44 | New Scientist | 11 December 2021
central – taking samples of the air and
monitoring the temperature, the moisture
content of the soil, how much had been
burned and the greenness of the canopy.
Over the course of the study, which ran from
2010 to 2018, they saw some dramatic shifts.
“The rainfall has reduced a lot, the temperature
has grown a lot, and the forest felt it,” says Gatti.Fatal blow
The hardest-hit areas were in the east. By
2018, the north-east study area was 37 per
cent deforested and the south-east 28 per cent.
Over the nine years, dry-season rainfall fell by
20 to 30 per cent and the average dry-season
temperature rose about 2°C. In the south-east,
in particular, where there is an “arc of
deforestation” because of encroaching cattle
and soya, this is delivering a fatal blow to the
forest. “The forest is now more dying than
growing,” says Gatti. As a result, the south-east
has flipped from being a carbon sink to a
carbon source. Rather than soaking up some
of our emissions, it is adding to them.
“This is the most troubling element,” says
Nobre. And the situation is getting worse.
According to Gatti, in the 50 years up to 2018, the
Amazon lost about 17 per cent of its forest cover.
In the past three years, the rate of deforestation
has accelerated dramatically and a further
1.5 per cent is being destroyed a year. Parts of the
east are now 40 per cent farmland and she says
she wouldn’t be surprised to see 50 per cent.
“This is amazing, crazy deforestation,” she says.
Given the levels of deforestation in the
southern Amazon, it isn’t unreasonable to
argue that these changes signal that, in this
region at least, the point of no return is
approaching. “Putting all these things together
we can say we are very, very, very close to this
tipping point,” says Nobre. “Some scientists
believe the tipping point may have already
been exceeded in portions of the Amazon.”
Lovejoy shares the sentiment. “We’re seeing
the ecological system of South America begin
to come apart,” he says.
What would that mean? According to Nobre,
once the threshold is exceeded, the forest will
degrade further even without any more active
deforestation. Eventually, over the course of
years or decades, up to 70 per cent of the
Amazon rainforest will flip to dry savannah.
Not everything will go. “We are only going tohave remaining forest near the Andes where
the concave shape of the Andes makes for
very high levels of rainfall,” says Nobre.
But that won’t save the Amazon, and
indeed the rest of the world, from disaster.
The Amazon covers an area of about 5.5
million square kilometres, more than 20 times
the area of the UK, and holds around 10 per
cent of the world’s species, a quarter of them
found nowhere else. It is a hotbed of cultural
diversity, with 30 million people from more
than 350 ethnic groups. It also supplies the
world with a vital ecosystem service in the
form of carbon sequestration. According to
Gatti, the forest stores at least 100 billion
tonnes of carbon above and below ground.
The loss of 70 per cent of the Amazon will
deposit more than 50 billion tonnes of that
stored carbon into the atmosphere, according
to Nobre – equivalent to roughly six years of
global carbon emissions from the burning of
fossil fuels and a tenth of what we can still
afford to emit from now on to give ourselves
a 50:50 chance of staying within 1.5°C of
warming. That would make reaching the Paris
Agreement target of no more than 1.5°C of
warming almost impossible, says Nobre.
“If we lose the Amazon, the global
temperature can grow 0.25 degrees,” saysAzevedo. That would be bad enough, but the
added fear is that it could push the climate past
one or more other potential tipping points,
such as the thawing of the Arctic permafrost
or the loss of an Antarctic ice sheet.
“These things are very dangerous because
they can create a cascading effect that will
impact the whole basis of the biosphere,” says
Robert Nasi, director-general of the Center for
International Forestry Research in Indonesia.
At the very least, the loss of a major chunk
of the Amazon could do irreparable harm to
neighbouring ecosystems of international
importance, including the high Andes and
the tropical savannah of the Cerrado.
Amid all this gloom, however, are reasons
for hope. Paulo Brando at the University of
California, Irvine, points out that the 20 to
25 per cent figure comes from computer
models that are inherently uncertain. One
especially thorny factor is rising levels of CO2,
which boosts the growth of vegetation and
may offset the deforestation somewhat.
Models that leave this out produce tipping
points at 20 to 25 per cent, but throw it in and
you suddenly get a wider range of outcomes.
The claim that the tipping point lies
somewhere between 20 and 25 per cent thus
remains a hypothesis, says Brando – albeit a
plausible and scary one. “If it’s supported by
observation, we are in huge trouble,” he says.
“The changes that we’re seeing today are in
agreement with predictions. But to jump
from there and say that we have initiated
this snowball effect that would lead to
savannisation of the Amazon, there are large
uncertainties.” Nonetheless, he still supports
urgent action. “The tipping point is something
that we don’t want to find out by doing.”
Some scientists are wary of crying “tipping
point” at all. “I think we in general have to be
careful about throwing that phrase around,
it’s kind of dangerous,” says Scott Denning,
an atmospheric scientist at Colorado State
University who wrote a commentary on Gatti’s
research in Nature. In the context of the
Amazon, it wrongly suggests that the entire
forest is doomed, he says. He does accept that
the south-east region has crossed a dangerous
threshold where it no longer helps to soak up
our carbon emissions. But that isn’t the same
as total collapse.
The Amazon also emits a lot of the potent
greenhouse gas methane, mostly from itsPeople working for a logging
company in the city of Portel
in the Brazilian Amazon“ The south-east of the Amazon has flipped
from being a carbon sink to a carbon source”
VICTOR^ MORIYAMA