Current CO2 levels, unheard of for 14 million years on Earth

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Agence France-Presse

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Current levels of carbon dioxide in the atmosphere have not been reached in 14 million years on Earth, reveals a large study that hints at the inhospitable climates humanity is heading towards .

This publication in the journal Science (New window) (in English) traces CO2 levels since 66 million from years before our era, to today's global warming, with unprecedented precision.

This shows us to what extent what we are doing is really, really unusual in the history of the Earth, explains lead author Baerbel Hoenisch to AFP, researcher at Columbia University in New York.

The last time our planet's atmosphere contained the same concentration of the main gas greenhouse gas (CO2) that today, about 420 ppm (parts per million), dates back about 14 to 16 million years.

It dates back much further than scientists previously estimated (3 to 5 million years).

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14 to 16 million years ago, there was, for example, no ice cap in Greenland.

However, our civilization is accustomed to the sea levels that ;we currently know that the warm tropics, the cold poles and the temperate regions benefit from a lot of precipitation, warns Baerbel Hoenisch.

Our species […] has only evolved for 3 million years. We have never experienced anything like these warm climates.

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A quote from Baerbel Hoenisch, Columbia University

Before the In the industrial era, the CO2 concentration in the atmosphere was around 280 ppm. This has increased by half with human activities, causing temperatures to rise by around 1.2°C.

And if our emissions continue, the concentration could rise to 600 or 800 ppm, levels reached during the Eocene (-30 to -40 million years ago). x27;years), before Antarctica was covered in ice and when the planetary fauna and flora were very different, with for example immense insects.

The study published Thursday inScienceis the result of seven years of work by a group of 80 researchers in 16 countries. Their conclusions are now considered a scientific consensus.

Their contribution does not lie in the collection of new data, but in painstaking work of reassessment and synthesis of already existing work to update them and classify them according to their reliability, which made it possible to use the best data in order to draw an overall picture.

To reconstruct past climates, a well-known technique consists of recovering from the depths of the ice caps air bubbles which have trapped the composition of the air the atmosphere of the time. But this technique only allows us to go back a few hundred thousand years.

To go further, you have to use indirect markers. The chemical study of ancient minerals, leaves or plankton has thus made it possible to deduce the CO2 concentration of older given periods.

Over the past 66 million years, the warmest period on Earth was around 50 million years ago, with a CO2 concentration of 1600 ppm and temperatures 12°C warmer than x27;today.

The latter declined slowly until 2.5 million years ago and the time of the ice ages, the concentration of CO2 falling again until #x27;at 270-280 ppm.

These levels remained stable until humanity burned fossil fuels at large scale.

According to the study, a doubling of the CO2 concentration rate would gradually warm the planet, over hundreds of thousands of years, until reaching +5 to 8°C, due to the effects in cascade that would lead to a rise in temperatures.

Thus, the melting of polar ice reduces their ability to reflect the sun's rays, which accelerates still cast iron, etc.

The study shows that 56 million years ago, the Earth's atmosphere experienced a rapid rise in CO2 concentration similar to that experienced today, which caused massive changes in ecosystems and took some 150,000 years to dissipate. p>

We are here for a very long time, unless we capture carbon dioxide from the atmosphere and stop our emissions very soon, summarizes Baerbel Hoenisch.