Does CO2 drive global surface temperatures?

The Ordovician-Silurian glaciation, amidst soaring CO₂ levels, highlights the relative insensitivity of global temperature to atmospheric CO2 concentration.

The Ordovician-Silurian glaciation and extinction event…

The Ordovician-Silurian glaciation and the associated extinction event, often referred to as the Late Ordovician Mass Extinction, was one of the five major extinction events in the history of life on Earth. This event, which took place approximately 445 million years ago, resulted in the loss of up to 85% of marine species, particularly affecting the brachiopods and bryozoans which were dominant marine animals of the time.

The diversity of marine animal families since late Precambrian time. The data for the curve comprise only those families that are reliably preserved in the fossil record; the 1,900 value for living families also includes those families rarely preserved as fossils. The several pronounced dips in the curve correspond to major mass-extinction events. Source: https://www.britannica.com/science/Ordovician-Silurian-extinction

The extinction event's timeline closely aligns with evidence of a major glaciation. Geological records suggest that during the Late Ordovician, a significant ice sheet formed on the continent of Gondwana, which at that time was located over the South Pole. As glaciers expanded, they locked up vast amounts of water, leading to a drop in sea levels. This drop had catastrophic impacts on marine environments, particularly shallow marine habitats such as continental shelves which harbored a significant proportion of marine life.

Later Ordovician (Katian) lands and oceans at about 450 Ma, with representative sites of the various brachiopod provinces described in the text. Source: https://www.sciencedirect.com/science/article/pii/S1342937X20302756

Several potential causes, discussed in detail later, have been proposed for the onset of this glaciation and the resultant mass extinction.

Whatever the combination of factors, the glaciation disrupted ecosystems and led to a massive die-off. Once the glaciation ended and the ice retreated, sea levels rose again, leading to a second wave of extinctions. After this tumultuous period, life rebounded in the Silurian period with the evolution and diversification of new species and groups.

CO2 levels in the Late Ordovician…