Strong coupling between atmospheric CO₂- and temperature change

Variations in the concentration of atmospheric carbon dioxide (CO₂) were strongly coupled with variation in Earth’s temperature on geological timescales. This is based on new research conducted by paleoclimatologists from Utrecht University, the NIOZ Royal Netherlands Institute for Sea Research and the University of Southampton. The results will be published in the November 5^th issue of Science.

The potential causal role of CO₂-emissions on Earth’s temperature is subject to fierce public debate. A team of Dutch and paleoclimatologists now shows for the first time that on long timescales (more than half a million years) variations in CO₂ and temperature were strongly coupled.

Climate change in the geological past

The authors reconstructed variations in sea-surface temperature and CO₂-levels during a period of climate change roughly 40 million years ago. They showed that over a period of about half a million years, temperatures increased by 4 to 6 degrees Centigrade, followed by gradual cooling. Reconstructions of atmospheric CO₂ concentrations across this same interval of climate change now show that CO₂ and temperature were closely coupled.

Fossil algae

The scientists investigated sediments recovered from the ocean floor to reconstruct changes in Earth’s climate and CO₂. The reconstruction of ancient CO₂ concentrations was based on fossil molecules of algae. The carbon composition of such algae is strongly controlled by the atmospheric CO₂ concentration during growth (photosynthesis). Therefore, the carbon composition of their fossil molecules provides a tool to reconstruct CO₂ concentrations dating back to 40 million years ago. Furthermore, information on the past marine ecosystem was derived from studying changes in the abundance of different groups of fossil plankton in order to refine the CO₂ -estimates.

Relationship between temperature and CO₂

A central theme in the global warming debate regards the potentially causal role of human-induced CO₂ -emissions. The large-scale changes in ancient CO₂ concentrations documented in this study strongly suggest that CO₂ had a leading role on long timescales. “To put it briefly, the change in CO₂ 40 million years ago was too large to have been the result of temperature change and associated feedbacks,” says Peter Bijl, paleoclimatologist and co-lead author. “Such a large change in CO₂ certainly provides a plausible explanation for the changes in Earth’s temperature.”

Publication

Report in Science: “Transient Middle Eocene Atmospheric CO₂ and Temperature Variations”, by Peter K. Bijl, Alexander J.P. Houben, Stefan Schouten, Steven M. Bohaty, Appy Sluijs, Gert-Jan Reichart, Jaap S. Sinninghe Damsté and Henk Brinkhuis, 5^th november 2010.

Expedition

Last year, members of the research team participated in an international expedition that recovered sediments from the Antarctic coast. Short movies that illustrate the procedures of ocean drilling can be found at www.youtube.com/oceanleadership