Adapted from The Reef: A Passionate History, by Iain McCalman, by arrangement with Scientific American/Farrar, Straus and Giroux, LLC (US/CAN), Scribe Publications (UK), Penguin Books (AUS/NZ). Copyright © 2014 by Iain McCalman.

Sir david attenborough, the well-known naturalist, stands at the lectern of the royal Society in Carlton House Terrace in London, on July 6, 2009, about to bring the afternoon's speaker to the stage. A ripple of expectation passes through the audience, eagerly anticipating a lecture entitled “Is the Great Barrier Reef on Death Row?” Then Sir David introduces J.E.N. Veron, the then 64-year-old former chief scientist of the Australian Institute of Marine Science. “But,” says Sir David, smiling broadly, “I'll call him Charlie, a name he carries because he shares Mr. Darwin's obsession with the natural world.” Without specifically saying so, Sir David is telling us that we are about to hear from a modern-day Charles Darwin.

Many of the scientists in the room already know how apt this comparison is: there are uncanny resemblances and intellectual links between today's speaker and the Royal Society's greatest ever Fellow. All Charlie Veron's friends know, too, that he has made himself an internationally famous scientist without ever losing Darwin's fierce independence, unquenchable curiosity and passionate love of nature. Charlie, Sir David says, is one of the world's greatest scientific authorities on corals and coral reefs. He has discovered and described more than 20 percent of the known coral species—the tiny invertebrates that form skeletons of calcium carbonate and often join together into giant communities. And he has produced definitive catalogues of all the world's corals. But today—Sir David's voice takes on a somber note—Charlie comes with a different task: to show us how coral reefs are the keys that can unlock the truth about the bewildering changes we have unleashed in our climate. Perhaps he may answer the question that nags at us all: Do the reefs tell us that the future is worse than we realize?

When the applause subsides, Charlie walks to the lectern, a wiry, tanned figure wearing a red shirt and dark jacket. In his husky Australian voice, he thanks Sir David and begins to tell a spellbound audience why the Great Barrier Reef off the coast of Australia, the most massive in the world, and all the earth's reefs face a likely mass extinction within the life span of the youngest listeners present.

The lecture and Charlie's 2008 book that underpins it, A Reef in Time: The Great Barrier Reef from Beginning to End, mark a shift in theme and tone for a man who has written so joyfully about coral reefs. For 40 years Charlie has celebrated their astonishing multiplicity and complexity. Now the audience hears him focusing all his intellect and passion to prophesy a reef apocalypse. It is obvious how much he would like to avert what he predicts. To have any chance of this, though, Charlie must answer the skeptic's question: How do you know? And then its brutal follow-up: Why should we care?

Knowledge Born of Sorrow

The beginning of Charlie's answer stems from a nagging puzzle about the divergences between the same species of corals at different locations—a puzzle Charlie pursued for decades. His quest took him to hundreds of reefs in both hemispheres and across the vast Indian and Pacific oceans. He dived and collected in Japan, the Philippines, Indonesia, the Cocos (Keeling) Islands and then, further afield, in Zanzibar and at the remote Clipperton atoll in the eastern Pacific. Always he traveled by boat, always he worked with locals, and always he spent hours underwater, observing and memorizing. What he found was that over geologic spans of time, corals intermix to produce new variations, reconnections between former variations and even “fuzzy” hybrids.

As he researched the diversity and evolution of the world's corals, Charlie became aware of a grave, looming problem. His realization of the trouble had personal as well as intellectual roots. In the midst of his long, testing labors, a tragedy drove him to think intently about mortality. Just as Charles Darwin, struggling to finalize his theory of evolution, had been shaken by emotional loss and domestic strain, so it was with Charlie Veron. In April 1980 Charlie was working in Hong Kong when he received a phone call from his wife, Kirsty, to say with horror that one of their two daughters, 10-year-old Noni, had drowned while playing in a creek with a friend. Weighed down by sorrow, life for Charlie and his wife dragged, and although they remained supportive of each other, they eventually agreed to divorce.

Charlie's intense personal reminder of the contingencies and fragilities of life found echoes in his research, culminating in his powerful 1995 book Corals in Space and Time. The writing forced him to investigate the fate of the world's corals in the past and present. He studied analyses of previous reef extinctions and accrued more and more evidence of the effects of changing sea levels, temperature stresses, predation by crown-of-thorns starfish and human-influenced changes in nutrient levels. All this sharpened his long-gestating concern about the health of the Great Barrier Reef and other world reefs.

Ironically, the book offered Charlie a personal lift—the chance of a second romance, with Mary Stafford-Smith, the scientist who edited the book and who became his new partner. Charlie and Mary began discussing the idea of a glossy, coffee-table book about corals for a general audience, “to open the eyes of the world to what was emerging as an urgent need to conserve corals,” he tells the audience. It was the crystallization of a new joint mission “to win some hearts as well as minds.” Around 70 underwater photographers gave their work for free, and illustrator Geoff Kelly produced exquisite drawings and paintings. Charlie supplied most of the encyclopedic thumbnail analyses. In October 2000 the three-volume Corals of the World was launched to critical acclaim at the International Coral Reef Symposium in Bali, where its message of reef fragility and degradation added to a rising global alarm.

An instinctive conservationist, Charlie had been troubled way back in the 1970s by the extent of the damage caused by coral-eating crown-of-thorns starfish. He had become convinced that numbers of them were soaring because of overfishing of the starfish's natural predators and that survival of the millions of larvae expelled annually into the ocean currents was enhanced by the growing levels of chemical pollution. (Crown-of-thorns larvae thrive in polluted waters.) What provoked him to fury, though, was the way in which the vested interests of tourism developers and politicians, combined with the craven behavior of government bureaucracies, worked to deliberately discourage scientists from studying the problem. It was the onset of a process, ubiquitous today, whereby scientists were no longer free to pick their own questions or seek their own answers.

Mass Bleaching

Looking back, Charlie says he realized that like most of his generation, he had taken for granted that “the oceans [were] limitless and the marine world indestructible,” including the vast, relatively well managed region of the Great Barrier Reef Marine Park. The fact that the Central Indo-Pacific functioned as the prime disperser of coral biodiversity had always been worrying because of the region's lack of legal protection. Diver friends had long urged him to visit the spectacular reefs of eastern Indonesia, but by the time he got there in the early 1990s it was too late. Reefs that had run for thousands of kilometers were now masses of rubble.

Charlie had seen his first patch of coral bleaching off the Great Barrier Reef's Palm Island in the early 1980s, a tiny clump of white skeleton that he photographed as a curio. “And then I saw a whammy, a mass bleaching event … where everything turns white and dies. Sometimes it's only the fast-growing branching corals, but some of the others are horrible to see; corals that are four, five, six hundred years old—they die, too.”

The first recorded global mass bleaching occurred between 1981 and 1982. The next major spate of mass bleaching, between 1997 and 1998, hammered reefs in more than 50 countries, even among the hot-water corals of the Arabian Sea. On the Great Barrier Reef, the bleaching coincided with the warmest sea temperatures ever recorded. In an even worse mass-bleaching event in 2001–2002, the global damage also confirmed a close connection with El Niño weather cycles. Catastrophic global warming had arrived. Peculiarly susceptible to increases in heat and light, corals were now alerting scientists to climatic changes.

Charlie's research told him that during El Niño weather cycles, the surface seawaters in the Great Barrier Reef lagoon, already heated to unusually high levels by greenhouse gas–induced warming, were being pulsed from a mass of ocean water known as the Western Pacific Warm Pool onto the reef's delicate living corals. When corals are exposed to temperatures two or three degrees hotter than their evolved maximum (31 degrees Celsius for Great Barrier Reef species), along with increased levels of sunlight, it is lethal. The powerhouse algae that live in the corals' tissues, providing their color and food through photosynthesis, pump out oxygen at levels toxic to their polyp hosts. The corals must expel their symbiotic life supports or die. Row on row of stark white skeletons are the result.

These damaged corals are capable of regeneration if water temperatures return to normal and water quality remains good, but the frequency and intensity of bleaching outbreaks are now such that the percentage of reef loss from coral deaths will increase dramatically. Charlie predicts that the widening and deepening of the Western Pacific Warm Pool through climate change will mean that “every year will effectively become an El Niño year as far as the corals are concerned.”

Past Predicts the Future

Charlie's hope is that some as yet unknown strains of symbiotic algae, better able to cope with a heat-stressed world, might eventually form partnerships with corals. Or that the adaptive energies of fast-growing corals such as Acropora might somehow outpace the rate of bleaching. Or that pockets of corals lying in shadowed refuges on cool, deep reef slopes or in deep waters might survive to become agents of future renewal.

But heat is not the only problem corals face. Other destructive synergies may be impossible to stop. Reefs, Charlie points out, are nature's archives. They are complex data banks that record evidence of environmental changes from millions of years ago up to the present. Imprinted in fossil typography are the stories of the mass extinction events of the geologic past, including their likely causes. These archives tell us that four out of the five previous mass extinctions of coral reefs on our planet were linked to the carbon cycle. They were caused by changes to the ocean's chemistry brought about by absorption of two primary greenhouse gases, carbon dioxide and methane, through a process of acidification of ocean water.

Today's culprits are the same gases, although their increased presence is not the result of the meteor strikes or volcanoes that caused earlier catastrophes. We humans are doing that work, knowingly pumping these gases into the atmosphere at unprecedented rates. Already the oceans, the planet's usual absorber of these gases, have reached a third of their capacity to soak them up and balance them chemically. Stealthily, the oceans have begun the process that scientists call commitment, the unstoppable inevitability of acidification that presages destruction long before it is clearly visible. Eventually—possibly as early as 2050—we will have reached the point where coral skeletons become soluble in seawater. Carbonate rock, including reefs, will start dissolving, like “a giant antacid tablet,” as Charlie describes it.

Phytoplankton, the food of tiny krill, a key element in the food web of the southern oceans, will be equally affected by acidification. And who knows what terrible chain of ecological consequences will follow? The earth's sixth mass extinction event will have arrived.

So, Charlie Veron, a man who has lived and worked on the Great Barrier Reef for most of his life, finds himself in the agonizing position of having to be a prophet of its extinction. We cannot wonder that he feels “very very sad. It's real, day in, day out, and I work on this, day in, day out. It's like seeing a house on fire in slow motion…. There's a fire to end all fires, and you're watching it in slow motion, and you have been for years.”

I know of few more poignant sights than the closing moments of Charlie's speech in July 2009 in that hushed room of scientists and citizens. Tossing aside his notes, he apologizes to the audience in a strained, faltering voice for having delivered such a miserable talk. He urges his listeners to think about what they have heard.

“Use your influence,” he pleads. “For the future of the planet, help get this story recognized. It is not a fairy tale. It is reality.”