Find in News Talk Sites Images For advanced search options, click here . Subscribe for free email updates . Click here to sign up, or log in . The method uses what is known as stomatal index and is based on carbon dioxide fluctuations in the Earth's atmosphere. The number of pores, or stomata, produced on the underside of the leaf is directly related to the carbon dioxide concentration in the atmosphere, Dilcher said.
More carbon dioxide means fewer stomata and vice versa.
It's a delicate balance the leaf is measuring. The plant senses the amount of CO2 in the atmosphere and adjusts accordingly. That leaves the door open on whether global warming during the past 100 years or so is a result of man-made greenhouse gases or part of a larger natural cycle. While the Science article deals with a fossil record of just a few hundred years, he said, a record going back as far as 10 million years could be created using the stomatal index method. If you wish to quote from any part of this story, please credit University Of Florida as the original source.