The fires that ravaged Australia in 2019-2020 were so massive that they sent as much smoke into the stratosphere as a large volcanic eruption, with significant consequences for the climate, according to a study published Thursday in the journal Science.
The stratosphere is the second layer constituting the atmosphere, above the troposphere (in which we live).
“We were extremely surprised” by these results, told AFP Ilan Koren, one of the two co-authors of the study and professor at the Weizmann Institute of Science in Israel.
The amount of smoke is comparable to that caused by the 1991 eruption of Mount Pinatubo in the Philippines, the second largest eruption in the 20th century.
The smoke “left Australia from the east, and came back to Australia from the west after two weeks, it’s unbelievable,” the researcher said. “I have never seen such an injection (of smoke) into the stratosphere.”
She reached this height because of a combination of three factors, according to the study. First, the intensity of the fires. Then, the fact that some of them were located very south, where the limit between the troposphere and the stratosphere is lower. Finally, because they were also located near a region of strong storms, which contributed to raising the smoke aloft.
The fact that they have reached this height is crucial: in the low atmosphere, the smoke remains only for a few days or weeks. “But when it reaches the stratosphere, it stays between several months or years,” says Ilan Koren.
In addition, the winds are stronger there, which has the effect of diffusing the smoke far and quickly.
“What you get is a thin blanket of smoke that covers the entire southern hemisphere for many months,” says Koren.
The researchers were able to prove the existence of this smoke from January 2020 to July, that is to say for six months, thanks to satellite observations. Then, it becomes too difficult to separate these fumes from other sources, but according to Ilan Koren, they “very probably” remain in part even today.
The main effect of this layer of smoke is to reflect and return part of the solar radiation: “This clearly has a cooling effect”, especially on the oceans located below, says the researcher. With potentially serious consequences, for example on algae that photosynthesize, particularly present in the southern hemisphere, he adds.
In addition, part of the radiation can be absorbed by the smoke, and on the contrary cause localized heating, the consequences of which “are not yet clear”.
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