Rapid rise in atmospheric CO2 marked the end of the Late Palaeozoic Ice Age
Atmospheric CO2 is thought to play a fundamental role in Earth's climate regulation. Yet, for much of Earth's geological past, atmospheric CO2 has been poorly constrained, hindering our understanding of transitions between cool and warm climates. Beginning ~370 million years ago in the Late Devonian and ending ~260 million years ago in the Permian, the Late Palaeozoic Ice Age was the last major glaciation preceding the current Late Cenozoic Ice Age and possibly the most intense glaciation witnessed by complex lifeforms. From the onset of the main phase of the Late Palaeozoic Ice Age in the mid-Mississippian ~330 million years ago, the Earth is thought to have sustained glacial conditions, with continental ice accumulating in high to mid-latitudes. Here we present an 80-million-year-long boron isotope record within a proxy framework for robust quantification of CO2. Our record reveals that the main phase of the Late Palaeozoic Ice Age glaciation was maintained by prolonged low CO2, unprecedented in Earth's history. About 294 million years ago, atmospheric CO2 rose abruptly (4-fold), releasing the Earth from its penultimate ice age and transforming the Early Permian into a warmer world.
EDIT
https://www.nature.com/articles/s41561-024-01610-2
EDIT
Our new study provides an original 80-million-year CO₂ record that tracks the climate during the descent into and emergence from the Late Palaeozoic ice age. We did this by looking at the fossilised shells of ancient clam-like creatures known as brachiopods. These shells store chemical fingerprints such as boron isotopes, which enable us to calculate how much CO₂ was in the atmosphere when the brachiopods were alive.
This type of CO₂ reconstruction from Earth's deep geologic past is entirely novel. Crucially, the reconstruction has a consistent timeline which enables us to bring together all pieces of the puzzle to demonstrate that the climate of the Late Palaeozoic era was closely regulated by CO₂.
What did the Late Palaeozoic climate and CO₂ look like? Our reconstruction showed that for part of this era the Earth's atmosphere sustained relatively low CO₂ (about 330 parts per million or ppm), reaching minimum values of about 200 ppm about 298 million years ago around the boundary between the Carboniferous and Permian periods. The low atmospheric CO₂ combined with less heat coming from the younger sun would have caused the intense "icehouse" conditions, with ice sheets extending as far as the planet's mid latitudes.
Our reconstruction also revealed an unexpected end to the icehouse period. Scientists previously thought that the Late Palaeozoic ice age gradually waned away, but our findings showed it ended much earlier. Around 294 million years ago, large-scale volcanic activity triggered a rapid rise - at least on geological timescales - in atmospheric CO₂, and Earth became warmer and drier.
While the past couple of decades have brought much progress in reconstruction of CO₂ from Earth's more recent past (in particular the past 60 million years where we have seafloor sediments), CO₂ reconstruction from the rock record has been long considered challenging. As such, our study pushes the boundaries in geological reconstruction of atmospheric CO₂ and provides a key to unlocking its history to the beginning of Earth's fossil record.
EDIT
https://theconversation.com/carbon-dioxide-has-been-regulating-earths-climate-for-hundreds-of-millions-of-years-new-study-246712