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Carbon Cuts and Techno-Fixes

10 Things To Do About the Greenhouse Effect (Some of Which Aren't Crazy)

By Robert Kunzig and Carl Zimmer
Jun 1, 1998 5:00 AMNov 12, 2019 4:09 AM


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There are two basic points of view on global warming: it’s a problem or it’s not. In most of the world that argument is over and the pessimists have won, but not in the United States. And yet politically, if not scientifically, the argument seemed to be settled long ago—on October 15, 1992, to be precise, when the United States became the fourth country, after Mauritius, the Seychelles, and the Marshall Islands, to ratify the United Nations Framework Convention on Climate Change. George Bush had signed the treaty at Rio de Janeiro four months earlier. It committed us to an objective: Stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. All the important details were missing; that’s what the meeting in Kyoto last December was all about. But as a nation we formally accepted the basic principle—global warming is a problem and something has to be done about it—back in 1992.

Assuming we have a problem, then, what should we do about it? Again there are two basic answers: stop doing things that warm the planet—burning fossil fuels, mostly—or go on polluting and fix the planet so it won’t warm. The Kyoto Protocol adopts the first answer, requiring the United States to emit 7 percent less of six greenhouse gases by the year 2012 than it did in 1990. Those cuts are much less than environmentalists would have liked—but since 1990 our emissions have surged. Fossil fuel prices have fallen, and so we are using more of them. The voluntary restraint that George Bush promised at Rio never happened. The Department of Energy predicts that by 2010, if nothing has changed, U.S. greenhouse emissions will be a third higher than they were in 1990.

So complying with the Kyoto Protocol would require a big effort. To reduce carbon emissions we would have to either tax or regulate them—which is why industry and union lobbyists have promised to see that the protocol isn’t ratified. They predict it would put a million Americans out of jobs and cut the gross national product by several percent. Whole industries would flee to developing countries, which did not commit to any emissions cuts at Kyoto. Unilateral economic disarmament, the head of the American Petroleum Institute called the agreement. An error of staggering dimensions.

Of course, industries that are about to be regulated often predict that the costs will be staggering. When the Environmental Protection Agency instituted tradable sulfur-dioxide-emissions permits in 1990—the system that may be a model for how to reduce carbon emissions—the permits were priced at $1,500 per ton, because that was the industry estimate of how much it would cost to stop emitting SO2. By 1996 those permits were trading for a tenth their initial price; apparently the industry estimate had been wrong. In the case of the Kyoto Protocol, some economists do predict disaster if it is adhered to, but others do not. A study completed last fall by the doe concluded that something close to the Kyoto cuts could be made at no net cost to the U.S. economy—because the money spent on controlling carbon would also save energy. The study assumed that carbon permits would sell for $50 a ton, or about 12.5 cents on a gallon of gas.

One industry criticism of the Kyoto agreement is certainly true, though: it alone will not prevent an environmental disaster, if indeed one looms in our future. Steep as they may seem, the Kyoto emissions cuts are nowhere near enough to stabilize greenhouse gas concentrations. They’ll just slow the rise a bit. Which brings us to the second response to global warming—the planet fixers.

For as long as there have been environmentalists worrying about global warming, there have been geoengineers designing simple solutions—on the backs of envelopes, as it were—that could spare us the pain of cutting our consumption of coal, oil, and gas. In 1992 a National Academy of Sciences panel, one that included environmental types alongside men from General Motors and DuPont, reviewed a number of these schemes. The panel found some of them plausible and worth investigating—including, for instance, the idea that we might point battleship guns straight up and fire 10 million one-ton shells full of sun-blocking dust into the stratosphere every year. Since that report, however, most of those ideas have not been pursued much. Geoengineers have a bit of an image problem: environmentalists are apt to see them as irresponsible tinkerers who haven’t grasped that tinkering with the planet is what got us into this mess—and whose fix-it schemes could distract the public from the real task of cutting carbon. Geoengineers, on the other hand, tend to see environmentalists as puritanical killjoys who find our control of nature sinful and like telling people what to do. The chasm is almost religious.

And yet sometime during the next century we may all have to get along. Today we can argue about whether the fingerprint of man-made global warming is evident yet in the results of climate models. Then it may be so evident—in the form of shifting climate zones and rising seas—that no model is needed to detect it. If we start now, and if the Kyoto agreement is followed by more stringent ones, we may be able to reduce carbon emissions enough to forestall a dramatic change. The first five items below describe some of the ways we might do this. But if there is one thing that the debate about Kyoto makes clear—not to mention our casual indifference to the promise we made at Rio—it is that we may not do enough soon enough to avoid changing the climate. Someday we may find ourselves needing a quick fix. And so the last five items describe a few geoengineering ideas, arranged along a scale of increasing wackiness. Read them and weep, or rejoice, as your faith dictates.

Begin at Home

The average American household sends 6,376 pounds of carbon in the form of carbon dioxide into the atmosphere every year. With 99 million households, that adds up to 287 million metric tons of carbon, or a fifth of U.S. emissions. (CO2 emissions are usually expressed in terms of the mass of the carbon; the total mass, including the oxygen, is about four times greater.) Some of the easiest and least futuristic savings are to be found on the home front. The operative metaphor here is not The Jetsons—it’s This Old House. Individuals can slash their carbon emissions merely by trying to cut their utility bills.

Simply wrapping a water heater in a $20 insulating jacket, for example, can save a homeowner $45 a year and eliminate 169 pounds of carbon. Efficient showerheads use half the hot water of conventional heads, cutting 379 pounds of carbon. And caulking can reduce heating bills by 25 percent and save 464 pounds a year. If every American house was spruced up in such ways, the United States could take care of a third of its obligation under the Kyoto agreement, according to Christopher Moser of the Safe Energy Communication Council.

Even more drastic cuts can be made when new houses are built. South-facing windows save heating costs, and trees can provide cooling shade in the summer. Double- or triple-pane windows with insulating pockets of gas let far less heat escape than the old single-pane kind, and many don’t cost much more. If home builders are feeling particularly ambitious, they can put solar panels on the roof or make the walls of rammed earth or adobe, which soak up heat during the day and release it into the house at night.

Instead of the typical home emitting 6,300 pounds of carbon per year, I can envision homes being just as comfortable emitting less than 2,700 pounds, says Richard Heede, of the Rocky Mountain Institute, an energy think tank. (Heede practices what he preaches: the house he recently built himself in Old Snowmass, Colorado, at a quarter the cost of a conventional house, uses one-eighth as much propane.) We know everything we need to know already. We just don’t pay enough attention to it.

Teach a Cow Some Manners

Compared with a car or a factory, a farm might not seem like a notable source of air pollution. But agriculture is responsible for a fifth of man-made greenhouse emissions. When farmers till fields, they break up the clumps of soil into fine particles, creating a football field’s worth of surface area on a square yard of field. Bacteria can attack the organic carbon on these surfaces—carbon that in previous years had been sucked out of the atmosphere by photosynthesizing plants—and digest it using the oxygen that flows freely through the plowed soil. In the process the bugs return carbon dioxide to the air.

Soil conservation experts have been designing new tilling machines that stir up less soil, leave behind larger clumps, and thus keep carbon from escaping. Researchers estimate that an acre in a typical U.S. cornfield has lost 33,000 pounds of carbon in the past century and will lose 357 more pounds in the coming 100 years. (Farmland loses carbon fastest during the first two decades of plowing.) With careful tillage and other methods, the trend could be reversed and the acre could store 6,500 pounds of carbon over the next century. Even larger carbon vaults could be built up elsewhere, says ecologist Emilio Laca of the University of California at Davis, by letting farmland revert to rangeland—which sucks in carbon and stores it in soil, roots, and peat. The steppes of central Asia are good candidates, according to Laca, because they were recently converted to agriculture and have been abandoned since the fall of the Soviet Union.

Unfortunately, carbon dioxide isn’t the only greenhouse gas that agriculture can kick up; there’s also methane. Humans emit only 360 million metric tons of it, but molecule for molecule, it traps 21 times more heat than carbon dioxide, and 30 to 40 percent of it comes from agriculture. The chief sources are rice paddies, lagoons of livestock manure, and grazing cattle. Methane-producing bacteria in a ruminant’s rumen—a chamber of its stomach—help it digest tough plant tissue, and as the animal regurgitates its cud, it belches out the methane. When cows are fed high-quality food, such as corn and alfalfa, the bacteria don’t have to work so hard and produce less methane. But that is only sometimes economical.

Don’t Commute in a Truck

When automobiles replaced horses at the turn of the century, they were an environmental boon: the horse manure that carpeted American cities disappeared, and with it a lot of tuberculosis-causing bacteria. But since then the number of cars has doubled every 25 years. In the United States alone, transportation produces 469 million metric tons of carbon a year, about a third of that from cars.

Lately the trend has not been great. Between 1973, the year of the opec oil embargo, and 1988 the average fuel economy of new American cars doubled, from 14 miles per gallon to more than 28. Since then it has stayed about the same. It’s not hard to see why: the federal government has not required further increases in efficiency, and gasoline is selling at pre-1973 prices (after inflation). The big three automakers now say they plan to achieve the prototype of an 80-miles-per-gallon car by 2004, by making engines more efficient and using lighter materials. Meanwhile, sales of sport-utility vehicles, which average below 20 miles a gallon, are booming. If people were to drive efficient cars around the suburbs instead, it would make a big difference—but without a hike in gas costs, it’s unlikely.

What will people drive when the gas era ends? Research is now moving chiefly in two directions. One is toward a battery-powered electric car. Some manufacturers are starting with hybrid designs: Toyota, for example, now sells a car in Japan that uses a small internal combustion engine to drive a generator that charges a battery. Below 18 miles an hour, the battery alone powers the car; at faster speeds, the engine takes over. In city traffic, the car gets 66 miles per gallon, and even at 75 miles per hour it gets more than 50.

Here in the United States the focus has been on developing an all-electric car—thanks in large part to California’s environmental regulations, which require that by 2003, 10 percent of the cars on the road produce zero emissions. General Motors has come out with a car that can travel 75 miles on one hour’s charge. Better performance may come from lithium batteries, which now power cameras and other small devices. Right now lithium looks very expensive, but it’s our belief that research can bring those costs way down, says Richard Moorer of the doe’s Office of Transportation Technologies. We want to see if lithium batteries can triple the range we’re getting out of lead-acid batteries.

Batteries are not the only way to power an electric car. There is also the so-called fuel cell, which strips the electrons off hydrogen found in a fuel such as gasoline and uses them to create an electric current. Car manufacturers are talking about a prototype being ready by 2004; such a vehicle would produce half the carbon emissions from a tank of gasoline as a conventional car. What’s particularly attractive about the latest fuel cells is that they are able to use a number of different fuels, such as gasoline mixed with ethanol from corn. In the more distant future, they might use compressed hydrogen and release no carbon at all.

But big savings are possible already. Frankly, having even a third of cars be very fuel efficient would have a large impact on our carbon-dioxide emissions, says Joseph Romm of the doe. We don’t have to replace every car on the road.

Create Industrial Ecosystems

In many countries, industry could cut a quarter of its carbon emissions just by refitting factories with the most efficient technology now available. Such improvements would shave only a few percent, however, from the 482 million metric tons that U.S. factories emit. To cut even more, we may have to rethink the way industry works.

Every factory needs both heat and electricity, which it typically gets from separate sources. But it’s possible to create both kinds of energy at the same time—an idea known as cogeneration. Instead of having to purchase all of its electricity from a power grid and using coal plants for heat, a pulp and paper mill can burn the wastes it has, creating electricity that it might use for pump motors and steam that it could use in drying, says Marilyn Brown of the Oak Ridge National Laboratory. Turbines are now being developed that burn natural gas or biomass fuel to generate both electricity and steam.

Cogeneration emerges out of a relatively new way of thinking about factories, known as industrial ecology. Natural ecosystems, unlike factories, recycle most of their waste—animal droppings and dead organic matter are scavenged by insects and bacteria, which build up the soil and become prey for other organisms. Industrial ecologists use that thrift as an inspiration for industrial design.

Their shining example is the town of Kalundborg, in Denmark. A coal-burning plant there generates electricity, and the excess steam is captured and pumped into Kalundborg’s 5,000 houses and many of its factories. An oil refinery gets 40 percent of the heat it needs; a pharmaceutical factory gets all it needs to make its drugs and warm its building. The steam also runs a fish farm, where 57 warmed ponds produce 250 tons of fish each year. The power plant’s sulfur-dioxide scrubber produces gypsum as a by-product, which is used by a nearby wallboard manufacturer. Cinders once shipped from the coal plant to a landfill are now used to make cement. The other factories, in turn, make profits from their own wastes. Fertilizers are made out of both the sludge from the fish ponds and the waste from the microbes used for producing the pharmaceuticals. The oil refinery supplies the wallboard company with petroleum by-products to fire its ovens. The power plant burns some of those, too, saving 30,000 tons of coal a year. All told, Kalundborg saves 130,000 tons of CO2 emissions a year.

At least 14 eco-industrial parks are being designed in the United States. But according to John Ehrenfeld, a chemical engineer at mit, the Danish success can’t be immediately reproduced. Kalundborg took about 35 years to develop, says Ehrenfeld. It was never planned. This was an evolution, a series of independent transactions. The eco-parks are trying to do it all at once, but my guess is that this first round will not be full-blown symbioses. I hope folks don’t get frustrated if it’s not happening instantly. Kalundborg is very seductive—because it’s a good idea.

Switch to the Sun (Or At Least to Gas)

The industrial revolution was built on electricity generated from coal, and two centuries later little has changed. In the United States the production of electricity accounts for 36 percent of carbon emissions—about 530 million metric tons. As the rest of the world industrializes, the global contribution of electricity to carbon emissions may well soar. India and China, with their booming populations and vast coal reserves, are expected to become leading polluters—which is why the lack of any commitment from them at Kyoto was a disappointment. By 2020, if business proceeds as usual, electricity generation will produce 2,300 to 4,100 million tons of carbon every year.

Business will indeed proceed as usual unless other cheap, powerful sources of electricity turn up soon. Nuclear power is expensive and unpopular, and no one has figured out how to dispose of the radioactive waste. Fusion power—the kind generated by the sun—will probably remain a pipe dream for decades. Hydropower is carbon-free and widely available—but dams are expensive blots on the landscape that drown whole ecosystems.

In the long run, solar energy may become the best option. Although photovoltaic cells have been touted for decades, they’ve always been too expensive. But in the past few years the way they are made has changed. They used to be crafted from silicon crystals, which were sawed into wafers. Now engineers can vaporize semiconductors such as cadmium and tellurium and then have them settle, atom by atom, onto a piece of plain glass. The result is an ultrathin solar cell that doesn’t squander raw materials and provides abundant electricity. Even now solar cells are so cheap that sales went up worldwide by 38 percent in 1997.

The cheaper solar cells become, the better chance they’ll have of supplanting some of those coal-fired power plants that will otherwise spring up in India and China. Solar energy researchers hope that the same laws of rapidly rising efficiency and plummeting cost that characterize the computer industry will apply to their own field. Once the money is there, I’m pretty sure we’ll see photovoltaic cells that will cost just one-fifth of what they cost now, predicts Ken Zweibel of the doe’s National Renewable Energy Laboratory. A company called Solar Cells in Toledo is now automating the entire process and predicts that the cost of building a solar power panel will drop to a dollar per watt—the same as coal and natural gas in many parts of the United States—in three to five years.

Even if that happens, solar power will not be how we meet the Kyoto targets. A more important way to reduce emissions in the next decade would be simply to convert some U.S. coal plants to natural gas, which burns a lot cleaner. Coal-fired boilers would have to be replaced with turbines powered by natural gas. According to researchers at the Oak Ridge National Laboratory, the government would have to require carbon-emissions permits at $25 to $50 per ton in order to make such a conversion financially attractive to coal-plant operators. But because gas-burning technology is so efficient, the researchers don’t think the tax would lead to a big price hike for consumers. If every coal plant located near a gas pipeline was converted, the U.S. would reduce its carbon emissions by 40 million tons a year.

Dump It Somewhere Else

In the middle of the North Sea, about halfway between Scotland and southern Norway, Statoil, the Norwegian oil company, has to get rid of 1 million tons of carbon dioxide a year. (That’s a quarter million tons of carbon.) The CO2 does not come from the burning of fossil fuels; it’s an impurity that must be removed from the natural gas that Statoil is extracting from its Sleipner West field. A decade ago, Statoil would just have pumped it into the air. But in 1991 Norway began taxing emissions at the rate of about $50 per ton of CO2 (or $200 per ton of carbon). A tax bill of $50 million didn’t make developing the field unprofitable. But it made other options for disposing of the CO2 worth considering.

This is the one Statoil chose. The natural gas at Sleipner West is pumped into the bottom of a 115-foot-tall tower filled with steel pellets. As it percolates up, it meets a fluid solution of amine coming down. The amine strips the CO2 from the natural gas, and as the fluid exits the bottom of the tower, the pressure on it is released, allowing the CO2 to bubble out of solution—and to get channeled back to the seafloor through a steel pipe. Half a mile below the seafloor, the pipe penetrates a cap of impermeable shale and enters a 700-foot-thick layer of extremely porous sandstone. At the bottom of that mushy layer, high-pressure CO2 squirts from small holes in the pipe.

The whole of this porous formation is filled with salt water, explains Olav Kaarstad, the researcher in charge of Statoil’s climate program. The CO2 will displace the salt water. Part of it will be dissolved in the water, and part of it will react with minerals, but most of it will form a big bubble. It will slowly rise and spread out under the shale roof. But that will take hundreds and hundreds of years. Statoil has been injecting carbon dioxide just since August 1996.

There is no reason the CO2 has to come from gas fields: it could come from power plants. We think of Sleipner as a demonstration project, says Kaarstad. This could be a technology for handling CO2 on a much larger scale. The shale-capped sandstone under Sleipner, he points out, extends under most of the North Sea. In theory, it could soak up more than a hundred times the annual CO2 output of all the countries of the European Union.

Seafloor sandstones are not the only possible reservoirs. For the past decade researchers in Japan have explored the idea of pumping CO2 directly into seawater, which contains 60 times as much CO2 as the atmosphere and presumably can take a little more. At one time they considered simply dumping cubes of dry ice over the side of a ship. But the current idea, explains Takashi Ohsumi of the Central Research Institute of the Electric Power Industry in Abiko, is to load liquid CO2 onto a tanker directly at a power plant—most Japanese power plants are on the coast. In the open Pacific 500 miles east of Japan, the CO2 would be transferred to a second ship, which would steam slowly back and forth and pump it down a 6,500-foot vertical pipe. The CO2 would emerge in a fine mist at the bottom and—it is hoped—spread around the world at depth instead of bubbling back up to the atmosphere. Three ships working full-time, Ohsumi estimates, could meet the needs of a single large (1 gigawatt) coal-fired power plant. Around 2010, he says, I hope a small CO2 disposal business will be started in Japan.

Researchers at mit are pursuing the same hope for the United States, albeit with much less government support. Their idea is to run pipelines directly out to sea from coastal power plants. The main danger is that the CO2 would make the water around the pipe more acidic. But if dispersed in fine droplets, says Eric Adams of mit—as it would be in either the Japanese or the mit scenario—the concentration might never be greater than what marine animals could tolerate. We believe you can reach zero impact, says Adams. So far, that conclusion is based only on a review of the rather limited biological literature on what acidity levels are lethal to plankton. But Adams and Howard Herzog of mit, in collaboration with Ohsumi and other Japanese and Norwegian researchers, are now organizing an actual experiment that will take place in 2000 on the coast of Hawaii. They will pump as much as a hundred tons of liquid CO2 out to sea, to a depth of several thousand feet, and monitor the acidity.

The mit researchers hate being called geoengineers—the CO2 they propose to put in the ocean, they point out, would otherwise go into the atmosphere, and after a long and potentially damaging stay there, it would be absorbed by the ocean anyway. If they can get CO2 to go directly into the ocean and stay there—still a big if, given the uncertainties about how seawater moves around—they would just be shortening the circuit to eliminate the damage. It’s really a carbon-management issue, says Herzog. If we don’t want to put the carbon in the atmosphere, where do we put it? The only other choice is to leave it in the ground. And that just doesn’t seem like it’s going to happen.

Fertilize the Ocean

The Marshall Islands in the western Pacific are a nation of 58,000 people living on 70 square miles of coral atolls whose average elevation is seven feet. A sea level rise caused by global warming would have a big effect on this country, which helps explain why it was one of the first to ratify the Rio treaty. Last year the government of the Marshalls also signed another document—a contract with a Springfield, Virginia, entrepreneur named Michael Markels. The contract gives Markels an option on the country’s entire Exclusive Economic Zone, an area of some 800,000 square miles—almost the size of the Louisiana Purchase, says Markels. Beginning in 2000, he and his new company, Ocean Farming, hope to start fertilizing those waters with iron. The idea is to create a fishery where now there is none, and also to draw carbon dioxide out of the atmosphere.

The underlying theory was first put forward a decade ago by the late John Martin of the Moss Landing Marine Laboratories on Monterey Bay, in California. Martin proposed that in vast regions of the sea that are mysteriously infertile—regions where the single-celled plants, or phytoplankton, don’t flourish even though they have all the nitrogen and phosphorus they need—there is a dearth of iron. The amount the plankton need is minute, but the main source is dust blowing off the land, and in the infertile regions, said Martin, there just isn’t enough. In 1995 his successors at Moss Landing, Kenneth Coale and Kenneth Johnson, proved him right. When they sprayed a five-mile-wide square of ocean near the Galápagos Islands with half a ton of iron sulfate, the water turned green with phytoplankton.

Martin himself had suggested that iron fertilization could be a last resort to help protect ourselves from global warming—the blooming plants would suck up CO2. The biggest infertile region is the Southern Ocean around Antarctica, which also happens to be a region of vigorous sinking currents. If that whole vast region were fertilized regularly with iron, Martin said—which was technically conceivable because the amount needed was so small—then much of the resulting boom in biomass would end up sinking to the ocean floor, taking carbon with it. In 1999 or 2000, Coale and Johnson hope to repeat their fertilization experiment in the Antarctic.

Meanwhile, Markels is pressing ahead—half-cocked, some oceanographers would say. Markels is not an oceanographer. He is a chemical engineer by training and a successful entrepreneur (he’s the retired founder of Versar, a large engineering company in Springfield). His key improvement on Martin’s idea is a better delivery system for the iron. In the Galápagos experiment, most of the iron oxidized, coagulated, and sank to the seafloor before the plants could use it. Markels has found a cheap way to prevent that. Iron is first reacted with lignic acid, a waste product from papermaking, and then wrapped in small wax pellets. When the pellets are scattered on the ocean, Markels thinks, the iron will seep slowly out of the wax, while the lignic acid chelator will protect it from oxidation.

After some inconclusive tests in the Gulf of Mexico last January, Markels is planning more tests there this summer. But by 2000 he hopes to be fertilizing the Marshalls eez. It’s not the ideal place, because the water there needs phosphate too—but in exchange for royalties, the Marshalls have given Markels property rights. We’re in this to make money, he emphasizes. By fertilizing 100,000 square miles of ocean continually and seeding the barren waters with anchovetas—tunas would swim in on their own to eat the anchovetas—Markels claims he can produce more fish in a year, about 100 million tons, than are currently harvested worldwide. By fertilizing 300,000 square miles, he thinks he can dispatch as much CO2 to the seafloor as the United States produces. He’s hoping polluters will pay him to do that one day.

Though his optimistic calculations probably shouldn’t be taken too seriously, in principle his scheme could work—it’s just that no one knows whether it will actually work off the Marshall Islands. Even if the plankton there did bloom with an iron supplement, no one knows how much of that carbon would really sink to the seafloor instead of getting belched back into the atmosphere. And no one, least of all Markels, knows what impact fertilization will have on the environment. Decaying plankton will draw oxygen out of the water, and that clearly could be dangerous to coral—the stuff the Marshalls are made of. Markels says he’ll do the fertilization well offshore. He sees no reason to think of farming the ocean any differently than we think of farming the land—as a boon to mankind. The main environmental impact, he predicts, is going to be happy fish.

Block That Sun

Before S. S. Penner retired from the University of California at San Diego, he was for two decades the director of its Energy Center. A chemist and an aeronautical engineer, he was also a prolific chairman of government committees, many of them having to do with how best to burn fossil fuels. In 1983, when Penner was invited to give a paper at an astronautical conference on some socially useful application of aircraft or satellites, global warming was beginning to be talked about a lot. A solution to that, Penner decided, would certainly be useful.

He considered first the possibility of putting 9 million 2,000-foot-wide Mylar balloons into orbit to block some sunlight. But a back-of-the-envelope calculation told him that the launch cost alone would run to $315 trillion. So Penner started to think smaller. Another quick calculation told him that if you used half-micron particles as reflectors, it would take surprisingly few of them to offset the greenhouse effect caused by a doubling of CO2—only about 15 million tons spread over the whole planet. If you put particles that small in the stratosphere, between 40,000 and 100,000 feet, they would stay up there for decades, Penner figured. His idea for how to get them there was downright elegant (at least compared with firing dust salvos at the stratosphere with battleships): if you just adjusted all the jet engines in the world so they burned a little richer and emitted 1 percent of their fuel as tiny particles of soot, you’d get your 15 million tons’ worth. The cost would be derisory. And you’d hardly know that the particles were there, says Penner.

Unfortunately, commercial jets don’t spend much time above 40,000 feet; Penner now says he has in mind a twenty-first-century world crisscrossed by high-flying ssts. And particles don’t stay in the stratosphere as long as Penner assumed, so canceling all of global warming wouldn’t be quite as cheap or easy as he figured. The eruption of Mount Pinatubo in 1991 shot a sulfurous plume up to 70,000 feet—but within three years even the smallest sulfate particles had fallen to Earth.

On the other hand, Pinatubo did cool the planet—by nearly a degree Fahrenheit, at least in the tropics. If you had a volcano like Pinatubo going off every two years, you would be completely offsetting CO2 warming, says V. Ramaswamy, a climate modeler at the Geophysical Fluid Dynamics Laboratory in Princeton. But that doesn’t mean we know yet how to do what the volcano did. The problem is not just the potential side effects of a stratospheric parasol—the particles might help destroy ozone—it’s that even the effects on climate are uncertain. Putting jet soot into the stratosphere would blocksunlight, but what would happen as the particles settled into the zone of clouds? A recent nasa study showed that jet contrails evolve into cirrus clouds as water droplets freeze around the sulfate and soot particles. Cirrus clouds, however, actually warm the planet—they bounce more heat back to Earth than sunlight to space. So sootier jet exhaust would not necessarily be a good thing.

Still, the basic idea—that it might be possible to cool the planet by scattering particles in the atmosphere—is not entirely wacky, as Ramaswamy puts it. A particle screen would certainly be cheap, and it could be dismantled quickly—by letting the particles fall to Earth—if things went awry. Many of the unanswered questions about it are ones climatologists are trying to answer anyway. But a focused look into the geoengineering possibilities would seem prudent. There has been no research program on this activity, says Penner. People are very reluctant to do this—and I think rightly. But I wasn’t saying go out and do this. I was saying go out and study this.

Dam That Sea

To Robert Johnson, a prudent hedge against climate disaster would be to start work on a dam across the Strait of Gibraltar, right now. Even before retiring from the Honeywell Corporation, where he spent a career working on physics problems related to heating and cooling buildings, Johnson had an interest in global climate control too. An adjunct professor at the University of Minnesota—a state that was once submerged under a thick sheet of ice—Johnson thinks an ice age could start again soon, as a result of global warming and the construction of the Aswa-n High Dam in Egypt. The Gibraltar dam is his idea for preventing that.

The idea that global warming could lead to a surge of northern ice sheets, if not a full-blown ice age, is counterintuitive but not crazy. The warming will cause more water to evaporate from the oceans, so globally it should increase precipitation. In places like northern Canada and Greenland it will still be cold enough for that precipitation to fall as snow. More snow could lead to more ice. And once you’ve given the ice sheets a kick in the butt, they don’t stop, says Johnson.

Johnson believes the last big kick came from the Mediterranean. Based on some 20-year-old oceanographic data, he proposes that dense, salty Mediterranean water, flowing due north after it leaves the Med at a depth of half a mile or more, slams into shoals and wells up to the surface off Ireland. There it also runs into the much larger North Atlantic Drift, the warm extension of the Gulf Stream. Today, says Johnson, that water mass flows on into the Norwegian Sea, where it helps warm northern Europe. But at the start of the last ice age, he claims, something different happened. The flow of freshwater into the Mediterranean from the Nile diminished, the Med got saltier, and so the outflow at Gibraltar increased. The upwelling off Ireland became powerful enough to push the North Atlantic Drift into the Labrador Sea. All that warm water increased evaporation there and rerouted snowstorms over eastern Canada. The ice sheets surged south.

Thanks to us, says Johnson, the next glacial kick may already be under way: Egyptian dams are already diverting 90 percent of the Nile. Global warming will make matters much worse by increasing evaporation from the Med. The next flip of the fluidic switch off Ireland could be less than a century away. The only way to stop it, Johnson thinks, is to reduce the flow of water out of the Med—by building a partial dam, twice as high as the Great Pyramid of Cheops and 420 times larger in volume, between Spain and Morocco. Atlantic water would still flow over a sill near Spain, and Med water would flow out through a gap in the middle. But the outflow would be cut in half.

What do people who actually study ocean currents think of Johnson’s fluidic switch hypothesis, let alone the idea of a Gibraltar dam? On the whole, not a whole lot. There is no evidence at all that Med water upwells and diverts the North Atlantic current, says Jim Price of the Woods Hole Oceanographic Institution, who is an expert on the Mediterranean outflow. But Johnson sees no wackiness in his suggestion that we should start designing the dam now. These things have to be researched, he says. You’ve got to feel your way, engineering-wise, because nothing like this has been done before. If you wait until the climate has changed, you’ll have a lot of hardship.

Do Nothing

Of course, we could just stick with the geoengineering scheme we’ve got—the one that consists of putting 7 billion tons a year of carbon in the form of carbon dioxide into the atmosphere, along with generous dollops of other greenhouse gases. Some people, mostly in the United States, do advocate that policy. Last fall, for instance, the Wall Street Journal published an opinion column by two chemists at the Oregon Institute of Science and Medicine, whose title should one day give historians a chuckle: Science Has Spoken: Global Warming Is a Myth. If science has said one thing clearly, it is that the planet will almost certainly get warmer. It’s just not clear whether the warming has begun already.

Or what the effects will be. They will probably be significant, and some may be nice: Manitoba (and Minnesota) may become more pleasant, and farms there more productive. On the other hand, Africa may be hit by severe droughts, coastlines everywhere could be threatened by rising seas, and the Gulf Stream could be shut down, bringing an abrupt chill to northern Europe. All of this is very uncertain—and so to some people, given the costs of doing something about global warming, doing nothing and hoping for the best seems rational. To others, that would be the wackiest scheme of all.

Cuts 2–5 reported by Jessica Gorman, Shanti Menon, Fenella Saunders, and Jeffrey Winters.

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