Special for Earth Day - Scientific American

The Blue Food

Revolution

Reinventing the Leaf

How Much is Left?

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Scientific American, February 2011Scientific American, February 2011

Meat consumption is rising worldwide, but production involves vast amounts of energy, water and emissions. At the same time, wild fisheries are declining. Aquaculture could become the most sustainable source of protein for humans.

Fish farming already accounts for half of global seafood production. Most of it is done along coastlines, which creates substantial water pollution.

Large, offshore pens that are anchored to the sea floor are often cleaner. Those farms, other new forms of aquaculture, and practices that clean up coastal operations could expand aquaculture significantly.

Questions remain about how sustainable and cost-effective the approaches can be.

i n b r i e f

February 2011, ScientificAmerican.com

fish raised in offshore pens, such as these yellowtail at Kona Blue Water Farms near Hawaii,

could become a more sustain-able source of protein for

humans than wild fish or beef.

susta i n a b i l i t y

The Blue Food Revolution

New fish farms out at sea, and cleaner operations along the shore, could provide the world

with a rich supply of much needed protein

By Sarah Simpson


Scientific American, February 2011

ever, it must operate in environmentally sound ways—and make its benefits better known both to a jaded public and to policy makers with the power to help or retard its spread.

In the past, condemnation might have been apt. When mod-ern coastal fish farming began about 30 years ago, virtually no one was doing things right, either for the environment or for the industry’s long-term sustainability. Fish sewage was just one of the issues. Shrimp farmers in Southeast Asia and Mexi-co clear-cut coastal mangrove forests to make ponds to grow their shrimp. In the salmon farms of Europe and the Americas, animals were often too densely packed, helping disease and parasites sweep through the populations. Fish that escaped farms sometimes spread their diseases to native species. Mak-ing matters worse, the aquaculture industry represented (and M

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N eil sims tends his rowdy stock like any de- voted farmer. But rather than saddling a horse like the Australian sheep drovers he grew up with, Sims dons a snorkel and mask to wrangle his herd: 480,000 silver fish corralled half a mile off the Kona coast of Hawaii’s Big Island.

Tucked discretely below the waves, Sims’s farm is one of 20 operations worldwide that are trying to take advantage of the earth’s last great agricultural frontier: the ocean. Their offshore locations offer a distinct advantage over the thousands of con-ventional fish farms—flotillas of pens that hug the coastline. Too often old-style coastal farms, scorned as eyesores and ocean polluters, exude enough fish excrement and food scraps to cloud the calm, shallow waters, triggering harmful algal blooms or snuffing out sea life underneath the pens. At offshore sites such as Kona Blue Water Farms, pollution is not an issue, Sims explains. The seven submerged paddocks, each one as big as a high school gymnasium, are anchored within rapid currents that sweep away the waste, which is quickly diluted to harm-less levels in the open waters.

Rather than taking Sims’s word for it, I put swim fins on my feet and a snorkel around my neck, high-step to the edge of his small service boat, and take the plunge. From the water, the double-cone-shape cage is aglow like a colossal Chinese lan-tern, with shimmering streams of sunlight and glinting forms of darting fish. To the touch, the material that stretches taut around the outside of the cage’s frame feels more like a fence than a net. The solid, Kevlar-esque material would repel hun-gry sharks as effectively as it contains teeming masses of Serio-la rivoliana, a local species of yellowtail that Kona Blue has do-mesticated as an alternative to wild tuna.

Why yellowtail? Many wild tuna fisheries are collapsing, and sushi-grade yellowtail fetches a high price. Sims and fellow ma-rine biologist Dale Sarver founded Kona Blue in 2001 to raise popular fish sustainably. But the company’s methods could just as well be applied to run-of-the-mill fish— and we may need them. The global population of 6.9 billion people is estimated to rise to 9.3 billion by 2050, and people with higher living standards also tend to eat more meat and seafood. Yet the global catch from wild fisheries has been stagnant or declining for a decade. Raising cows, pigs, chickens and other animals consumes vast amounts of land, freshwater, fossil fuels that pollute the air and fertilizers that run off and choke rivers and oceans.

Where will all the needed protein for people come from? The answer could well be new offshore farms, if they can function ef-ficiently, and coastal farms, if they can be cleaned up.

Cleaner Is Betterto some scientists, feeding the world calls for transferring the production of our animal protein to the seas. If a blue food rev-olution is to fill such an exalted plate at the dinner table, how-

Sarah Simpson� is a freelance writer and contributing editor for Scientific American. She lives in Riverside, Calif.

f e e d I n g t h e wo r l d

Protein Supply: Land or Sea?

who Is Poised to Provide It?

the world needs More Protein

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ASIAN COUNTRIES produce the vast majority of aquaculture fish and shellfish.

CROP AND GRAZING areas, at today’s yields, would have to rise by 50% to 70% to meet 2050 food needs; such land may not exist.

WORLD POPULATION will increase from 6.9 billion to 9.3 billion by 2050.

2010 2050

AQUACULTURE produces 47% of the global seafood people consume. It could sustainably provide 62% of the world’s total protein by 2050 if it continues to grow at its current annual rate of 7.4% and agriculture continues its 2.0% growth rate.

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Graphics by Jen Christiansen


still does) a net drain on fish mass; wild forage fish—small, cheap species that humans do not prefer but that bigger, wild fish eat—are captured in large quantities and ground into feed for the bigger, tastier, more expensive farmed fish folks favor.

Clearly, such ills were not good for business, and the indus-try has devised innovative solutions. Kona Blue’s strategy of sit-uating the farm within rapid offshore currents is one example. Other farmers are beginning to raise seaweed and filter-feeding animals such as mollusks near the fish pens to gobble up waste. Throughout the industry, including freshwater pens, improve-ments in animal husbandry and feed formulations are reduc-ing disease and helping fish grow faster, with less forage fish in their diets. It may still be a long time before environmental groups remove farmed fish from “don’t buy” lists, however.

Some cutting-edge thinkers are experimenting with an even bolder move. Nations exercise sole rights to manage waters out to 200 nautical miles from their shores—a vast frontier un-tapped for domesticated food production. Around the U.S., that frontier measures 3.4 million square nautical miles. Submerged fish pens, steered by large propellers, could ride in stable ocean currents, returning months later to their starting points or a distant destination to deliver fresh fish for market.

Ocean engineer Clifford Goudey tested the world’s first self-propelled, submersible fish pen off the coast of Puerto Rico in late 2008. A geodesic sphere 62 feet in diameter, the cage proved surprisingly maneuverable when outfitted with a pair of eight-foot propellers, says Goudey, former director of M.I.T. Sea Grant’s Offshore Aquaculture Engineering Center. Goudey imagines launching dozens of mobile farms in a steady pro-

gression within a predictable current that traverses the Carib-bean Sea every nine months.

feedIng frenzythe aspect of marine (saltwater) aquaculture that has been hardest to fix is the need to use small, wild fish as food for the large, farmed varieties. (The small fish are not farmed, because a mature industry already exists that catches and grinds them into fish meal and oil.) The feed issue comes into pungent focus for me when Sims and I climb aboard an old U.S. Navy trans-port ship cleverly transformed into a feeding barge. The sea swell pitches me sideways as I make my way to the bow, calling to mind a bumpy pickup truck ride I took long ago, across a semifrozen Missouri pasture to deliver hay to my cousin’s Here-fords. The memory of sweet-smelling dried grass vanishes when I grab a handful of oily brown feed from a 2,000-pound sack propped open on the deck. The pellets look like kibble for a small terrier but reek of an empty anchovy tin.

The odor is no surprise; 30 percent of Kona Blue’s feed is ground up Peruvian anchovy. Yellowtail could survive on a veg-etarian diet, but they wouldn’t taste as good, Sims explains. Nor would their flesh include all the fatty acids and amino acids that make them healthy to eat. Those ingredients come from fish meal and fish oil, and that is the issue. “We are often pillo-ried because we’re killing fish to grow fish,” Sims says. Salmon farming, done in coastal pens, draws the same ire.

Detractors worry that rising demand from fish farms will wipe out wild anchovies, sardines and other forage fish. Before modern fish farming began, most fish meal was fed to pigs and

Map by XNR Productions

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Fish farms near shore and farther out into the ocean could expand greatly in federal waters.

A country’s “exclusive economic zone” extends up to200 nautical miles from its coast. The U.S. zone (blue)is the world’s largest, covering 3.4 million square nautical miles—more than its land area.1970

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Five Ways to Raise Seafood

Most farmed marine fish are raised in on-shore tanks or coastal pens, but cages are increasingly being anchored farther offshore. At least one mobile, prototype en closure, submerged and steered by prop ellers, has been tried way out in the open ocean. Entrepreneurs are also grow-ing seaweed and mussels on lines placed next to coastal pens and might do the same around offshore wind turbines.

Open Ocean CagesIn the future, a series of mobile, submerged pens, each steered by propellers or thrusters, could ride in predictable currents, arriv ing at a distant des tination months later when fish are mature. Machinery would dispense feed stored in the central spar.

Offshore CagesYoung fish are placed in an anchored cage the size of a gymnasium. Flooding the central spar submerges the pen until the fish grow mature. A boat or barge sends food inside through tubes, and natural currents sweep away excrement. The pen is raised for harvesting and cleaning.

chickens, but today aquaculture consumes 68 percent of the fish meal. Consumption has lessened under advanced feed for-mulas, however. When Kona Blue started raising yellowtail in 2005, its feed pellets were 80 percent anchovy. By early 2008 the company had reduced the share to 30 percent—without sacrificing taste or health benefit, Sims says—by increasing the concentration of soybean meal and adding chicken oil, a by-product of poultry processing. The compound feed pellets are a big improvement over the egregious practice of dumping whole sardines into the fish cages. Unfortunately, this wasteful habit remains the norm among less responsible farmers.

A goal for the more enlightened proprietors is a break-even ratio, in which the amount of fish in feed equals the weight of fish produced for market. Farmers of freshwater tilapia and catfish have attained this magic ratio, but marine farmers have not. Because 70 percent of Kona Blue’s feed is agricultural pro-tein and oil, it now needs only 1.6 to 2.0 pounds of anchovies to produce one pound of yellowtail. The average for the farmed salmon industry is around 3.0. To achieve no net loss of marine protein, the industry would have to reduce that ratio. Still, farmed fish take a far smaller bite than their wild equivalents do: over its lifetime, a wild tuna may consume as much as 100 pounds of food per pound of its own weight, all of it fish.

The pressure to reduce sardine and anchovy catches will in-crease as the number of fish farms grows. Aquaculture is the fastest-growing food production sector in the world, expanding at 7.5 percent a year since 1994. At that pace, fish meal and fish oil resources could be exhausted by 2040. An overarching goal, therefore, is to eliminate wild fish products from feed altogether, within a decade or so, asserts marine ecologist Carlos M. Duarte, who directs the International Laboratory for Global Change at the Spanish Council for Scientific Research in Majorca.

One breakthrough that could help is coaxing the coveted omega-3 fatty acid DHA out of microscopic algae, which could replace some of the forage fish content in feed. Advanced Bio-Nu trition in Columbia, Md., is testing feed that contains the same algae-derived DHA that enhances infant formula, milk and juice now sold in stores. Recently researchers at Australia’s Commonwealth Scientific and Industrial Research Organiza-tion coaxed DHA out of land plants for the first time. Duarte suggests that fierce competition for agricultural land and fresh-water means that fish farmers should eventually eliminate soy, chicken oil and other terrestrial products as well, instead feed-ing their flocks on zooplankton and seaweed, which is easy to grow. (Seaweed already accounts for nearly one quarter of all marine aquaculture value.)

Despite improvements in marine fish farming, prominent en-vironmentalists and academics still shoot it down. Marine ecol-ogist Jeremy Jackson of the Scripps Institution of Oceanography says he is “violently opposed” to aquaculture of predatory fish and shrimp—basically, any fish people like to eat sashimi-style. He calls the practice “environmentally catastrophic” in the pres-sure it puts on wild fish supplies and insists it should be “illegal.”

sMarter than Beef jackson’s point, echoed by other critics, is that the risk of col-lapsing forage fisheries, which are already overexploited, is too great to justify serving up a luxury food most of the world will never taste. Far better would be to eat the herbivorous sardines and anchovies directly instead of farmed, top-end predators.

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Turbine CollarsMussels and seaweed readily cling to synthetic lines and grow naturally. The lines could be strung around or between turbines in offshore wind farms to enhance investment and to help reduce competition for offshore space.

Onshore TanksAll marine fish are hatched in tanks on land. Many are moved to pens at sea when old enough (fingerlings), but some innovators are also raising fish to harvestable size in onshore tanks, where pollutants, disease and escaped fish can be controlled.

Coastal PensHeavy mesh pens are relatively easy to anchor and maintain. Automated feeders can minimize food waste by turning off when infrared sensors on the seafloor detect falling pellets. Seaweed and mussels that feed on fish waste can, if raised immediately “downstream,” reduce pollution and add revenue. Trays of waste munching

organisms, such as red sea urchins, can also be placed

below the pens.

February 2011, ScientificAmerican.com Illustration by Don Foley

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Sims agrees that we should fish lower on the food web but says that does not mean we need to eat lower. “Let’s get real. I eat an-chovies on my pizza, but I can’t get anyone else in my family to do it,” he says. “If you can get a pound of farmed sushi for every pound of anchovy, why not give people the thing they want to eat?”

Certain people scoff at fish consumption—whether wild-caught or farm-raised—on the premise that the planet and its human inhabitants would be healthier if people ate more plants. But society is not rushing to become vegetarian. More people are eating more meat, particularly as populations in the developing world become wealthier, more urban and more Western. The World Health Organization predicts a 25 percent increase in per capita meat consumption by 2050. Even if con-sumption held steady, crop and grazing areas would have to in-crease by 50 to 70 percent, at current yields, to produce the food required in 2050.

That reality begs for a comparison rarely made: fish farming versus terrestrial farming. Done right, fish farming could pro-vide much needed protein for the world while minimizing the expansion of land-based farming and the attendant environ-mental costs.

Land-based farmers have already transformed 40 percent of the earth’s terrestrial surface. And after 10,000 years to work out the kinks, major problems still abound. Cattle eat tremen-dous amounts of heavily fertilized crops, and pig and chicken farms are notorious polluters. The dead zones underneath coastal fish farms pale in comparison to the huge dead zones that fertilizer run-off triggers in the Gulf of Mexico, Black Sea and elsewhere and to the harmful algal blooms that pig farm effluent has caused in Chesapeake Bay.

A growing number of scientists are beginning to compare

the environmental impacts of all the various protein produc-tion systems, so that society can “focus its energies on efficient-ly solving the most demanding problems,” writes Kenneth M. Brooks, an independent aquatic environmental consultant in Port Townsend, Wash. Brooks estimates that raising Angus beef requires 4,400 times more high-quality pasture land than sea-floor needed for the equivalent weight of farmed Atlantic salm-on filets. What is more, the ecosystem below a salmon farm can recover in less than a decade, instead of the centuries it would take for a cattle pasture to revert to mature forest.

An even more compelling reason to raise protein in the sea may be to reduce humanity’s drain on freshwater. As Duarte points out, animal meat products represent only 3.5 percent of food production but consume 45 percent of the water used in agriculture. By shifting most protein production to the ocean, he says, “land agriculture could grow considerably without ex-ceeding current levels of water use.”

Of course, collecting and transporting soybean meal and chicken oil and feeding fish flocks all consume energy and cre-ate emissions, too. Fuel consumption and emissions are greater for farms that are farther from shore, but both types of farming rate better than most fishing fleets. The only way offshore farm-ers can be profitable right now is to raise high-priced fish, but costs can come down: a few experimental farms are already raising cost-competitive mussels in the ocean.

enVIronMental dIstInCtIons if providing more fish to consumers is an answer to meeting global demands for protein, why not just catch more fish di-rectly? Many wild fisheries are maxed out, right at a time when global population, as well as per capita demand for fish, is boom-

farmed yellowtail grow more efficiently than wild fish, which expend much energy hunting and evading predators.


ing. North Americans, for example, are heeding health experts’ advice to eat fish to help reduce the risk of heart attacks and im-prove brain function.

What is more, fishing fleets consume vast amounts of fuel and emit volumes of greenhouse gases and pollutants. Widely used, indiscriminate fishing methods, such as trawling and dredging, kill millions of animals; studies indicate that at least half the sea life fishers haul in this way is discarded as too small, overquota or the wrong species. All too often this so-called by-catch is dead by the time it is tossed overboard. Aquaculture eliminates this waste altogether: “Farmers only harvest the fish in their pens,” Sims notes.

Goudey points out another often overlooked reality: you can grow fish more efficiently than you can catch them. Farmed fish convert food into flesh much more effectively than their wild brethren, which expend enormous amounts of energy as they hunt for food and evade predators, seek a mate and reproduce. Farmed fish have it easy by comparison, so most of their diet goes into growth.

Kona Blue’s yellowtail and most farmed salmon are between one and three years old at harvest, one-third the age of the large, wild tuna targeted for sushi. The younger age also means farmed fish have less opportunity to accumulate mercury and other persistent pollutants that can make mature tuna and sword fish a potential health threat.

Indeed, fish farming already accounts for 47 percent of the seafood people consume worldwide, up from only 9 percent in 1980. Experts predict the share could rise to 62 percent of the to-tal protein supply by 2050. “Clearly, aquaculture is big, and it is here to stay. People who are against it re-ally aren’t getting it,” says Jose Villalon, aquaculture director at the World Wildlife Fund. Looking only at the ills of aquaculture is misleading if they are not compared with the ills of other forms of food production. Aqua-culture affects the earth, and no number of improvements will eliminate all problems. But every food production system taxes the environment, and wild fish, beef, pork and poultry produc-ers impose some of the greatest burdens.

To encourage good practices and help distinguish clean fish farms from the worst offenders, the World Wildlife Fund has co-founded the Aquaculture Stewardship Council to set global stan-dards for responsible practices and to use independent auditors to certify compliant farms. The council’s first set of standards is expected early this year. The council believes certification could have the greatest effect by motivating the world’s 100 to 200 big seafood retailers to buy fish from certified farms, rather than trying to crack down directly on thousands of producers.

The Ocean Conservancy’s aqua culture director George Leon-ard agrees that this kind of farm-to-plate certification program is an important way to encourage fish farmers to pursue better sustainability practices. As in any global industry, he says, cheap, unscrupulous providers will always exist. Setting a regu-latory “floor” could require U.S. farmers to behave responsibly “without making it impossible for them to compete.”

That point is key. Only five of the world’s 20 offshore instal-lations are in U.S. waters. Goudey thinks more aquaculture en-trepreneurs would dive in if the U.S. put a licensing system into place for federal waters, from three nautical miles offshore to the 200-mile boundary. “No investor is going to back a U.S. op-eration when there are no statutes granting rights of tenancy to

an operation,” Goudey asserts. All U.S. farms exist inside the three-mile-wide strip of water that states control, and only a few states, such as Hawaii, allow them. California has yet to grant permits, despite government estimates that a sustainable offshore fish-farming industry in less than 1 percent of the state’s waters could bring in up to $1 billion a year.

ProteIn PolICy to grow, and do so sustainably, the fish-farming industry will need appropriate policies and a fairer playing field. At the mo-ment, robust government fuel subsidies keep trawling and dredg-ing fleets alive, despite their well-known destruction of the sea-floor and the terrible volume of dead by-catch. Farm subsidies help to keep beef, pork and poultry production profitable. And powerful farm lobbies continue to block attempts to curtail the flow of nitrogen-rich fertilizer down the Mississippi River. “Al-most none of these more traditional ways of producing food have received the scrutiny that aquaculture has,” Brooks says. The public has accepted domestication of the land but main-tains that the ocean is a wild frontier to be left alone, even though this imbalance may not be the most sustainable plan for feeding the world.

Policy shifts at the federal and regional levels may soon open up U.S. federal waters. In January 2009 the Gulf of Mexico Fish-ery Management Council voted in favor of an unprecedented plan for permitting offshore aquaculture within its jurisdiction, pending approval from higher levels within the U.S. National Oceanic and Atmospheric Administration. NOAA will evaluate

the plan only after it finalizes its new national aqua-culture policy, which addresses all forms of the indus-try and will probably include guidance for the devel-opment of a consistent, nationwide framework for regulating commercial activities. “We don’t want the

blue revolution to repeat the mistakes of the green revolution,” says NOAA director Jane Lubchenco. “It’s too important to get it wrong, and there are so many ways to get it wrong.”

Given relentlessly rising demand, society has to make hard choices about where greater protein production should occur. “One of my goals has been to get us to a position where, when people say food security, they don’t just mean grains and live-stock but also fisheries and aquaculture,” Lubchenco says. Duarte suggests we take some pressure off the land and turn to the seas, where we have the opportunity to do aquaculture right, rather than looking back 40 years from now wishing we had done so.

As for Neil Sims’s part of the blue food revolution, he is courting technology companies for upgrades. Tools such as ro-botic net cleaners, automated feeders and satellite-controlled video cameras to monitor fish health and cage damage would help Kona Blue’s crew manage its offshore farms remotely. “Not just so we can grow more fish in the ocean,” Sims says. “So we can grow more fish better.”

M o R e t o e x P l o R e

The State of World Fisheries and Aquaculture 2008. Fao, 2009.Will the Oceans Help Feed Humanity? Carlos M. duarte et al. in BioScience, Vol. 59, no. 11, pages 967–976; december 2009.Sustainability and Global Seafood. Martin d. smith et al. in Science, Vol. 327, pages784–786; February 12, 2010.Will Farmed Fish Feed the World? an analysis from the Worldwatch institute. www.worldwatch.org/node/5883

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Scientific American, October 2010 Illustrations by Cherie Sinnen

Artificial leaves could use sunlight to produce hydrogen fuel for cars and power plants.

E N E RGY

Reinventing the Leaf The ultimate fuel may come not from corn or algae but directly from the sun itself

By Antonio Regalado

L ike a fire-and-brimstone preacher, nathan s. Lewis has been giving a lecture on the energy crisis that is both terrifying and exhilarating. To avoid potentially debilitating global warm-ing, the chemist from the California Institute of Technology says civilization must be able to generate more than 10 trillion watts of clean,

carbon-free energy by 2050. That level is three times the U.S.’s average energy demand of 3.2 trillion watts. Damming up every lake, stream and river on the planet, Lewis notes, would provide only five trillion watts of hydroelectricity. Nuclear power could manage the feat, but the world would have to build a new reac-tor every two days for the next 50 years.

Before Lewis’s crowds get too depressed, he tells them there is one source of salvation: the sun pours more energy onto the earth every hour than humankind uses in a year. But to be saved, Lewis says, humankind needs a radical breakthrough in solar-fuel tech-nology: artificial leaves that will capture solar rays and churn out chemical fuel on the spot, much as plants do. We can burn the fuel,

as we do oil or natural gas, to power cars, create heat or generate electricity, and we can store the fuel for use when the sun is down.

Lewis’s lab is one of several that are crafting prototype leaves, not much larger than computer chips, designed to produce hydrogen fuel from water, rather than the glucose fuel that nat-ural leaves create. Unlike fossil fuels, hydrogen burns clean. Other researchers are working on competing ideas for captur-ing the sun’s energy, such as algae that has been genetically altered to pump out biofuels, or on new biological organisms engineered to excrete oil. All these approaches are intended to turn sunlight into chemical energy that can be stored, shipped and easily consumed. Lewis argues, however, that the man-made leaf option is the most likely to scale up to the industrial levels needed to power civilization.

Fuel From Photonsalthough a few lab prototypes have produced small amounts of direct solar fuel—or electrofuel, as the chemicals are sometimes called—the technology has to be improved so the fuel can be

Natural energy: Plants produce their own chemical fuel—sugar—from sun-light, air and water, without producing harmful emissions.

Man-made leaf: Researchers are devis-ing artificial leaves that could similarly convert sunlight and water into hydro-gen fuel, which could be burned to power

cars, create heat or generate electricity, ending dependence on fossil fuels.Nano solution: To be practical, this so-lar-fuel technology would have to be

made cheaply in thin, flexible sheets, per-haps from silicon nanowires, and use in-expensive catalysts that help to generate hydrogen efficiently.

i n b r i e f

Antonio Regalado is a science and technology reporter and the Latin America contributor to Science magazine. He lives in São Paulo, Brazil, where he writes about energy topics, including renewables.

Scientific American, October 2010

manufactured on a massive scale, very inexpensively. To power the U.S., Lewis estimates the country would need to manufac-ture thin, flexible solar-fuel films, instead of discrete chiplike devices, that roll off high-speed production lines the way news-print does. The films would have to be as cheap as wall-to-wall carpeting and eventually cover an area the size of South Carolina.

Far from being a wild dream, direct solar-fuel technology has been advancing in fits and starts ever since President Jimmy Carter’s push for alternative energy sources during the 1970s oil shocks. Now, with a new energy and climate crunch looming, solar fuel is suddenly gaining attention. Researcher Stenbjörn Styring of Uppsala University in Sweden, who is developing artifi-cial systems that mimic photosynthesis, says the number of con-sortiums working on the challenge has ballooned from just two in 2001 to 29 today. “There are so many we may not be counting correctly,” he adds.

In July the Department of Energy awarded $122 million over five years to a team of scientists at several labs, led by Lewis, to develop solar-fuel technology, one of the agency’s three new energy research priorities. Solar fuels “would solve the two big problems, energy security and carbon emissions,” says Steven E. Koonin, the top science ad min is-trat or at the doe. Koonin thinks sun-to-fuel schemes face “formi-dable” practical hurdles but says the tech nology is worth invest-ing in be cause “the prize is great enough.”

In photosynthesis, green leaves use the energy in sunlight to rear-range the chemical bonds of water and carbon dioxide, producing and storing fuel in the form of sugars. “We want to make some-thing as close to a leaf as possi-ble,” Lewis says, meaning devices that work as simply, albeit producing a different chemical out-put. The artificial leaf Lewis is designing requires two principal elements: a collector that converts solar energy (photons) into electrical energy (electrons) and an electrolyzer that uses the electron energy to split water into oxygen and hydrogen. A cata-lyst—a chemical or metal—is added to help achieve the splitting. Existing photovoltaic cells already create electricity from sun-light, and electrolyzers are used in various commercial processes, so the trick is marrying the two into cheap, efficient solar films.

Bulky prototypes have been developed just to demonstrate how the marriage would work. Engineers at Japanese automaker Honda, for example, have built a box that stands taller than a refrigerator and is covered with photovoltaic cells. An electro-lyzer, inside, uses the solar electricity to break water molecules. The box releases the resulting oxygen to the ambient air and compresses and stores the remaining hydrogen, which Honda would like to use to recharge fuel-cell cars.

In principle, the scheme could solve global warming: only sunlight and water are needed to create energy, the by-product is oxygen, and the exhaust from burning the hydrogen later in a fuel cell is water. The problem is that commercial solar cells con-tain expensive silicon crystals. And electrolyzers are packed with the noble metal platinum, to date the best material for catalyz-

ing the water-splitting reaction, but it costs $1,500 an ounce.That means Honda’s solar-hydrogen station will never power

the world. Lewis calculates that to meet global energy demand, future solar-fuel devices would have to cost less than $1 per square foot of sun-collecting surface and be able to convert 10 percent of that light energy into chemical fuel. Fundamentally new, massively scalable technology such as films or carpets made from inexpensive materials are needed. As Lewis’s Caltech col-league Harry A. Atwater, Jr., puts it, “We need to think potato chips, not silicon chips.”

Finding a Catalystthe search for such technology remains at an early stage, despite several decades of on-again, off-again work. One pioneer-ing experiment shows why. In 1998 John Turner of the National Renewable Energy Laboratory in Golden, Colo., built a device about the size of a matchbook that when placed in water and exposed to sunlight kicked out hydrogen and oxygen at a prodi-gious rate and was 12 times as efficient as a leaf. But Turner’s cre-ation depended on rare and expensive materials, including plati-num as the catalyst. By one estimate, Turner’s solar-fuel cell cost $10,000 per square centimeter. That might do for military or sat-ellite applications, but not to power civilization.

Noble metals, often the best catalysts, are in short supply. “That’s the big catch in this game,” Styring says. “If we want to save the planet, we have to get rid of all those noble metals and work with cheap minerals like iron, cobalt or manganese.” Another difficulty is that the water-splitting reaction is highly corrosive. Plants handle that by constantly rebuilding their photosynthetic machinery. Turner’s solar-fuel cell lasted just 20 hours.

Today Turner’s research is consumed with devising succes-sive generations of catalysts that each are a bit cheaper and of solar collectors that each last a little longer. At times the search is agonizingly hit or miss. “I am wandering through the forest looking for a material that does what I want,” Turner says. “Prog-ress has been minimal.”

Other teams are also chasing catalysts, including one led by Daniel G. Nocera of the Massachusetts Institute of Technology. In 2008 Nocera and a colleague hit on an inexpensive combination of phosphate and cobalt that can catalyze the production of oxy-gen—one necessary part of the water-splitting reaction.

Even though the prototype device was just a piece of the puzzle—the researchers did not find a better catalyst for creat-ing hy dro gen, the actual fuel—M.I.T. touted it as a “major leap” toward “artificial photosynthesis.” Nocera began predicting that Americans would soon be cooking up hydrogen for their cars using affordable backyard equipment. Those bold claims have not sat well with some solar-fuel experts, who maintain that research has decades to go. Others are more bullish: the doe and the venture capital firm Polaris Venture Partners are supporting Nocera’s ongoing work at Sun Catalytix, a company he created in Cambridge, Mass.

At Caltech, meanwhile, Lewis has been working on a way to collect and convert the sun’s photons—the first step in any solar-fuel device—that is much cheaper than conventional, crystalline silicon solar cells. He has designed and fabricated a collector made of silicon nanowires embedded in a transparent plastic film that, when made larger, could be “rolled and unrolled like a blan-ket,” he says [see box on opposite page]. His nanowires can con-vert light into electric energy with 7 percent efficiency. That

If we want to save the planet,

we have to get rid of all those

noble metals and work

with cheap minerals like

iron to catalyze reactions.

October 2010, ScientificAmerican.com

pales in comparison to commercial solar cells, which are up to 20 percent efficient. But if the material could be made inexpen-sively enough—those sheets rolling off a press like newsprint—lower efficiency could be acceptable.

Researchers also debate whether hydrogen is the best choice for solar fuel. Teams working with biological organisms that produce liquid biofuels say these fuels are easier to store and transport than hydrogen. But hydrogen gas is flexible, too: it can be used in fuel-cell cars, burned in power plants to generate electricity, and even serve as a feedstock in producing synthetic diesel. Nevertheless, “the key is to make an energy-dense chemi-cal fuel,” with minimal carbon emissions, Lewis says. “Let’s not get hung up on which one.”

Real-life leaves prove that sunlight can be converted in to fuel using only common elements. Can humankind imitate this pro-cess to rescue the planet from global warming? The prognosis is not clear. “The fact that we can’t solve the problem with off-the-shelf components is why it’s an exciting time to be working in this

h ow i t wo r k s

Solar Nanowires Mimic NaturePlants harness the sun’s energy to convert carbon dioxide and water into glucose—chemical fuel that can be used or stored (left). Research-ers are devising artificial leaves that use sunlight to split water

molecules, creating hydrogen fuel. Nathan Lewis’s group at the California Institute of Technology is designing a small leaf with arrays of silicon nanowires that could produce hydrogen (right).

Semiconductor nanowire

ChloroplastPhoton

Thylakoid

Stroma

Glucose Hydrogen

Oxidation catalyst

Reduction catalyst

natural leaf artificial leaf

area,” Lewis says. But he is worried that society—including policy makers, government funding agencies and even scientists—still has not grasped the size of the energy problem or why revolution-ary solutions are needed. That is why he spends so much time on the lecture circuit, preaching solar salvation: “We are not yet treating this problem like one where we can’t afford to fail.”

m o R e T o e x P l o R e

Powering the Planet: Chemical Challenges in Solar Energy Utilization. Nathan S. Lewis and Daniel G. Nocera in Proceedings of the National Academy of Sciences USA, Vol. 103, No. 43, pages 15729–15735; October 24, 2006.In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+. Matthew W. Kanan and Daniel G. Nocera in Science, Vol. 321, pages 1072–1075; August 22, 2008.Powering the Planet with Solar Fuel. Harry B. Gray in Nature Chemistry, Vol. 1, No. 7; April 2009.Energy-Conversion Properties of Vapor-Liquid-Solid-Grown Silicon Wire-Array Photocathodes. Shannon W. Boettcher et al. in Science, Vol. 327, pages 185–187; January 8, 2010.

iNterActiVe VerSiON At www.ScientificAmerican.com/interactive

e–

Energy in. Solar photons are absorbed by a photoactive material: in plants, thylakoids inside a chloroplast; in artificial water-splitting arrays, semiconductor nanowires.

Oxidation. Absorbed photon energy knocks electrons from water molecules in the chloroplast or array, which splits the molecules into hydrogen ions (H+) and oxygen.

Reduction. in plants, H+ ions combine with electrons and carbon dioxide to form glucose in the stroma. in the array, H+ ions move

through a membrane and combine with electrons to form hydrogen molecules.

Fuel out. Both processes create a storable, trans portable fuel: glucose in plants; hydrogen in arrays.

Semiconductor nanowire

H2O

H+

O2

H2

CO2

Sc ie ntif ic Americ An September 2010

2010 2020

1940 1980 2060 2100

World production rateMillion barrels per day

80

70

60

50

40

30

20

10

0

World Cumulative production

trillion barrels

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0.002014 1940 1980 2020 2060 2100

Peakproduction

annual Change in Glacier thickness

Gain

Loss

no data1976–1985 1986–1995 1996–2005

Up to 0.25 mMore than 0.25 m

if the 20th century was an expansive era seemingly without boundaries—a time of jet planes, space travel and the Inter-net—the early years of the 21st have showed us the limits of our small world. Regional blackouts remind us that the flow of energy we used to take for granted may be in tight supply. The once mighty Colo-rado River, tapped by thirsty metropolises of the desert West, no longer reaches the ocean. Oil is so hard to find that new wells extend many kilometers underneath the seafloor. The boundless atmosphere is now

reeling from two centuries’ worth of green-house gas emissions. Even life itself seems to be running out, as biologists warn that we are in the midst of a global extinction event comparable to the last throes of the dinosaurs.

The constraints on our resources and environment—compounded by the rise of the middle class in nations such as China and India—will shape the rest of this cen-tury and beyond. Here is a visual account-ing of what we have left to work with, a map of our resources plotted against time.

A graphical accounting of the limits to what one planet can provide

<< By michAel moyer >> with reporting By cArinA storrs

[ environment ]

?Sc ie ntif ic Americ An

lefthow much

is

Experience an interactive version of this article at www.ScientificAmerican.com/interactive JEn

Ch

rist

ian

sEn

w w w.Sc ient i f i c American .com Sc ie ntif ic Ame ric An 75

2010 2020

1940 1980 2060 2100

World production rateMillion barrels per day

80

70

60

50

40

30

20

10

0

World Cumulative production

trillion barrels

2.00

1.75

1.50

1.25

1.00

0.75

0.50

0.25

0.002014 1940 1980 2020 2060 2100

Peakproduction

annual Change in Glacier thickness

Gain

Loss

no data1976–1985 1986–1995 1996–2005

Up to 0.25 mMore than 0.25 m

[ fossil fuels ]

2014 >> the peak of oil the most common answer to “how much oil is left” is “depends on how hard you want to look.” as easy-to-reach fields run dry, new technologies allow oil companies to tap harder-to-reach places (such as 5,500 meters under the Gulf of Mexico). traditional statistical models of oil supply do not account for these

advances, but a new approach to production forecasting explicitly incorporates multiple

waves of technological improvement. though still controversial, this multi-

cyclic approach predicts that global oil production is set to peak in four

years and that by the 2050s we will have pulled all but 10

percent of the world's oil from the ground.

[ water ]

1976–2005 >> glacier melt acceleratesGlaciers have been losing their mass at an accelerating rate in recent decades. in some regions such as Europe and the americas, glaciers now lose more than half a meter each year.


2030

1,500

1,000

500

0

total renewable Water per Capita Cubic meters per person per year

2008 2025

Ethiopia

Ukraine

india

netherlandsUzbekistan

hungary

oman

syrian arab republicPakistan

republic of Moldova

singaporeJordanisrael

saudi arabiaEgypt

permian–triassic extinctionDuration: 720,000 to 1.2 million yearsspecies lost: 80%–96%

Cretaceous–tertiary extinctionDuration: less than 10,000 yearsspecies lost: 75%

Current11,000 years ago to the present and beyondspecies lost: to be determined

?

rate of species loss (arrow angle):

8.0%–9.6% per millennium

rate of species loss:

15% per millennium

rate of species lossPrehuman:0.01%–0.1% per millennium

1900–2000:1%–10% per millennium

2000–2100 (projected):2%–20% per millennium

drYinG out

2008 2025


[ minerals ]

2028 >> indiumindium is a silvery metal that sits next to platinum on the periodic table and shares many of its properties such as its color and density. indium tin oxide is a thin-film conductor used in flat-panel televisions. at current pro-duction levels, known indium reserves contain an 18-year world supply.

[ minerals ]

2029 >> silverBecause silver naturally kills microbes, it is increasingly used in bandages and as coatings for consumer products. at current production levels, about 19 years’ worth of silver remains in the ground, but recycling should extend that supply by decades.

[ water ]

2025 >> battle over water

in many parts of the world, one major river supplies water to multiple countries. Climate

change, pollution and population growth are putting a significant strain on supplies. in some

areas renewable water reserves are in danger of dropping below the 500 cubic meters per person per year considered a minimum for a functioning society.

[ food ]

>> fewer fishFish are our last truly wild food, but the rise in demand for seafood has pushed many species to the brink of extinction. here are five of the most vulnerable.

hammerhead sharks have declined by 89 percent since 1986. the animals are sought for their fins, which are a delicacy in soup.

potentiAl hot SpotS

eGYpt: a coalition of countries led by Ethiopia is challenging old agreements that allow Egypt to use more than 50 percent of the nile’s flow. Without the river, all of Egypt would be desert.

eAStern europe: Decades of pollution have fouled the Danube, leaving down-stream countries, such as hungary and the republic of Moldova, scrambling to find new sources of water.

middle eASt: the Jordan river, racked by drought and diverted by israeli, syrian and Jordanian dams, has lost 95 percent of its former flow.

Former Soviet union: the aral sea, at one time the world’s fourth-largest inland sea, has lost 75 percent of its water because of agricultural diversion programs begun in the 1960s.

asia

north africa

Middle East

Europe

Jaso

n L

EE (fi

sh)

2030

1,500

1,000

500

0

total renewable Water per Capita Cubic meters per person per year

2008 2025

Ethiopia

Ukraine

india

netherlandsUzbekistan

hungary

oman

syrian arab republicPakistan

republic of Moldova

singaporeJordanisrael

saudi arabiaEgypt

permian–triassic extinctionDuration: 720,000 to 1.2 million yearsspecies lost: 80%–96%

Cretaceous–tertiary extinctionDuration: less than 10,000 yearsspecies lost: 75%

Current11,000 years ago to the present and beyondspecies lost: to be determined

?

rate of species loss (arrow angle):

8.0%–9.6% per millennium

rate of species loss:

15% per millennium

rate of species lossPrehuman:0.01%–0.1% per millennium

1900–2000:1%–10% per millennium

2000–2100 (projected):2%–20% per millennium

drYinG out

2008 2025

w w w.Sc ient i f i c American .com Sc ie ntif ic Americ An

[ biodiversity ]

>> our mass extinctionBiologists warn that we are living in the midst of a mass extinction on par with the other five great events in Earth’s history, including the Permian-triassic extinction (also known as the Great Dying; it

knocked out up to 96 percent of all life on Earth) and the Cretaceous-tertiary extinction that killed

the dinosaurs. the cause of our troubles? Us. human mastery over the planet has pushed

many species out of their native habitats; others have succumbed to hunting or

environmental pollutants. here we compare our current extinction with

its predecessors using the latest estimates of species loss per

year. if trends continue—and unfortunately, species loss is

accelerating—the world will soon be a far less

diverse place.

[ minerals ]

2030 >> goldthe global financial crisis has boosted demand for gold, which is seen by many as a tangible (and therefore lower-risk) investment. according to Julian Phillips, editor of the Gold Forecaster newsletter, probably about 20 years are left of gold that can be easily mined.

russian sturgeon have lost spawning grounds because of exploitation for caviar. numbers are down 90 percent since 1965.

Yellowmouth grouper may exist only in pockets of its former range, from Florida to Brazil.

european eel populations have declined by 80 percent since 1968; because the fish reproduces late in life, recovery could take 200 years.

orange roughY off the coast of new Zealand have declined by 80 percent since the 1970s because of overfishing by huge bottom trawlers.


2050

Developedcountries

Developingcountries

daily per Capita Calorie Availability

3,000

2,000

1,000

0

Food prices (U.s. dollars per metric ton)

rice Wheat Maize

argentina

australia

Brazil

China

india

Mexico

russia

U.s.

Pacific northwest

rockies and Plains

southeast

southwest Plains

2.2%

the effects of Global Warming on AgriculturePercent change in production for the world's eight largest growers (by the 2080s)

400

300

200

100

0

2000

2050 no climate change

2050 With climate change–15.6%

–4.4%

6.8%

–28.8%

–25.7%

6.2%

8%

26%

47%

–18%

–25%

2040


[ food ]

2050 >> feeding a warming worldresearchers have recently started to untangle the complex ways rising temperatures will affect global agriculture. they expect climate change to lead to longer growing seasons in some countries; in others the heat will increase the frequency of extreme weather events or the prevalence of pests. in the U.s., productivity is expected to rise in the Plains states but fall further in the already struggling southwest. russia and China will gain; india and Mexico will lose. in general, developing nations will take the biggest hits. By 2050 counteracting the ill effects of climate change on nutrition will cost more than $7 billion a year.

[ minerals ]

2044 >> copperCopper is in just about everything in infrastructure, from pipes to electrical equipment. Known reserves currently stand at 540 million metric tons, but recent geologic work in south america indicates there may be an additional 1.3 billion metric tons of copper hidden in the andes Mountains.

[ biodiversity ]

>> mortal threatsas the total number of species declines, some have fared worse than others [see “our Mass Extinction,” on preceding page]. here, at the right, are five life-forms, the estimated percentage of species thought to be endangered, and an example of the threats they face.

mammals 18 percent endangered

the Iberian lynx feeds on rabbits, a prey in short supply in the lynx’s habitat ever since a pediatrician introduced the disease myxomatosis from Australia to France in 1952 to kill the rabbits in his garden. Ja

son

LEE

(spe

cies

)

2050

Developedcountries

Developingcountries

daily per Capita Calorie Availability

3,000

2,000

1,000

0

Food prices (U.s. dollars per metric ton)

rice Wheat Maize

argentina

australia

Brazil

China

india

Mexico

russia

U.s.

Pacific northwest

rockies and Plains

southeast

southwest Plains

2.2%

the effects of Global Warming on AgriculturePercent change in production for the world's eight largest growers (by the 2080s)

400

300

200

100

0

2000

2050 no climate change

2050 With climate change–15.6%

–4.4%

6.8%

–28.8%

–25.7%

6.2%

8%

26%

47%

–18%

–25%

2040

Sc ie ntif ic Americ An

amphibians 30 percent endangered

Archey’s frog has been devastated by a fungal disease in its native new Zealand.

birds 10 percent endangered

the black-necked crane suffers from habitat loss in the wetlands of the tibetan plateau.

lizards 20 percent endangered

the blue spiny lizard must retreat from the sun before it overheats; higher temperatures have cut down on the time it can forage for food.

plants 8 percent endangered

the St. Helena redwood is native to the island in the South Atlantic where napoleon lived his last years. its excellent timber led to exploitation; by the 20th century only one remained in the wild.


2060 2070

1820 1920 2020

Annual production (u.K.)Millions of metric tons

300

200

100

0

Peakproduction

1820 1870 1920 2020

Cumulative production (u.K.)Billions of metric tons

30

20

10

0

90%

1984 1850

projected Cumulative productionBillions of metric tons

600

90%

2072

200

2150 2000

400

1900 1950 2050 2100

Wor

ld

u.S.

90% China90%


[ water ]

2060 >> changing the course of a riverClimate change will shift weather patterns, leading to big changes in the amount of rain that falls in any given region, as well as the amount of water flowing through streams and rivers. scientists at the U.s. Geological survey averaged the results of 12 climate models to predict how streamflow will alter over the next 50 years. While East africa, argentina and other regions benefit from more water, southern Europe and the western U.s. will suffer.

[ fossil fuels ]

2072 >> limits of coal Unlike oil, coal is widely thought to be virtually inexhaustible. not so, says David rutledge of the California institute of technology. Governments routinely overestimate their reserves by a factor of four or more on the assumption that hard-to-reach seams will one day open up to new technology. Mature coal mines show that this has not been the case. the U.K.—the birthplace of coal mining—

offers an example. Production grew through the 19th and early 20th centuries, then fell as supplies

were depleted. Cumulative production curves in the U.K. and other mature regions have

followed a predictable s shape. By extra-polating to the rest of the world’s coal

fields, rutledge concludes that the world will extract 90 percent of

available coal by 2072.

JEss

iCa

hU

PPi (

map

)

predicted streamflowPercent change in 2041–2060(compared with 1970–2000)

–40% 0 40%

2060 2070

1820 1920 2020

Annual production (u.K.)Millions of metric tons

300

200

100

0

Peakproduction

1820 1870 1920 2020

Cumulative production (u.K.)Billions of metric tons

30

20

10

0

90%

1984 1850

projected Cumulative productionBillions of metric tons

600

90%

2072

200

2150 2000

400

1900 1950 2050 2100

Wor

ld

u.S.

90% China90%

w w w.Sc ient i f i c American .com Sc ie ntif ic Americ An

[ water ]

2070 >> himalayan icesnow melt from the himalayas is a prime source of water for asia’s major river valleys, including the Yellow, Yangtze, Mekong and Ganges. By 2070 ice-covered landmass in the himalayas could decrease by 43 percent.

[ water ]

2100 >> the alpsParts of the alps are warming so quickly that the rhone Glacier is expected to have disappeared by the end of the century.

[ minerals ]

2560 >> lithiumBecause lithium is an essential component of the batteries in electric cars, many industry analysts have worried publicly that supplies won’t keep up with growing demand for the metal. still, known lithium reserves are big enough to keep us supplied for more than five centuries, even ignoring the vast supply of lithium in seawater.

WATER Global Glacier Changes: Facts and Figures. U.n. Envi ron-ment Program/World Glacier Monitoring service, 2008; aQUastat Database, U.n. Food and agriculture organization; “Global Pattern of trends in streamflow and Water availability in a Changing Climate,” by P.C.D. Milly et al., in Nature, Vol. 438; nov. 17, 2005. FOOD Climate Change: Impact on Agriculture and Costs of Adaptation, by Gerald C. nelson et al. international Food Policy research institute, Washington, D.C., 2009; Global Warming and Agriculture: Impact Estimates by Country, by William r. Cline. Center for Global Development, Washington, D.C., 2007. OIL “Forecasting World Crude oil Production Using Multicyclic hubbert Model,” by ibrahim sami nashawi et al., in Energy Fuels, Vol. 24, no. 3; March 18, 2010. COAL David rutledge, submission to International Journal of Coal

Geology, 2010. MINERALS Mineral Commodity Summaries 2010. U.s. Geological survey. BIODIVERSITY “Consequences of Changing Biodiversity,” by F. stuart Chapin iii et al., in Nature. Vol. 405; May 11, 2000; “Quantifying the Extent of north american Mammal Extinction relative to the Pre-anthropogenic Baseline,” by Marc a. Carrasco et al., in PLoS ONE. Vol. 4, no. 12; Dec. 16, 2009; “re-assessing Current Extinction rates,” by nigel E. stork, in Biodiversity Conservation, Vol. 19, no. 2; Feb. 2010; “the Future of Biodiversity,” by stuart L. Pimm et al., in Science, Vol. 269; July 21, 1995; “are We in the Midst of the sixth Mass Extinction? a View from the World of amphibians,” by David B. Wake and Vance t. Vredenburg, in Proceedings of the National Academy of Sciences USA, Vol. 105, supplement 1; aug. 12, 2008.

[ sources ]

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