If CO2 Caused Mid-Pliocene Warming, What Caused late-Pliocene Cooling? You Guessed!

By Paul Homewood


The Pliocene Epoch


 In yesterday’s post about the Antarctic turning green, we saw this claim:

Current levels of carbon dioxide (CO²) in the atmosphere could lead to conditions comparable with the Pliocene period three million years ago, experts say.

The last time levels of the atmosphere were as high as today – at around 400 parts per million (ppm) – was during this geological epoch.


As I noted, it was more likely that the warmer climate led to higher levels of CO2, and not the other way about.

But what caused the climate to cool down again in the late Pliocene?

Many theories have been advanced, but inevitably one bunch of wallies have blamed it on a decrease in atmospheric carbon dioxide!




 It is thought that the Northern Hemisphere experienced only ephemeral glaciations from the Late Eocene to the Early Pliocene epochs (about 38 to 4 million years ago), and that the onset of extensive glaciations did not occur until about 3 million years ago. Several hypotheses have been proposed to explain this increase in Northern Hemisphere glaciation during the Late Pliocene. Here we use a fully coupled atmosphere-ocean general circulation model and an ice-sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the Greenland ice sheet in particular. We find that Greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the Late Pliocene. By contrast, our model results suggest that climatic shifts associated with the tectonically driven closure of the Panama seaway, with the termination of a permanent El Niño state or with tectonic uplift are not large enough to contribute significantly to the growth of the Greenland ice sheet; moreover, we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the Earth’s orbit.



They do not offer an explanation of how or why CO2 levels fell. Nor can they explain why the bout of global warming in the mid-Pliocene did not lead to runaway warming, via higher levels of CO2, melting ice caps etc.

But I expect they received nice fat grants for their junk science.



April 7, 2019 at 01:01PM

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