Daniel Rothman works on the top floor of the building that houses the Massachusetts Institute of Technology (MIT) Department of Earth, Atmospheric and Planetary Sciences, a big concrete domino that overlooks the Charles River in Cambridge, Massachusetts. Rothman is a mathematician interested in the behaviour of complex systems, and in the Earth he has found a worthy subject. Specifically, Rothman studies the behaviour of the planet’s carbon cycle deep in the Earth’s past, especially in those rare times it was pushed over a threshold and spun out of control, regaining its equilibrium only after hundreds of thousands of years. Seeing as it’s all carbon-based life here on Earth, these extreme disruptions to the carbon cycle express themselves as, and are better known as, “mass extinctions”.

Worryingly, in the past few decades geologists have discovered that many, if not most, of the mass extinctions of Earth history – including the very worst ever by far – were caused not by asteroids as they had expected, but by continent-spanning volcanic eruptions that injected catastrophic amounts of CO2 into the air and oceans.

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.

So long, and thanks for all the fish.