7 Billion

by National Geographic

  Ocean acidification adds yet another threat, one that may be less immediate but ultimately more devastating to hard, reef-building corals. It undermines their basic, ancient structure—the stony skeleton that’s secreted by millions upon millions of coral polyps over thousands of years.

  Coral polyps are tiny animals that form a thin layer of living tissue on the surface of a reef. They’re shaped a bit like flowers, with six or more tentacles that capture food and feed it to a central mouth. (Many corals actually get most of their food from algae that live and photosynthesize inside them; when corals bleach, it’s because stress has prompted the polyps to expel those dark symbionts.) Each polyp surrounds itself with a protective, cup-shaped exoskeleton of calcium carbonate that contributes to the collective skeleton of the whole colony.

  To make calcium carbonate, corals need two ingredients: calcium ions and carbonate ions. Acids react with carbonate ions, in effect tying them up. So as atmospheric CO2 levels rise, carbonate ions become scarcer in the water, and corals have to expend more energy to collect them. Under lab conditions coral skeleton growth has been shown to decline pretty much linearly as the carbonate concentration drops off.

  Slow growth may not matter much in the lab. Out in the ocean, though, reefs are constantly being picked at by other organisms, both large and small. (When I went snorkeling off One Tree Island, I could hear parrotfish chomping away at the reef.) “A reef is like a city,” said Ove Hoegh-Guldberg, who used to direct the One Tree Island Research Station and now heads the Global Change Institute at Australia’s University of Queensland. “You’ve got construction firms and you’ve got demolition firms. By restricting the building materials that go to the construction firms, you tip the balance toward destruction, which is going on all the time, even on a healthy reef. In the end you wind up with a city that destroys itself.”

  By comparing measurements made in the 1970s with those taken more recently, Caldeira’s team found that at one location on the northern tip of the reef, calcification had declined by 40 percent. (The team was at One Tree to repeat this study at the southern tip of the reef.) A different team using a different method has found that the growth of Porites corals, which form massive, boulderlike clumps, declined 14 percent on the Great Barrier Reef between 1990 and 2005.

  OCEAN ACIDIFICATION seems to affect corals’ ability to produce new colonies as well. Corals can, in effect, clone themselves, and an entire colony is likely to be made up of genetically identical polyps. But once a year, in summer, many species of coral also engage in “mass spawning,” a kind of synchronized group sex. Each polyp produces a beadlike pink sac that contains both eggs and sperm. On the night of the spawning all the polyps release their sacs into the water. So many sacs are bobbing around that the waves seem to be covered in a veil of mauve.

  Selina Ward, a researcher at the University of Queensland, has been studying coral reproduction on Heron Island, about ten miles west of One Tree, for the past 16 years. I met up with her just a few hours before the annual spawning event. She was keeping tabs on a dozen tanks of gravid corals, like an obstetrician making the rounds of a maternity ward. As soon as the corals released their pink sacs, she was planning to scoop them up and subject them to different levels of acidification. Her results so far suggest that lower pH leads to declines in fertilization, in larval development, and also in settlement—the stage at which the coral larvae drop out of the water column, attach themselves to something solid, and start producing new colonies. “And if any of those steps doesn’t work, you’re not going to get replacement corals coming into your system,” Ward said.

  The reefs that corals maintain are crucial to an incredible diversity of organisms. Somewhere between one and nine million marine species live on or around coral reefs. These include not just the fancifully colored fish and enormous turtles that people visit reefs to see, but also sea squirts and shrimps, anemones and clams, sea cucumbers and worms—the list goes on and on. The nooks and crevices on a reef provide homes for many species, which in turn provide resources for many others.

  Once a reef can no longer grow fast enough to keep up with erosion, this community will crumble. “Coral reefs will lose their ecological functionality,” Jack Silverman, a member of Caldeira’s team at One Tree, told me. “They won’t be able to maintain their framework. And if you don’t have a building, where are the tenants going to live?” That moment could come by 2050. Under the business-as-usual emissions scenario, CO2 concentrations in the atmosphere will be roughly double what they were in preindustrial times. Many experiments suggest that coral reefs will then start to disintegrate.

  “Under business as usual, by mid-century things are looking rather grim,” Caldeira said. He paused for a moment. “I mean, they’re looking grim already.”

  CORALS, OF COURSE, are just one kind of calcifier. There are thousands of others. Crustaceans like barnacles are calcifiers, and so are echinoderms like sea stars and sea urchins and mollusks like clams and oysters. Coralline algae—minute organisms that produce what looks like a coating of pink or lilac paint—are also calcifiers. Their calcium carbonate secretions help cement coral reefs together, but they’re also found elsewhere—on sea grass at Castello Aragonese, for instance. It was their absence from the grass near the volcanic vents that made it look so green.

  The seas are filled with one-celled calcifying plants called coccolithophores, whose seasonal blooms turn thousands of square miles of ocean a milky hue. Many species of planktonic foraminifera—also one-celled—are calcifiers; their dead shells drift down to the ocean floor in what’s been described as a never ending rain. Calcifiers are so plentiful they’ve changed the Earth’s geology. England’s White Cliffs of Dover, for example, are the remains of countless ancient calcifiers that piled up during the Cretaceous period.

  Acidification makes all calcifiers work harder, though some seem better able to cope. In experiments on 18 species belonging to different taxonomic groups, researchers at the Woods Hole Oceanographic Institution found that while a majority calcified less when CO2 was high, some calcified more. One species—blue mussels—showed no change, no matter how acidified the water.

  “Organisms make choices,” explained Ulf Riebesell, a biological oceanographer at the Leibniz Institute of Marine Sciences in Kiel, Germany. “They sense the change in their environment, and some of them have the ability to compensate. They just have to invest more energy into calcification. They choose, ‘OK, I’ll invest less in reproduction’ or ‘I’ll invest less in growth.’” What drives such choices, and whether they’re viable over the long term, is not known; most studies so far have been performed on creatures living for a brief time in tanks, without other species that might compete with them. “If I invest less in growth or in reproduction,” Riebesell went on, “does it mean that somebody else who does not have to make this choice, because they are not calcifying, will win out and take my spot?”

  Meanwhile, scientists are just beginning to explore the way that ocean acidification will affect more-complex organisms such as fish and marine mammals. Changes at the bottom of the marine food web—to shell-forming pteropods, say, or coccolithophores—will inevitably affect the animals higher up. But altering oceanic pH is also likely to have a direct impact on their physiology. Researchers in Australia have found, for example, that young clownfish—the real-life versions of Nemo—can’t find their way to suitable habitat when CO2 is elevated. Apparently the acidified water impairs their sense of smell.

  DURING THE LONG HISTORY of life on Earth, atmospheric carbon dioxide levels have often been higher than they are today. But only very rarely—if ever—have they risen as quickly as right now. For life in the oceans, it’s probably the rate of change that matters.

  To find a period analogous to the present, you have to go back at least 55 million years, to what’s known as the Paleocene-Eocene Thermal Maximum or PETM. During the PETM huge quantities of carbon were released into the atmosphere, from where, no one is quite sure.
Temperatures around the world soared by around ten degrees Fahrenheit, and marine chemistry changed dramatically. The ocean depths became so corrosive that in many places shells stopped piling up on the seafloor and simply dissolved. In sediment cores the period shows up as a layer of red clay sandwiched between two white layers of calcium carbonate. Many deepwater species of foraminifera went extinct.

  Surprisingly, though, most organisms that live near the sea surface seem to have come through the PETM just fine. Perhaps marine life is more resilient than the results from places like Castello Aragonese and One Tree Island seem to indicate. Or perhaps the PETM, while extreme, was not as extreme as what’s happening today.

  The sediment record doesn’t reveal how fast the PETM carbon release occurred. But modeling studies suggest it took place over thousands of years—slow enough for the chemical effects to spread through the entire ocean to its depths. Today’s rate of emissions seems to be roughly ten times as fast, and there’s not enough time for the water layers to mix. In the coming century acidification will be concentrated near the surface, where most marine calcifiers and all tropical corals reside. “What we’re doing now is quite geologically special,” says climate scientist Andy Ridgwell of the University of Bristol, who has modeled the PETM ocean.

  Just how special is up to us. It’s still possible to avert the most extreme acidification scenarios. But the only way to do this, or at least the only way anyone has come up with so far, is to dramatically reduce CO2 emissions. At the moment, corals and pteropods are lined up against a global economy built on cheap fossil fuels. It’s not a fair fight.

  Chapter 4: Bangladesh: The Coming Storm

  BY DON BELT

  Don Belt previously reported on the Indian subcontinent in September 2007 (Pakistan) and October 2008 (India). Jonas Bendiksen’s last feature was on the melting Himalayan glaciers (April 2010).

  WE MAY BE SEVEN MILLION SPECKS on the surface of Earth, but when you’re in Bangladesh, it sometimes feels as if half the human race were crammed into a space the size of Louisiana. Dhaka, its capital, is so crowded that every park and footpath has been colonized by the homeless. To stroll here in the mists of early morning is to navigate an obstacle course of makeshift beds and sleeping children. Later the city’s steamy roads and alleyways clog with the chaos of some 15 million people, most of them stuck in traffic. Amid this clatter and hubbub moves a small army of Bengali beggars, vegetable sellers, popcorn vendors, rickshaw drivers, and trinket salesmen, all surging through the city like particles in a flash flood. The countryside beyond is a vast watery flood-plain with intermittent stretches of land that are lush, green, flat as a parking lot—and wall-to-wall with human beings. In places you might expect to find solitude, there is none. There are no lonesome highways in Bangladesh.

  We should not be surprised. Bangladesh is, after all, one of the most densely populated nations on Earth. It has more people than geographically massive Russia. It is a place where one person, in a nation of 164 million, is mathematically incapable of being truly alone. That takes some getting used to.

  So imagine Bangladesh in the year 2050, when its population will likely have zoomed to 220 million, and a good chunk of its current landmass could be permanently underwater. That scenario is based on two converging projections: population growth that, despite a sharp decline in fertility, will continue to produce millions more Bangladeshis in the coming decades, and a possible multifoot rise in sea level by 2100 as a result of climate change. Such a scenario could mean that 10 to 30 million people along the southern coast would be displaced, forcing Bangladeshis to crowd even closer together or else flee the country as climate refugees—a group predicted to swell to some 250 million worldwide by the middle of the century, many from poor, low-lying countries.

  “Globally, we’re talking about the largest mass migration in human history,” says Maj. Gen. Muniruzzaman, a charismatic retired army officer who presides over the Bangladesh Institute of Peace and Security Studies in Dhaka.

  “By 2050 millions of displaced people will overwhelm not just our limited land and resources but our government, our institutions, and our borders.” Muniruzzaman cites a recent war game run by the National Defense University in Washington, D.C., which forecast the geopolitical chaos that such a mass migration of Bangladeshis might cause in South Asia. In that exercise millions of refugees fled to neighboring India, leading to disease, religious conflict, chronic shortages of food and fresh water, and heightened tensions between the nuclear-armed adversaries India and Pakistan.

  Such a catastrophe, even imaginary, fits right in with Bangladesh’s crisis-driven story line, which, since the country’s independence in 1971, has included war, famine, disease, killer cyclones, massive floods, military coups, political assassinations, and pitiable rates of poverty and deprivation—a list of woes that inspired some to label it an international basket case. Yet if despair is in order, plenty of people in Bangladesh didn’t read the script. In fact, many here are pitching another ending altogether, one in which the hardships of their past give rise to a powerful hope.

  For all its troubles, Bangladesh is a place where adapting to a changing climate actually seems possible, and where every low-tech adaptation imaginable is now being tried. Supported by governments of the industrialized countries—whose greenhouse emissions are largely responsible for the climate change that is causing seas to rise—and implemented by a long list of international nongovernmental organizations (NGOs), these innovations are gaining credence, thanks to the one commodity that Bangladesh has in profusion: human resilience. Before this century is over, the world, rather than pitying Bangladesh, may wind up learning from her example.

  Girl Power

  National efforts have raised primary school enrollment to 16.7 million students, with an emphasis on girls, who now outnumber boys in school.

  MORE THAN A THIRD OF THE WORLD’S PEOPLE live within 62 miles of a shoreline. Over the coming decades, as sea levels rise, climate change experts predict that many of the world’s largest cities, including Miami and New York, will be increasingly vulnerable to coastal flooding. A recent study of 136 port cities found that those with the largest threatened populations will be in developing countries, especially those in Asia. Worldwide, the two cities that will have the greatest proportional increase in people exposed to climate extremes by 2070 are both in Bangladesh: Dhaka and Chittagong, with Khulna close behind. Though some parts of the delta region may keep pace with rising sea levels, thanks to river sediment that builds up coastal land, other areas will likely be submerged.

  But Bangladeshis don’t have to wait decades for a preview of a future transformed by rising seas. From their vantage point on the Bay of Bengal, they are already facing what it’s like to live in an overpopulated and climate-changed world. They’ve watched sea levels rise, salinity infect their coastal aquifers, river flooding become more destructive, and cyclones batter their coast with increasing intensity—all changes associated with disruptions in the global climate.

  On May 25, 2009, the people of Munshiganj, a village of 35,000 on the southwest coast, got a glimpse of what to expect from a multifoot rise in sea level. That morning a cyclone, called Aila, was lurking offshore, and its 70-mile-an-hour winds sent a storm surge racing silently toward shore, where the villagers, unsuspecting, were busy tending their rice fields and repairing their nets.

  Urban Challenge

  Sanitation systems are faltering as Bangladeshis crowd into cities.

  Shortly after ten o’clock Nasir Uddin, a 40-year-old fisherman, noticed that the tidal river next to the village was rising “much faster than normal” toward high tide. He looked back just in time to see a wall of brown water start pouring over one of the six-foot earthen dikes that protect the village—its last line of defense against the sea.

  Within seconds water was surging through his house, sucking away the mud walls and everything else. His three young daughters jumped onto the kitchen table, screaming as cold salt w
ater swirled around their ankles, then up to their knees. “I was sure we were dead,” he told me months later, standing in shin-deep mud next to a pond full of stagnant green water the color of antifreeze. “But Allah had other plans.”

  As if by a miracle, an empty fishing boat swept past, and Uddin grabbed it and hoisted his daughters inside. A few minutes later the boat capsized, but the family managed to hang on as it was tossed by waves. The water finally subsided, leaving hundreds of people dead along the southwest coast and thousands homeless. Uddin and most of his neighbors in Munshiganj decided to hunker down and rebuild, but thousands of others set out to start a new life in inland cities such as Khulna and Dhaka.

  THOUSANDS OF PEOPLE ARRIVE in Dhaka each day, fleeing river flooding in the north and cyclones in the south. Many of them end up living in the densely populated slum of Korail. And with hundreds of thousands of such migrants already, Dhaka is in no shape to take in new residents. It’s already struggling to provide the most basic services and infrastructure.

  Yet precisely because Bangladesh has so many problems, it’s long served as a kind of laboratory for innovative solutions in the developing world. It has bounced back from crisis after crisis, proving itself far more resourceful than skeptics might have guessed. Dhaka is home to BRAC, the largest nonprofit in the developing world, held up as a model for how to provide basic health care and other services with an army of field-workers. Bangladesh also produced the global micro-finance movement started by Nobel Peace laureate Muhammad Yunus and his Grameen Bank.