Current CO2 levels not seen on Earth in 14 million years – Radio-Canada.ca

Current levels of carbon dioxide in the atmosphere have not been reached on Earth for 14 million years, according to a major study that highlights the inhospitable climate humanity is heading towards.

This paper in the journal Science (New Window) tracks CO2 levels from 66 million years B.C. BC to today’s global warming with unprecedented precision.

“This shows us the extent to which what we are doing is really, really unusual in Earth’s history,” lead author Baerbel Hoenisch, a researcher at Columbia University in New York, told AFP. York.

The last time our planet’s atmosphere contained the same concentration of the most important greenhouse gas (CO2) as it does today, about 420 ppm (parts per million), was about 14 to 16 million years ago.

This happened much longer ago than scientists previously thought (3 to 5 million years).

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

However, our civilization is used to the sea levels we are currently experiencing, to the hot tropics, to the cold poles and to temperate regions that benefit from a lot of precipitation, warns Baerbel Hoenisch.

Our species […] has only evolved for 3 million years. We have never experienced anything like this hot climate.

Before the industrial age, the CO2 concentration in the atmosphere was around 280 ppm. Human activity has increased this value by half, resulting in a temperature increase of around 1.2°C.

And if our emissions continue, concentrations could rise to 600 or 800 ppm, levels reached in the Eocene (-30 to -40 million years ago), before Antarctica was covered in ice and when wildlife and planetary flora were still very high Huge insects, for example, were different.

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

Their contribution lies not in the collection of new data, but in the careful reassessment and synthesis of existing works in order to update them and classify them according to their reliability, which made it possible to use the best data to build an overall picture.

To reconstruct past climates, a well-known technique involves recovering air bubbles from the depths of ice caps that captured the composition of the atmosphere at that time. However, using this technique we can only go back a few hundred thousand years.

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

Over the past 66 million years, the warmest period the Earth has ever experienced was about 50 million years ago, with CO2 levels at 1,600 ppm and temperatures 12°C warmer than today.

The latter slowly decreased until 2.5 million years ago and during the ice ages, the CO2 concentration fell to 270-280 ppm.

These values ​​remained stable until humanity burned fossil fuels on a large scale.

Catastrophic consequences

According to the study, doubling the CO2 concentration rate would gradually warm the planet over hundreds of thousands of years until it reaches +5 to 8°C due to the cascading effects an increase would cause.

Thus, the melting of polar ice reduces its ability to reflect the sun’s rays, which further accelerates the melting, etc.

The study shows that 56 million years ago, CO2 concentrations in Earth’s atmosphere rose at a similar rate to today, causing massive changes in ecosystems and taking about 150,000 years for CO2 concentrations to dissipate.

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