The Amazon rainforest is still burning.

Blazes have been torching the world’s largest tropical forest for three weeks now. French President Emmanuel Macron called it an “international crisis” and put the fires on the agenda of the G7 meeting over the weekend, triggering a diplomatic spat with Brazilian President Jair Bolsonaro. G7 countries promised €20 million in aid for the rainforest, which Bolsonaro said Tuesday he would reject.

Brazil’s National Institute for Space Research (INPE) has reported at least 74,000 fires in the Amazon this year so far, an increase of 84 percent compared to the same time last year.

The smoke from the fires has cast a pall stretching across the country and reaching coastal metropolises like São Paulo.

It’s an alarming increase because the Amazon almost never burns on its own and the increase in fires this year has been so dramatic. The region is usually too wet to ignite, so the vast majority of fires are caused by humans. Some of the blazes are started by farmers aiming to clear land, some by illegal loggers trying to cover their tracks, and some by negligence. Fires and logging had been on the decline for years in the Amazon until Bolsonaro, who made his intentions to exploit the Amazon perfectly clear, took office last year.

Bowing to domestic protests and international pressure, Bolsonaro deployed the military over the weekend to fight the fires now burning across six Brazilian states.

But when the smoke dissipates and the flames die down to embers, another perilous threat is looming for the Amazon rainforest. Scientists warn that if enough of the forest is lost, it could enter a spiral of collapse. This is an outcome with global consequences, and if we cross this threshold of deforestation, it could be a point of no return.

The Amazon rainforest plays an important, complicated role in the regional and global climate

The rain in the rainforest is not an accident of geography or meteorology. The towering mahogany, kapok, and Brazil nut trees of the Amazon play important parts in the orchestra of the region’s water system.

The trees take in rainwater through their roots, move it up into the canopy, and release it into the air, a process called evapotranspiration. The trees also release volatile organic compounds that react to form tiny particles. These particles serve as nucleation points to form clouds and eventually lead to more rainfall.

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Multiply this pattern by the hundreds of billions of trees in the rainforest and you get a powerful mechanism for recycling water and generating rainfall that keeps even the thirstiest of trees quaffed in hot tropical weather.

This rainfall pattern helps sustain agriculture throughout Brazil and top up reservoirs that hydrate major cities, feeding and quenching the thirst of millions.

But these trees are rapidly disappearing, along with the shrubs, grasses, fungi, and soil bacteria that work alongside them to circulate moisture. The rate of deforestation in the Amazon has picked up again after years of decline, with roughly a soccer field-size area lost every minute.

Once the rainforest loses a certain amount of area, this orchestra will fall out of tune. There will not be enough remaining tropical woodlands to continually evaporate and condense moisture through the forest. Without this cycling of rainfall, downwind vegetation will not get enough water. That flora in turn will weaken and move less moisture through the air, resulting in less rainfall for the forested areas even further downwind. These parched trees will become more vulnerable to pests and fire. The mighty stalwarts of the Amazon will shrivel up, and a wave of death will start at the periphery and propagate throughout as much of it degrades from a dense tropical forest into a sparse savanna. The cycle will continue without our input. And there will be little we can do to stop it.

This is a scenario known as a forest dieback.

Scientists now think that all the stresses humanity is placing on the Amazon rainforest — agriculture, logging, global warming — mean that we’re closer to such an event than we realized before. “We believe that negative synergies between deforestation, climate change, and widespread use of fire indicate a tipping point for the Amazon system to flip to non-forest ecosystems in eastern, southern and central Amazonia at 20-25% deforestation,” wrote researchers Carlos Nobre and Thomas Lovejoy in an editorial in the journal Science Advances. (Then-New York Times reporter Justin Gillis wrote about the history of research on the dieback scenario in the Amazon in 2011.)

The World Wildlife Fund estimates that 17 percent of the Amazon rainforest has been lost in the past 50 years. Brazil’s INPE reported that deforestation in the Brazilian Amazon surged 88.4 percent in June compared to June 2018. The recently burned forest area will add to that growing cumulative total of deforestation.

Which means the Amazon is creeping closer to the threshold.

Now, not every bit of research points to such a scenario. Some scientists anticipate the rainforest will change into a seasonal forest rather than a savanna. Other findings show that the rainforest won’t collapse but will degrade differently in different regions of the jungle.

However, diebacks have happened before. The United Kingdom experienced a dieback of ash trees due to a fungal infection that started in the 1990s and continues to ravage the species today.

The total cost of #AshDieback to the UK is estimated to be £15 billion, and it is expected to kill 95-99% of our ash trees.



Find out how we are working in a race against time to safeguard our trees for the future: https://t.co/kgK6S7mHig https://t.co/cEkSXaQQWK — Woodland Trust (@WoodlandTrust) August 27, 2019

Huge climatic variations led to a dieback in Hawaii in the 1980s. Droughts, beetles, and storms in recent years are pushing forests in Germany toward collapse. On a larger scale, the Carboniferous rainforest collapse 300 million years ago led to a global extinction event and left a permanent mark on the evolution of life.

And if one happens in the Amazon, it could ripple throughout the planet, so it’s a risk worth taking seriously.

Losing the Amazon rainforest has global consequences and could be irreversible

In addition to deforestation from industry, the Amazon rainforest is under pressure from rising average temperatures. Researchers project the water stresses in the region from climate change will increase in the coming decades as the dry season gets drier.

That loss of forest can in turn exacerbate changes in the climate, a pattern that scientists have been warning about for decades. Craig Allen, a research ecologist at the US Geological Survey, explained it thusly in a 2009 report for the United Nations Food and Agriculture Organization:

One consequence of substantial forest dieback is redistribution of within-­ecosystem carbon pools and rapid losses of carbon back to the atmosphere. For instance, climate-driven effects of forest dieback, insect and disease mortality and fire impacts have recently turned Canada’s temperate and boreal forests from a net carbon sink into a net carbon source (Kurz et al., 2008). Similarly, it is possible that “widespread forest collapse via drought” could transform the world’s tropical moist forests from a net carbon sink into a large net source during this century (Lewis, 2005).

The Amazon, with all its plants, animals, and soils, is an enormous reservoir of carbon. So as it degrades due to deforestation and climate change, it will go from soaking up carbon dioxide in the atmosphere to becoming a net emitter of heat-trapping gases.

We’re already seeing a long-term decline in the amount of carbon the Amazon can absorb, with capacity shrinking by one-third in the 2010s compared to the 1990s. If we keep burning down forests and spewing greenhouse gases, the switch could flip in the other direction. There are about 90 billion metric tons of carbon embedded in the Amazon, equal to about a decade’s worth of greenhouse gas emissions. So losing the rainforest has a huge potential to warm the planet.

Can we do anything to stop it?

Yes, but there are no easy fixes. There is immense economic and social pressure to cut down the rainforest and develop it for farming, pasture, and mineral extraction. For example, Brazil is the largest exporter of beef in the world, which drives a huge chunk of demand for clearing the rainforest.

In a 2018 study in the Proceedings of the National Academy of Sciences, researchers tabulated the costs of tactics needed to avert a dieback scenario in the Amazon. They concluded that 20 adaptation measures — better water management, decentralized renewable energy, no-fire agriculture techniques — would cost $120 billion, while mitigation measures like reducing reforestation would cost $64 billion. It’s expensive, but the authors say it’s a bargain compared to the social and economic damages from a dieback. The low-end estimate for the cost of a dieback in the Amazon was $957 billion over 30 years. The high-end estimate was $3.5 trillion.

Restoring the rainforest is no easy task either. It requires not just planting trees but bringing back an ecosystem, including the wildlife, waterways, and other plants, each acting in balance with one another. It’s a process that could take decades.

Some regions, such as those deforested for mining and oil drilling, may have severe contamination of the water and soil, which would require extensive remediation before a forest could return.

The most critical task at hand is to retain what’s left. That means stopping the ongoing fires and deforestation as quickly as possible. From there, Brazil’s government and the world as a whole will have to pick up the thorny task of developing a mechanism to protect and restore the Amazon rainforest in face of rising demand for food, fuel, and land for a growing population.