__How I learned to love crop residue. __
I'm trained to make things work. With a PhD in electrical engineering, I've done time in both industrial labs and universities, questing after ever-faster electronic devices. I'm also a writer of hard science fiction, the type of SF where the science is (one hopes) done right. To demonstrate what a dash of science mixed with a healthy dose of imagination can do, I write a column for the Bulletin of the Science Fiction and Fantasy Writers of America. There I've imagined a variety of outlandish-but-theoretically-possible projects: using dirty diapers to form a ring system around the planet to signal alien civilizations; moving the moon close enough to Earth to generate monster tides that wash over Florida; turning the sun into the ultimate rocket engine, one capable of transporting the entire solar system to nearby stars; and spawning an entire race of creatures from nothing more than a bit of rancid potato salad and a healthy dose of radiation.
But all that was easy compared with trying to become an atmospheric scientist.
Atmospheric science is always politically volatile, often technically bizarre, and consistently dominated by one issue: global warming. Three years ago, while the UN was wrestling with the problem in Kyoto, I was casting about for a column topic, so I decided to jump into the fray, to see if I could figure out a way to reduce the CO2 emissions that are responsible for heating up the planet.
The Kyoto Protocol specifies that by sometime between 2008 and 2012, the US will reduce its CO2 emissions by a percentage that, based on current emission levels, works out to a ton of carbon per American per year, or 300 million tons. Since CO2 is a by-product of combustible fuels (oil, gas, wood), the simplest, most obvious solution is to burn less fuel. For my column I usually like a challenge, so I took it upon myself to find a way to bring about US CO2 reductions without easing off the combustion throttle.
It sounded impossible. But I remembered reading something the year before about an emerging trend among farmers to stop plowing crop residues back into the soil. Crop residues are the parts of plants (corn stalks, for example) that remain in the field once the crop has been harvested. The conventional wisdom used to be that plowing this material back in was good for the soil, but it's now known that the process actually degrades organic content. Consequently, farmers are moving toward minimal replowing and even no-till methods, which involve leaving crop residue on the surface to rot away.
But when the crop residue rots, almost all the carbon it contains is released into the air as CO2. The total amount of residue generated annually by the three main crops produced in the US - corn, soybeans, and wheat - comes to 600 million tons. By weight, 40 percent of these residues consist of carbon, giving you 240 million tons of carbon, close to the 1 ton of carbon per US citizen that would satisfy the Kyoto agreement.
But if you could somehow keep the carbon from reentering the atmosphere, you would reduce the amount of atmospheric carbon by 240 million tons. In practical terms, this is no different than reducing the CO2 emissions from smokestacks and tailpipes by the same amount.
A few related facts: The atmosphere holds 720 billion tons of carbon. The oceans, with 38 trillion tons, are the ultimate carbon sink. If we stopped pumping CO2 into the air, atmospheric CO2 levels would drop as the gas became absorbed into the ocean. Another fact: What we call the ocean is not one but two oceans, one lying atop the other. About 1 kilometer down, beneath the thermocline (the boundary layer that separates the two oceans), the water temperature is nearly 0° Celsius and lacks sufficient oxygen to transform decaying material into CO2. Go 3 kilometers down, and the water is not only frigid but is essentially trapped: It takes 1,000 years for it to circulate up through the thermocline and back to the surface.
So you've got the carbon and you know where to put it - the deep ocean. The only other question is how much carbon is generated by the act of sequestering the crop residue. You need to transport this residue to the sequestering site by truck, train, or boat; the shipping process burns fuel, which generates CO2. If you generate more carbon than you sequester, the whole enterprise is useless. Fortunately, the bulk of US crop residue is generated in the Midwest - relatively near the Gulf of Mexico, a perfect deep-ocean site. Even assuming transportation distances of 1,000 miles (coupled with large trucks that get only 5 miles per gallon while hauling 20 tons of residue), for every 1,000 pounds of carbon you hide on the ocean floor, the math looks pretty good: You release only about 40 pounds of carbon into the atmosphere getting it there. Not a bad trade-off.
A big advantage of this approach is that the infrastructure needed to collect and transport crop residue is already in place - it's the same one used to transport crops to market. After the harvest, when this infrastructure is idle, it can be used to move the leftovers. Using the same back-of-the-envelope calculations as above, and assuming gas costs $2 a gallon, every ton of carbon sequestered would cost about $55. The cost of removing CO2 from the smokestacks of electrical generating stations, by contrast, is estimated to be between $70 and $140 a ton. So residue dumping is relatively cheap, too.
I called my idea crop residue sequestering, or CRS, and I admit it sounded crazy, almost too easy - even to me. But as I learned when I surveyed the landscape of ideas, CRS is tame compared to many of the schemes to reduce global warming that have been proposed by scientists and amateurs alike.
The folks making these proposals fall into two broad categories. Some, the ecoengineers, want to tweak a naturally occurring process to remove carbon; and some seek ways to alter the heat balance of the planet - I call them geoengineers.
The classic tweaking approach involves fertilizing the ocean to increase phytoplankton growth, which in turn pulls more CO2 out of the atmosphere to feed the floral bloom. Other approaches can be as simple as growing more trees or as complicated as using chemical and biological scrubbers to cut down the CO2 before it escapes from chimneys. All these schemes have a common element: sequestration. A few plans call for dumping the carbon beneath depleted gas and oil fields or inside salt domes, but the most popular dumping site is the bottom of the ocean. One idea suggests freezing the CO2 into denser-than-water dry ice torpedoes and dumping them into the ocean. The torpedoes would penetrate the ocean floor and bury themselves.
The heat-balance types, however, don't even bother with CO2. The planet is getting too hot? Simply cool it down by manipulating global heat flow. Central to these schemes is the idea of making the planet a bit more reflective to incoming sunlight ("increasing its albedo,"as atmospheric scientists put it). If Earth's cloud cover were to increase by 4 percent, its surface would cool sufficiently to mitigate the effects of a CO2-induced greenhouse effect. One way to make this happen would be to trigger the formation of ice crystals in the upper atmosphere with dust or soot. Any particulate in the high atmosphere will attract water vapor, forming ice crystals that will reflect incoming sunlight. If jets burned their fuel using a slightly richer mix, the resulting particulate might be able to create that additional 4 percent cloud cover. Other simple approaches include shooting 1-ton shells of dust from naval cannons, and burning sulfur-rich fuels in oceangoing ships and letting the sulfur particulate circulate into the upper atmosphere naturally.
But who wants more cloudy days? Some scientists propose releasing millions of highly reflective, aluminum-coated helium balloons into the upper atmosphere, or deploying 55,000 100-square-kilometer sun shields in space. Others focus on making the surface of the planet more reflective: painting rooftops white; adding a bit of sand to asphalt and roadways to brighten them and cause them to reflect more light; spraying reflective foams or encouraging the growth of reflective biofilms on the ocean surface; and even towing icebergs from the extreme northern and southern latitudes to the central latitudes, where they would be more efficient reflectors of light, since in those locations the sun hangs directly overhead rather than on the far horizon as it does at the poles.
The ultimate in simplicity - suggested only half-jokingly by SF writer Gregory Benford - is to encourage the 6 billion inhabitants of the planet to dress in white and don big white floppy hats, a stylish approach known as "albedo chic."
CRS seemed at least as sane as the plans outlined in these proposals. So I decided to really go for it, to put my idea before the global warming experts to see how they would react. I enlisted the help of Benford, who is a professor of physics at UC Irvine as well as the author of such books as Timescape and Eater. As it happened, we had a chance to get together soon; both of us were planning to attend the inaugural Conference of the Mars Society in Boulder, Colorado.
Amid discussions of Martian meteorites, planetary terraforming, and the latest and greatest spacecraft propulsion systems, we commandeered a hallway couch and cranked out a draft of our paper on CRS. In the age of email and the Internet, face-to-face meetings are still the way real scientific work gets done; the best reason to attend a technical conference is to hang out in the corridors, crunch a few numbers with fellow researchers, and soak up some all-important gossip. This face-to-face meeting brought us to an epiphany, one that I think is critically important, but which would turn out to be a major stumbling block when it came to presenting CRS to the scientific community.
We discovered a strange thing about the 7.2 billion tons of CO2 generated by human activity and dumped into the atmosphere each year: Only half of it stays there. The other half is quickly absorbed by growing plants and the ocean and held for a very long time. This is part of the global carbon cycle - the system of pathways through which carbon wends its way from atmosphere to biosphere and back.
This raised a question: Generally speaking, is it more efficient to sequester CO2 before it enters the atmosphere, or is better to release it, let the global carbon cycle remove half of it, and then use a process like CRS to remove a portion of the CO2 that remains? The answer seemed obvious: Forget about all those methods that collect CO2 as it flies up the world's smokestacks, and concentrate instead on amplifying the global carbon cycle's effect, which is automatic and free of charge. We folded this larger argument into the CRS paper and sent it to the two most widely read and respected journals around, Science and Nature. Our Plan B was the journal Climatic Change.
Science and Nature weren't interested (compared with the detection of extrasolar planets and quantum teleportation, dumping crop residue off the sides of boats isn't very sexy, I guess). Climatic Change bit.
But first there was the peer review that every scientific article must undergo before publication. Here we ran into some problems. We were not told that our idea was crackpot fantasy - the peer review process is far too genteel for that. Instead we were informed that "this is a creative concept that might eventually yield an interesting paper - the current paper is not yet there. It needs much more thought." And as for our epiphany that, in general, hijacking the global carbon cycle was the best way to rid the world of its excess CO2, we were told that "the authors do not appear to understand the global carbon cycle."
The editor of Climatic Change told us that if we could address the reviewers' concerns, we could resubmit the paper. Fair enough. There were some genuine problems - in particular, we didn't distinguish between organic and inorganic carbon in our discussion of carbon's circuit through the biosphere. The reviewers spent several pages showing why our numbers couldn't possibly be correct, without realizing that we had grouped inorganic and organic carbon together. (This is one of the dangers of being an outsider - we didn't realize that atmospheric scientists generally consider the biosphere to contain only organic carbon.)
We rewrote from scratch. And as we did so, we began to receive not-so-subtle feedback from readers to whom we'd given the paper. One confessed that his first thought was that CRS was fundamentally a bad thing: Because it takes advantage of the global carbon cycle to sequester CO2, it could actually encourage polluters to emit more pollutants, rather than cut down on emissions. Then it slowly dawned on us. We were not fighting a technical battle so much as a moral one.
It was a battle I ultimately lost. To satisfy the reviewers, who held the keys to the atmospheric science kingdom, I cut out the larger implication that ecohacking is inherently more efficient than trying to sequester carbon at its source - though the CRS concept itself made it through the peer review process. My paper, titled "Sequestering of Atmospheric Carbon Through Permanent Disposal of Crop Residue,"will be published in Climatic Change within the next 12 months. After three long years, I'm part of the club - but I doubt I'll ever really feel like I belong, because even if CRS proves to be a bad idea and not a single bale of crop residue ever gets tossed off a boat, I will always believe that hacking the carbon cycle is our only real chance of fixing this global-warming mess.
