carbon dioxide in the atmosphere is at its highest levels in at least several million years, thanks to humans burning fossil fuels on a massive scale over the past two centuries.

But where does 419 parts per million (ppm) – the current concentration of greenhouse gases in the atmosphere – fall in Earth's history?

This is a question that an international community of scientists, which includes key contributions by geologists at the University of Utah, is sorting out by examining a large number of markers in the geological record that provide clues about the contents of the ancient atmosphere. Their preliminary study was recently published in the journal Sciencesrebuilding a company₂ Concentrations date back to the Cenozoic Era, the era that began with the extinction of dinosaurs and the appearance of mammals 66 million years ago.

Glaciers contain air bubbles, providing scientists with direct evidence of this Carbon dioxide levels go back 800,000 years, according to U of T geology professor Gabe Bowen, one of the study's authors. But this record does not extend deep into the geological past.

“Once you lose ice samples, you lose direct evidence. You no longer have samples of atmospheric gas that you can analyze,” Bowen said. “So you have to rely on indirect evidence, what we call proxies. “It is difficult to work with these agents because they are indirect.”

This graph shows carbon dioxide concentrations in Earth's atmosphere, expressed in parts per million (ppm), throughout the Cenozoic Era from preindustrial times to 65 million years ago. These are estimates based on proxies encoded in the geological record. Color-coded bars represent global temperature reconstructed from independent proxy data. The dashed line represents where carbon dioxide concentrations are today at 420 ppm. Credit: Gabe Bowen, University of Utah

“Proxies” in the geological record

These clues include isotopes found in minerals, the formation of fossilized leaves, and other geological evidence that reflects the chemistry of the atmosphere. One proxy stems from the foundational discoveries of UCLA geologist Thor Serling, himself a co-author of the new study, and whose previous research determined that carbon isotopes in ancient soils indicate the presence of carbon dioxide in the past.₂ Levels.

But the strength of these proxies varies, and most cover narrow segments of the past. He called the research team Cenozoic Company₂ Agent integration projectOr Cinco₂PIP, which was organized by Columbia University Climatologist Bärbel Hüneş set out to evaluate, classify and combine available proxies to create a high-resolution record of atmospheric carbon dioxide.₂.

“This represents some of the most comprehensive and statistically accurate approaches to interpreting carbon dioxide₂ “Over the past 66 million years,” said co-author Dustin Harper, a postdoctoral researcher in Bowen's lab. “Some of the new takeaways are that we're able to combine multiple proxies from different archives of sediment, whether it's in the ocean or on land, and that's really not 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 CO2₂ A record of 540 million years to the dawn of complex life.

At the beginning of the Industrial Revolution — when humans began burning coal, and then oil and gas to fuel their economies — carbon dioxide was in the atmosphere₂ It was about 280 ppm. A heat-trapping gas is released into the air when these fossil fuels burn.

Looking ahead, concentrations are expected to rise to between 600 and 1,000 ppm by 2100, depending on the rate of future emissions. It is not clear exactly how these future levels will affect the climate.

But there is no reliable map of past carbon dioxide₂ The levels could help scientists more accurately predict what future climates might look like, according to U of T biology professor William Anderegg, director of the U of T. Wilkes Center for Climate and Policy.

“This is a very important synthesis that has implications for future climate change as well, especially the key processes and components of the Earth system that we need to understand to anticipate the speed and magnitude of climate change,” Anderegg said.

Today's 419 ppm is the highest carbon dioxide has been in 14 million years

At times in the past when the Earth was a warmer place, carbon dioxide levels rose₂ It was much higher than it is now. However, the 419 ppm recorded today represents a sharp, potentially dangerous, and unprecedented rise in modern geological history.

“Eight million years before the present, there was maybe a 5% chance it was carbon dioxide₂ “The levels were higher than they are today, but we have to go back 14 million years before we see the levels we think they were today,” Bowen said.

In other words, human activity has changed the atmosphere dramatically within a few generations. As a result, climate systems around the world are showing alarming signs, such as powerful storms, prolonged drought, deadly heat waves, and ocean acidification.

Strong understanding of atmospheric carbon dioxide₂ Variation across geological time is also essential for deciphering and learning from different features of Earth's history. Changes in carbon dioxide in the atmosphere₂ It is likely that climate contributed to mass extinctions, as well as evolutionary innovations.

During the Cenozoic, for example, there was a long-term decline in carbon dioxide₂ The associated climate cooling may have led to changes in plant physiology. Classify Competition and dominance, which in turn influenced the evolution of mammals.

“More accurate understanding of past trends in carbon dioxide₂ It is therefore fundamental to understanding how modern species and ecosystems emerged, and what may happen in the future.

Reference: “Towards a Cenozoic history of atmospheric carbon dioxide.”₂“By the Cenozoic Carbon Dioxide Proxy Integration Project (CenCO2PIP) Consortium*†, Bärbel Hönisch, Dana L. Royer, Daniel O. Bricker, Pratigya J. Polisar, Gabriel J. Bowen, Michael J. Henehan, Ying Cui, Margaret Stainthorsdóttir, Jennifer C. McElwain, Matthew J. Cohen, Anne Pearson, Samuel R. Phelps, Kevin T. Ono, Andy Ridgewell, Eleni Anagnosto, Jacqueline Osterman, Marcus P. S. Badger, Richard S. Barkley, Peter K. Bell, Thomas P. Chalk, Christopher R. Scottis , Elwyn de la Vega, Robert M. DeConto, Kelsey A. Diez, Vicki Ferrini, Peter J. Franks, Claudia F. Jolliffe, Markus Gutjahr, Dustin T. Harper, Laura L. Haynes, Matthew Hopper, Katherine E. Snell, Benjamin A. Kiessling, Wilfred Conrad, Tim K. Loewenstein, Alberto Malinverno, Maxence Guermec, Luz Maria Mejia, Joseph N. Milligan, John J. Morton, Lee Nordt, Ross Whiteford, Anita Ruth Nibelcic, Jeremy K. C. Rogenstein, Morgan F. Schaller, Nathan D. Sheldon, Cindia Sosedian, Elise B. Wilkes, Caitlin R. Witkowski, Yi J. Zhang, Lloyd Anderson, David J. Burling, Clara Bolton, Thor E. Serling, Jennifer M. Cotton, Jiawei DA, Douglas D. Eckhardt, Gavin L. Foster, David R. Greenwood, Ethan J. Hyland, Elliot A. Gagnitsky, John B. Jasper, Jennifer B. Kowalczyk, Lutz Kunzmann, and Wolfram M. Korchner, Charles E. Lawrence, Carolyn H. Lear, Miguel A. Martinez Botti, Daniel P. Maxbauer, Paulo Montana, P. David A. Nafs, James W. B. Ray, Markus Reitzsch, Gregory J. Retzsch, Simon J. Ring, Osamu Seki, Julio Sepulveda, Ashish Sinha, Tiki F. Tesvamichael, Aradhna Tripathi, Johan van der Berg, Jimin Yu, James C. Zachos, and Liming Zhang, December 8 2023, Sciences.
doi: 10.1126/science.adi5177