How much CO2 was present in the air in prehistoric times is a question that needs answering. It could go a long way in our understanding of climate change. Knowing the levels present in today’s air is of course, easy. We just measure it with the innumerable tools we have. But just how do we go about measuring the levels in the atmosphere of prehistoric times?
Araucarias are coming to the rescue as an answer to this unique problem. Araucarias are evergreen coniferous trees. Today their population is sparse, but in prehistoric times they were the dominant vegetation around the planet.
Studying Araucarias is of significance because one of the simplest ways to gauge CO2 is through stomatal pores in leaves. It’s not a secret that plants tend to decrease the number of pores when the atmospheric CO2 is increased. Count the number of pores and you can have a fair idea of CO2 concentrations. This relationship between number of stomata and CO2 varies from species to species and can be ascertained by counting the pores of plants grown in the lab, under different amounts of CO2. Leaves preserved in herbariums can be compared to data available for CO2 concentrations and a relationship drawn out.
Matthew Haworth, at the Istituto di Biometeorologia in Florence, Italy says,
“With this observation it is possible to use the number of stomata on the leaves of fossil plants to calculate the concentration of atmospheric carbon dioxide in which those leaves developed. This so-called stomatal method works beautifully over the last 1.5 million years where you have the same species living as today.”
Araucarias nowadays are not very common, but 200 million years ago they were the majority in the world’s forests. These trees evolved in a period when the concentration of CO2 in the atmosphere was a lot higher than it is today and for that reason araucarias are good candidates to gauge the levels of CO2 in the atmosphere during the age of dinosaurs.
Araucarias also do not show the so called ‘ceiling effect’ where plant species stop decreasing the amount of stomata if the CO2 concentration is above 400 parts per million. As Haworth says,
“It really limits the effectiveness of the technique during periods of high concentrations of carbon dioxide, which are obviously the periods we are most interested in to compare with current rising CO2.”
The results of the study have been published in the journal, Oecologia and prove that araucarias can step in and be useful gauges of past CO2 levels, especially during times when CO2 concentration was higher than today.