Carbon Dioxide and Climate Change

Scientists at Utrecht University, working with colleagues at the NIOZ Royal Netherlands Institute for Sea Research and the University of Southampton have been studying one of the hottest episodes of Earth's climate history, the Middle Eocene Climatic Optimum (MECO), which occurred around 40 million years ago in order to understand the relationship between Earth's climate and atmospheric carbon dioxide.

Algae use photosynthesis to harvest the energy of the sun, converting carbon dioxide and water into the organic molecules required for growth. Different isotopes of carbon are incorporated into these molecules depending on the environmental conditions under which algae grow. Ancient climate can therefore be reconstructed by analysing the carbon isotope ratios of molecules preserved in fossilised algae.

Using fossilised algae preserved in sediment cores extracted from the seafloor near Tasmania, Australia, by the Ocean Drilling Program, the scientists refined their estimates of carbon dioxide levels using information on the past marine ecosystem derived from studying changes in the abundance of different groups of fossil plankton.

Their analyses indicate that MECO carbon dioxide levels must have at least doubled over a period of around 400,000 years. In conjunction with these findings, analyses using two independent molecular proxies for sea surface temperature show that the climate warmed by between 4 and 6^oC over the same period, suggesting that increased amounts of carbon dioxide in the atmosphere played a major role in global warming during the MECO.

The rapid increase in atmospheric carbon dioxide levels around 40 million years ago approximately coincides with the rise of the Himalayas and may be related to the disappearance of an ocean between India and Asia as a result of plate tectonics, the large scale movements of the Earth's rocky shell (lithosphere).

References:

1. P. K. Bijl, A. J. P. Houben, S. Schouten, S. M. Bohaty, A. Sluijs, G.-J. Reichart, J. S. Sinninghe Damste, H. Brinkhuis. Transient Middle Eocene Atmospheric CO2 and Temperature Variations. Science, 2010; 330 (6005): 819 DOI: 10.1126/science.1193654
2. P. N. Pearson. Increased Atmospheric CO2 During the Middle Eocene. Science, 2010; 330 (6005): 763 DOI: 10.1126/science.1197894

Further Reading
http://www.ausetute.com.au/greenhouse.html
http://www.ausetute.com.au/ccycle.html
http://www.ausetute.com.au/carbon14.html
http://www.ausetute.com.au/isotopes.html

Study Questions

1. Write a chemical equation showing the conversion of atmospheric carbon dioxide into glucose by photosynthesis.
2. Explain what is meant by the term isotope.
3. Give the names and symbols of the three naturally occurring isotopes of carbon.
4. Which isotope of carbon is the most abundant?
5. Which isotopes of carbon are stable?
6. Which isotopes of carbon are unstable (radioactive)?
7. Write a nuclear decay equation for the unstable carbon isotope(s).
8. Explain how ancient climate can be reconstructed by analysing the carbon isotope ratios of molecules preserved in fossilised algae.