Carbon dioxide levels in the atmosphere were significantly higher around 50 million years ago than scientists previously thought, according to new findings.
The findings point to the earth being more sensitive than feared to increased greenhouse gases.
That the level of carbon dioxide in the atmosphere affects the global temperature has been known for a long time. But researching things that happened tens of millions of years ago, i.e. as far back as the extinction of the dinosaurs, is difficult and there have been many different ways of measuring and calculating.
Now 80 researchers from 16 countries have gone through all available knowledge about how the carbon dioxide content in the atmosphere has varied and tried to clean up among studies and data. Their conclusion is that the Earth’s climate is significantly more sensitive to greenhouse gases than current models show.
High levels before
A common assumption today is that for every doubling of the amount of carbon dioxide in the atmosphere, the temperature will rise between 1.5 and 4.5 degrees. But the new study points out that a doubling is rather an increase of up to 6 degrees.
“We have known for a long time that by adding carbon dioxide to the atmosphere we raise the temperature. But this study gives us a much better picture of how sensitive the climate is in the longer term,” says Bärbel Hönisch, the study’s lead author, in a press release.
The conclusions published in the scientific journal Science provide a solid foundation to stand on, according to Thorsten Mauritsen, professor at the Department of Meteorology at Stockholm University who researches the climate.
– There have been many divided opinions about how greenhouse gases in the atmosphere varied in ancient times. It is good that such a large group of researchers now set the framework for us who use data and make calculations. This allows us to make better analyses, he says.
Plenty of life
A discovery made by the researchers behind the study is that the carbon dioxide content in the atmosphere during the beginning of the Cenozoic era, “the present time of life on Earth”, can explain the very warm climate that prevailed on Earth at that time. A time when there was plenty of life on earth.
– It is interesting that the carbon dioxide levels were probably about four times as high as today but that life flourished, says Birger Schmitz, professor of geology at Lund University who researches the earth’s climate far back in time.
He points out that the situation today is different as we are eight billion people living on earth and that the temperature increases that human emissions of greenhouse gases lead to can have a major impact socially.
– But it is fantastic that the researchers have taken a hold of this and that we now know better what the uncertainties are and which models we can rely on in research.
FACT This is how scientists reveal how much greenhouse gases there were in the past
There are different ways to find out the amount of carbon dioxide in the atmosphere in the Earth’s antiquity. By studying fossils from plants, you can see how many split openings there are on leaves. Cleavage openings are microscopic pores that clearly vary with the level of carbon dioxide in the air.
You can also chemically analyze fossil animal shells made of lime and gain knowledge about ancient climates and carbon dioxide content.
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