The bushfires incidents that happened in Australia from 2019 to 2020 have been very extreme. The study revealed that the fire incidents led to millions of tons of smoke particles getting released into the atmosphere. The smoke particles followed a typical pattern of settling to the ground after a day or week. The researchers uncovered the "perfect storm" of circumstances that swept the particles emitted from those fires into the upper atmosphere and spread over the entire Southern Hemisphere.
The study was conducted by two Israeli Scientists and the paper has been published in Science. The particles that reached the stratosphere which is the upper layer of the atmosphere get through volcanic eruptions. The smoke emitted in the extreme eruptions dims the sun and cools the planet. The researchers Prof. Ilan Koren of the Weizmann Institute of Science’s Earth and Planetary Science Department and Dr. Eitan Hirsch, the Head of the Environmental Sciences Division at the Israel Institute for Biological Research in Ness Tziona had noticed an extreme increase in a satellite-based measure of particle loading in the atmosphere called aerosol optical depth(AOD).
They found that this smoke caused record-breaking levels of aerosols over the Southern Hemisphere, as much as that from a moderate volcanic eruption. The severity was caused by a combination of the vigour of the fires and their location at a latitude with a shallow tropopause and within the midlatitude cyclones belt. This aerosol increase caused considerable cooling over oceanic cloud-free areas.
Pyrocumulus clouds were the clouds fueled by the energy of the fire and were considered as a means of transporting smoke to the stratosphere. The researchers also noticed that pyrocumulus clouds formed only over a small fraction of the duration of the fire, and they were mostly seen over fires burning on the central part of the coast. The elevated smoke levels could act as cloud condensation nuclei allowing the clouds to develop deeper.
The particles in the stratosphere had air move in a steady, linear fashion. The strong current was moving them eastwards over the ocean to South America and back over the Indian Ocean toward Australia. The particles were slowly settling around the entire hemisphere. The press release by the Weizmann Institute of Science quoted Hirsch as saying,
"People in Chile were breathing particles from the Australian fires."
The particles by sailing on an endless air current remained airborne for much longer than lower atmosphere smoke particles. Koren said that the effect of the smoke on the atmosphere was cooling though they still do know how much influence cooling and dimming had on weather patterns. He added that the burning cannot be stopped but the precise location of those fires help in finding different effect it has on the environment. Koren said
For people on the ground, the air may have just seemed a bit hazier or the sunsets a bit redder. But such a high AOD – much, much higher than normal – means sunlight was getting blocked, just as it does after volcanic eruptions.”
“There are always fires burning in California, in Australia and in the tropics, he added