Nor does it seem likely that sulfate aerosols can be used to raise or lower the globe's temperature uniformly. There are bound to be regional effects. Tambora is a good case in point. At the same time the haze from the event was freezing Canadians and New Englanders, it was also producing torrential floods in China, and drought, famine, and cholera in India—both by altering the monsoon.11
Tambora, of course, was an uncontrolled injection of sulfur into the atmosphere from a single point in Indonesia. Humans could have greater control by injecting the stuff into the stratosphere at a slower rate, from a multitude of sources. But do we really understand atmospheric processes well enough to control all the variables? And even if we do, is it possible to keep from spinning off unwanted effects on some parts of the globe? As anyone who's ever heard of the jet stream knows, the upper atmospheric winds aren't uniform. “That has implications for who has this stuff over their heads and who doesn't,” says Adrian Tuck, a meteorological chemist at the National Oceanic and Atmospheric Administration and author of a textbook on atmospheric turbulence.
Studies of a related geoengineering trick—spraying sea salt into the air in an endeavor to make the skies cloudier—have found that there's definitely a potential problem with regional winners and losers. “You can get cooling, but it's inhomogeneous,” said Olivier Boucher, a climate scientist at Britain's Met Office. And he added, “You don't necessarily get the cooling where you want it.” Worse, Boucher's model found that some areas had increased rainfall, while others wound up more prone to droughts.
Another model, by Katherine Ricke, then of the Department of Engineering and Public Policy at Carnegie Mellon University, found that sulfate aerosol-based geoengineering might combat drought in Brazil and China while increasing it in the Western U.S. The model examined only a limited range of scenarios, so the specifics aren't set in stone. But the basic finding is significant. “This simple example illustrates that optimizing geoengineering activities would mean very different things for different nations,” she said.
Other effects would be due to the scattering of sunlight, making that which does reach the ground more diffuse. Just to start with, solar power generation would be reduced, particularly forms of it that use mirrors to concentrate sunlight to produce intense heat. (The scattered light would be harder to focus.) Green plants, however, might be more efficient. Studies have found that photosynthesis works better in diffuse light.
Aesthetically, blue skies would be replaced by a white haze. Night skies would be hazier, too, making it harder to conduct ground-based astronomical observations. If ever-increasing quantities of aerosols are needed to combat ever-increasing greenhouse gases in the lower air, we might even wind up fogging the atmosphere so thoroughly that the average person never sees a truly starlit sky except in pictures from orbital telescopes. How would that affect humanity's view of its place in the universe?
* * * *
High-Altitude Transport
Let's assume that none of these are deal-breakers. Can we actually get enough sulfate aerosols into the stratosphere to do the trick? The answer is a qualified “yes.”
Alex Eliseev of the A. M. Obukhov Institute of Atmospheric Physics in Moscow, Russia, has estimated that we'd need five to ten teragrams of sulfur (ten to twenty teragrams of sulfur dioxide) per year by 2050, and more than ten teragrams of sulfur per year by 2100.12
But maybe we don't need to use sulfur dioxide. The gas of choice would be hydrogen sulfide (H2S), which gets the same quantity of sulfur up there at nearly half the weight. Once dispersed, we could (hopefully) rely on the atmosphere to turn the hydrogen sulfide into the desired sulfate aerosols.
Putting five to ten teragrams of material into the stratosphere isn't inconceivable. One solution would simply be to quit removing sulfur from jet fuel—or even start adding extra sulfur to it. But there are at least two problems with that. One is that except on flights across the Arctic, where the stratosphere is relatively low, these planes don't normally fly high enough. The other is that high-sulfur fuel might be hard on engines—not to mention the possible dangers to the next jetliner to fly along the same route. “I think the idea that you just add this to commercial airplanes is so unrealistic as to be fantasy,” says David Keith, of the University of Calgary, Alberta.
Besides, Keith says, if we're going to attempt to reengineer the planet, we might as well use the right equipment. Given what's at stake, he says, “The cost of doing this with specially designed aircraft would be very small.”
Robock suggests using military aircraft. “We have hundreds of KC-135 tankers used to fuel jet airplanes,” he says. “They can fly into the stratosphere with ninety-one tons each.” Fifteen such planes, flying three missions each, per day, are all that is needed for a teragram.
The main drawback is that the KC-135 tankers can only fly high enough to reach the stratosphere in the Arctic. Getting high enough in the tropics would require fighter jets. (Robock estimates that each teragram would require one hundred sixty-seven F-15C Eagles, working year-round.) It could also be done with balloons (37,000 a day, by Robock's estimate), naval artillery (8,000 shots per day), or—if we had one—a space elevator. Other than the space elevator, none of these are beyond the reach of a determined, global program.
Nor would it be prohibitively expensive. Sulfur is cheap, especially since we're already collecting it as a pollutant. The planes exist. KC-135 tankers, Robock estimates, can be operated for about five million dollars each per year, including spare parts. Even if fighter jets were used, it would be a tiny dent in the overall military budget.
“There are many reasons why geoengineering might be a bad idea,” he says. “But just from the point of view of, ‘Could we get it up there?’ it seems like that wouldn't be the limiting factor.”
Other options are also economically feasible. Naval rifles could do the job for twenty billion dollars a year, Robock says, as could balloons—though he notes that the fall of millions of spent balloons each year might be an annoying form of “trash rain.”
That said, there are enormous practical problems. To begin with, we don't know how sulfur disperses when released from a plane, balloon, or artillery shell, rather than a volcano. And the global-cooling models, Turco says, all assume an “aged” gas cloud of uniform-size particles, as was produced by Pinatubo. Dispersal from airplanes would produce a different type of cloud, with a greater diversity of particle sizes. These won't be as efficient at cooling, which means we might need, say, twice as much sulfur as volcano-based estimates would predict.
Other problems are even more basic. It's one thing to lift millions of tons of hydrogen sulfide into the stratosphere in tanker jets. But how do you get the gas out of the tank? If you simply try to spray it out, Turco worries, it might just form a super-dense cloud that quickly falls out of the stratosphere. We'd probably need a specialty nozzle whose performance specifications aren't even known yet.
Robock agrees. At present, he says, we simply don't know how to produce particles of the appropriate size.
Nor does anybody know much about the atmospheric chemistry that might turn hydrogen sulfide into sulfate aerosols. “The idea seems to be that if we get it there, it will magically do its thing,” says Turco.
A related problem is keeping track of the aerosol cloud so we know where and when to release sulfur for optimum effect. That, Turco says, will require a monitoring system comparable to what we now use for weather prediction. “You can't afford to make any mistakes,” he says. “You have to understand what's going on.”
* * * *
Seeding the Cirrus
All of this has led some experts to favor a different approach, which attempts to alter the Earth's natural cloud layers.
There are two approaches. One, suggested by David Mitchell of the Desert Research Institute in Reno, Nevada, is to attempt to reduce the prevalence of cirrus clouds, the high, thin bands common both in fair weather and in the advance of storms.
Normally we
think of clouds as reflecting sunlight, cooling the planet. But cirrus clouds do the reverse. That's because they're so thin they let most of the light through—then trap heat reflected from the Earth's surface.
Mitchell's idea is to cool the planet by seeding these clouds with something that causes them to form larger ice crystals than the ones that normally comprise them. These larger crystals would be too big to stay that high in the air and would begin to fall, causing the clouds to literally rain (or snow) out of the sky.
Such an approach might not require as much specialty equipment as would sulfate aerosols. Because the clouds are at lower elevations than those that would need to be reached with sulfates, the seeding materials might be introduced into passenger jet fuel, or injected directly into the jet exhaust. “The delivery mechanism may exist if you can get the airline industry to go along with it,” says Mitchell.
It might also be environmentally benign. One of the many concerns about sulfates is that they might interfere with the ozone layer. Cloud seeding would be unlikely to have this effect. Also, it's aesthetically better. Skies would remain blue—bluer, in fact than they are now. (On the other hand, sunsets might become a bit boring, since cirrus clouds often contribute to the more spectacular effects.)
Another proposal, called cloud whitening, focuses on lower clouds. Unlike cirrus clouds, these reflect enough more than enough sunlight to offset any heat that they otherwise might trap. They're also easy to make. As was mentioned earlier, all that's required is a fleet of ocean vessels designed to spray seawater into the air. One advocate of this is John Latham of the National Center for Atmospheric Research, in Boulder, Colorado. As far back as 2002, he proposed using salt spray to increase cloud cover over the oceans, possibly by mounting the sprayers on freighters or passenger liners.13
In a 2008 paper in Nature Geoscience, Philip Boyd of the University of Otago, New Zealand, ranked cloud whitening equal to sulfate aerosols in terms of its scientific rationale and start-up costs, and better in terms of potential side effects.14 Keith also has good things to say about it, noting that part of the attraction is that it uses natural materials to alter a natural part of the atmosphere. (It would also be quite inexpensive.)15
A big issue with any of these schemes, of course, is that we need to be able to shut them down if they backfire. “A proposal that . . . cannot be arrested quickly . . . should not be considered further,” Boyd concludes in his review article. From this perspective, cloud whitening, cirrus cloud seeding, and sulfate aerosols all score high marks. If we inject sulfur into the upper atmosphere, then decide to quit, the haze should dissipate within a couple of years. Cloud whitening can be halted even faster than that, and cirrus clouds should regenerate fairly quickly if we were to quit seeding them out.
Less clear is whether we might produce lasting impacts on regional climates. For better or worse, all of these methods carry the risk of changing rainfall patterns, and there's no guarantee they'd shift back if we decided to halt.
But the biggest risk of any such program is the one we began with: the danger of becoming addicted to them, allowing them to become permanent programs, rather than short-term fixes designed to buy time. Letting this happen, Boucher says, “is a little like building a nuclear program without figuring out how you're going to decommission it in the end.”
There are also moral problems. Martin Bunzl, an ethicist from Rutgers University, puts them simply: “What if this works for most people, but some people get screwed?” The biggest losers might include the one to two billion people in parts of Asia where there's a risk of disrupting the monsoon. Before beginning such a vast, global experiment, we need to do our best to make sure we fully understand what we're doing, as well as mitigating the potential for harm.
“Right now,” adds Keith, “the ratio of real research to hype and blogospheric chatter is overwhelmingly in favor of the latter.”
* * * *
Inertia + Uncertainty
But we may not have unlimited time for study. Even if we halted our use of fossil fuel today, it would take the atmosphere a long time to recover. Meanwhile, the planet would continue to warm—though the degree to which this would occur is unclear. “There's a great deal of uncertainty about how much climate change we get, even if we stop emitting tomorrow,” says Keith. “There is some probability that you would have enough carbon dioxide in the atmosphere to have climate changes you really would not like, especially in the high arctic.”
Not to mention that there's also social and technological inertia. If we decided today to abandon fossil fuels, how long would it take to achieve it? Years? Decades? “You have a system with gigantic inertia and uncertainty,” Keith says. “Uncertainty plus inertia equals danger.”
If all of this sounds a bit “on the one hand this, on the other hand that,” welcome to the club. Deciding to re-engineer the planet's thermostat isn't a decision that should be taken lightly. “There's a long record of humans trying to engineer fixes and having the fixes be worse than the diseases,” Keith says.
But, he notes, sometimes we've actually succeeded in fixing things. “Doing this might be less risky than not doing it,” he says.
* * * *
About the Author:
Richard A. Lovett has contributed more than 75 stories and articles to Analog since his first appearance eleven years ago. A self-described geophysics junkie, he once co-held the record for most successive meetings of the American Geophysics Union attended by a member of the press. He only regrets not discovering earth sciences before going on a geology field trip during his last term of college. His own academic training is in astrophysics, law, and economics: fields in which, sadly, hiking boots are not standard attire.
Copyright © 2010 Richard A. Lovett
* * * *
1 One widely cited estimate says that global temperatures fell by 1.2 degrees C. The original source for this, however, is hard to pin down.
2 Donald Olson, “When the Sky Ran Red: The Story Behind The Scream", Sky and Telescope, February 2004. Online, see: www.skyandtelescope.com/about/pressreleases/3308421.html.
3 It was the culmination of a string of bad few years for volcanoes. Four other major eruptions occurred in 1812-14.
4 Abstracts are available at www.agu.org.
5 A scaled-down version of this has been called nuclear autumn. See Richard A. Lovett, “Nuclear Autumn: The Consequences of a ‘Small’ Nuclear War,” Analog Science Fiction and Fact, 78(4), April 2008, pp. 30-35.
6 When it comes down, it produces acid rain. Compared to the amount of acid rain that humans already cause by other means, however, this would not be a major problem.
7 Bulletin of the Atomic Scientists, May/June 2008, pp 14-18, 59.
8 Jacob Darwin Hamblin, “Gaming World War III at Lowestoft: Marine Scientists and Post-Thermonuclear Survival,” paper presented at Oregon State University, May 15, 2009.
9 In support, Robock cited James R. Fleming, “The Climate Engineers,” Wilson Quarterly, Spring 2007, pp. 46-60.
10 O. Hoegh-Guldberg, et al, “Coral Reefs Under Rapid Climate Change and Ocean Acidification,” Science, December 14, 2007.
11 Tambora can also be credited with producing the dawn of science fiction. In 1816, the bleak weather helped induce Mary Shelley to write Frankenstein. For more details on Tambora, see Jelle Zeilinga de Boer and Donald Theodore Sanders, Volcanoes in Human History (2002), pp. 138-56
12 Like many of the other scientists cited in this article, Eliseev made this estimate at the Fall 2008 American Geophysical Union meeting.
13 See Richard A. Lovett, “From Salt Foam to Artificial Oysters: Innovative Solutions to Global Warming,” Analog, July/August 2003, pp. 43-51
14 Philip W. Boyd, “Ranking geo-engineering schemes,” Nature Geoscience, Nov. 2008, 722-24
15 One drawback is that it would be done largely over oceans. This might have a major impact on the processes that produce El Niño weather patterns, with global repercussions in rainfall distri
bution.
[Back to Table of Contents]
* * *
Short Story: THE LONG WAY AROUND
by Carl Frederick
* * * *
Illustrated by Vincent Di Fate
* * * *
The ways a tool was designed to be used are not the only ways it can be used. . . .
* * * *
During the descent, the First Lunar Outpost resembled toys set out on the sand. In a rough straight line were the FLO Center, the Oxygen Furnace Complex about five kilometers distant, and the Silent Earth Radio Telescope some twenty-five kilometers further.
Standing now at the open hatch of the lander, Adrian gazed out. Low in the sky, its lower limb kissing the horizon, the bright disk of the full Earth cast a blue-gray luminance onto the nighttime lunar landscape. He rested his gaze on the Oxygen Furnace, his responsibility now, but then looked upward as a light in the sky caught his attention. The exhaust of the deceleration rocket.
Suspended from the supply rocket by a hundred meters of unmeltable ceramic fiber, hung a huge container delineated by blinking red beacons.
“Sort of pretty, isn't it?” came Victor's voice from the radio speaker in Adrian's helmet, sounding tinny and distant even though he stood just behind Adrian with their helmets almost touching.
“Welcome to Mare Smythii,” came another voice. “Home of the one and only First Lunar Outpost.”
Adrian looked down from the hatch and saw a space-suited figure in an open vehicle with bulbous wheels and an attached utility trailer. The figure waved.
“That is our mayor,” said Victor, “Ralph Bernard.”
“Mayor of a thriving metropolis of ten,” came Ralph's voice, resonant even over the little speaker, “yourselves included.”
Adrian waved back, then clambered down the metal ladder to the surface. Victor followed.
Ralph indicated the person sitting next to him in the front seat of the moon buggy. “This is Dr. Kimberly Wells. She's our botanist.”
Analog SFF, July-August 2010 Page 9