CO2 concentration is likely to further raise temperatures

June 24 () –

Doubling the amount of CO2 in the atmosphere could cause an increase in the Earth’s average temperature from 7 to a maximum of 14 degrees.

This is demonstrated by sediment analysis of the Pacific Ocean off the coast of California carried out by researchers from NIOZ (Royal Netherlands Institute for Sea Research) and the universities of Utrecht and Bristol. Their results were published in Nature Communications.

“The temperature increase we found is much higher than the 2.3 to 4.5 degrees that the UN climate expert groupthe IPCC, has been estimating so far,” said first author Caitlyn Witkowski.

The researchers used a 45-year-old drill core extracted from the bottom of the Pacific Ocean. “I realized that this core is very attractive to researchers, because the ocean floor at that location has had oxygen-free conditions for many millions of years,” he said. it’s a statement Professor Jaap Sinninghe Damsté, senior scientist at NIOZ and professor of organic geochemistry at Utrecht University.

“In this way, organic matter is not decomposed as quickly by microbes and more carbon is preserved,” explains Damsté, who also directed Witkowski’s doctoral thesis, which includes this research.

“CO2 from the last 15 million years has never before been examined in one place,” explains Witkowski. The first thousand meters of the drill core correspond to the last 18 million years. From this record, the researchers were able to extract an indication of the past sea water temperature and an indication of former atmospheric CO2 levelsusing a new approach.

The researchers obtained the temperature using a method developed 20 years ago at NIOZ, called the TEX86 method. “This method uses specific substances that are present in the membrane of archaea, a different class of microorganisms,” explains Damsté.

“These archaea optimize the chemical composition of their membrane depending on the water temperature in the upper 200 meters of the ocean. “Substances from that membrane can be found as molecular fossils in ocean sediments and are analyzed to this day.”

The researchers developed a new method to derive past atmospheric CO2 content using the chemical composition of two specific substances commonly found in algae: chlorophyll and cholesterol. This is the first study to use cholesterol for quantitative CO2 and the first study to use chlorophyll for this time period. To create these substances, algae must absorb CO2 from the water and fix it through photosynthesis.

Damsté said: “A very small fraction of the Earth’s carbon occurs in a ‘heavy form’, 13C instead of the usual 12C. Algae have a clear preference for 12C. However, the lower the CO2 concentration in water, more algae will also use the rare 13C. Therefore, the 13C content of these two substances is a measure of the CO2 content of the ocean water. And that in turn, according to the laws of solubility, correlates with the CO2 content of the atmosphere.”

Using this new method, it appears that CO2 concentration fell from about 650 parts per million 15 million years ago to 280 just before the industrial revolution.

When researchers compare derived temperature and atmospheric CO2 levels over the past 15 million years, They find a strong relationship.

The average temperature 15 million years ago was more than 18 degrees: 4 degrees higher than today and about the level that the UN climate expert group, the IPCC, predicts for the year 2100 in the most extreme scenario.

“This research therefore gives us an idea of ​​what the future could hold if we take too few measures to reduce CO2 emissions and also implement few technological innovations to offset the emissions,” Damsté said.

“The clear warning from this research is that CO2 concentration is likely to have a stronger impact on temperature than we are taking into account at the moment”.