The last time carbon dioxide in the atmosphere reached current levels was 14 million years ago, according to a major study. Since industrialization began in the 18th century, human activity has increased CO₂ levels by 50%.
The work, published in the journal Science, covers the period from 66 million years ago to the present and analyzes biological and geochemical signatures from the deep past to reconstruct historical CO₂ data with the highest scale and precision than ever before.
The study is the result of seven years of work by a team of 80 researchers from 16 countries and is now considered the updated consensus of the scientific community.
“It really made it clear to us that what we were doing was very, very unusual historically,” lead author Bärbel Hönisch from the Columbia Climate School's Lamont-Doherty Earth Observatory in the US told AFP.
Historical record of CO2 in the atmosphere
The analysis shows that the last time the air contained 420 parts per million (ppm) of carbon dioxide was 14 to 16 million years ago, when there was no ice in Greenland and people's ancestors rarely moved from the forests to the mountains.
At the end of the 18th century, the concentration of carbon dioxide in the atmosphere was about 280 parts per million, which means that humans have increased the amount of this greenhouse gas, which traps heat in the atmosphere, by about 50% and is harming the planet.
“What is important is that Homo, our species, only evolved three million years ago. “So our civilization today is at sea level, with warm tropical zones, extremely cold zones and temperate zones with heavy rainfall,” Hoenisch said.
These values were last measured in the Eocene epoch, 30 to 40 million years ago, before Antarctica was covered with ice and the world's flora and fauna were very diverse; For example, giant insects still roam the planet.
The team does not collect new data, but synthesizes, evaluates and validates published articles based on current scientific evidence, then ranks them according to the level of evidence, and then combines the highest rated articles into a new schedule.
Scientists have confirmed that the warmest period in the last 66 million years occurred 50 million years ago, when CO2 levels reached 1,600 ppm and temperatures rose by 12°C before a sustained decline began.
2.5 million years ago, carbon dioxide concentrations were 270 to 280 ppm, triggering a series of ice ages. These levels persisted when modern humans emerged 400,000 years ago and continued until our species began burning fossil fuels on a large scale.
The team estimates that doubling CO2 emissions would warm the planet by 5 to 8 degrees Celsius, but over a long period of hundreds of thousands of years, during which rising temperatures would trigger a domino effect on Earth's systems.