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Why scientists worry about fires in the Amazon


The fires underway in the Amazon rainforest are larger and more frequent this year and continue to weaken one of the richest terrestrial ecosystems.

An area destroyed by fires near Porto Velho, in the state of Rondonia, Brazil, on 24 August. CARLOS FABAL / AFP

The fires that hit the Amazon rainforest in recent weeks have been invited until the G7, the summit bringing together some of the world's largest economies in Biarritz, between August 24 and 26. At the end of the event, the seven countries offered $ 20 million to help Brazil fight the fires before its president, Jair Bolsonaro, refused the proposal.

If fires occur every year by destroying thousands of square kilometers of the world's largest primary forest, current fires worry conservationists as they become more intense after years of declining deforestation.

In 2019, fires far from the levels of the past but increasing

Cumulative area of ​​the Amazonian forest burned each year in Brazil.

Source: Brazilian Institute for Space Research (INPE)

And the policy of Jair Bolsonaro, elected in October 2018, is not foreign to the renewed concern observed this summer for this ecosystem more fragile than it seems.

Read also: "Bolsonarism appears in all its destructive power"

According to an August 26 article in the journal Science , deforestation is clearly the cause of these fires. The number of fires detected by the INPE (Brazilian Agency for Space Research) and NASA satellites is the highest since 2010, when El Niño caused a severe drought. This year's season is not particularly dry, but the ten most affected municipalities are also those with the highest rates of deforestation, according to the Amazon Institute for Environmental Research (IPAM).

Deforestation has suddenly resumed in the summer of 2019, after a period of stagnation

Amazonian forest area destroyed per month, since August 2015

Source: Brazilian Institute for Space Research (INPE)

Thus, the same typical patterns of deforestation are observed along the agricultural frontier of the forest, according to Paulo Artaxo, physicist specializing in the atmosphere at the University of Sao Paolo: the trees are first slaughtered, before the remaining vegetation is burned to make way for pasture or crops. "There is no doubt that this increase in fire activity is associated with a sharp increase in deforestation," according to the researcher.

This deforestation has several concrete consequences that go far beyond the Brazilian environment.

  • CO2 emissions into the atmosphere

The first consequence is obviously the release into the air of a very large amount of carbon dioxide (CO2), the main greenhouse gas contributing to the warming of the Earth's climate. Because the combustion of biomass naturally emits CO2, but also because the death of trees releases all the carbon that has been sequestered for decades.

It is still far too early to know how much CO2 will be emitted by current events in the Amazon basin, but the quantities released by giant fires are not negligible. A study published in 2002 in the journal Nature showed that the giant fires of Borneo, Indonesia, in 1997 (the largest known, 79 000 km² destroyed) have released between 810 million and 2.57 billion tons (Gt) of carbon , which contributed to the greatest increase in CO2 atmospheric concentration since the data was recorded in 1957 .

CO2 emissions from Borneo24 Gt0.81 -2.57 GtIn 1997, Borneo forest fires accounted for up to 10% of global emissions. Source: Nature & Global Carbon Project

To have an order of magnitude, Brazil has emitted between 1 and 1.5 billion tonnes of CO2 in 2017, and global emissions of CO2 reached 37.1 billion tonnes in 2018.

Read also Fires in the Amazon: a seasonal plague "amplified by the positions of Jair Bolsonaro"
  • Destruction of carbon sinks

The destruction of forests, especially as primary forests such as the Amazon, the largest and richest on the planet, deprives it of what is called a "carbon sink", that is to say the ability of plants to absorb carbon. By limiting the concentration of CO2 in the atmosphere, these carbon sinks are crucial to fight global warming.

Recent publications in Science and Nature have shown that with the exception of primary forests - that is, unmanaged forests, which are declining year by year (down 10% in tropical areas between 1990 and 2015) - forests, worn out by droughts and deforestation, played less and less of this role of absorption, or could become net emitters of CO2.

  • Destruction of biodiversity

The destruction of the Amazon rainforest directly threatens the exceptional biodiversity it hosts. This ecosystem, which represents only 1% of the world's land surface, is home to 10% of known species and is estimated to account for up to 25% of biodiversity.

According to the WWF (World Wide Fund for Nature), there were 40,000 plant varieties, 2.5 million insect species, 427 mammal species, 1,293 bird species, 378 reptile species, 427 amphibian species and 3,000 species of fish, many of which are endemic, that is, specific to this region. But given the very partial knowledge of the richness of life in the Amazon Basin, these numbers are very probably well below the actual count.

In addition to the danger inherent in forest fires, endemic species are threatened with extinction because of the richness of this primary forest, making it irreplaceable by secondary forests that would have regrown later (although research conducted to this end show that recreated secondary forests reach a high degree of biodiversity).

Article reserved for our subscribers Read also The fires in the Amazon cause a diplomatic crisis between France and Brazil

This biodiversity is also the wealth of hundreds of indigenous peoples who have lived in the Amazon Basin for a long time, whose culture and even survival are closely linked to the forest and its resources.

Article reserved for our subscribers Read also Philippe Descola: "In the Amazon, it is first of all the living environment of the Amerindians who is destroyed"
  • Drying of the climate

Tropical forests such as the Amazon rainforest not only host an extraordinary biodiversity and sequester large amounts of carbon, they also partially regulate the climate, locally and globally. So much so that the Amazon is sometimes called the "green ocean".

The moisture of the forest generates what is called evapotranspiration: large amounts of water evaporate and form clouds, which in turn cause rainfall to irrigate the soil. This participates in the hydrological cycle of the Amazon basin, that is to say the water cycle. However, this balance is considered fragile.

Deforestation, through the exploitation of forest resources or forest fires, reduces the amount of water that evaporates and makes the climate drier in an area whose temperatures are expected to increase by about 3.3 ° C. here the end of the century. Less water vapor means less rainfall, more arid soils, more regular and larger droughts, which in turn will lead to more devastating forest fires and increasing difficulties in cultivating formerly deforested lands, now more sensitive to erosion.

These issues go far beyond the Amazon basin. The climate of South America, and even the whole world would be affected as the regulatory role of the Amazon rainforest is critical. The multiplication of major droughts (2005, 2010, 2015-2016) suggests to some scientists that there may be a tipping point that, if crossed, would gradually disrupt this hydrological cycle that is essential for climate. "If we destroy enough forest, we could tilt the Amazon into a much drier climate, which can become a savannah. It would be a big loss for our planet and a virtual "game over" for the fight against climate change , according to Roel Brienen, professor at the University of Leeds, UK, interviewed by NBC News on August 23rd.

Two American and Brazilian researchers, Thomas Lovejoy and Carlos Nobre, estimated in an editorial published in Science in 2018 that a deforestation of 20 to 25% of the Amazon could collapse this cycle. It is estimated today that just over 19% of the forest has been destroyed since 1970.

Article reserved for our subscribers Read also Fires: the Amazon pays the policy of the Brazilian president

The Amazon, "lung of the planet"? Not really

Discussions and writings around the dramatic fires ravaging the Amazon rainforest often use the metaphor of "lung of the planet" to designate the nearly six million square kilometers that make up the largest forest of the globe.

If the expression - rightly - emphasizes the disturbing consequences of the gradual disappearance of this forest, it over-represents (slightly) the role of the Amazon in the "breathing" of our planet. According to work published in 1998 in Science , it represents about 7% of photosynthesis that produces the oxygen of the atmosphere we breathe, and which absorbs carbon dioxide that heats as slowly as surely Earth.

If "lung" there is, it is rather at the bottom of the oceans than in the South American greenery, since almost half of the terrestrial oxygen is manufactured by photosynthesis of phytoplankton. It is therefore to these tiny planktons living in suspension in the water that we owe our oxygen. Oxygen levels are however not at risk, as it is present (it constitutes 20.95% of the Earth's atmosphere). According to Scott Denning, professor of atmospheric science at the University of Colorado, the burning of all the organic matter on the planet would consume one percent of the Earth's oxygen.

Find all the decoding explanatory articles in our "To understand" section .

Gary Dagorn

Source: lemonde

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