In August 2019, headlines emerged about fires all across the Amazon rainforest. These fires
have been linked to deforestation being carried out by farmers in the region, in order to
make land available for agriculture and cattle production. But what exactly does losing the
Amazon mean for us, and for the health of our planet?
To answer this question, we must first understand the mechanism of evapotranspiration. When
plants absorb CO2 for photosynthesis, they lose water vapour from their leaves through
a process known as transpiration. This, coupled with evaporation of water from forest surfaces,
enables the Amazon to maintain a wetter atmospheric boundary layer. This provides rainfall to
all regions of the Amazon, including the drier South, which would receive less rain had the
forest not existed. This rainfall also travels westward, irrigating agricultural fields and
supplying fresh water to communities all across South America, from the Atlantic coast to
the Andes.
As forest cover is lost, less water is recycled back to the atmosphere and more flows out
in rivers to the ocean, thus less is available to come back down as rain. Scientists think
that, given extensive deforestation, the Amazon rainforest could eventually reach a tipping
point, after which evapotranspiration would reduce to the point when the forest would
no longer generate enough precipitation to sustain its current size. Such a reduction
in evapotranspiration could lead to degradation of the Amazon into savanna or seasonal forest.
Scientists know that this type of ecosystem transition is possible because it has happened
in the past -- in the Sahara around 6 or 7 million years ago. As a result of changes
in Earth’s orbit, the planet cooled and dried, turning what used to be a fertile grassland
into the vast desert that we know the Sahara to be today. While the shift in the Sahara
was the result of geophysical forces over a relatively long time scale, the current
situation in the Amazon is the consequence of human actions over a relatively short period
of time. The potential transition of the Amazon from a rainforest to a drier ecosystem, such
as seasonal forest or grassland, would be devastating for Brazil’s agribusiness sector,
which relies on irrigation from Amazonian rainfall for the success of its crop harvests.
It would also eliminate one of the most biodiverse ecosystems on the planet, and release vast
stores of carbon to the atmosphere, which will accelerate global warming.
The Amazon rainforest is home to millions of species of plants, animals and fungi, all
of which act as organic reservoirs that keep carbon from the atmosphere locked in their
bodies. However, when the rainforest is burned, the carbon that is stored in plant and animal
mass is released to the atmosphere as carbon dioxide, which is a potent greenhouse gas.
In fact, deforestation is the main source of greenhouse gas emissions in Brazil.
However, it doesn’t stop there. With the current rate of global biodiversity loss due
to pollution, habitat loss and invasive species, scientists believe we are at the start of
the sixth mass extinction in Earth’s geological history -- the only one that can be directly
attributed to the actions of a single species: humans. Deforestation in the Amazon will further
exacerbate this crisis, as it is home to roughly 10% of all species on the planet. Biodiversity
is incredibly valuable, as it provides economic, cultural, and environmental services for humans.
For example, rainforest plants contain compounds used in pharmaceuticals to treat all kinds
of illnesses, from malaria to cancer to glaucoma.
Deforestation poses great threats to the health of the Amazon, and to our planet at large.
Although it may provide economic gain in the short-term, it poses severe long-term risks
that would be detrimental both to Brazil’s economy and health. Damage to the Amazon is
bound to have consequences for our future, unless we take action now. See the video description
to learn more about efforts to preserve the Amazon.