Settled science: You know what caused past rapid warming? Comet impact. Or burning peat. Or volcanic eruptions. Or oceans burping.

Scripps: Warming more common than thought - SignOnSanDiego.com

"There have been many speculative hypotheses put forward to explain the rapid warming events from comet impact, burning peat (presumably from natural sources of ignition like lightning strikes or spontaneous combustion), volcanic eruptions that 'cook' organic goo in the sea bed creating greenhouse gases, or the massive degassing of gas hydrates in the sea floor or permafrost.

"Our study shows that 'on-off events are probably not the explanation for what is clearly a recurrent phenomenon. Instead, we argue that CO2 is stored in the deep sea and periodically burped out of the deep ocean into the atmosphere, where it caused global change."