Mankind only lived in an atmosphere rich in carbon dioxide in 1965

Humans have never lived with the high carbon dioxide atmospheric conditions that have become the norm on Earth over the past 60 years, according to a new study including a researcher from Texas A & M University.

Entitled "Low CO2 levels of the Pleistocene Era" and published in Nature Communications Today, the study shows that during the 2.5 million years of the Pleistocene era, carbon dioxide concentrations averaged 250 parts per million. Current levels, by comparison, exceed 410 parts per million. The study shows that in 1965, atmospheric concentrations of carbon dioxide on the Earth exceeded 320 parts per million, a peak never reached for 2.5 million years.

"According to this study, of the first Homo erectus, which currently dates from 2.1 to 1.8 million years ago, up to 1965, we lived in a low carbon dioxide environment – concentrations were lower at 320 parts per million, "said Yige Zhang, co-author of the study and an assistant professor in the oceanography department of the College of Geosciences. "So, this current environment rich in carbon dioxide is not just an experience for the climate and the environment, it is also an experience for us, for ourselves."

Carbon dioxide is a greenhouse gas that contributes to the warming of the earth's atmosphere and is considered a driver of global climate change, Zhang said.

"It is important to study the atmospheric concentrations of CO2 (carbon dioxide) in the geological past, because we know that there are already consequences on the climate and that there will be more of consequences on the climate, and one of the ways to know the consequences is to examine the history of the Earth, "Zhang said. "Then we can see what kind of CO2 level we had, what the climate looked like and what the relationship was between them."

Da Jiawei, Xianqiang Meng and Junfeng Ji, all from Nanjing University in China, and Gen Li from the California Institute of Technology, co-authored the research.

Scientists analyzed soil carbonates from the Loess Plateau in central China to quantify carbon dioxide levels in the atmosphere up to 2.5 million years ago. Climatologists often use ice cores as a "reference" in physical climate records, Zhang said, but ice cores only cover the last 800,000 years.

By analyzing the paleogenic carbonates found in the ancient soil, or paleosols, of the Loess Plateau, scientists have reconstructed the Earth's carbon dioxide levels.

"The Loess Plateau is an incredible place to see the accumulations of wind and wind dust and soil," Zhang said. "The first dusts identified on this shelf date from 22 million years ago, so the recordings are extremely long.The loess and palaeosol layers contain soil carbonates that record atmospheric carbon dioxide. if we have very attentive eyes. "

"Specifically, the carbonates formed during soil formation usually reach an isotopic carbon balance with the ambient CO2 of the soil, which is a mixture of atmospheric CO2 and CO2 produced by soil respiration," said Jiawei Da of the Nanjing University. "Through the application of a two-component mixing model, we can reconstruct paleo-CO2 levels using carbonates in fossil soils."

Using these materials and techniques, researchers constructed a history of Pleistocene carbon dioxide.

"Our reconstructions show that, for the entire Pleistocene period, carbon dioxide averaged about 250 parts per million, which is the same as the values ​​of the last 800,000 years," Zhang said.

"Our Paleosol-based CO2 estimates are consistent with early Pleistocene CO2 snapshots recovered in the old Antarctic blue ice, suggesting that the Earth's system operated at low levels of CO2 throughout the Pleistocene" , said Junfeng Ji of Nanjing University.

We have evolved in a low carbon environment, Zhang said, and we do not see how humans will evolve and be affected by current levels of carbon dioxide.