Key points:
- Researchers developed a new approach to extract seawater temperature and ancient atmospheric CO2 levels.
- Using a combination of archaea and algae measurements, the team found that the average temperature 15 million years ago was over 18 degrees – 4 degrees warmer than today.
- These results provide a glimpse of what the future may be without a reduction and offset of CO2 emissions.
A new study finds that a doubling of the amount of CO2 in the atmosphere could cause an increase in the average temperature of earth from 7 to as much as 14 degrees. These findings, published in Nature Communications, represent a temperature rise that is much larger than previously estimated.
Researchers extracted a 45-year-old drill core from the bottom of the Pacific Ocean. This core came from an ocean location that has had oxygen-free conditions for millions of years, which results in more preserved carbon. The upper thousand meters of the drill core correspond to the past 18 million years.
Using the core, the team turned to a novel approach to gather information about the past seawater temperature and ancient atmospheric CO2 levels. They derived the temperature using the TEX86 method – a technique that tracks the specific substances present in the membrane of archaea. For the CO2 measurements, the team analyzed the chemical composition of chlorophyll and cholesterol found in algae. The new method revealed that the CO2 concentration dropped from about 650 parts per million, 15 million years ago, to 280 just before the industrial revolution.
Researchers then plotted the derived temperature and atmospheric CO2 levels of the past 15 million years against each other to show that the average temperature 15 million years back was over 18 degrees – 4 degrees warmer than today and about the level that the UN climate panel predicts for 2100 in the most extreme scenario.
“This research gives us a glimpse of what the future could hold if we take too few measures to reduce CO2 emissions and also implement few technological innovations to offset emissions,” explained Sinninghe Damsté, professor at Utrecht University. “The clear warning from this research is: CO2 concentration is likely to have a stronger impact on temperature than we are currently taking into account.”