by David Middleton, July 10, 2020 in WUWT

If the Earth was 3-4 °C warmer with a much higher sea level 3.3 million years ago, with about the same CO₂ concentration, what does this say about the potency of it as a climate control knob?

The last time CO₂ levels were this low, Earth was in the deepest ice age of the Phanerozoic Eon, the Pennsylvanian (Late Carboniferous)-Early Permian.

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Figure 5. Phanerozoic temperatures (pH-corrected) and carbon dioxide. The Miocene is the first epoch of the Neogene Period (Berner et al, 2001 and Royer et al., 2004) (older is toward the left).

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