In Spring last year, carbon dioxide concentrations passed 400 parts per million in the atmosphere — a level not seen since the Pliocene era (3-5 million years ago), and perhaps not even then. We know that the Pliocene was a warm world without glacial cycles, and that the climate of the tropical Pacific was also structurally different. This lecture discussed the causes and implications of this discrepancy.

One of the slides is particular unsettling.

 Chris Brierley, (UCL, Geography) explains how based on proxy records, obtained from geochemistry analysis were used to calculate the temperatures during the Pliocene. Based on the obtained information (5C temperature increase and 400ppm during the Pliocene), he then modeled this climate.

The model shows an atmospheric uniform warm temperature layer up to the poles, void of the Hardly cell, thus convection can occur everywhere, and hence the possibility for global Hurricane formation. Storm formation was then computed and above picture shows the storm tracks.

Because the model can not replicate the 5C temperature rise found in the climate proxy records of the Pliocene yet, and ocean gateway behavior, he tried to modulate the climate trends, added known feedback processes, which were able to increase the temperature by only 2C.

The IPCC has set a 2C temperature increase as an upper bound for global warming, the study discussed here suggest that this target is a target for a disaster.