Understanding the earth’s climate, how it has changed over time and the factors that influence that change can offer clues about what to expect in the future.
In research recently published by The Geological Society of America in the journal, Geology, Lauren Michel, climate change scientist and assistant professor at Tennessee Tech, worked with colleagues from across the U.S. and in Ethiopia to assess the relationship between the concentration of the atmosphere’s heat-trapping greenhouse gas, carbon dioxide, and global temperature. By applying a new model for measuring atmospheric CO2 concentration from leaf fossils, the scientists found support for their understanding of greenhouse gases and climate change: when carbon dioxide increased between two time intervals millions of years ago, temperature also increased.
Greenhouse gases in earth’s atmosphere affect the surface temperature of the earth. In their research, Michel and her colleagues worked to reconstruct the levels of carbon dioxide that were present in the past. To know what those levels were like, they looked at geological samples from fossil sites in Ethiopia, where leaves 27 and 22 million years old were well preserved.
“The carbon isotope values and the level of stomata in the leaves tells you something about the amount of carbon in the atmosphere at the time the leaves were forming,” Michel said.
The concept of an increase in temperature being associated with higher levels of carbon dioxide and water vapor in the atmosphere is not new. It is what scientists have thought to be true for some time. However, when studying climate indicators found in a segment of the rock record, some previous models actually showed a decoupling of these factors.
“We didn’t understand why this was happening,” Michel said. “It didn’t go with what we thought we knew about greenhouse gases and temperature. What was causing that decoupling was this big unknown question. This study is so important because it showed that there were problems with the models we were using.”
With the new model reaffirming a relationship between the amount of carbon dioxide in the atmosphere and global temperature, Michel said other scientists can start looking at other questions about climate change. Answering questions about the rate of change and which factors changed first, for example, will ultimately give a clearer picture of the earth’s climate change patterns.
“I think it is really valuable to understand the relationship of greenhouse gases and climate factors represented in the rock record so we can have a better idea of what we can expect in the future and how we can prepare for that,” Michel said. “I think about that all the time living in the south. I want to know if it is getting hotter here. I want to know if it is going to continue to get hotter here. I want to know if I need to buy a better air conditioning system when I renovate my house.”
Michel began work on this research project during her post-doctoral time at Southern Methodist University and the resulting paper published in Geology by The Geological Society of America was written during her first year at Tennessee Tech.
Other scientists who worked on the project include Tekie Tesfamichael, Bonnie Jacobs and Neil Tabor of Southern Methodist University; Ellen Currano of the University of Wyoming; Mulugata Feseha of Addis Ababa University in Ethiopia; Richard Barclay with the National Museum of Natural History at the Smithsonian Institution; John Kappelman of the University of Texas, Austin; and Mark Schmitz of Boise State University.
To read the full paper, “Settling the issue of ‘decoupling’ between atmospheric carbon dioxide and global temperature: [CO2]atm reconstructions across the warming Paleogene-Neogene divide,” visit https://pubs.geoscienceworld.org/geology/article/doi/10.1130/G39048.1/516665/settling-the-issue-of-decoupling-between .