Special Report: Is the Amazon near a tipping point? Three real-world studies are ominous

Rainforest Resources

21/10/2021 12:00

(For more Reuters Special Reports, click on  SPECIAL/ )
    By Stephen Eisenhammer
    OURO PRETO DO OESTE, Brazil, Oct 21 (Reuters) - Gertrudes
Freire and her family came to the great forest in search of land
and rain. They found both in abundance on that day half a
century ago, but the green wilds of the southwestern Amazon
would prove tough to tame.
    When they reached the settlement of Ouro Preto do Oeste in
1971, it was little more than a lonely rubber-tapper outpost
hugging the single main road that ran through the jungle like a
red dust scar.
    Sitting on the porch of the family farmhouse in the
sweltering heat of the Amazon dry season, Gertrudes, now 79 with
neat gray hair tucked behind her ears and a smile that shows
half a dozen stubborn teeth, recalls the hardship and hope.
    Her children remember the fear. Fear of forest jaguars,
indigenous tribes and the mythological Curupira: a creature with
backward-turned feet who misleads unwelcome visitors to leave
them lost among the trees.
    The family carved their home from the forest. They built
their walls from the tough trunks of the cashapona tree and
thatched a leaky roof from the broad palms of the babassu. There
was no electricity, and some days the only food was foraged
Brazil nuts. At night, in hungry darkness they would listen to
the cascading rain. Life was damp.
    Until it wasn't.
    Near the Freire home, there was a stream so wide that the
children – aged between 5 and 12 when they arrived – would dare
each other to reach the other side. They called it Jaguar's
Creek. Now it's not a meter wide and can be cleared with a
single step.
    The loss of such streams, and the wider water problems they
are a part of, fill scientists with foreboding.
    Covering an area roughly the size of the contiguous United
States and accounting for more than half of the world's
rainforest, the Amazon exerts power over the carbon cycle like
no other terrestrial ecosystem on Earth. The tree loss from an
extremely dry year in 2005, for example, released an additional
quantity of carbon dioxide into the atmosphere equivalent to the
annual emissions of Europe and Japan combined, according to a
2009 study published in Science magazine.
    As more and more of the forest is cut down, researchers say
the loss of canopy risks hitting a limit – a tipping point –
after which the forest and local climate will have changed so
radically as to trigger the death of the Amazon as rainforest.
In its place would grow a shorter, drier forest or savannah.
    The consequences for biodiversity and climate change would
be devastating, extinguishing thousands of species and releasing
such a colossal quantity of carbon dioxide into the atmosphere
that it would sabotage attempts to limit global climate change.
    The Amazon tipping point would mark a final shift in the
rainforest's ability to sustain itself, an inflection point
after which the trees can no longer feed traversing clouds with
enough moisture to create the quantities of rain required to
survive.
    Climate models have foreseen other so-called tipping points
disrupting Earth's long-balanced systems, for example warming
that causes Siberian permafrost to thaw and release huge amounts
of emissions, or Greenland's Ice Sheet melting at such a rate
that annual snowfall can no longer make up for the loss.
    Exactly where that point is in the Amazon, science is not
yet decided. Some researchers argue that current modeling isn't
sophisticated enough to predict such a moment at all. But
evidence is mounting that in certain areas, localized iterations
of the tipping point may already be happening.
    Reuters has tracked three extended experiences of the Amazon
to give a real-world view of degradation once only predicted by
computer simulations.
    A family that has farmed this once-lush part of rainforest
for almost 50 years. A scientist couple who have monitored
thousands of individual trees for decades. And an atmospheric
chemist who has collected air samples from far above the canopy
for years. Their perspectives reveal the long-term impact of
deforestation: on rainfall, on the remaining forest and on
global emissions. Taken together, they show the dangerous extent
of the changes wrought on the world's largest rainforest, and a
possible glimpse of things to come.
    Even as science learns more about the far-reaching impact of
destruction that began many years or even decades ago,
deforestation has surged under President Jair Bolsonaro, who
supports further opening the Amazon for mining and agriculture.
Last year, an area larger than Lebanon was cut from the
rainforest, and though preliminary data for 2021 points to a
slight year-on-year decline, deforestation remains at a level
not seen in Brazil since 2008.
    Ecologist Paulo Brando, one of the leading scientists
studying the changing health of the Amazon rainforest, sums it
up: "There's a limit to how much shit the system can take."
    
    LAND OF THIRST
    Year after year, the Freire family hacked and sawed farther
into their patch of forest on Brazil's western frontier.
    In 1976, after clearing a couple of hectares and getting
permission to use some of their neighbor's pasture too, they
invested in 10 heifer calves and a bull – the start of a dairy
business that would over the years grow into a successful herd
of about 400 head.
    But a fear of drought haunted their work. They had come from
the Vale do Jequitinhonha, 2,500 kilometers (1,553 miles) to the
east, where decades of slash-and-burn agriculture had dried and
degraded the land, plunging its people into poverty. The
semi-arid strip became notorious as the "Valley of Misery." Even
while water was plentiful, they sensed the same could happen in
their new home.
    Soil erosion, like that which plagued the Vale do
Jequitinhonha, often follows rapid and chaotic agricultural
expansion. Land stripped of native vegetation, especially when
transformed into pasture and pounded hard by grazing cattle,
loses ability to retain water in soil and foliage. Rain runs off
the altered surface in sudden surges, dragging topsoil into
streams and rivers that then clog and dry.
    Brazil is blessed with the largest freshwater reserves in
the world. But the relentless rise of one of the world's
agricultural powerhouses combined with changes in global climate
are helping to drive a loss of this vital resource. Data
released this year by MapBiomas, a collaboration between
universities, nonprofit groups and technology companies, found
Brazil lost 15% of its surface water in the three decades prior
to 2020.
    For the Freires, the last bits of doubt about the drying of
the land seeped away on a parched day in 1991. A cowhand told
Gertrudes the cattle were so thirsty, they were nuzzling the
bottom of dried-out springs, sucking the sand in search of
moisture.
    She acted swiftly and put in a complex system of pipes and
pumps to draw water for the cattle from springs that had not yet
gone dry.
    Controversially, she began reforesting too. Gertrudes had
little idea of what she was doing but trusted her instincts,
sharpened by years of drought in the homeland she'd abandoned.
    Her neighbors – and husband – thought she was crazy as she
planted trees around water sources and along streams and vowed
that the last remaining patch of virgin forest, at the far end
of the property, should remain intact.
    Her words weren't always heeded. "I came back from one short
trip away and my husband had cleared another patch" for pasture,
she remembers, shaking her head.
    Gertrudes sensed that rainfall was changing too.
    Several scientific studies have found the same. Because
tropical forests influence rainfall, deforestation can change
their pattern. One influential 2011 paper looking at 30 years of
precipitation data found that the onset of rains in Rondonia
state, where the family lives, had been delayed by up to 18
days.
    Research since then has backed up this trend. A major report
this year, which brought together around 200 scientists, said
available data pointed to a dry season that "has expanded by
about one month in the southern Amazon region since the middle
1970's."
    Antonio Deuseminio, an agroecologist with decades of
experience in the rainforest, is helping farmers replant trees
and bring water back to their properties. He works for a
subdivision of the Ministry of Agriculture focused on cacao,
which he says has the oldest weather data in the area. Although
total rainfall hasn't changed significantly in Ouro Preto do
Oeste, the dry season has gotten longer and drier, Deuseminio
says. For agriculture this is a serious problem, because crops
and grasses don't have long enough roots to find water when
there's no rain.
    The drier climate makes reforesting harder too. Twenty years
ago, rainforest species could be planted straight into the bare
soil. Deuseminio says he must now first plant drought-resistant
trees, and only once these have grown enough to provide shade
and improve the soil, after five years or so, can he follow up
with classic Amazon species. Rainforest saplings now struggle to
survive, he says, in this part of the Amazon.
    
    DEATH ON THE BORDER
    Decades of farming have made the Freires sensitive to the
changing rains. But to the untrained eye, the slow shifts in
surviving forests - like the one at the end of the family's farm
- are harder to see. Detecting these changes can require years
of methodical study, sweaty painstaking work, with tape measures
and walking boots and notebooks.
    Ecologists Ben Hur Marimon Jr. and Beatriz Marimon have
spent so long in their forest plots that they've befriended many
of the trees. They're saddened by those they have lost over the
years. Of late, they are losing more and more.
    The couple conduct research at the local campus of the Mato
Grosso State University in Nova Xavantina, a soy town of 20,000
people located about 1,200 kilometers east from the Freire
farmhouse. The surrounding area is a biome borderland, an
in-between space where the Cerrado savannah transitions into the
Amazon rainforest. The trees that remain, they say, offer a
vision of the future.
    "This is tomorrow, today," Beatriz says, crunching through a
dry patch of forest on the edge of town. Ben Hur finishes the
thought. "This is the border of the Amazon, its protective wall,
and it's dying."
    If the tipping point marks the irreversible march of
savannah over rainforest, scientists predict the process would
first occur in forests where savannah and rainforest are already
intertwined.
    Ben Hur is 58, with a neatly trimmed white beard and frayed
walking boots – a chewed victim of their dog. Beatriz, 55, has
long gray hair tied back in a practical ponytail. The couple met
in the 1980s while studying forest engineering in the state
capital, Cuiaba. The two have basically worked together ever
since. "He likes to talk; I like to do," jokes Beatriz.
    To monitor the forests, the couple tag trees of varying
sizes and species across their plots with bits of metal that
look like military dog tags. They return at regular intervals –
anything from three months to three years – and measure tree
circumference, height and carbon dioxide respiration. Trees that
haven't made it are added to a list of the dead.
    Rainforests recycle vast quantities of water by returning
rainfall to the sky through soil evaporation and plant
transpiration, by which water absorbed in the roots is released
via a plant's leaves. In the Amazon, moisture that comes off the
Atlantic Ocean is transported for thousands of miles across the
South American continent, falling as rain and rising again as
vapor as many as seven times until it hits the mountain wall of
the Andes. On hot days, after a downpour, the forest can look
like it's steaming.
    But large-scale deforestation disrupts this process,
reducing the number of trees to such an extent that
precipitation levels fall or become more concentrated over a
shorter wet season. In some parts of wide-ranging Nova Xavantina
over the past 30 years, Ben Hur says, rainfall has fallen by as
much as 30%.
    As precipitation changes, streams and sources disappear, and
the remaining forest turns drier. Local temperatures also
increase – particularly on edges where forest and farmland meet.
Those vast flat agricultural clearings increase the strength of
winds, which can rip through woodland and tear down the tallest,
oldest trees.
    The drier forest is also more vulnerable to fire, which is
still widely used for clearing farmland here. As more trees die
– from wind, drought and fire – their deaths increase the
likelihood of such extreme weather in the future, creating a
deadly feedback loop.
    Early experiments that mimicked extreme drought in the
Amazon had led scientists to think the drier climate would kill
older trees first, but what Ben Hur and Beatriz have found is
the opposite. With longer roots, the largest trees are usually
the most resilient – at least to drought. Instead, says Ben Hur,
pointing to the brown leaves of a nearby plant, it's the
saplings that die. The forest loses its future.
    For Ben Hur and Beatriz, the degrading forests around Nova
Xavantina demonstrate that the tipping point may already be
happening there on a local level. The major question remains
whether this same process could occur on a huge scale over
entire swaths of the Amazon basin – and if so, when?
    Celebrated Brazilian climatologist Carlos Nobre, who has
helped popularize the idea of the tipping point over the past
decade, puts the precipice at between 20% and 25% deforestation
of the original Amazon canopy. We are currently at about 17%,
according to the major report with 200 scientists published this
year. Nobre believes we could see mass dieback across eastern,
southern and central Amazonia within as little as 15 years.
Others aren't so sure.
    Marina Hirota, an earth system scientist who worked on
models before switching to field work, says current simulations
oversimplify the diverse vegetation, soil type and topography
found across the Amazon basin. In her view, there's not yet
enough evidence to say where the tipping point is or even if
such a single threshold exists for sure. The models need to be
improved first, she says.
    Hirota considers it more likely that deforestation would
trigger multiple smaller tipping points in different locations
across the Amazon, similar to what Ben Hur and Beatriz have seen
in Nova Xavantina.
    But many scientists think putting a single number on the
tipping point is still important as a clarion call, even if it's
too complex to currently prove. Once you're able to prove it,
ecologist Brando argues, it will already be too late.
    "We know there's a cliff out there, and so even if we're not
exactly sure where it is, we need to slow down," Brando says.
"Instead, we're rushing towards it with our eyes closed."
    
    VIEW FROM ABOVE
    In the decades that Ben Hur and Beatriz were listing trees
and wrapping them with tape measures, the atmospheric chemist
Luciana Gatti was mastering how to catch carbon dioxide from the
skies.
    While the view from the ground found trees struggling under
hotter and drier temperatures, Gatti wanted to understand what
these changes meant for the Amazon's role in global climate
change.
    Gatti, 61, first specialized in reactive gases and began her
career at Brazil's Nuclear and Energy Research Institute. After
the 1992 Earth Summit in Rio de Janeiro, she turned to the
Amazon, joining a crop of home-bred scientific talent striving
for a bigger Brazilian role in global climate research. She now
works for INPE, Brazil's space research agency, where her narrow
office is cluttered with family photographs and lanyards from
past conferences. On her desk sits a stress ball shaped like
planet Earth.
    Since the Industrial Revolution, scientists estimate that
roughly a quarter of all fossil fuel emissions have been
absorbed by forests and other land vegetation and soils, chief
among them the Amazon.
    Through the 1980s and 1990s, as mass human migration to the
Amazon was just beginning, the rainforest drew down some 500
million tons of carbon from the atmosphere every year, more than
the current annual emissions of Germany, Britain, Italy and
France combined. Photosynthesis by the forests' billions of
trees, using carbon dioxide to live and grow, served as a vital
buffer against climate change.
    As migration increased and more of the Amazon was cleared
for agriculture, scientists knew the forest's ability to suck in
carbon would be hit. But no one knew quite how much.
    To try and get an answer, Gatti squeezed into a roaring
single-engine four-seater plane armed with a padded suitcase
packed with glass flasks. From up over the canopy, she could
sometimes see the scale of destruction, the gray smoke billowing
from burning trees and the yellow patches of earth shorn of the
forest green.
    Gatti's earliest air samples date back to 2000, from a
single point in the eastern Amazon. But she found the data too
narrow and volatile to give a picture of the carbon balance for
the whole basin, so over the following years she expanded the
work, training teams and contracting light aircraft to fill
flasks of forest air from four parts of the Amazon: Santarem and
Alta Floresta in the east and Tefe and Rio Branco in the west.
    Since then, the aircraft have taken more than 600 vertical
profiles – a series of samples taken at different altitudes over
a given spot. At one point Gatti doubted her results. She grew
depressed. The data didn't make sense. It couldn't be true. It
showed the southeastern Amazon was releasing more carbon that it
was absorbing, even in rainy years when scientists had expected
the forest to be in better health. It meant a part of the
rainforest was no longer helping to slow climate change, but
adding to the emissions driving it.
    She changed her methodology. Changed it again. And again. In
total, she went through seven methodologies before eventually
accepting what had seemed impossible. The southeastern Amazon is
not only a net producer of carbon, but even when you strip out
the fires, the forest alone – or the non-fire net biome exchange
– is a carbon source. Scientists widely regard the results,
recently published in Nature, as the most definitive so far on
the changing carbon fluxes of the rainforest.
    The western part of the Amazon, protected by its remoteness,
is in better health and can still absorb substantial amounts of
carbon, the study shows. But it's not enough to compensate for
the polluting east, where ranching and soy farming have cut deep
into the rainforest. The so-called lungs of the Earth are
coughing up smoke. "We are losing the southeastern part of the
forest," Gatti says.
    Gatti thinks her numbers show that certain parts of the
Amazon may already be at their tipping point. She believes the
data points to the same process that Ben Hur and Beatriz have
witnessed, but on a greater scale: Rainforest species such as
the brazil nut and the ironwood giving way to trees like mabea
fistulifera and ouratea discophora that are more tolerant of the
drier, hotter climate. Such regime change releases huge
quantities of carbon and would help explain the forest's
flagging ability to draw down emissions.
    "It is a path without return," Gatti says.
    
    WATER A CONSTANT WORRY
    Back in Ouro Preto do Oeste, the Freires bemoan the driest
dry season any of them can remember. It is mid-August, and the
first rains used to come by now, they say. The dry season, once
just three months, now stretches for four or five. Across the
whole country, reservoirs are dangerously low as Brazil suffers
one of its worst droughts in a century.
    The family is diversifying to try and shield their business
from drought, building out capacity in breeding and beef cattle
to complement their milk production. They've also started an
organic soap business and want to plant corn.
    Water is a constant worry. Some nearby farmers have already
sold their land – mostly to larger cattle ranchers who address
the problem by digging deep wells or piping water over long
distances.
    "It's going to get even drier," says Gertrudes, looking out
over her farm's yellow grass as two cats laze comatose in the
stifling afternoon heat. In the distance, smoke hazes the
horizon as newly slashed forest burns. "The water will finish." 
  

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For an online version    https://www.reuters.com/investigates/special-report/climate-un-amazon-tipping-point/
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 (Reporting by Stephen Eisenhammer; editing by Kari Howard)
 ((Stephen.Eisenhammer@thomsonreuters.com;
Kari.Howard@thomsonreuters.com;))