Wednesday, September 11, 2019

3280. The Limits of Clean Energy

By Jason Hickel, Foreign Policy, September 6, 2019
Strong winds blow sand at a wind farm in the Coachella Valley on May 6, 2019 in Palm Springs, California. MARIO TAMA/GETTY IMAGES

The conversation about climate change has been blazing ahead in recent months. Propelled by the school climate strikes and social movements like Extinction Rebellion, a number of governments have declared a climate emergency, and progressive political parties are making plans—at last—for a rapid transition to clean energy under the banner of the Green New Deal.

This is a welcome shift, and we need more of it. But a new problem is beginning to emerge that warrants our attention. Some proponents of the Green New Deal seem to believe that it will pave the way to a utopia of “green growth.” Once we trade dirty fossil fuels for clean energy, there’s no reason we can’t keep expanding the economy forever.

This narrative may seem reasonable enough at first glance, but there are good reasons to think twice about it. One of them has to do with clean energy itself.
The phrase “clean energy” normally conjures up happy, innocent images of warm sunshine and fresh wind. But while sunshine and wind is obviously clean, the infrastructure we need to capture it is not. Far from it. The transition to renewables is going to require a dramatic increase in the extraction of metals and rare-earth minerals, with real ecological and social costs.

We need a rapid transition to renewables, yes—but scientists warn that we can’t keep growing energy use at existing rates. No energy is innocent. The only truly clean energy is less energy.

In 2017, the World Bank released a little-noticed report that offered the first comprehensive look at this question. It models the increase in material extraction that would be required to build enough solar and wind utilities to produce an annual output of about 7 terawatts of electricity by 2050. That’s enough to power roughly half of the global economy. By doubling the World Bank figures, we can estimate what it will take to get all the way to zero emissions—and the results are staggering: 34 million metric tons of copper, 40 million tons of lead, 50 million tons of zinc, 162 million tons of aluminum, and no less than 4.8 billion tons of iron.

In some cases, the transition to renewables will require a massive increase over existing levels of extraction. For neodymium—an essential element in wind turbines—extraction will need to rise by nearly 35 percent over current levels. Higher-end estimates reported by the World Bank suggest it could double.

The same is true of silver, which is critical to solar panels. Silver extraction will go up 38 percent and perhaps as much as 105 percent. Demand for indium, also essential to solar technology, will more than triple and could end up skyrocketing by 920 percent.
And then there are all the batteries we’re going to need for power storage. To keep energy flowing when the sun isn’t shining and the wind isn’t blowing will require enormous batteries at the grid level. This means 40 million tons of lithium—an eye-watering 2,700 percent increase over current levels of extraction.

That’s just for electricity. We also need to think about vehicles. This year, a group of leading British scientists submitted a letter to the U.K. Committee on Climate Change outlining their concerns about the ecological impact of electric cars. They agree, of course, that we need to end the sale and use of combustion engines. But they pointed out that unless consumption habits change, replacing the world’s projected fleet of 2 billion vehicles is going to require an explosive increase in mining: Global annual extraction of neodymium and dysprosium will go up by another 70 percent, annual extraction of copper will need to more than double, and cobalt will need to increase by a factor of almost four—all for the entire period from now to 2050.

The problem here is not that we’re going to run out of key minerals—although that may indeed become a concern. The real issue is that this will exacerbate an already existing crisis of over-extraction. Mining has become one of the biggest single drivers of deforestation, ecosystem collapse, and biodiversity loss around the world. Ecologists estimate that even at present rates of global material use, we are overshooting sustainable levels by 82 percent.

Take silver, for instance. Mexico is home to the Peñasquito mine, one of the biggest silver mines in the world. Covering nearly 40 square miles, the operation is staggering in its scale: a sprawling open-pit complex ripped into the mountains, flanked by two waste dumps each a mile long, and a tailings dam full of toxic sludge held back by a wall that’s 7 miles around and as high as a 50-story skyscraper. This mine will produce 11,000 tons of silver in 10 years before its reserves, the biggest in the world, are gone.

To transition the global economy to renewables, we need to commission up to 130 more mines on the scale of Peñasquito. Just for silver.

Lithium is another ecological disaster. It takes 500,000 gallons of water to produce a single ton of lithium. Even at present levels of extraction this is causing problems. In the Andes, where most of the world’s lithium is located, mining companies are burning through the water tables and leaving farmers with nothing to irrigate their crops. Many have had no choice but to abandon their land altogether. Meanwhile, chemical leaks from lithium mines have poisoned rivers from Chile to Argentina, Nevada to Tibet, killing off whole freshwater ecosystems. The lithium boom has barely even started, and it’s already a crisis.

And all of this is just to power the existing global economy. Things become even more extreme when we start accounting for growth. As energy demand continues to rise, material extraction for renewables will become all the more aggressive—and the higher the growth rate, the worse it will get.

It’s important to keep in mind that most of the key materials for the energy transition are located in the global south. Parts of Latin America, Africa, and Asia will likely become the target of a new scramble for resources, and some countries may become victims of new forms of colonization. It happened in the 17th and 18th centuries with the hunt for gold and silver from South America. In the 19th century, it was land for cotton and sugar plantations in the Caribbean. In the 20th century, it was diamonds from South Africa, cobalt from Congo, and oil from the Middle East. It’s not difficult to imagine that the scramble for renewables might become similarly violent.

If we don’t take precautions, clean energy firms could become as destructive as fossil fuel companies—buying off politicians, trashing ecosystems, lobbying against environmental regulations, even assassinating community leaders who stand in their way.

Some hope that nuclear power will help us get around these problems—and surely it needs to be part of the mix. But nuclear comes with its own constraints. For one, it takes so long to get new power plants up and running that they can play only a small role in getting us to zero emissions by midcentury. And even in the longer term, nuclear can’t be scaled beyond about 1 terawatt. Absent a miraculous technological breakthrough, the vast majority of our energy will have to come from solar and wind.

None of this is to say that we shouldn’t pursue a rapid transition to renewable energy. We absolutely must and urgently. But if we’re after a greener, more sustainable economy, we need to disabuse ourselves of the fantasy that we can carry on growing energy demand at existing rates.

Of course, we know that poorer countries still need to increase their energy use in order to meet basic needs. But richer countries, fortunately, do not. In high-income nations, the transition to green energy needs to be accompanied by a planned reduction of aggregate energy use.

How might this be accomplished? Given that the majority of our energy is used to power the extraction and production of material goods, the Intergovernmental Panel on Climate Change suggests that high-income nations reduce their material throughput—legislating longer product life spans and rights to repair, banning planned obsolescence and throwaway fashion, shifting from private cars to public transportation, while scaling down socially unnecessary industries and wasteful luxury consumption like the arms trade, SUVs, and McMansions.

Reducing energy demand not only enables a faster transition to renewables, but also ensures that the transition doesn’t trigger new waves of destruction. Any Green New Deal that hopes to be socially just and ecologically coherent needs to have these principles at its heart.

Saturday, September 7, 2019

3279. As the Amazon Burns, It’s Time to Roll Up Our Sleeves

By Derrick Jensen, Fair Observer, September 5, 2019

The Amazon is burning. This is what the end of the world looks like. Oh, and there’ll be more forests burn, more forests felled by chainsaws, more wetlands drained, more rivers dammed, more grasslands plowed, oceans further toxified and emptied of fish.
And each of these is what the end of the world looks like.
The end of the world looks like factory trawlers pulling in net after net full to bursting with fish — the fish’s eyes popping out from the pressure of all those bodies squeezed together. It looks like puffins starving to death. It looks like emaciated polar bears. It looks like whales washing up on shore and walruses not finding ice on which to rest.
The end of the world looks like plows digging into grasslands, turning over soil and killing all who live there, even down to bacteria. It looks like rows of mono-crops, as far as the eye can see.
The end of the world looks like humans staring at screens, clucking their tongues at the destruction of forests far away, never noticing that they themselves — whether they’re in London, New York, Paris, Rome, Athens, Beirut, Beijing or Baghdad — are standing in clear-cuts.
The end of the world looks like cities, with most of their residents never giving a thought to who and what was killed to build that city, never giving a thought to who and what was killed to mine, manufacture and move everything they consider necessary to their lives, and never thinking about what is necessary to life and what is not.
The end of the world looks like humans turning the planet to human use. Or rather attempting to, because it’s not possible to turn this wild and fecund Earth totally to human use, and this attempting is itself what is causing the end of the world.
From the beginning of this culture, it has been so. When you think of Iraq, is the first thing you think of cedar forests so thick that sunlight never touches the ground? That’s what it was like, prior to the beginning of this culture. The first written myth of Western civilization is Gilgamesh deforesting the hills and valleys of Iraq to make a great city.
Have you heard of Mesopotamian elephants? Most of us haven’t. They were exterminated to make way for this culture. And when you think of the Arabian Peninsula, do you think of oak savannas? These forests were cut for export to fuel the economy, to build cities.
The Near East was heavily forested. We’ve all heard of the cedars of Lebanon. They still have one on their flag. The great forests of North Africa were felled to make the Phoenician and Egyptian navies. Greece was heavily forested. So was Italy. So was France. The great forests of Britain came down to make the navy that allowed the sun never to set on the British Empire.
This is what this culture does. Forests precede us and deserts dog our heels.
The end of the world was not written into human existence. For most of our species’ time on Earth, we’ve lived sustainably. The Tolowa Indians lived where I live now for at least 12,500 years, and when the dominant culture arrived, salmon still ran so thick they turned entire rivers “black and roiling” with their bodies. There was no such thing as “ancient redwood forests.” There was only “home” — a home filled with trees thousands of years old, a home filled with nonhumans in abundance most of us literally cannot conceptualize.
Can you imagine — and this moves us across the continent — flocks of passenger pigeons so large they darken the sky for days at a time, flying 60 miles per hour and sounding like rolling thunder? Can you imagine so many whales that the air looks foggy, just from their breath? Can you imagine fish in such abundance that they slow the passage of ships? Can you imagine entire islands so full of great auks that one European explorer said they could load every ship in France and it would not make a dent? Well, they did, and it did, and the last great auk was killed in the 19th century.
How did the world get to be so full of life in the first place? By each creature making the world richer by living and dying. Salmon make forests stronger by their lives and deaths. Redwood trees do the same. Buffalo make grasslands stronger by their lives and deaths. Wolves do the same. And humans can do the same. But not living the way we do.
The Tolowa were not alone in their sustainability. There have been sustainable cultures the world over. The San of southern Africa, for example, evolved in place. They have lived there, in human terms, forever.
And how have humans lived sustainably in place? Simple. By not destroying the places where they lived, and by not destroying other places either. By improving the habitat on its own terms by their presence. The Tolowa made land-use decisions, just as all other beings on the land do, and just as we make land-use decisions. But the Tolowa made these land-use decisions on the assumption they would be living in a place for the next 500 years. That assumption changes everything about how you make decisions and how you live. It is the difference between life and death, between sustainability and the end of the world.
The end of the world was not written into human existence. It was, however, written into the story of Gilgamesh. The end of the world is written into this way of life of converting the Earth solely to human use. It was written into existence with the plow, and with the cities the plow makes possible.
The logic is simple and inescapable. If you convert the land that previously grew bushes and trees that fed elephants into wheat that feeds humans, you can grow more humans per hectare. Many of these humans can become a standing army. And you can use those trees you cut down to build ships of war. You now have a competitive military advantage over those who live sustainably, over those who do not destroy their land base. Further, because you’ve degraded your own land base, you must expand into other land bases. But fortunately for you, you’ve got a standing military.
This is the last 6,000 years of history. This is the story of the end of the world.
More than 90% of forests on the planet have been destroyed. The same is true for wetlands, grasslands, seagrass beds, large schools of fish, wildlife populations in general.
This culture is killing the planet. It doesn’t have to be this way. Not every culture has lived this way. Not every culture has killed the planet.
Recently, more and more people are talking about the possibility of human extinction. That possibility has entered our consciousness enough that, in December 2018, The New York Times published an op-ed asking whether it would be better for the Earth if humans went extinct.
As the Amazon burns, here’s the thing that haunts me. How is it that this culture can contemplate the end of the Amazon rainforest, contemplate the end of elephants, great apes, insects, fish in the oceans? How is it that it can blithely destroy life on Earth? How is it that it can with not much horror contemplate human extinction, but cannot contemplate stopping this way of life?
If aliens came from outer space and did to Earth what this culture is doing — change the climate; burn the Amazon; deforest the planet; vacuum the oceans and put dioxin in every mother’s breastmilk; and bathe the world in plastics, endocrine disrupters and neurotoxin — we would know exactly what to do. We would resist. We would fight as though our lives depend on it. We would destroy the aliens’ infrastructure that allows them to wage war on the planet that is our only home.
Or, put another way, if the Amazon could take on human manifestation, what would it do? If salmon could take on human manifestation, how long would dams stand? If humans from the future could come to our time, how would they act?
As the writer Lierre Keith often says, “If there are any humans left 100 years from now, they are going to ask what the fuck was wrong with us that we didn’t fight like hell when the world was going down.”
Many of us who know history might have fantasies of how we would have acted were we alive under German occupation in World War II or under British colonial rule. Right now, we are facing the end of the world. We have the opportunity and the honor to protect the planet that gave us our lives.
The time is now. Roll up your sleeves and get to work. Life on this planet needs you.

3278. Poetry: I Bow Down

By Jamie K. Reaser, Conversations with Mary: Words of Attention and Devotion, 2019
Photo: Jamie K. Reaser. 

I Bow Down

I bow down.
I bow down to the sky that oversees
the liars and the truthsayers.
I bow down to the earth that conveys
the rich and the poor.
I bow down to the child that will lead
tomorrow and the child that leads
today and the child that must become
an angel because we won’t follow
the children otherwise.

What I stand for is that which
I bow down to:

that which says we’re not done
yet, there’s a lot more to learn
to love.
I Bow Down

I bow down.
I bow down to the sky that oversees
the liars and the truthsayers.
I bow down to the earth that conveys
the rich and the poor.
I bow down to the child that will lead
tomorrow and the child that leads
today and the child that must become
an angel because we won’t follow
the children otherwise.

What I stand for is that which
I bow down to:

that which says we’re not done
yet, there’s a lot more to learn
to love.

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Sunday, September 1, 2019

3277. Poetry: We Have Not Come to Take Prisoners

By Hafiz (Khwāja Šamsu d-Dīn Muḥammad Hāfez-e Šīrāzī)
 We Have Not Come to Take Prisoners

We have not come here to take prisoners
But to surrender ever more deeply
To freedom and joy.
We have not come into this exquisite world
to hold ourselves hostage from love.
Run my dear, from anything
That may not strengthen
Your precious budding wings,
Run like hell, my dear,
From anyone likely to put a sharp knife
Into the sacred, tender vision
Of your beautiful heart.
We have a duty to befriend
Those aspects of obedience of our house
And shout to our reason
"Oh please, oh please
come out and play."
For we have not come here to take prisoners,
Or to confine our wondrous spirits
But to experience ever and ever more deeply
our divine courage, freedom, and Light!

3276. What Genetics Is Teaching Us About Sexuality

By Steven M. Phelps and
As researchers in biology and sociology who are also gay men, we have long wondered (and debated) whether sexual orientation has any biological basis. We followed the ascent in the 1990s of the “gay gene” finding — which claimed that male sexual orientation was linked to specific DNA markers — and then watched as that result was called into question. We have wondered whether the two of us, who differ in so many ways, could really trace our common identity to a shared biology.

New data are finally giving us answers.

A study published Thursday in Science looked at the DNA and sexual behavior of nearly 500,000 people. It found that the sex of your sexual partners is, in fact, influenced by your genes. But it also found that it was not possible to predict your sexual behavior from your DNA alone. The study suggested, in other words, that while biology shapes our most intimate selves, it does so in tandem with our personal histories — with the idiosyncratic selves that unfold in a larger cultural and social context.

The researchers, who included one of us (Dr. Wedow), analyzed the genetic markers of people who responded to the question “Have you ever had sex with someone of the same sex?” From these data, the researchers estimated that genetic differences account for roughly one-third of the variation in same-sex behavior. The study also identified several DNA sequence variants associated with having had a same-sex experience.
So, yes, your sex life is influenced by your genes.

This conclusion fits with our personal experiences and intuitions. Sexual desire is typically stable, something we often are aware of from our first longings. Furthermore, one of the several DNA variants identified in Thursday’s study is involved in gonad development, which accords with previous research that links sexual orientation to hormone exposure.

But the study’s findings also complicate the relationship between genetics and sexuality.

For one thing, the results make clear that there is no single biology of sexual behavior. It turns out, for example, that the genes influencing same-sex behavior in females are often different from those that shape behavior in males. It also turns out that the genes associated with having occasional same-sex experiences are unlinked to having exclusively same-sex experiences.

In addition, people who only occasionally have same-sex partners tend to have genetic variants associated with having more sexual partners overall, and with personality traits like “openness to new experience.” In contrast, the study found that exclusively same-sex behavior had little correlation with the biology of personality. For some people, same-sex behavior may be a form of exploration. For many others, it is not.

Researchers since the 1940s have described sexual orientation as a single trait that exists on a scale, ranging from “exclusively heterosexual” to “exclusively homosexual.” But the new study suggests that sexuality is more diverse than that — many different things, rather than one thing in greater or lesser degrees.

Although valuable, the study does have limits. The sample size is enormous by historical standards, but the sample still excludes most minority groups. This not only impairs our ability to make generalizations across people with different ancestries, it also overlooks the cultural variation within and among groups.

Similarly, the study examines only the binary distinction between same-sex and opposite-sex behavior; it does not examine gender (as opposed to biological sex) or the many other varieties of sexual interest. In order to advance science for everyone, we need studies that explore the full diversity of genetics and experience.

It’s also important not to overstate the role of genes. The study found that genetically related people tend to be similar in their behavior, which tells us that sexuality has influences buried somewhere in the DNA. But when the researchers tried to add up the contributions of each DNA variant they examined, they could predict less than 1 percent of the variation among study participants.

So researchers could never predict sexual behavior from DNA alone. In fact, we’ve known this for a while. Even if you have a homosexual identical twin — someone who shares all of your DNA — you are still more likely to be straight than gay.

Many people are wary of genetic research into sexuality because they fear that scientific findings could be used to advance discrimination. They worry that people will attempt to eliminate same-sex behavior using gene-editing technologies like CRISPR or by screening embryos. But the genetic science of sexuality shows us that neither effort would work.

We must also recognize that bigotry needs no data. No facts will sway those who want to police the intimacies of consenting adults. Rather than consign ourselves to ignorance out of fear, we should use these powerful new data ethically and thoughtfully to arrive at a fuller understanding of who we are.
It’s prejudice, not knowledge, that threatens us.

Friday, August 30, 2019

3275. The Anthropocene: The Amazon Could Self-Destruct

By Max Fisher, The New York Times, August 30, 2019

As fires rage across the Amazon, a growing number of scientists are raising the alarm about a nightmare scenario that could see much of the world’s largest rainforest erased from the earth.

Climate change, along with the fires and other man-made forces, appear on the verge of triggering a significant change in the Amazon’s weather system.

No one knows for sure whether and when this might happen, though some scientists who study the Amazon ecosystem call it imminent. If it does happen, a body of research suggests, the Amazon as a whole would cross a tipping point and begin to self-destruct — a process of self-perpetuating deforestation known as dieback.

If that is left unchecked, half or more of the rainforest could erode into savanna, according to some estimates, and then the rainforest, which has long absorbed the world’s greenhouse gases, could instead begin to emit them.

Subscribe for original insights, commentary and discussions on the major news stories of the week, from columnists Max Fisher and Amanda Taub.

The Amazon’s plant life stores an estimated 100 billion tons of carbon. By comparison, every coal plant worldwide combined emitted 15 billion tons of carbon in 2017. So even if only a small proportion of the trees destroyed by large-scale deforestation burn, this longtime buffer against climate change could instead become a driver of it.

A continentwide transformation remains theoretical, and is still debated by scientists. But some believe that the Amazon could pass this tipping point soon, or may have already.

Asked for a best guess as to when the Amazon might cross that threshold, Thomas Lovejoy, a prominent environmental scientist, said that he and another scientist based in Brazil, Carlos Nobre, had independently arrived at the same estimate: 20 to 25 percent deforestation.

The number was a “hip shot,” Dr. Lovejoy said. And deforestation alone would not set off the cycle, but was shorthand for a more complex set of drivers.

The Brazilian government’s own estimate for deforestation of the Amazon stands at 19.3 percent, though some scientists consider this an undercount.

A Threat Greater Than Fires

The world may one day look back and find the warnings of ecological catastrophe embedded in research papers like one led by Jennifer Balch, an expert on fire.

Before Jair Bolsonaro became president of Brazil and oversaw this summer’s drastic increase in man-made fires in the Amazon rainforest, Dr. Balch and her colleagues set out to study what was then a rarer phenomenon.

They subjected plots of rainforest to a decade of small but repeated fires like those set by farmers, and they found something alarming. After enough cycles, even if the fires caused only moderate damage, if rainfall dropped, the trees began dying off in huge numbers.

The proportion of plant life that died after a fire suddenly spiked from 5 or 10 percent to 60 percent — sudden ecological death.

“We were able to document that, yes, the Amazon does have a tipping point,” Dr. Balch said of her team’s experiment, which is still going on. “And it can happen in a very short period of time.”

But what most disturbed the scientists was how this phenomenon seemed to fit into a larger cycle — one that implicated the rainforest as a whole.

That cycle is triggered by four forces, all but one of them man-made: roads, fires, invasive grasses and climate change.

Roads, along with other forms of construction, fragment the rainforest, leaving each acre of plant life less able to endure a fire or resist its spread.

“As fragmentation is happening, you’re exposing a lot more forest edges,” Dr. Balch said. Those edges are more susceptible to drying out and other dangers.

Invasive grasses are one of those dangers, lingering at forest edges. Even a small fire can wipe out a rainforest’s undergrowth. Then grasses rush in, setting a blanket of dry, flammable plant life — and making the next fire far more damaging.

Climate change, by heating the Amazon, has made its dry seasons dryer and more hospitable to those grasses. As fires clear undergrowth, they carve out new, vulnerable forest edges and dry out forests, exacerbating the effects of climate change.

But what makes those forces so dangerous is not that they kill trees — it’s that they reduce rainfall.

In a healthy rainforest, plant life absorbs rainwater and groundwater, then sweats it back out into the atmosphere as moisture, seeding more rain. But once a section of rainforest has been thinned and fragmented, it gives off less moisture. Rainfall decreases, and the ground, of course, grows drier.

As a result, the next fire burns hotter and reaches deeper, causing more damage. Past a certain point, the forest no longer produces enough rain to survive.

“There’s already evidence that this can take place on phenomenal scales,” said Daniel Nepstad, an environmental scientist who studies the Amazon. “This is the imminent risk that could overshadow deforestation as a risk to this forest.”

Dieback occurs when each of these elements — fires, invasive grasses, reduced rainfall — trigger a chain reaction, acting like the components of a combustion engine.

That cycle is supercharged at every stage by climate change. That means the sudden death that Dr. Balch’s team observed in a few isolated plots could play out across the rainforest as a whole.

Repeated studies have found that deforestation leads to reductions in rainfall — and can even extend the annual dry season by a full month. There are already indications that Amazon deforestation will lead to catastrophic reductions in rainfall.

A study led by Claudia Stickler, an environmental economist, projected that, under current rates of deforestation in the area around Brazil’s Belo Monte hydroelectric dam, rainfall will decline so precipitously that the dam will generate only 60 percent of its planned output.

“If you talk to indigenous groups, they all say that rainfall has changed,” Dr. Nepstad said. “This is, to me, what we need to be focused on.”

Could the Amazon Die?
There are two prevailing theories for what might happen past the Amazon’s tipping point.

One is that cycles of destruction will play out only where damage is most severe. Over time, each acre of rainforest that is dried out or destroyed would put neighboring areas at greater risk, potentially accelerating as it spreads. But dieback in one stretch need not necessarily put the entire rainforest at risk.

In the more dire scenario, enough disruptions could upend the Amazon’s weather system as a whole, eventually transforming the region from rainforest into savanna.

No one knows for sure whether this is possible, much less likely. But Dr. Lovejoy, the environmental scientist, underscored that rain and weather patterns are continental — and rely on a full, healthy Amazon.

“The models, and they’re pretty consistent,” he said, “suggest that the combination of fire and climate change and deforestation will weaken the hydrological cycle of the Amazon to the point where you just get insufficient rainfall in the south and the east, and then part of the central Amazon, to actually support a rainforest.”

In either scenario, the Amazon is thought to be approaching a point past which it will begin driving its own destruction.

Scientists stress that the cycle, if caught early, could feasibly be stopped. But, once it begins, it would most likely only accelerate.
“It really makes no sense to figure out precisely where the tipping point is by tipping it,” Dr. Lovejoy said.

A Climate Change Time Bomb

In the late 1990s, a team at the University of Exeter tested an idea that was considered somewhat contrarian.

Could the Amazon rainforest — one of the world’s greatest absorbers of greenhouse gases, and therefore buffers against climate change — become a driver of climate change instead?
They designed a computer simulation to test whether trees might someday die in sufficient numbers as to put more carbon into the atmosphere than the healthy trees sucked up.

The simulation spit out a year: 2050. That was when the rainforest would become a net emitter of greenhouse gasses. The findings were heavily debated.

As the warning signs of large-scale dieback have mounted, more scientists have come to see that scenario as a threat not just to the Amazon’s inhabitants and Brazil’s economy, but to a world already struggling to confront climate change.

“It’s a lot of carbon,” Dr. Lovejoy said. “It’s a really big number.”
And it’s not just the Amazon.

“This is a global phenomenon,” said Dr. Balch, who has studied grasslands in the United States that could pose a similar threat. Dr. Nepstad said that he had found warning signs in the rainforests of Indonesia and the Democratic Republic of Congo.

Dr. Lovejoy compared this moment to the years before the onset of the Dust Bowl, in which mismanagement and drought turned American plains states into wastelands during the 1930s.
“Nobody really saw that coming,” he said. “The difference between then and now is we do see it coming and we know enough not to do it.”