The last time atmospheric carbon dioxide levels consistently matched today’s anthropogenic levels was 14 million years ago, according to a major new study published Thursday that paints a bleak picture of where Earth’s climate is headed.

The paper, published in the journal Science, covers the period from 66 million years ago to the present and analyzes biological and geochemical signatures of the deep past to reconstruct historical CO2 emissions with greater precision than ever before.

“This really makes us realize that what we’re doing is very, very unusual in Earth history,” lead author Berbel Henisch, of the Lamont-Doherty Earth Observatory at Columbia Climate School, told AFP.

The new analysis shows, among other things, that the last time air contained 420 parts per million (ppm) of carbon dioxide was 14 to 16 million years ago, when Greenland was ice-free and human ancestors had just transitioned from forests. This goes back much further than the 3-5 million year period suggested by previous analysis.

In the late 1700s, carbon dioxide in the atmosphere was around 280 parts per million; This meant that humans had already caused a 50 percent increase in greenhouse gas emissions; This trapped heat in the atmosphere and warmed the planet by 1.2 degrees Celsius. compared to the situation before industrialization.

“The important thing is that our species, Homo, evolved only 3 million years ago,” Henisch said.

And so our civilization, as it is today, is adjusted to sea level, warm tropics, cool poles, and temperate regions with high rainfall. If global CO2 emissions continue to increase, we could reach 600-800 ppm by 2100.

These levels were last observed during the Eocene epoch, 30-40 million years ago, before Antarctica was covered in ice and at a time when the world’s flora and fauna looked very different; giant insects, for example, still roamed the Earth.

ancient plants

The new study is the result of seven years of work by a consortium of 80 researchers from 16 countries and is now considered an updated consensus of the scientific community. The team did not collect new data; instead, it synthesized, reevaluated, and validated published studies based on updated scientific evidence, ranked them by their level of reliability, and then combined the most popular study into a new timeline.

Many people are familiar with the concept of drilling into ice sheets or glaciers to extract ice cores, whose air bubbles reveal the past composition of the atmosphere, but these are often hundreds of thousands of years old, only now being exposed.

Paleoclimatologists use “surrogates” to look deeper into the past: By examining the chemical composition of ancient leaves, minerals, and plankton, they can indirectly obtain atmospheric carbon from that time.

The researchers confirmed that before a long decline began, the hottest period in the last 66 million years occurred 50 million years ago, when CO2 emissions rose to 1,600 parts per million and temperatures were 12 degrees warmer.

2.5 million years ago the carbon dioxide concentration was 270-280 parts per million, which started a series of ice ages. This level remained at the same level 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 a doubling of CO2 emissions would warm the planet by 5 to 8 degrees Celsius, but this would occur over a long period of hundreds of thousands of years, and the increase in temperature would have a ripple effect throughout Earth’s systems. Melting polar ice caps, for example, would reduce the planet’s ability to reflect solar radiation, creating a reinforcing feedback loop.

However, Henisch emphasized that the new study, as before, is directly related to politicians. Carbon records show that 56 million years ago, Earth experienced a similarly rapid release of carbon dioxide that caused major changes in ecosystems and took about 150,000 years to dissipate.

“If we don’t sequester carbon dioxide, remove it from the atmosphere and stop our emissions soon, we’re going to be in this for a very long time,” he said. Source