Start small: picture our species sucking vast reservoirs of carbon out of the ground, vaporizing it, and stuffing it into the atmosphere the way you shove a pillow into a too-small pillowcase.
Now remember, the Earth is a closed system, so any such feat of imagination must be accompanied by a similar feat in the other direction. Where did all that subterranean carbon come from in the first place? Right. From plants. Which pulled it out of the atmosphere some 70 million years ago or so.
But wait, that means there’s a carbon cycle shuttling molecules around the planet on a scale far larger – and longer – than the standard elementary school model of rabbits nibbling clover and then exhaling.
How does it work? Well, in the dim geologic past, before we started ruining the air with jet-skis, great volcanic belches expelled carbon dioxide from deep within the Earth. As the Times reported this week, eruptions 550 million years ago raised CO2 levels to as much as 18x their present-day values, trapping heat and eventually growing all those lush, steamy swamps pictured in the dinosaur books.
So how did CO2 levels drop to a measly pre-industrial 280 parts per million? Once you let a gas escape into the atmosphere, how do you get it back underground?
Turns out that if you’ve got long enough to wait, the Earth’s rocks will do it for you. In a process called chemical weathering, falling rainwater mixes with carbon dioxide to make weak carbonic acid. The acid dissolves elements like calcium, silicon, and magnesium out of rocks, leaving a molecule called bicarbonate to run off into a nearby stream. Carbon dioxide has now left the atmosphere.
So all you really need to reduce carbon dioxide levels in the air is a whole lot of rocks. The Himalaya is a good place to start. In fact, MIT geologist Maureen Raymo noticed that the rise of the Himalaya 50 million years ago marked the beginning of Earth’s cooling into a series of ice ages. She suggested that as those massive mountains weathered, they drew enough CO2 from the atmosphere to reduce the then-raging case of greenhouse effect. And since there’s still roughly 29,028 feet of Himalaya (and rising) left to weather, maybe they’re our best friends in the fight against a warmer tomorrow.
And if that’s not cool(ing) enough, consider the Appalachians, that eastern-U.S. range that 18th century naturalist William Bartram described as “those fuzzy little mountains.” As most of us hear at some point, they once rivaled the stature of the Rockies and the Himalaya, they’re just a lot older. Recently, Seth Young and Matthew Saltzman of Ohio State University learned that a similar weathering effect may have made CO2 levels plummet while the Appalachians were in their prime 450 million years ago.
As for New Scientist’s suggestion for storing carbon dioxide in rocks while producing geothermal energy with whatever doesn’t stick, that does sound like a neat idea but just for the record doesn’t involve any weathering.
And finally, thanks for sticking with me during these few busy weeks. I was at a fascinating meeting last week learning about how many dimensions the universe has and what it means when you recognize your own DNA in the dung of an extinct giant sloth.