Neil Tabor

Research: SMU-led fossil study finds carbon dioxide link to global warming 22 million years ago

Fossil leaves from Ethiopia

Variations in the concentration of atmospheric carbon dioxide affect carbon fixation during photosynthesis and can be measured on a preserved fossil leaf like this one from Ethiopia.

Fossil leaves from Africa have resolved a prehistoric climate puzzle — and also confirm the link between carbon dioxide in the atmosphere and global warming.

Research until now has produced a variety of results and conflicting data that have cast doubt on the link between high carbon dioxide levels and climate change for a time interval about 22 million years ago.

But a new study has found the link does indeed exist for that prehistoric time period, say SMU researchers. The finding will help scientists understand how recent and future increases in the concentration of atmospheric carbon dioxide may impact the future of our planet, they add.

The discovery comes from new biochemical analyses of fossil leaves from plants that grew on Earth 27 million years ago and 22 million years ago, said geologist Tekie Tesfamichael, an SMU postdoctoral fellow in Earth Sciences and a lead scientist on the research.

The new analyses confirm research about modern climate — that global temperatures rise and fall with increases and decreases in carbon dioxide in our atmosphere — but in this case even in prehistoric times, according to the SMU-led international research team.

Carbon dioxide is a gas that is normally present in the Earth’s atmosphere, even millions of years ago. It’s dubbed a greenhouse gas because greater concentrations cause the overall temperature of Earth’s atmosphere to rise, as happens in a greenhouse with lots of sunlight.

Recently greenhouse gas increases have caused global warming, which is melting glaciers, sparking extreme weather variability and causing sea levels to rise.

The new SMU discovery that carbon dioxide behaved in the same manner millions of years ago that it does today has significant implications for the future. The finding suggests the pairing of carbon dioxide and global warming that is seen today also holds true for the future if carbon dioxide levels continue to rise as they have been, said Tesfamichael.

“The more we understand about the relationship between atmospheric carbon dioxide concentrations and global temperature in the past, the more we can plan for changes ahead,” said Tesfamichael.

“Previous work reported a variety of results and conflicting data about carbon dioxide concentrations at the two intervals of time that we studied,” he said. “But tighter control on the age of our fossils helped us to address whether or not atmospheric carbon dioxide concentration corresponded to warming — which itself is independently well-documented in geochemical studies of marine fossils in ocean sediments.”

The researchers reported their findings in Geology, the scientific journal of the Geological Society of America. The article is “Settling the issue of ‘decoupling’ between atmospheric carbon dioxide and global temperature: [CO2]atm reconstructions across the warming Paleogene-Neogene divide.”

Co-authors from the Roy M. Huffington Department of Earth Sciences in Dedman College are professors Bonnie Jacobs, an expert in paleobotany and paleoclimate, and Neil J. Tabor, an expert in sedimentology and sedimentary geochemistry. Other co-authors are Lauren Michel, Tennessee Technological University; Ellen Currano, University of Wyoming; Mulugeta Feseha, Addis Ababa University; Richard Barclay, Smithsonian Institution; John Kappelman, University of Texas; and Mark Schmitz, Boise State University.

— Written by Margaret Allen

> Read the full story at the SMU Research blog: smuresearch.com

Research Spotlight: Four professors named 2011 Ford Research Fellows

SMU's 2011 Ford Research FellowsFour outstanding SMU researchers have been named as the University’s 2011 Ford Research Fellows. This year’s recipients are Johan Elverskog, Religious Studies, Dedman College; Thomas Hagstrom, Mathematics, Dedman College; Neil Tabor, Earth Sciences, Dedman College; and Sze-kar Wan, New Testament, Perkins School of Theology.

Established in 2002 through a $1 million pledge from SMU Trustee Gerald J. Ford, the fellowships help the University retain and reward outstanding scholars. Each recipient receives a cash prize for research support during the year.

Above, the new Ford Research Fellows were honored by the SMU Board of Trustees during its May meeting (left to right): Sze-kar Wan, Thomas Hagstrom, Johan Elverskog and Neil Tabor.

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