Earth System scientists describe the Anthropocene as a “no-analog state,” a time when conditions on Earth have changed in unprecedented ways. A new study confirms and extends that conclusion, showing not only that humans have never before experienced carbon dioxide levels this high, but that our ancestors didn’t either.
Greenhouse gas levels haven’t been this high since at least half a million years before homo erectus walked the Earth.
Previous studies traced long-term CO2 levels by studying ancient ice in Antarctica — they showed that CO2 levels varied between 170 and 280 parts per million for 800,000 years, but that seems to be as far back as we can go with ice.
The new study, by researchers from Nanjing University, Texas A&M University, and the California Institute of Technology, examined ancient soils in the Loess Plateau in north-central China, an area where windblown dust and soil has been accumulating for millions of years.
The mix of carbon isotopes in the soil varies with age, allowing the researchers to construct a detailed carbon dioxide history going back to the beginning of the Pleistocene epoch, 2.6 million years ago.
Their reconstructions show that during the entire Pleistocene, carbon dioxide concentrations ranged from 183 to 292 parts per million, and averaged about 230 — confirming and substantially extending Antarctic ice studies.
Until the mid-20th century, no human had ever experienced higher CO2 levels than that. In May 2019, the global CO2 level reached 414.7 ppm — that’s 42 percent higher than the Pleistocene and Holocene maximum and 80% higher than the 2.6 million year average.
And the Anthropocene has barely begun.
Jiawei Da, Yi Ge Zhang, Gen Li, Xianqiang Meng & Junfeng Ji, “Low CO2 levels of the entire Pleistocene epoch,” Nature Communications, September 25, 2019