Their headline is a little less wonky: Hothouse Earth.
No matter — it's still a typically great National Geographic story.
Just how much carbon was injected into the atmosphere during the Paleocene-Eocene Thermal Maximum, or PETM, as scientists now call the fever period, is uncertain. But they estimate it was roughly the amount that would be injected today if human beings burned through all the Earth's reserves of coal, oil, and natural gas. The PETM lasted more than 150,000 years, until the excess carbon was reabsorbed. It brought on drought, floods, insect plagues, and a few extinctions. Life on Earth survived—indeed, it prospered—but it was drastically different. Today the evolutionary consequences of that distant carbon spike are all around us; in fact they include us. Now we ourselves are repeating the experiment.
The PETM "is a model for what we're staring at—a model for what we're doing by playing with the atmosphere," says Philip Gingerich, a vertebrate paleontologist at the University of Michigan. "It's the idea of triggering something that runs away from you and takes a hundred thousand years to reequilibrate."
Even better than the story, perhaps, is the pic of the Arctic then and now:
But best of all, sez me, is the conclusion:
Fossil fuel burning has released more than 300 billion tons of carbon since the 18th century—probably less than a tenth of what's still in the ground or of what was released at the PETM. That episode doesn't tell us what will happen to life on Earth if we choose to burn the rest. (Global emissions set another record last year.) Maybe there will be a burst of evolutionary innovation like the one that gave rise to our primate ancestors; maybe this time, with all the other pressures on species, there will be mass extinctions. The PETM merely puts the choice in long perspective. Tens of millions of years from now, whatever becomes of humanity, the whole pattern of life on Earth may be radically different from what it would otherwise have been—simply because of the way we powered our lives for a few centuries.
People talk about changing the world. We're doing it right now, every day.