In all of human history, we haven’t lived with the kind of atmosphere we have today

Environment

We humans have officially entered uncharted territory. In the roughly 2.5 million years our kind has walked the Earth, never before have we endured such an atmosphere.

New research on ancient soil has now confirmed that carbon dioxide levels in the past sixty years are the highest we’ve experienced in all of human history.

Throughout the entire Pleistocene era – which started 2,580,000 years ago – the authors found concentrations of CO2 were, on average, roughly 250 parts per million.

Yet in the past sixty years or so, that consistency has appeared to rapidly unravel. Today, the findings suggest, our planet has reached 415 ppm for the first time in 2.5 million years.

“According to this research, from the first Homo erectus, which is currently dated to 2.1 to 1.8 million years ago, until 1965, we have lived in a low-carbon dioxide environment – concentrations were less than 320 parts per million,” explains geoscientist Yige Zhang from Texas A&M University.

“So this current high-carbon dioxide environment is not only an experiment for the climate and the environment – it’s also an experiment for us, for ourselves.”

To figure out where we are going, first requires us to know where we’ve been. Studying past climates, Zhang says, can help provide some of that perspective and hopefully help us navigate our uncertain future.

Because they trap tiny bubbles of air, ice cores are often used by climate scientists as a record of the historical CO2 levels in our planet’s atmosphere. But these samples only go back hundreds of thousands of years and not millions.

To dive deeper into Earth’s history, Zhang and his colleagues turned to soil. As a natural part of the carbon cycle on Earth, soil creates carbonates when it is formed, and these tiny traces can be useful as indicators of past climates.

Analysing carbonates in fossil soils from the Loess Plateau in China, the team was therefore able to reconstruct CO2 levels from millions of years ago.

“The Loess Plateau is an incredible place to look at aeolian, or wind, accumulation of dust and soil,” says Zhang.

“The earliest identified dust on that plateau is from 22 million years ago. So, it has extremely long records.”

While it’s true that soil carbonates are only a proxy for ancient climates, the results from the Loess Plateau appear to match other estimates, which were made using ice cores and blue ice records instead.

Zhang and his team, however, are still not content. They plan on refining their techniques for soil analysis to improve their estimates even more, potentially using the technique on soils as old as 23 million years.

“The past is the key to our future,” Zhang told The Eagle.

“Earth has a long history, and a lot of things from climate and life and environment have changed. .. Paleoclimate is important for us to learn about the past and maybe to predict the future.”

The findings were published in Nature Communications.

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