2023-05-10 21:28:00
“The planet has a long memory. The fires that ravaged Australia in 2019-20 were so catastrophic that they fueled the major La Niña weather phenomenon that began in late 2020, according to a new study published on Wednesday.
La Niña is characterized by a lower temperature of the waters of the South Pacific Ocean, with important consequences for the whole planet, for example in terms of predicting floods or droughts. A La Niña episode has just ended following raging for three years, which is rare.
According to the study, because of the emissions from the fires, a larger cloud layer formed, which further blocked the sun’s rays. This helped cool the temperature of an area of the Pacific Ocean, one of the key ingredients for triggering La Niña. “Many people quickly forgot regarding the fires in Australia, (…) but the impacts of the fires persisted for several years,” said John Fasullo, lead author of the study, published in the journal Science Advances, in a statement.
As much smoke as a volcanic eruption
Scientists have already established in the past that volcanic eruptions might influence this phenomenon. By projecting particles called aerosols into the atmosphere, they reflect the sun’s rays and cause a cooling effect, which can create favorable conditions for La Niña.
However, following the fires that occurred in Australia in 2019 and 2020, which ravaged around 18 million hectares, a study had estimated that these fires had projected into the atmosphere as much smoke as a volcanic eruption. This time, the researchers therefore sought to study in detail the impact that these fires had on the climate.
For this, they carried out two simulations: both started in August 2019, but one took into account the emissions from the fires as observed by satellites, while the other only integrated the usual average emissions. . The researchers found that the Australian fires had caused a significant chain reaction. Aerosols formed by their emissions cleared cloud cover over the southern hemisphere, particularly off Peru, cooling and drying the air in the region. This had the effect of shifting the area where the south and north winds (trade winds) meet.
Result: a cooling for several years of the South Pacific Ocean, where La Niña is formed, explains the press release from the National Center for Atmospheric Research (NCAR), to which the authors of the study are affiliated.
Global implications
According to John Fasullo, this work helps to explain some questions regarding the formation of the La Niña episode which has just ended. This one was unusual because it did not follow a strong El Niño episode, its counterpart which tends to raise temperatures – and which is likely to form this year. In addition, in June 2020, a few months before the start of La Niña, some forecasts still leaned towards “neutral” conditions, that is to say where neither El Niño nor La Niña were favoured.
“This work is a very interesting example of how regional processes, like fires, can have global implications, shaping the course of significant climate events like La Niña,” commented Pete Strutton, a professor at the University of Tasmania, and who did not participate in the study. The researchers’ results also underline the importance of incorporating actual emissions from fires into future climate models, as well as weather forecasts. These are set to multiply with global warming caused by human activities.
“With climate change, emissions from fires will also change,” said John Fasullo. “But we don’t have those reactions in our models. The goal of our current work is to include these effects as realistically as possible. »
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