It is true that the research had purely scientific and wide-ranging ambitions, aiming to reconstruct the fluctuations of atmospheric CO2 over the last 66 million years. The project lasted seven years and involved a long analysis and a selection of many geological records, which had to take into account uncertainties and chronological models still to be refined.
In any case, the results are clear. First of all, they confirm a clear relationship between CO2 levels and the rise in the Earth’s global average temperature. It has been established that a doubling of atmospheric CO2 could raise the planet’s average temperature by 5-8 °C: an increase that would be dramatic, to say the least, and considerably higher than previously forecast. Moreover, the current level of CO2 in the atmosphere, at 420 ppm and caused mainly by human activity (the scientists who conducted the research have no doubts about this), has not been reached in the last 14 million years.
“We have known for some time that adding CO2 to the atmosphere raises the temperature,” said Bärbel Hönisch, researcher at Columbia University and coordinator of the study, “but this work gives us a much more solid idea of how sensitive the climate is on long timescales.”
But how is it possible to reconstruct the level of CO2 in the very remote geological past? The authors of the study used both direct measurements, such as the analysis of air bubbles trapped in ice cores from the polar regions, and indirect ones, such as the study of chemical signals in plants, minerals and fossil organisms.
“The isotopic composition of the carbonate shells of certain planktonic organisms preserved in marine sediments, or of coral skeletons, allows us to reconstruct the climate of the past,” explains Paolo Montagna, researcher at Cnr-Isp and co-author of the work. “By combining direct and indirect measurements from various geological archives, we managed to obtain a detailed reconstruction of atmospheric CO2 levels over the last 66 million years. This reconstruction was then compared with the temperature evolution curve to obtain a more complete picture.”
Beyond the admittedly interesting findings on distant geological eras, what concerns and worries us ordinary mortals of the 21st century most is the current situation and how it may develop. On this Professor Montagna is clear: “The current concentration of CO2 has exceeded 420 ppm, marking a 50% increase compared with the levels reconstructed for the end of the 18th century. Values this high have not been reached in the last 14 million years, and this trend, if not mitigated, could bring CO2 concentrations to 600-800 ppm by the end of this century.”
And as has been said, according to the scientists this would mean, for a doubling of CO2 in the atmosphere, a corresponding rise in the global average temperature of 5-8 °C: well beyond, therefore, current estimates (and curiously closer to the hypotheses formulated in the nineteenth century by the Swedish Nobel Prize-winning physicist Arrhenius).
“We cannot say what the temperature will be in 2100,” observes one of the authors of the study, Dana Royer, of the American Wesleyan University, “but we can say that there will be slow, cascading effects that will last for thousands of years.”
“This scenario highlights the urgent need to tackle greenhouse gas emissions and to develop effective strategies to counter climate change,” concludes Hönisch. One can hardly disagree.
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