invasive species that love a recession
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The New Math of Population From fertility rates to city size, could bigger be better for the environment?
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Contents Conservation | Vol. 10 No. 4 | October-December 2009
Be Fruitful & Multiply?
Population growth, from an environmental viewpoint, has always seemed like an open-and-shut case. Less is more. But what if that equation has changed? By David Malakoff page 41
Fish-free fish feed
A new generation of unruly adolescent wildlife has some experts wondering whether what we’re missing isn’t so much habitat as adult supervision.
Another black mark for biofuels
By Dawn Stover
Invasive species love a recession
Frog legs: yummy but deadly
Designing an artificial river
Up on the Farm Growing 11,000 heads of lettuce in a space the size of five parking spots
Shipwreck unleashes mysterious plague
Sick Puppies Prairie dogs served up Jell-O spiked with ‘black death’ vaccine
Carbon sinks under Antarctic ice
Electric Sweat Synthetic leaf generates power with tiny beads of water
An Ounce of Prevention High-tech chip delivers early diagnosis of coral disease
Invasion of the Flying Fish A wall of bubbles could stop the onslaught of millions of Asian carp
A Shady Scheme Radical plan would grow a massive forest in the Sahara to cool the planet
A radical alternative to marine reserves
Lighten Up Cartoons by Sidney Harris
Survivor By Eric Roston
Book Marks Shades of Green Stewart Brand’s challenge to environmentalists
New twist on cold war
Cities store more CO2 than tropical rainforests
The (Un)Natural Order of Things
Have we unwittingly exchanged the language of the living world—the names of real plants and animals—for a vocabulary of Tony the Tigers and Geico geckos? By Carol Kaesuk Yoon
Journal Watch ■
Plus: Elephants on the Edge, No Impact Man, Picturing Climate Change, and more
Bathtub Analogy Doesn’t Hold Water By William L. Chameides
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In 1695, a forward-thinking demographer predicted global population would hit 500 million by the year 2000. This sounds laughable at a time when population is closing in on nine billion. But you might be more sympathetic once you realize how complicated the population picture really is. This issue’s cover story (“Be Fruitful & Multiply?,” page 12) uncovers some reasons why population predictions have been so off-base. It also explores some surprises that cutting-edge thinkers have uncovered, such as the environmental perils of depopulation. Such warnings would have seemed ridiculous 40 years ago, when Paul Ehrlich’s book The Population Bomb spawned apocalyptic fears. Ehrlich declared population growth would outpace agricultural production and usher in mass starvation. While his core concern—that population would strain resources—was on the mark, Ehrlich couldn’t foresee quantum leaps in agricultural productivity or fertility rates that would decline as countries grew more developed. In other words, unraveling the population equation is far more complicated than Ehrlich and others suspected. That’s because the variables in the population-environment equation—from consumption habits to technological innovation—form an extraordinarily convoluted web. For example, new research suggests that fertility rates keep fluctuating as countries progress; after years of precipitous decline, fertility rates in some highly developed countries are rising again. Some scholars argue that this might be good for the environment. Fearing that a smaller human population might set off a chain of events leading to environmental catastrophe, they say we should aim for the magic number of 2.1 children per woman, which would keep the overall population total steady. As we read through these twists and turns, we notice some eerie similarities between Ehrlich’s 1960s warnings and today’s climate fears. The concerns about climate change and the catastrophes it could bring are valid, and the predictions are alarming. But in a system as complex as global climate, you also have to wonder which elements of the equation will completely surprise us. One lesson is that, even as the scientific and environmental communities sound the alarm, it’s important to train a skeptical eye on our assumptions. As Jim Harrison wrote in the novel True North: “Every day I wake up and wonder how many things I’m dead wrong about.” —The Editors
Your guide to the latest conservation research
©Thomas Jackson/Getty Images
Urban Chill Factor Cities store more CO2 than tropical rainforests do
more organic carbon is stored in cities and suburbs than anywhere else—even tropical forests. This startling result comes from the first complete carbon-storage tally of human-dominated ecosystems in the contiguous United States. The researchers added up the amount of carbon tucked away in everything from houses to household pets. They found that in 2000, cities, suburbs, and ex-
Acre for acre,
urbs accounted for 10 percent of total land-based carbon storage. Generally, nearly two-thirds of that carbon is kept under wraps in urban soils, its decay slowed beneath pavement and buildings. Vegetation accounts for another fifth of the stored carbon; slow-to-rot garbage trapped in landfills, a tenth; and wood in building struc-
tures, five percent. People themselves, it turns out, don’t lock up much carbon. Neither do their pets. Cities had a denser carbon profile in comparison to sprawling suburbs and exurbs. “Because of the population density (in cities), you have multiple layers of carbon,” explains lead author Galina Churkina, a scientist at the Leibniz-Centre for Agricultural Landscape Research. Churkina says that, to slow climate change, we need to stop taking urban carbon for granted, espe-
• Vol. 10 No. 4 | October-December 2009 3
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cially since the character of cities is never static. Instead of being seen solely as an environmental blight, cities and towns could be seen as mechanisms to protect or increase carbon stocks. Building homes and furniture that use more wood products could help, as could strategically planted trees and gardens. But storing up carbon isn’t always as simple as it sounds. For example, Los Angeles and New York are already pursuing ambitious tree-planting goals, partly with carbon storage in mind. Churkina cautions that, without taking maintenance needs such as fertilizer and water into account, even planting a tree could backfire and increase net carbon emissions. ❧ —Jessica Leber Churkina, G., D. Brown, and G. Keoleian. 2009. Carbon stored in human settlements: the conterminous United States. Global Change Biology DOI:10.111/j.12652486.2009.02002.x
In the Cold of Battle Wars in Europe are linked to cooler periods
Peace Prize to U.S. President Barack Obama, the Nobel committee noted his efforts to meet the challenge of climate change. Climate change could trigger mass migrations and higher competition for resources, leading to “increased danger of violent conflicts and wars,” the committee wrote. But two scientists argue in Climatic Change that the link between climate change and war has not been adequately quantified.
In awarding the 2009 Nobel
Evolution of war conflicts, temperature, and precipitation in central Europe —Conflicts —Precipitation —Temperature
2 1 0 -1 -2 1500 1550 1600
The team analyzed historical records of violent conflicts in Europe over the past thousand years, as well as temperature and precipitation data and climate reconstructions. They found that pre-industrial wars were actually correlated with colder periods, echoing a 2006 study that revealed a similar pattern in China. Those early conflicts might have been fueled by poor harvests, the authors speculate. As Europe became industrialized and agricul-
tural techniques improved, the link between temperature and war weakened considerably. Global warming is therefore unlikely to increase violent conflicts in Europe, the team says, but the pattern could be different in the tropics. “It does not follow that a warmer future would be more peaceful,” they write. ❧ —Roberta Kwok Tol, R. and S. Wagner. 2009. Climate change and violent conflict in Europe over the last millennium. Climatic Change DOI:10.1007/s10584-009-9659-2.
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Photo courtesy of Louise Zattelman
It’s a Fish-eatfish World Fish-feed substitutes can keep aquaculture from depleting oceans The aquaculture industry is mired in a
dilemma. On the one hand, 2009 was a landmark year—for the first time, aquaculture provided a whopping 50 percent of global seafood supplies, up from just 25 percent in 1995. And that trend is bound to continue. With wild catch stagnant or declining, aquaculture will play a key role in meeting the seafood demands of a world population that’s zooming toward 8 billion. But a troubling reality looms: the aquaculture industry’s expanding hunger for wild fish, which it uses as feed, threatens the wild populations on which aquaculture depends. Rosamond Naylor, a Stanford University economist, was looking for 6
a way out of this dilemma when she recently convened an international team of scientists and policy experts. Naylor has spent much of her career studying aquaculture and other types of food production and wanted to forge a consensus on exactly how the industry should move toward sustainability. Now, in a paper in Proceedings of the National Academy of Sciences, Naylor and her colleagues map out not only how far the industry has come but also how much farther it must go. First, the good news: since 1995, the proportion of wild fish that goes into each pound of farm-raised fish and shrimp has dropped dramatically. The bad news? Aquaculture production is rising so fast that the industry is still consuming more and more wild fish overall. With this in mind, the research team evaluated various plans for moving away from wild fish as a feed source.
• Vol. 10 No. 4 | October-December 2009
One key question is how to ensure that farmed fish get adequate protein and fat in their diets. Wild omnivorous fish such as salmon and tuna get these nutrients from the fish they eat—usually anchovies, sardines, and mackerel. Most of the global catch of these smaller species is ground into fish meal (for protein) and fish oil (for fats) and is incorporated into feed pellets—not only for fish but also for pigs, chickens, and pets. And aquaculture’s share of these commodities has doubled over the past decade; the industry now consumes fully 68 percent of the world’s fish meal and 88 percent of its fish oil. Naylor’s team concluded that the most-pressing issue is finding alternatives to fish oil. Not just any oil substitute will do, since it is specifically the long-chain omega-3 fatty acids such as DHA that make fish such a boon for good health. Easy-to-come-by substi-
Naylor, R. et al. 2009. Feeding aquaculture in an era of finite resources. Proceedings of the National Academy of Sciences 106(36):15103–15110. (1) Naylor, R. et al. 2000. Effect of aquaculture on world fish supplies. Nature 405:1017–1024.
wouldn’t be enough to reach the EPA’s goal of reducing the hypoxic zone to 5,000 square kilometers by 2015, the team concluded. To meet that target, the U.S. will need to undertake an “aggressive nutrient management strategy,” they say. Possible solutions could include constructing wetlands or building buffer zones to intercept runoff. ❧ —Roberta Kwok Costello, C. et al. 2009. Impact of biofuel crop production on the formation of hypoxia in the Gulf of Mexico. Environmental Science & Technology DOI:10.1021/es9011433.
More Biofuel Woes Fuel crops stymie restoration of gulf dead zone Meeting U.S. goals for biofuel production will increase nutrient runoff to the Gulf of Mexico, making it more difficult to reduce the size of the gulf ’s “dead zone.” U.S. energy policy dictates that 36 billion gallons of renewable fuel must be produced annually by 2022. But a task force led by the Environmental Protection Agency is also aiming to shrink the Gulf of Mexico’s hypoxic zone, a lowoxygen area that can reach 14,600 square kilometers. Excess nitrate from agricultural runoff is thought to play a large role in hypoxic zone formation, which continuously kills and disrupts marine life. In a study published in Environmental Science & Technology, researchers calculated the nitrate output of various crop combinations that could be used to meet the U.S. biofuels mandate. Relying on crops such as switch grass, rather than corn, for cellulosic ethanol would cut nitrate output by 20 percent, they found. But that still
© Morten Kjerulff/iStock.com
Freeloaders in Hard Times Global recession linked to spike in marine invasives As if job losses, foreclosures, and the credit crunch weren’t enough to worry about, researchers have raised yet another possible downside of the economic crisis. Merchant ships are sitting idle at ports, potentially accumulating marine organisms that could be carried to other parts of the world when business picks up. For years, ships that transport organisms on their hulls have likely helped nonnative marine species invade new habitat around the globe, resulting in damage to both ecosystems
• Vol. 10 No. 4 | October-December 2009 7
tutes such as canola oil provide calories but not the DHA. Industrial fermentation processes for extracting the so-called healthy oils out of microalgae deliver some hope. They’re already being used to provide DHA supplements in juice and infant formula, and preliminary results for using the ingredients in salmon feed look promising. Australian scientists have also coaxed genetically modified canola to produce long-chain omega3s. But both oil alternatives are still prohibitively expensive. “There’s not a silver bullet out there,” Naylor says. A quick fix would be to eliminate fish meal in the diets of vegetarian fish such as carp and tilapia. According to the PNAS report, farmers have already reduced the share of fish meal in carp diets by 50 percent between 1995 and 2007; during that same period, the fish meal in tilapia diets dropped by nearly two-thirds. Yet tilapia and carp farmers fed their combined stock more than 12 million metric tons of fish meal—more than 1.5 times the amount consumed by all farmed shrimp and salmon. Naylor’s team calls on policymakers to create incentives to encourage feed alternatives and improve management of the underlying fisheries. Without a concerted effort, though, the study’s take-home message is no different from the last line of a cautionary report Naylor published nine years ago in Nature: “An expanded aquaculture industry poses a threat, not only to ocean fisheries, but also to itself.” (1) ❧ —Sarah Simpson
and economies. Coating the hulls can prevent “biofouling,” but many of these treatments lose their effectiveness on inactive ships. For instance, a 200-meter ship could amass more than 20 metric tons of organisms if left unused for a long period of time, the authors write. Since the financial crisis hit, cargo throughput has dropped at several major ports, the researchers say. Singapore, Hong Kong, Busan, Long Beach, and Hamburg have seen declines of 13.7 to 27.1 percent between 2008 and 2009, according to data from port companies. Idle ships are lingering around Malaysia, Indonesia, and the Philippines, and anchor times longer than three months have been reported, the team writes in Marine Pollution Bulletin. Grounded ships may not be cleaned properly before departure because of the expense and long waits for maintenance, the authors say. That could result in an unusually high number of nonnative marine organisms arriving at destination ports when the economy recovers. ❧ —Roberta Kwok Floerl, O. and A. Coutts. 2009. Potential ramifications of the global economic crisis on human-mediated dispersal of marine nonindigenous species. Marine Pollution Bulletin DOI:10.1016/j.marpolbul.2009.08.
President Obama eating frog legs. ©Saul Loeb/AFP/Getty Images
Last Legs The not-so-healthy appetite for frog legs Overharvesting has long been considered a contributor to frog declines, but no one had ever quantified the harvest. Now, researchers have used 20 years of United Nations statistics to find that roughly 8,000 to 10,000 metric tons of frogs’ legs are traded internationally each year. Add in estimates of those eaten in the countries where they’re caught, and the research team thinks as many as 1 billion wild frogs are harvested annually, a great many of them in Indonesia and Vietnam. Overall, the biggest frog importers are France, the U.S. (where they’re a Cajun specialty), Belgium, and Luxembourg. Such importing nations started out with local, seasonal harvests of native species; when those declined, they began importing. In the 1970s and 1980s, India, Bangladesh, and Pakistan were the biggest suppliers. As frog populations there dropped, Indonesia and other Asian nations stepped in. Now Ecuador and Brazil appear to be developing export markets, too. Led by Ian Warkentin of Canada’s Memorial University, the research team fears a disheartening
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parallel to the fishing industry, notorious for depleting one stock and then moving on to tap out another. Still, a lack of data on what species are in trade or exactly where they come from prevents the researchers from being certain any given frog harvest is unsustainable. (One problem: frogs are usually skinned before shipping, which confounds identification.) As important first steps, the scientists recommend gathering better population data and tracking and certifying frog legs that enter the global market. ❧ —Rebecca Kessler Warkentin, I.G. et al. 2009. Eating frogs to extinction. Conservation Biology 23(4): 1056–1059.
Do the Twist Researchers build an artificial river to hone restoration technology
how to make a river meander in the lab, according to a report in Proceedings of the National Academy of Sciences. The research could help determine the best strategies for stream restoration. The team carved an artificial streambed with one bend into a 17-meter-long basin filled with sand. They planted alfalfa sprouts on the sides to strengthen the banks, then ran water through the channel for 136 hours. By the end, the river had developed five bends and appeared to function like a naturally meandering stream. One key element was the use of sand to plug small channels along the sides of the river, the authors say. This goes against a common practice in stream-restoration projects, which Scientists have figured out
photo courtesy of Thierry Work USGS
often aim to eliminate fine sediment. Maintaining stream-bank strength with vegetation was also critical. Now that scientists have a working lab version of a meandering river, they can test different stream restoration techniques and build computational models of the process, says lead author Christian Braudrick of the University of California, Berkeley. Researchers could then use the models to predict how streams will change over the course of decades, rather than over just a few years. ❧ —Roberta Kwok Braudrick, C. 2009. Experimental evidence for the conditions necessary to sustain meandering in coarse-bedded rivers. Proceedings of the National Academy of Sciences 106:16936-16941.
Wrecking a Reef Abandoned ship triggers hostile ecosystem takeover Around 1991, the long-line fishing vessel Hui Feng No. 1 mysteriously foundered on Palmyra Atoll, a group of Pacific islets fringed with spectacularly lush coral reefs. While little is known about the crash itself—the wreck was never reported to authorities and appears to have been simply abandoned— scientists are piecing together a picture of how its aftermath threatens to decimate the atoll’s pristine reefs.In 2004, a marine biologist exploring the
wreck noticed a few unexpected residents in the area. They were Rhodactis howesii, coral-like organisms that, by growing in monocultures, occasionally cover sections of a reef, blotting out the other marine life. A year later, more of the organisms appeared, and by September 2007, R. howesii had spread over roughly one square kilometer of reef surrounding the ship—the biggest corallimorph invasion on record. Scientists are nearly certain that the wreck and the invader are linked— the invasion radiates from the ship, with the number of R. howesii decreasing with distance—but they are still trying to piece together exactly how. Thierry Work, a wildlife disease specialist monitoring the wreck, and his colleagues suspect a few R. howesii were living humbly on Palmyra well
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Photo courtesy of Rear Admiral Harley D. Nygren, NOAA Corps
before the long-liner came crashing in. Iron leaching from the wreck might have sparked the corallimorph bloom. Now Work fears the invasion may be self-perpetuating. Corallimorphs can reproduce asexually; every storm washing through the reef fragments the organisms, creating new ones that continue the spread. Work hopes money can be found to remove the iron-spewing wreck, but after that not much can be done to stem the corallimorph takeover. Meanwhile, the wreck of the Hui Feng No. 1 serves as a warning that abandoned ships and other man-made debris may pose a greater danger to reefs than previously suspected and should be removed as soon as possible. ❧ —Rebecca Kessler Work, T.M., G.S. Aeby, and J.E. Maragos 2008. Phase shift from a coral to a corallimorph-dominated reef associated with a shipwreck on Palmyra Atoll. PLoS ONE 3(8):e2989.
Southern Exposure Retreat of Antarctic ice uncovers new carbon sinks
and glaciers in parts of Antarctica has exposed thousands of square kilometers of water, opening up new habitat for plant and animal communities that could act as carbon sinks, according to a paper in Global Change Biology. Many climate-change studies have focused on “positive” feedback loops: the worse things are, the worse they’ll get. For instance, the melting of sea ice due to global warming will cause the Earth to reflect less light, heating up the planet even more. Climate change is also predicted
The loss of ice shelves
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to reduce forest area, leaving fewer trees to remove carbon dioxide from the atmosphere. The new paper views climate change through a different lens: the authors studied how sea-ice loss might actually counteract global warming. Using historical data, photographs, and satellite images, they calculated that the Antarctic Peninsula had lost 23,900 square kilometers of sea ice and coastal glacier cover during the past half-century. The exposure of underlying waters has enabled the formation of phytoplankton, zooplankton, and seabed animal communities— which could contain 910,000 metric tons of carbon, the team estimates. Those plants and animals hold about as much carbon as 6,000 to 17,000 hectares of tropical rainforest, the authors say. As Antarctic ice continues to retreat over thousands
of years, they predict, new marine life could fix more than 50 metric megatons of carbon per year. ❧ —Roberta Kwok Peck, L.S. et al. 2009. Negative feedback in the cold: ice retreat produces new carbon sinks in Antarctica. Global Change Biology. DOI:10.1111/j.1365-2486.2009.02071.x
Fish Here Researchers propose radical alternative to marine reserves
effective in bolstering fish populations, but implementing them is often difficult. Despite dire warnings about fisheries nearing collapse, less than one percent of the world’s oceans are currently protected. In a recent paper in PLoS ONE, two Canadian researchers offer a bold new approach to achieving the goals of fisheries sustainability and marine species conservation. Natalie Ban and Amanda Vincent, of the University of British Columbia, say it’s time to turn conventional wisdom on its head: rather than debate which ocean areas should be protected, managers should focus on which areas should be open to fishing. Ban and Vincent’s conceptual approach begins by imagining a maximally protected ocean with no commercial fishing. A modeling tool is
Marine reserves have proven
then used to sequentially “open” highly productive fishing regions until a desired level of catch is reached. The goal of the exercise is to achieve potential harvests close to those of today while minimizing the total area fished. Ban and Vincent explore the new approach using spatial catch data for 13 commercial fisheries in British Columbia. Results show that 95 to 98 percent of current catch levels could be achieved by opening just 70 to 80 percent of the areas currently fished, leaving roughly one-quarter of British Columbia’s marine habitat protected from commercial harvest. Although not chosen for their ecological value, the protected zones—under a five-percent catch-reduction scenario—would include significant percentages of all major marine-habitat types. The authors acknowledge that their approach is highly data-dependent and needs further refinement. Nevertheless, they say it offers several advantages over today’s methods for identifying and establishing large-scale reserves. The process could achieve yield reductions in each individual fishery, leaving none disproportionately affected by closures. Debates could shift away from the costs and benefits of each proposed reserve area to the broader question of to what extent catches should be reduced in order to meet sustainability and conservation goals. And for any targeted harvest level, the model offers multiple alternatives for open and closed zones which could then be negotiated among fishers, managers, and conservation organizations. ❧ —Scott Norris
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Ban N.C. and A.C.J. Vincent. 2009. Beyond marine reserves: exploring the approach of selecting areas where fishing is permitted, rather than prohibited. PLoS ONE DOI:10.1371/journal.pone.0006258.
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in a suburban parking lot wedged between a busy supermarket and a sit-down restaurant. It was October 1969 in Hayward, California. About 100 young activists—dubbed “anti-population protesters” by reporters—were staging a “starvein” to dramatize the perils of overpopulation. Just the year before, Stanford University ecologist Paul Ehrlich and his wife Anne had published The Population Bomb, a bestseller warning that the planet faced too many people consuming too much. Now, one of Ehrlich’s former students, a creative type named Stewart Brand, was organizing the faux-famine to carry his mentor’s message to the streets. “Are you ready to die?” asked a sign posted by the activists, who pledged to fast for a week in a makeshift enclosure christened “Lifeboat Earth.” Fast-forward 40 years and Brand—who went on to create the influential Whole Earth Catalog and to pioneer online communities—has made something People were starving to death
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Population growth, from an environmental viewpoint, has always seemed like an openand-shut case. Less is more. But what if that equation has changed?
By David Malakoff Illustration by Istvan Banyai
of an about-face. Now, he’s worried that Lifeboat Earth could ultimately end up with too few people to stay afloat. About half of the planet’s people now produce too few children to replace themselves. Russia alone has lost nearly five percent of its population since 1993, with no end in sight. In a provocative new book*, Brand warns that this sort of plummeting birthrate could be “terrible news for the environment,” since the trend could sow social and economic chaos. And he’s not the only one worried. For decades, the leaders of baby-poor nations have struggled to reverse the decline—with little success. Some new—and controversial—research, however, could ease fears of a pending population implosion. In August, demographers revealed that birth rates in the wealthiest nations are rising again, reversing declines once deemed irreversible. One scholar said the surprising news opened an exciting “new chapter” in the planet’s population story. And The Economist gushed that the baby boomlet could herald “the environmentalist’s nirvana of uncoerced zero population growth.” Wait a second, you say? Fewer babies bad for the planet? More people create a green nirvana? It’s enough to make a population bomber’s head spin. 7
Best Guesses: A Sampling of Forecasts for World Population in 2000 In 1695, one demographer predicted global population would reach about 500 million by the year 2000. Although forecasts have gotten more accurate over time, predicting population remains tricky due to complicated variables ranging from consumption rates to technological innovation.
Well before Brand and his crowd were smoking
dope and starving in a suburban parking lot, a quieter and more-academic revolution was taking place among demographers. After World War II, the nascent United Nations asked a Princeton University demographer named Frank Notestein to launch a
3.3 3 2.5 1.96
1 0.5 0
*Whole Earth Discipline by Stewart Brand (2009). See page 43 for an excerpt.
Actual World Population in 2000: 6.1 Billion
The seeming contradictions, however, reflect some shifting and increasingly nuanced views of population growth that have emerged over the past 40 years. Some scholars are challenging conventional notions about the environmental impact of more people and embracing some seemingly counterintuitive solutions, such as bigger cities. Others say that fixating on forecasts of total global population—now projected to be 7.8 billion to 10.8 billion by 2050—is a bad idea. “Sheer numbers do not tell the whole story,” argue demographers George Martine and José Miguel Guzman. “A world population of 7.8 billion could actually inflict greater damage on the global environment than one with 10.8 billion.” Such ideas are bound to “make some environmentalists uncomfortable,” Stewart Brand says. But he believes “the core environmentalist panic about overpopulation is quietly being undermined, but the news hasn’t gotten around.”
1695 1924 1928 1936 1945 1957 1963 1965 1966 1968 1973 1974 1977 1978 1979 1979 1980 1980 1980 Source: Caselli G., J. Vallin, and G. Wunsch (eds.). 2006. Demography: Analysis and Synthesis, volumes 1–4: A Treatise in Population. Academic Press, Burlington, Massachusetts.
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Head Count If it were a reality show, they might call it “The Ultimate Head Count.” But while forecasting global population might never make for compelling cable, the problem has fascinated scholars for more than 300 years. And it seems they’re getting better at calculating credible numbers. Even before Thomas Malthus warned in 1798 that humankind faced “gigantic inevitable famine,” an English civil servant named Gregory King had already made the earliest-known prediction. In 1695, he tallied births and deaths and figured that there would be 780 million people on Earth in 2050—a mere 7 to 10 billion below current estimates. Since then, demographers have learned there is more to forecasting population than just life and death. They also must take into account wealth, urbanization, education levels, access to birth control, and even natural disasters and war. How has this more-sophisticated calculus fared? Much better, concludes a four-volume 2005 tome titled Demography: Analysis and Synthesis. (1) It looks back at 20 efforts, dating from 1924 to 1980, to project Earth’s population in the year 2000—which turned out to be about 6.1 billion. In general, the earliest estimates were too low by half, while a few from the late 1960s were a bit too high—“perhaps due to apocalyptical talk of the time on the population explosion.” By the 1990s, however, the most-widely used projections produced by the United Nations were off by less than one percent, concludes a 2001 study in Demographic Research. Now, demographers are focused on 2050. Their best guess for world population then is 9.1 billion—but it will be another 41 years before we know whether their numbers are right. ❧
1. Caselli G., J. Vallin, and G. Wunsch (eds.). 2006. Demography: Analysis and Synthesis, volumes 1–4: A Treatise in Population. Academic Press, Burlington, Massachusetts.
©Peter Mason/Getty Images
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broad study of population trends. As Notestein crunched the numbers, he noticed something that had also intrigued a few researchers before him: As people got richer and more urbanized, they tended to have fewer babies. Indeed, at some point, richer people stopped having enough babies to replace Total Fertility themselves, leading to Rate shrinking populations. t In a 1945 treatise, n 1975 8 Notestein dubbed this s 2005 6 phenomenon “the demographic transition”—and ever since, it has shaped 4 how we think about 3 population growth. The concept, for instance, has 2 forced modern demographers to pare back some 1.5 of the highest estimates of 1.2 peak populations (which have ranged up to 15 bil0.3 0.6 0.8 0.9 0.95 lion) because economic Human development index growth has outpaced expectations, putting downward pressure on Back on the Upside Conventional wisdom reproduction. holds that, as countries “I wish I had realized that the professional grow more developed, demographers were really rolling their eyes at all fertility rates decline. However, new research of our frantic heaving around,” Brand says now. indicates that fertility “They were essentially right about the impact rates in some highly of the demographic transition.” developed countries Today some 60 nations, accounting for are rising again. (1) about half of the world’s population, have “transitioned” and no longer produce enough children to stave off population declines without immigration. In some countries, birthrates have dropped to just 1.2 children per woman—far below the “magic number” of 2.1 needed to keep a population stable. Most are wealthier nations such as Italy (1.2), the United States (about 2.0) and Russia (1.1). But some aren’t, such as heavily Catholic Mexico (2.0) and Brazil (1.3); even China’s birthrate has dropped to about 1.7. In the nations with the lowest birthrates, population declines could be shockingly rapid. Brazil’s birthrate of 1.3, for instance, could ultimately mean its population will be cut in half in just 45 years—and then in half again within the next 45 years.
• Vol. 10 No. 4 | October-December 2009
This may seem like cause for environmental celebration, but not everyone is letting their guard down—at least not yet. Shrinking populations can mean there aren’t enough young workers to sustain a vibrant economy or pay for social welfare programs that support the poor and the elderly and help tamp down political instability. Low birthrates “could mean perpetual economic crisis, which would be terrible news for the environment,” Brand notes. “In an economic crisis, there is neither money nor attention for responsible stewardship. There is no long-term thinking or action. Wars become more likely, and wars are deadly for the environment.” To avoid that scenario, many barren nations are experimenting with “pro-baby” policies. France, for instance, provides free daycare and cash bonuses to willing parents. And Australia launched a “three-child” campaign: “One for mum, one for dad, and one for the country.” So far, however, they haven’t made much of a dent in the overall trend. Most pro-birth policies have failed to push fertility rates above 2.1. And as a startling new paper in Nature suggests, those political leaders (and Australian ad-copy writers) may be up against far larger forces than they ever imagined. (1) Indeed, those forces may throw yet another unexpected curve into the human population trajectory. In August of this year, the Nature study revealed that in 18 of the wealthiest nations— including the United States, Germany, and France—birthrates appear to have mysteriously started climbing again after decades of decline. (1) The unexpected reversal provides a different outlook for the twenty-first century, conclude the authors, led by demographer Mikko Myrskylä of the University of Pennsylvania. Myrskylä’s team looked at how two factors influencing population changed in more than 100 nations between 1975 and 2005. One was “total fertility”—the number of children a woman living in a particular nation was expected to have. The other was a human development index (HDI) score developed by the United Nations. The HDI combines per capita GDP, education, and life expectancy to measure how
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Published on Jun 17, 2010