Imagine the big picture of climate change on our planet.
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.
surf.bird.scribble. 
I especially like the direction that the writing is taking in your blog; you have consistently taken a big picture approach from a newly discovered angle culled from the journals and make it understandable. Often with amusing titles/pictures (which are nice), but the content is what keeps me coming back…
While I am continually impressed by this planet’s ability to deal with the damage we inflict, I’m also concerned that it won’t be dealt with rapidly enough to save us from a lot of pain.
E.g., a good deal of that weak carbonic acid would fall in the oceans as well, decreasing pH. More would make its way into shallow water areas as runoff from developed coastlines. Lower pH inhibits coral growth, and as reefs degrade they are less able to serve as nurseries for many food fish.
Of course you are already familiar with that, so I can only imagine my reason for articulating it is either to show I am familiar with it as well, or to use it as a jumping-off point to ask for your thoughts on the recent report predicting the collapse of most fisheries within the next 40 years or so. Let’s just assume the latter is my true motivation, shall we?
Eric – you’re right about the timescale, of course. Our species has been around for only about a million years and it took many times that long for Himalayan weathering to pull CO2 levels back down from their Paleocene highs. Chemical weathering is a fix for the planet’s ills, but not for ours. Save the humans!
As for ocean pH, the chemistry involved is complicated by the buffering relationships between CO2, carbonic acid, and bicarbonate. It’s made more complicated by phytoplankton that fix CO2 but in so doing change the buffering relationships and in some cases make more net CO2 available. I have been trying to work up a post about this for a while now, but despite all the clever, patient people who have tried to explain it to me I haven’t got a good enough grasp yet.
Still, it’s no question that ocean acidification spells bad news for coral reefs. And unlike terrestrial arguments that plants can adapt to growing levels of CO2, in the ocean the corals are up against some immutable chemical relationships. As I understand it, just a small shift in pH could leave the reef corals thermodynamically unable to form the mineral, aragonite, that makes up their skeletons.
Obviously, that’s a disaster for reef creatures. What it means for non-reef food fish I’m not sure. But ocean acidification is what MBARI chemist Peter Brewer calls “An Inconvenient Truth, Part II.” The atmosphere is delivering CO2 into the ocean over most of the planet — even the new, terribly remote monument in the northwest Hawaiian Islands isn’t protected from that.
Well, if that’s too discouraging to end on, perhaps you can take heart that 2048 will probably not see the world’s last Filet O Fish come out of the deep fryer. The Knight Science Journalism Tracker has the story, from a Baltimore Sun article: http://ksjtracker.mit.edu/?p=1550
Happy reading, and thanks for writing.