Or maybe the oceans became stratified and nutrient-starved, and phytoplankton suffered. Or perhaps it was a lack of oxygen in the ocean that suffocated everything, or maybe it got just too damn hot. Some paleontologists have thrown up their hands and yielded to this overdetermination of kill mechanisms at the end-Permian, proposing an inelegant Murder on the Orient Express hypothesis of mass extinction that implicates the entire suite of killers. A new study, though, claims to pinpoint the primary killer from this murderers’ row: Among the slew of Very Bad Things implicated in the worst calamity the Earth has ever known, it was the global-warming-driven ocean anoxia that stands out as the primary agent of Armageddon. And in this reaper of the Paleozoic, the study’s authors see a future menace.

“I think this study shows the end of the road that we’re heading down,” says the lead author, Justin Penn of the University of Washington, about our modern, warming, and increasingly suffocating oceans.

As we’ve known since the 1860s, carbon dioxide is a very important greenhouse gas, and if you increase the amount of it in the atmosphere, it makes the planet warmer. At the end of the Permian, the volcanoes of Siberia, by burning through a giant basin filled with coal and other carbon-rich rocks, emitted enough carbon dioxide to warm the planet by a sweltering 10 degrees Celsius or so. Coincidentally, this is about the same magnitude of warming predicted for humanity in a modern burn-it-all scenario.

“If we are truly the stupidest intelligent species ever, we probably could do the same thing,” says Curtis Deutsch, a co-author on the study. “As it is, we’re headed toward 3 to 4 degrees Celsius of warming by the end of the century, which is nothing to sniff at. But 10 degrees isn’t that off the charts.”

As the world warmed 10 degrees more than 250 million years ago, up to 96 percent of species in the ocean went extinct (for comparison, roughly zero percent of modern species in the ocean have gone extinct so far in what’s been called “the sixth extinction”). For all the planet knew, it was time for complex life to close up shop after a nice quarter-billion-year run. After several millennia of eruptions from the Siberian Traps, the fossil record remained startlingly impoverished for almost 10 million years, before limply convalescing in the ensuing Triassic period.

Read: Earth is not in the midst of a sixth mass extinction.

To tease out what was primarily responsible for all this death in the oceans—in this, “the Great Dying”—Penn and his colleagues developed a climate model, not dissimilar to those used to project future warming on our own modern world. Only in Penn’s model, the continents were reunited. This was Pangaea, the mythic supercontinent that reached its apotheosis in the Permian period, joining Morocco with New Jersey and India with Antarctica. Then the team lit this ancient world on fire.