The 6th ...

Illustration: Alex Mellon for the Guardian : Getty Images

Yours truly has waxed "eloquently" about extinction events with emphasis given to The Great Dying during the Permian/Triassic geologic period around 252 million years ago to today as the 6th, aka The Holoscene, ramps up with unprecedented speed, a man-made catastrophe promising to change how earth conducts business in ways unimagined just five years ago.

The dodo became extinct during the mid-to-late 17th century due to habitat destruction, overhunting, and predation by introduced mammals.[1] It is an often-cited example of a human-driven extinction.[2]

As a matter of perspective, The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 million years ago, a duration of 60 ± 48 thousand years. With the 6th, we're talking realtime. 

Put enough CO2 into the system all at once, and push the life-sustaining carbon cycle far enough out of equilibrium, and it might escape into a sort of planetary failure mode, where processes intrinsic to the Earth itself take over, acting as positive feedback to release dramatically more carbon into the system. This subsequent release of carbon would send the planet off on a devastating 100-millennia excursion before regaining its composure. And it wouldn’t matter if CO2 were higher or lower than it is today, or whether the Earth was warmer or cooler as a result. It’s the rate of change in CO2 that gets you to Armageddon.

This is because the carbon cycle is happy to accommodate the steady stream of CO2 that issues from volcanoes over millions of years, as it moves between the air and oceans, gets recycled by the biosphere, and ultimately turns back into geology. In fact, this is the carbon cycle. But short-circuit this planetary process by overloading it with a truly huge slug of CO2 in a geologically brief timespan, beyond what the Earth can accommodate, and it may be possible to set off a runaway response that proves far more devastating than whatever catastrophe set off the whole episode in the first place. There could be a threshold that separates your run-of-the-mill warming episodes in Earth history – episodes that life nevertheless absorbs with good humour – from those that spiral uncontrollably toward mass extinction.

It took 14 million years for earth to recover. Think about that, I know I have.