Impossible to forget the images of charred forests, koalas in flames and plumes visible from space: the fires that bruised Australia at the end of 2019-beginning of 2020 are still in everyone's mind.
But they also left a lasting mark on the atmosphere, as a study published Thursday in the journal Science sadly reveals.
The 2019-2020 Southern Summer bushfires injected massive amounts of smoke particles into the Earth's atmosphere.
They disrupted the chemical composition of the stratosphere, the second layer of the atmosphere where the ozone layer is located, to a level never seen in fifteen years of observations.
Some of these changes, such as the increase in chlorine-containing compounds, have the potential to destroy ozone, which protects the Earth's surface from the Sun's harmful ultraviolet rays.
Since 2005, "no other year has had continuously low levels of O3
(ozone)
" and "over such a long period", explains the study.
Peter Bernath, from the University of Waterloo in Canada and his colleagues point out that after the discovery of a gigantic hole in the ozone layer in 1985, the prohibition of deleterious substances allowed it to be reduced.
However, the increasing frequency of large forest fires could "delay the recovery of stratospheric ozone, which is currently expected to return to 1980 levels around 2052-2060", thus wiping out previous efforts.
Tipping point in the Amazon
For this study, the scientists used data from the infrared spectrometer of the Atmospheric Chemistry Experiment (ACE) satellite, which makes it possible to study the composition of the atmosphere.
Their observations thus confirm a worrying vicious circle: with climate change, severe forest fires are becoming more frequent, which releases greenhouse gases that accentuate global warming.
In addition to Australia, spectacular fires have ravaged California and the Amazon in recent years.
Last week, another study, published in Nature Climate Change, rightly warned of the high probability that the Amazon rainforest is approaching the tipping point where a tropical forest turns into savannah, with signs of loss of resilience observed in more than 75% of its area since the early 2000s. The causes: climate change and deforestation.
In Nature, this Wednesday, researchers also argue that suppressing fires and planting trees in savannahs may not lead, over several decades, to substantial increases in carbon storage, which is necessary to limit global warming. .
Despite these pessimistic prospects, there is good news all the same, according to the same scientists: the savannah itself would act as a carbon sink and frequent fires in this environment would not have a significant impact on the climate.
