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WASHINGTON • The bush fires that struck Australia between 2019 and last year were so big that, according to a study published in the journal Science, they spewed as much smoke into the stratosphere as a large volcanic eruption with serious consequences for the environment.
The stratosphere is the second layer of the atmosphere directly above the troposphere in which People live. « It was a big surprise for us, » said study co-author Ilan Koren, professor at the Weizmann Institute of Science in Israel, on Thursday. « I’ve never seen an injection (of smoke) like this into the stratosphere, » he said.
The amount of smoke released into the atmosphere by the fires is comparable to the amount released by the outbreak of Mount Pinatubo in the Philippines in 1991, the second largest in the 20th century.
The researchers said the smoke drifted east from Australia and returned from the west two weeks later.
« We could see the smoke complete a whole circulation in two weeks, » said Professor Koren. « I’ve never seen such a powerful event spread so quickly. »
First, the fires themselves were intense. Second, they occurred in an area in the far south of Australia, where the distance between the troposphere and the stratosphere is shorter than anywhere else.
And finally, the fires took place near strong storms that contributed to the smoke being higher into the atmosphere.
The fact that the smoke was able to rise so high is crucial to understanding its environmental impact: Usually this smoke only stays in the lower part of the atmosphere for a few days or weeks.
« But as soon as it gets into the stratosphere, it stays from months to years « , explained Prof. Koren.
The winds are stronger up there, so that the smoke can spread further and faster than would otherwise be possible.
« Basically, we get a very thin blanket of smoke that covers the entire hemisphere for many months, » said Prof. Koren.
The researchers were able to monitor the smoke in the stratosphere for six months from January to July last year he watch satellite surveillance. Eventually it became too difficult to separate the smoke from the Australian bushfires from the smoke in the stratosphere, which may have come from other sources.
« But most likely there is still a signature of the smoke in the stratosphere today, » said Prof. Koren.
The main effect of the smoke, which remains in the atmosphere for so long, is that it can reflect the radiation coming from the sun.
According to Prof. Koren, this « definitely has a cooling effect overall » , especially on the ocean, which may disrupt processes such as photosynthesis by algae in the southern hemisphere.
« The consequences of the warming of the smoke in the stratosphere are not yet clear, » said Prof. Koren.
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