This rule is actually "an order of magnitude best estimate", which means it's more of a range, somewhere between 0.1 to 10 deaths per 1000 tons of carbon burned.

That leaves a lot of room for scenarios even more dire than the one outlined here.

"When climate scientists run their models and then report on them, everybody leans toward being conservative, because no one wants to sound like Doctor Doom," explains Pierce.

"We've done that here too and it still doesn't look good."

Translation: 10 billion people will die.

2nd translation: Almost everyone will die.