Current CO2 levels are the highest in 14 million years – 12/07/2023 – Environment

Current levels of carbon dioxide (CO_two) in the atmosphere are the highest recorded on Earth in 14 million years, revealed an extensive study released this Thursday (7), which evokes the inhospitable climatic conditions that humanity is facing.

Published in the journal Science, the study tracks CO levels_two from 66 million years before Christ to the present day, with unprecedented precision.

“This shows us to what extent what is being done now is really unusual in the history of the Earth,” explained to AFP the study’s main author, Baerbel Hoenisch, a researcher at Columbia University in New York.

The last time the planet’s atmosphere contained the same concentration of the main greenhouse gas (CO_two) which today, about 420 ppm (parts per million), was between 14 million and 16 million years ago, when, for example, there was no ice cover on Greenland.

This goes back much further than scientists previously estimated (between 3 million and 5 million years ago).

Climate unknown to humanity

“Our civilization is used to current sea levels, the hot tropics, the cold poles and temperate regions, which benefit from a lot of rainfall,” says Baerbel Hoenisch.

The scientist highlights that our species “began to evolve only three million years ago” and that “we have never experienced anything similar to this hot climate”.

Before the industrial era, the concentration of CO_two in the atmosphere it was around 280 ppm. With human activities, they grew by 50%, which caused an increase in temperatures of around 1.2°C.

And if emissions continue, the concentration could increase to 600 or 800 ppm, rates reached during the Eocene (between 30 million and 40 million years ago), before Antarctica was covered in ice and when wildlife and flora in the planet were very different, with, for example, huge insects.

From plankton to CO_two

The study published this Thursday in the journal Science is the result of seven years of work by a group of 80 researchers from 16 countries. Its conclusions are considered a scientific consensus.

The contribution of this research does not consist so much in the compilation of new data, but in the detailed work of reevaluating and synthesizing existing works to update them and classify them according to their reliability, which made it possible to use the best data to be able to draw a general picture .

To reconstruct past climates, a well-known technique consists of recovering from the depths of the polar ice cap the air bubbles that captured the composition of the atmosphere at the time.

But this technique only allows us to go back hundreds of thousands of years. To go further, you must resort to indirect markers. The chemical study of ancient leaves, minerals or plankton has thus made it possible to reduce the concentration of CO_two in more remote times.

Ripple effects

Over the past 66 million years, the hottest period recorded on Earth dates back to around 50 million years ago, with a concentration of CO_two of 1,600 ppm and temperatures 12°C warmer than today.

These levels slowly decreased until about 2.5 million years ago and the time of the glaciations, when the concentration of CO_two it fell back to 270-280 ppm.

They then remained stable until humanity began burning fossil fuels on a large scale.

According to the study, a doubling of the CO concentration rate_two it would gradually warm the planet over hundreds of thousands of years, until it reached 5°C to 8°C more, due to the cascading effects that an increase in temperatures would cause.

Thus, the melting of polar ice reduces its ability to reflect the sun’s rays, further accelerating the process.

The study shows that 56 million years ago, the Earth’s atmosphere experienced a rapid increase in CO concentration_two similar to what we know today and that this caused massive changes in ecosystems that took around 150 thousand years to dissipate.

“We’re going to be in this for a long time unless we capture carbon dioxide from the atmosphere and stop our emissions as quickly as possible,” summarized Baerbel Hoenisch.