With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change (11 page)

He has covered the 2.5-acre plot with more than 5,000 transparent plastic panels, which let in the sunlight but divert the rain into wooden gutters that drain to canals and a moat. Meanwhile, high above the forest canopy, he has erected gantries linked by catwalks, so that he can study the trees in detail as the artificial drought progresses. The work was all done by hand to avoid damaging the dense forest, and the scientists soon found they were not alone. The canals became "congregating places for every kind of snake you can imagine," says Nepstad. Caimans and jaguars cruised by, just, it seemed, to find out what was going on.

The results were worth the effort. The forest, it turns out, can handle two years of drought without great trouble. The trees extend their roots deeper to find water and slow their metabolism to conserve water. But after that, the trees start dying. Beginning with the tallest, they come crashing down, releasing carbon to the air as they rot, and exposing the forest floor to the drying sun. By the third year, the plot was storing only about 2 tons of carbon, whereas a neighboring control plot, on which rain continued to fall, held close to 8 tons. The "lock was broken" on a corner of one of the planet's great carbon stores. The study shows that the Amazon is "headed in a terrible direction," wrote the ecologist Deborah Clark, of the University of Missouri, discussing the findings in Science. "Given that droughts in the Amazon are projected to increase in several climate models, the implications for these rich ecosystems are grim."

Everywhere in the jungle, drought is followed by fire. So, in early 2005, Nepstad started an even more audacious experiment. He set fire to another stretch of forest with kerosene torches. "We want to know if recurring fire may threaten the very existence of the forest," he says. The initial findings were not good: the fires crept low along the forest floor, and no huge flames burst through the canopy. The fire may even have been invisible to the satellites that keep a constant watch overhead. But many trees died nonetheless, as their bark scorched and the flow of sap from their roots was stanched.

Nepstad's experiments are part of a huge international effort to monitor the health of the Amazon, called the Large-scale BiosphereAtmosphere Experiment in Amazonia. From planes and satellites and gantries above the jungle, researchers from a dozen countries have been sniffing the forest's breath and assessing its survival strategies. The current estimate is that fires in the forest are releasing some 200 million tons of carbon a year-far more than is absorbed by the growing forest. The Amazon has become a significant source of carbon dioxide, adding to global warming. More worrying still, the experiment is discovering a drying trend across the Amazon that leaves it ever more vulnerable to fires. Nepstad's work suggests that beyond a certain point, the forest will be unable to recover from the fires, and will begin a process of rapid drying that he calls the "savannization" of the Amazon.

And even as he concluded his drought experiment, nature seemed to replicate it. The rains failed across the Amazon through 2005, killing trees, triggering fires, and reducing the ability of the forest to recycle moisture in future-thus increasing the risk of future drought. Nepstad's experiments suggest that the rainforest is close to the edge-to permanent drought, rampant burning, savannization, or worse. In the final weeks of 2005, the rains returned. The forest may recover this time. But if future climate change causes significant drying that lasts from one year to the next, feedbacks in the forest could realize Nepstad's worst fears.

The 2005 drought was caused by extremely warm temperatures in the tropical Atlantic-the same high temperatures that are believed to have caused the record-breaking hurricane season that year. The rising air that triggered the hurricanes eventually came back to earth, suppressing the formation of storm clouds over the Amazon. And, as I discovered at Britain's Hadley Centre for Climate Prediction, that is precisely what climate modelers are forecasting for future decades.

The Hadley Centre's global climate model is generally regarded as one of the world's top three. And it predicts that business-as-usual increases in industrial carbon dioxide emissions worldwide in the coming decades will generate warmer sea temperatures, subjecting the Amazon to repeated droughts, and thus creating "threshold conditions" beyond which fires will take hold. The Amazon rainforest will be dead before the end of the century. Not partly dead, or sick, but dead and gone. "The region will be able to support only shrubs or grass at most," said a study published by the Hadley Centre in 2005.

Not all models agree about that. But the Hadley model is the best at reproducing the current relationship between ocean temperatures and Amazon rainfall, so it has a good chance of being right about the future, too. Nepstad himself predicts that a "megafire event" will spread across the region. As areas in the more vulnerable eastern rainforest die, they will cease to recycle moisture back into the atmosphere to provide rainfall downwind. A wave of aridity will travel west, creating the conditions for fire to rip through the heart of the jungle.

With the trees gone, the thin soils will bake in the sun. Rainforest could literally turn to desert. The Hadley forecast includes a graph of the Amazon's forest's future carbon. It predicts that the store of a steady 77 billion tons over the past half century will shrink to 44 billion tons by 2050 and 16.5 billion tons by the end of the century. That, it calculates, would be enough to increase the expected rate of warming worldwide by at least 50 percent.

The Amazon rainforest does not just create rain for itself. By one calculation, approaching 6 trillion tons of water evaporates from the jungle each year, and about half of that moisture is exported from the Amazon basin. Some travels into the Andes, where it creates clouds that swathe some mountains so tightly that their surfaces have never been seen by satellite. Some blows south to water the pampas of Argentina, some east toward South Africa, and some north toward the Caribbean. The forest is a vital rainmaking machine for most of South America. As much as half of Argentina's rain may begin as evaporation from the Amazon.

But the benefits of the great Amazonian hydrological engine extend much further, and are not restricted to rainfall. The moisture also carries energy. A lot of solar energy is used to evaporate moisture from the forest canopy. This is one reason why forests stay cooler than the surrounding plains. And when the moisture condenses to form new clouds, that energy is released into the air. It powers weather systems and high-level winds known as jets far into the Northern Hemisphere. Nicola Gedney and Paul Valdes, two young climate researchers at the University of Reading, have calculated that this process ultimately drives winter storms across the North Atlantic toward Europe. "There is a relatively direct physical link between changes over the deforested region and the climate of the North Atlantic and western Europe," they say. If the rainforest expires, the hydrological engine, too, is likely to falter, and the link will be cut.

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WILDFIRES OF BORNEO

Climate in the mire from burning swamp

The smoke billowed through Palangkaraya. One of the largest towns in Borneo was engulfed in acrid smog denser even than one of London's old pea-soupers. It blotted out so much sun that there was a chill in the air of a town more used to the dense, humid heat of the rainforest that encircled it. This was late 1997, and the rainforest was burning. The most intense El Nino event on record in the Pacific Ocean had stifled the storm clouds that normally bring rain to Borneo and the other islands of Indonesia. Landowners took advantage of the dry weather to burn the forest and carve out new plantations for palm oil and other profitable crops. The fires got out of control, and the result was one of the greatest forest fires in human history. The smoke spread for thousands of miles. Unsighted planes crashed from the skies, and ships collided at sea; in neighboring Malaysia and distant Thailand, hospitals filled with victims of lung diseases, and schools were closed. The fires became a global news story. The cost of the fires in lost business alone was put at tens of billions of dollars.

But it was not just the trees that were burning. The densest smoke was in central Borneo, around Palangkaraya, where the fires had burrowed down, drying and burning a vast peat bog that underlay the forest. The peat, 6o feet deep in many places, was the accumulated remains of wood and forest vegetation that had fallen into the swamps here over tens of thousands of years. Even after the rains returned, the peat continued to smolder for months on end. When the smoke finally cleared, most of the swamp forest was burned and black, and skeletons of trees poked from charred ground that had shrunk in places by a yard or more.

The burning of the Borneo swamp was part of a wider global assault on tropical rainforests-for timber and for land. But there were aggravating factors here. Until recently, the swamps were empty of humans. Local tribes and modern farmers alike had found them inhospitable and inaccessible. But in the early 19gos, Indonesia's President Suharto decreed that an area of the central Borneo swamp forest half the size of Wales should be drained and transformed into a giant rice paddy to make his country selfsufficient in its staple foodstuff. Some 2,500 miles of canals were dug to drain the swamp. Some 6o,ooo migrant farmers were brought in from other islands to cultivate the rice. The soils proved infertile, and virtually no rice was ever grown. The megaproject was abandoned. But its legacy lingers, as the canals continue to drain the swamps, and the desiccated peat burns every dry season. Especially during El Ninos.

This is no mere local environmental disaster. Jack Rieley, a British ecologist with a love of peat bogs who has adopted the central Borneo swamps for his field studies, says the disaster is of global importance. At least half of the world's tropical peat swamps are on the Indonesian islands of Borneo, Sumatra, and West Papua. And the largest, oldest, and deepest of them are in central Borneo, where they cover an area a quarter the size of England and harbor large populations of sun bears and clouded leopards, as well as the world's largest surviving populations of orangutans. They also contain vast amounts of carbon-perhaps 5o billion tons of the stuff. That is almost as much as in the entire Amazon rainforest, which is more than ten times as large. One acre of Borneo peat swamp contains 88o tons of carbon.

Tropical peat swamps are a major feature of the planet's carbon cycle. They are important amplifiers of climate change, capable of helping push the world into and out of ice ages by capturing and releasing carbon from the air. For thousands of years, they have been keeping the world cooler than it might otherwise be, by soaking up carbon from the air. For that carbon to be released now, as the world struggles to counter global warming, would be folly indeed. But that is what is happening. Rieley estimates that during the El Nino event of 1997 and 1998, as Palangkaraya disappeared for months beneath smoke, the smoldering swamps lost more than half a yard of peat layer, and released somewhere between 88o million and 2.8 billion tons of carbon into the atmosphere: the equivalent of up to 40 percent of all emissions from burning fossil fuels worldwide that year.

At first there was some skepticism about his figures. Few other researchers had been to Borneo to see what was going on. But in 2004, U.S. government researchers published a detailed analysis of gas measurements made around the world. It showed that roughly 2.2 billion tons more carbon than usual entered the atmosphere during 1998-and two thirds of that excess came from Southeast Asia. The Borneo fires must have contributed most of that, and burning peat was almost certainly the major component. "We are witnessing the death of one of the last wilderness ecosystems on the planet, and it is turning up the heat on climate change as it goes," says Rieley. "What was once one of the planet's most important carbon sinks is giving up that carbon. The whole world is feeling the effect."

Every year, farmers continue burning forest in Borneo to clear land for farming. And whenever the weather is dry, those fires spread out through the jungle and down into the peat. Satellite images suggest that 12 million acres of the swamp forests were in flames at one point during late 2002. And 2002 and 2003 were the first back-to-back years in which net additions to the atmosphere's carbon burden exceeded 4.4 billion tons. Rieley reckons that the burning swamp forests contributed a billion tons of that.

It looked as if smoldering bogs in remote Borneo were single-handedly ratcheting up the speed of climate change. They show, says David Schimel, of the National Center for Atmospheric Research (NCAR), in Boulder, Colorado, how "catastrophic events affecting small areas can have a huge impact on the global carbon balance." Fire in Borneo and the Amazon may be turning the world's biggest living "sinks" for carbon dioxide into the most dynamic new source of the gas in the twenty-first century.

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SINK TO SOURCE

Why the carbon cycle is set for a U-turn

It seemed too good to be true. Throughout the 198os and 199os, evidence grew that wherever forests survived around the world, they were growing faster. And as they did so, they were soaking up ever more carbon dioxide from the air. Despite deforestation in the tropics, the world's forests overall were a strong carbon sink. Most researchers assumed that the extra growth happened because rising concentrations of carbon dioxide in the atmosphere made it easier for trees to absorb the gas from the air. Provided that the other ingredients for photosynthesis, such as water and nutrients, were available, the sky was the limit for growing plants. The "CO, fertilization effect" entered the climate scientists' lexicon.

In 1998, at the height of this enthusiasm, a group of carbon modelers at Princeton University scored what looked like a political as well as a scientific bull's-eye. Song-Miao Fan and colleagues claimed in a paper in Science to have discovered "a large terrestrial carbon sink in North America." The U.S. and Canada, they said, had become a hot spot for carbon absorption, as trees grew on abandoned farmland and previously logged forests, and carbon dioxide in the air boosted growth. They calculated the sink at a stunning 2.2 billion tons a year-more than enough to offset the two countries' total annual emissions from power plants, cars, and the rest. Thanks to their trees, the biggest polluters on the planet were "carbon neutral."