Verheerende Buschbrände hatten von August 2019 bis März 2020 in sechs der insgesamt acht australischen Bundesstaaten und Territorien mehr als zwölf Millionen Hektar Land verwüstet.
© PETER PARKS
Washington – According to an Israeli study, the devastating forest fires in Australia in 2019 and 2020 caused as much smoke to rise into the stratosphere as a huge volcanic eruption. The fact that smoke from forest fires reaches the second layer of the earth’s atmosphere is extremely unusual and has serious effects on the environment, the authors write in their on Thursday in the specialist magazine Science published study.
“I have never seen such an injection (of smoke) into the stratosphere,” said Ilan Koren, professor at the Israeli Weizmann Institute for Science and co-author of the study. According to the study, as much smoke rose into the earth’s atmosphere from the Australian forest fires as from the eruption of the Pinatubo volcano in the Philippines in 1991 – the second worst volcanic eruption of the 20th century.
According to the scientists, the smoke initially migrated away from Australia towards the east – only to approach the continent two weeks later from the west coast. “We saw that the smoke was completely circulated in two weeks,” said Koren.
Three causes of unusual phenomenon
The authors name three causes for the highly unusual phenomenon: The forest fires were very intense during the observation period. They also occurred in a region in southern Australia where the distance between the troposphere – the lowest layer of the earth’s atmosphere – is shorter than elsewhere. Finally, it played a role that the forest fires occurred near strong winds. This contributed to the fact that the smoke reached higher levels in the atmosphere.
Normally, smoke from forest fires only stays in the lower part of the earth’s atmosphere for a few days or weeks, the authors emphasize. “But once it reaches the stratosphere, it stays for months or years,” said Koren. Because the winds are stronger in this layer of the earth’s atmosphere, the smoke can spread faster and stronger. The result is “a very thin blanket of smoke that lies over the hemisphere for months,” said Koren.
Satellite data evaluated by the researchers showed that the smoke remained in the stratosphere from January to July 2020. After that, the scientists were no longer able to distinguish the smoke caused by the forest fires from other smoke. However, traces of the smoke from the forest fires in the stratosphere are very likely still today, emphasized Koren.
Smoke can reflect radiation from the sun
The problem is that smoke lingering in the atmosphere can reflect the sun’s rays. Overall, this “definitely has a cooling effect”, especially on the ocean. This could possibly lead to an interruption of natural processes, such as the photosynthesis of algae in the southern hemisphere.
The smoke can also absorb solar radiation, which, according to the researchers, can lead to local warming effects. “The consequences of warming smoke in the stratosphere are not yet known,” said Koren. (APA / AFP)