The Amazon is approaching an irreversible tipping point

THE AMAZON basin, most of which sits within the borders of Brazil, contains 40% of the world’s tropical forests and accounts for 10-15% of the biodiversity of Earth’s continents. Since the 1970s nearly 800,000km² of Brazil’s original 4m km² (1.5m square miles) of Amazon forest has been lost to logging, farming, mining, roads, dams and other forms of development—an area equivalent to that of Turkey, and bigger than that of Texas. Over the same period, the average temperature in the basin has risen by about 0.6°C. This century, the region has suffered a series of severe droughts.

Both the reduction in tree coverage and the change in climate were endangering the forest’s future well before Brazil’s general elections of October 2018. But after that the forest faced another threat: Jair Bolsonaro, the new president, and arguably the most environmentally dangerous head of state in the world.

From 2004 to 2012 the rate of deforestation in the Brazilian Amazon slowed. The government’s environmental protection agency, Ibama, was strengthened. Other countries, and global NGOs, nagged and encouraged; in 2008 an international Amazon Fund was created to help pay for protection. Not a moment too soon, said rainforest scientists. They had begun to suspect that, if tree loss passed a certain threshold, the deforestation would start to feed on itself. Beyond this tipping-point, forest cover would keep shrinking whatever humans might try to do to stop it. Eventually much of the basin would be drier savannah, known as cerrado. As well as spelling extinction for tens of thousands of species, that devastation would change weather patterns over much of South America and release into the atmosphere tens of billions of tonnes of carbon, worsening global warming.

This hopeful period of slower deforestation was not to last. Even before Mr Bolsonaro, deforestation began to tick up (see chart 1). In 2012, under then-president Dilma Rousseff, Brazil’s congress passed a new forest code that gave amnesty to those who had taken part in illegal deforestation before 2008. In 2017 Michel Temer, the next president, signed a law that streamlined the privatisation of occupied public lands, which spurred land grabs in the Amazon. During the deep recession of 2014-16 the environment ministry’s budget was slashed. Between August 2017 and July 2018 Brazil lost 7,900km² of Amazon forest—nearly a billion trees—the highest rate of deforestation for a decade.

Heaven’s high canopy

According to preliminary satellite data, since Mr Bolsonaro took office in January, the Amazon has lost roughly 4,300km² of forest, which means this year’s total will surely outstrip last year’s. This is not a fluke. The president appears to want the country to return to the time of Brazil’s military dictatorship, when big infrastructure projects prompted widespread destruction in the name of development.
A few of Mr Bolsonaro’s plans have been curbed. Pressure from Tereza Cristina, the agriculture minister, and the farm lobby led him to withdraw his threat to leave the Paris climate agreement and from abolishing the environment ministry—mostly because deals with disapproving European firms would be at risk. A bill introduced by Flávio Bolsonaro, the president’s eldest son and a senator in his own right, to eliminate a requirement for farmers to preserve some natural vegetation on land they clear has not yet passed. The supreme court blocked a decree to transfer powers over the demarcation of indigenous reserves from the justice ministry to Ms Cristina’s—which would have “put the fox in charge of the chicken coop,” argues Randolfe Rodrigues, an opposition senator.
But even without the biggest changes, Mr Bolsonaro’s government can still encourage, directly or indirectly, a large amount of deforestation, by not enforcing the laws that prohibit it. On February 28th the environment minister, Ricardo Salles, fired 21 of Ibama’s 27 state heads, following the president’s orders to “clean out” the agency. Most have yet to be replaced, including all but one in the Amazon states. The environment ministry has started to flag up in advance where and when anti-logging operations will take place. Between January and May, Ibama imposed the lowest number of fines for illegal deforestation in a decade.
Mr Salles says that “the role of the state is to protect landowners’ property rights”. He wants to use donations from Norway and Germany to the 3.6bn reais ($950m) Amazon Fund to compensate landowners for land that had been turned into conservation areas, even though most of it was occupied illegally.
Deforesters appear emboldened. According to the Indigenist Missionary Council, a Catholic group, the number of illegal invasions in indigenous areas has jumped. On July 24th miners with guns invaded a village in the northern state of Amapá, killed one of its leaders and expelled the residents. Satellite data show a drastic rise in the year-on-year deforestation rate starting in May, the beginning of the dry season. In July, more than 1,800km² was cleared, three times more than last year.
These statistics tell only part of the story. The Amazon matters to the global climate because it is a sink of carbon, mitigating warming. If the rainforest were to die back, the large amount of greenhouse gases this would release would speed up that process. But the climate matters to the Amazon, too. It is sensitive to changes in temperature and rainfall, as well as to atmospheric carbon-dioxide levels.
The Amazon is unique among tropical rainforests in that it produces a lot of its own rainfall. As moisture travels from the Atlantic to Peru, the Amazon’s trees recycle some of it; around half the forest’s rain is reused this way. Rainwater is pulled up from the roots to the canopy, where it is released back to the atmosphere to fall as rain again. Not only does this provide moisture to the region, the evaporation off the leaves also has a local cooling effect.
This is what has led to worries about tipping-points. In an influential paper in 2007 Gilvan Sampaio and Carlos Nobre of Brazil’s National Institute for Space Research forecast that, were 40% of the forest to perish, the loss of water-recycling capacity would mean very little of the rest would have enough rainfall to survive.

Trees rudely hollowed

Alongside the threat from deforestation, the forest’s capacity to water itself can be weakened by rising temperatures. Beatriz Marimon and Ben Hur Marimon, at the University of Mato Grosso in Nova Xavantina, have kept tabs for decades on dozens of plots in the transição, the margin between the wet Amazon and the drier cerrado. Today, Mr Marimon says, they are seeing “two warmings in one”. On top of global warming are changes that result from deforestation, which removes the air-conditioning effect provided by water evaporating from the trees’ leaves.

A study by Divino Silvério and colleagues at the Amazon Environmental Research Institute, published in 2015, found that converting forest to pasture increased land temperatures by 4.3°C; if pasture was then turned over to arable crops, things warmed a little more. The transição is already hotter and drier than most of the rainforest. Clearing more of its patchwork of forest, farms and savannah makes the remaining woodland even hotter.
Ms Marimon has also observed that temperatures above 40°C dry out trees, making them more likely to fall in strong winds. The fragmentation brought about by farming creates isolated patches of forest. If they lose access to seed banks in the soil and water sources, such disconnected fragments are less able to recover.
How plants respond to carbon-dioxide levels probably exacerbates matters. The more carbon dioxide in the air, the less air plants need to process in order to photosynthesise. The less air they take in, the less water vapour they let out. As a consequence, the plants both do less to cool their immediate environment (because less water evaporates) and also make the atmosphere less moist. This has been shown to be happening in other watersheds, though there is not yet conclusive evidence from the Amazon.
Clearances also lead to local drying. Satellite data show that air which passes over primary rainforest produces twice as much rain a few days later than that which passes over farmland. In 2012 scientists at the University of Leeds predicted that continued deforestation would cause rainfall in the Amazon to drop by 12% in the wet season and by 21% in the dry season by 2050.
The forest’s dry season started to lengthen in the 1970s; the rains which used to come in October now come in November. This might have been an effect of deforestation; there is some evidence that water returned to the atmosphere by trees is particularly important in getting the rainy season going. The most dramatic effect of drying seen by scientists, though, is not a shorter wet season. It is the disproportionate impact of the years in which rainfall is particularly low.

This century has already seen three unusually harsh droughts, in 2005, 2010 and 2015. That of 2015 corresponds to an El Niño event—a see-saw effect in Earth’s climate whereby a shift in the flow of energy between the atmosphere and the ocean in the central Pacific produces a predictable pattern of climate anomalies all through the tropics and beyond (see chart 2). The correlation between El Niño events and droughts in the Amazon, most notably in the south-eastern part, predates human activities. But those activities may, at a global level, increase the frequency and intensity of El Niño events. At the local level they worsen the damage that droughts do.
The El Niño drought in 2015 was particularly severe. In Nova Xavantina more than a third of the trees in some of the Marimons’ study plots died in its aftermath. The region around the city of Santarém, farther north and deep in the Amazon, saw flames as tall as buildings tear through the forest, enveloping the canopy in thick black smoke that stretched for miles and turned the sunlight red. For months after the fires died down, the forest floor smouldered. Hundred-year-old trees dried out and died.
Nearly four years later, the forest is still recovering. At one part of the Tapajós National Forest reserve, where 580km² (11% of the total area) burned, saplings have shot up among the ashes of their giant forebears, but it will be years before they form a canopy. A second round of fires in 2017 burned nearly a quarter of another reserve, where 75 communities of river-dwellers make their living fishing and hunting.
Fires are not new to the Amazon, but recently they seem to have been more frequent and intense. This kicks off a vicious cycle. Dead trees open gaps in the canopy, allowing more light and wind to reach the forest floor, which becomes hotter, drier and more prone to burn again. This year is expected to be a mild El Niño year, which means higher temperatures and less rain for the area around Santarém. Fires could rage again. If that happens, says Joice Ferreira, a biologist at the Brazilian Agricultural Research Corporation, the debris left over from the previous fires will serve as fuel for the flames. “After that,” she says, “there won’t be many trees left.”
Over the past 50 years 17% of the rainforest has been lost, some way from the 40% tipping-point proposed in 2007. But last year Mr Nobre and Thomas Lovejoy of George Mason University, after taking account of climate change and fire as well as deforestation, revised the estimate of the threshold to 20-25%. That is uncomfortably close to today’s figure. Mr Nobre says the recent droughts and floods could be the “first flickers” of permanent change. Carlos Rittl of the Brazilian Climate Observatory, a consortium of research outfits, expects Mr Bolsonaro’s tenure to see deforestation pass 20%. If Mr Lovejoy and Mr Nobre are right, that could be disastrous—once the tipping-point is transgressed, much of the rest of the forest could follow in just a matter of decades.

To shade the barren wild

Even now, the service that the Amazon provides the rest of the world as a sink for carbon dioxide appears to be declining. Simon Lewis of University College London, and colleagues, analysed observations of 321 plots across the Amazon basin. They found that in primary forests plants absorb, on average, a third less carbon dioxide than they did in the 1990s, owing to increasing tree mortality. In a paper published in 2011 Mr Lewis argued that carbon lost to the atmosphere through tree death and fire in the droughts of 2005 and 2010 might offset as much as a decade’s worth of carbon-dioxide absorption by the forest.
Not everyone is so gloomy. Forests that are diverse, like the Amazon, are likely to have drought-resistant species that can fill the niche left by drought-prone ones without a loss of biomass, points out Kirsten Thonicke of the Potsdam Institute for Climate Impact Research, a German think-tank. Secondary forests store significant amounts of carbon, though far less than primary ones. One study found that as a secondary forest grows, it recovers 1.2% carbon storage per year, so a 20-year-old secondary forest would store roughly 25% of the carbon stored by a primary forest. There are ways to mitigate the biomass loss from logging and ranching, by being careful about which trees to cut and reforesting afterwards. In Paris Brazil pledged not just to halt illegal deforestation by 2030 but also to reforest 120,000km².
Such attempts at mitigation look increasingly unlikely. In June Mr Bolsonaro published a decree which indefinitely extends the 2019 deadline for farmers to begin replanting illegally deforested land. This not only reduces the chances of reforestation. It reinforces the message: the government will turn a blind eye to more. Similarly, if his son’s bill were to pass it would legalise the deforestation of some 1.5m km². Clearing that would emit nearly 65bn tonnes of carbon dioxide—equivalent to Brazil’s emissions over the past 27 years.
In July President Bolsonaro called deforestation data “lies” and said he wanted to review them before they were released to the public. Hamilton Mourão, the vice-president, says that other countries’ professed concern for the Amazon masks “covetousness” for precious minerals in the region. Mr Salles, the environment minister, likes to point out that many rich countries cut down their own forests but have not fulfilled promises to pay Brazil not to do the same. “You can’t give Brazil the onus of being the world’s lungs without any benefits,” he argues.

The trees stood bare

Mr Salles is right that the countries responsible for the bulk of emissions should compensate Brazil for its role in absorbing them. In return Brazil must protect, rather than destroy, the rainforest. In June a trade deal between the EU and Mercosur—Brazil, Argentina, Paraguay and Uruguay—was announced at the G20 summit, which includes a commitment to implement the Paris climate agreement. It has yet to be approved; it is also unclear how much it will sway the president to curb his infrastructure plans, or indeed his rhetoric.
Concerns about what Brazil’s climate policies might do to the country’s reputation could spur local resistance to Mr Bolsonaro’s anti-environmental turn. Fears for the climate itself may yet do more. “We have no doubt that the forest has a direct effect on the rain cycle,” says Artemizia Moita, the sustainability director of a farming group that has 530km² of soyabean and cattle farms. “If we keep deforesting,” she asks, “how will we keep producing?” Unlike other farmers she admits she is worried about climate change.
For many, any shift in attitudes will already come too late. Magdalena is an elderly woman who has spent her life as a river-dweller in one of the rainforest’s reserves. She used to hunt deer and armadillo to make her living. Now she treks 13km to buy beef from a local village. “All the game is gone,” she laments. ■