After more than two years of careful analysis, we have a snapshot of the atmosphere of our planet from about 2 million years ago. And it’s not as we all believed it to be.
We know that about 1 million years ago, the cycle of the Earth’s ice ages shifted out of nowhere, with longer and deeper freezes happening every 100.000 years, and not every 40,000 years.
There’s nothing in the orbit of the planet that can explain this sudden change, which is known as MPT – Mid-Pleistocene transition. Other explanations show that there must have been a long-term decline in the concentrations of the atmospheric CO2, which cooled the planet significantly. The air bubbles which were trapped in the Antarctic ice sheet have shown a quite different scenario. 1.5 million years ago, the ancient atmosphere had low CO2 levels, as per paleoclimatologist Yige Zhang from Texas A&M University.
These are the first direct observations of the atmospheric greenhouse gases, and that’s before the ice ages started to take longer. They showed a long-term decline in the CO2, which was one of the reasons behind the planet’s ice age cycle.
The oldest sample of ice that it was tested for CO2 levels was about 800,000 years old. Some estimates are based on the chemistry of the sediments of Earth, which are used as a proxy for greenhouse gas levels. They also need to be verified.
This new analysis of ice, which used precise measurements, showed that even if, during the glacials, the CO2 levels stayed above the lows, which took place in the deep glacials of the past 800,000 years, the maximum concentration of CO2 in interglacials did not decline.