Johannesburg - For three years South Africa has been in the grasp of a rare La Niña event and now scientists believe they have found the smoking gun that triggered this unusual weather phenomena.
Smoke was what they believe birthed the three-year long La Niña and lots of it.
The catastrophic Australian bush fires that occurred in 2019-2020 are suspected to have caused the latest La Niña that brought wetter than usual conditions to South Africa.
Scientists from the National Centre for Atmospheric Research in Boulder, Colorado, in the US argued in a paper, published in the journal Science Advances, that smoke from the burning of an estimated 46 million acres of the Outback contributed to the cooling of the Pacific ocean thousands of kilometres away.
“Many people quickly forgot about the Australian fires, especially as the COVID pandemic exploded, but the Earth system has a long memory, and the impacts of the fires lingered for years,” John Fasullo, the lead author of the study, said in a statement.
La Niña, or the “little girl”, brings wetter conditions to some countries and is caused by the cooling of parts of the Pacific ocean.
The opposite is El Niño, the “little boy”, which brings drier conditions and is triggered by warmer ocean water in the pacific.
But three La Niñas in a row is rare so much so that there have only been three such events since 1950.
The latest La Niña began in the summer of 2020-21.
The scientists’ research involved using supercomputers to create simulations of the weather. The starting point of these simulations was just before the bush fires took hold.
One of the simulations incorporated the emissions from the massive wildfires.
What the scientists saw was that the smoke from these fires quickly encircled the Southern Hemisphere.
Unlike a volcanic eruption that sends particles high into the atmosphere where they cool the climate by reflecting sunlight, the smoke from the wildfires is believed to have “brightened” the cloud decks across the Southern Hemisphere.
This in turn cooled and dried the air off the coast of Peru which had the effect of cooling the Tropical Pacific ocean.
Climatologists have been nervously eyeing the switch between La Niñas and El Niños in recent years. The concern is that climate change will affect the frequency of these two weather systems.
Scientists have in the past hypothesised that human-caused warming would probably produce more El Niños resulting in more droughts in places like South Africa.
However, recent research has suggested that in the short term, climate change might even trigger more La Niñas. The mechanics behind this is not yet fully understood.
While farmers across parts of South Africa have enjoyed higher than average rainfall over the last three growing seasons, the La Niñas have also brought devastating flooding.
Earlier this year, the Vaal Dam was forced to open several sluice gates flooding the Middle Vaal river, while last year 448 people were killed during the so-called Durban floods.
But the extended run of La Niñas appears to be coming to an end.
“Right now we are in the neutral phase, but there looks to be an El Niño coming, with the forecast suggesting quite a high probability,” explains Dr Sarah Roffe, of the Institute for Soil, Climate and Water at the Agricultural Research Council.
An El Niño could bring droughts and hotter than normal conditions, adds Roffe.
“Then there is the question of how long this El Niño is going to last,” she says.