- The 2019-2020 Australian bushfires threw up so much ash into the atmosphere that it resulted in a cooling of the southern Pacific and hence a La Niña climate phenomenon, a new study says.
- Volcanic eruptions that send vast ash plumes into the atmosphere are thought to trigger La Niña events, but this is the first time a fire has been recorded as doing so.
- La Niña can produce ruinous weather conditions in contrasting ways, from additional hurricanes in North America and droughts in the Horn of Africa, to crop failures in South America.
- The study’s findings call into question the assumption in current climate models that biomass emissions — including from bushfires — will decrease over time.
Smoke from the catastrophic 2019-20 Australian bushfires may have tipped the planet into a La Niña climate phenomenon lasting almost three years, according to new research published May 10 in the journal Science Advances.
“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,” the study’s lead author, John Fasullo at the U.S.-based National Center for Atmospheric Research (NCAR), said in a statement.
La Niña events typically occur every three to seven years, when colder sea surface temperatures form in the Pacific Ocean. The cooler water temperatures alter circulation in the atmosphere, leading to increased rainfall and cold in some regions, and dry and hot conditions in others.
However, this La Niña event was unusual in both duration and timing. The most recent La Niña lasted for three northern winters and didn’t follow an El Niño, the opposite phenomenon caused by warmer sea surfaces. It was only the third triple-year La Niña since records began in the 1950s.
The NCAR-led research was part of a broader investigation into how emissions reductions during the coronavirus pandemic impacted the climate, Fasullo told Mongabay.
“The fires were a major climate event at that time and so it seemed logical to address their effects as well,” he wrote in an email.
The study, titled “A multiyear tropical Pacific cooling response to recent Australian wildfires in CESM2,” used the NCAR’s most-advanced climate model — Community Earth System Model, version 2 (CESM2) — to measure the impact of the Australian fires on climate change-related emissions.
“CESM2 has major advances in its representation of clouds, smoke, and their interaction that allows us to more accurately depict the processes that are at the core of the wildfire-La Niña interaction,” Fasullo told Mongabay.
The research was funded by three U.S. government institutions: NASA, the National Science Foundation, and the Department of Energy.
Past research has suggested the volume of dust generated by major volcanic eruptions can contribute to the formation of La Niña.
“We were quite surprised as, to our knowledge, this is the first study to document the triggering of an ENSO [El Niño-Southern Oscillation] event by wildfire emissions,” Fasullo said. “Studies on volcanic eruptions suggested it might be possible, but wildfires have never been shown to have this influence.”
Particles ejected by volcanoes can climb tens of kilometers into the atmosphere, where they can reflect sunlight directly, leading to cooling. In the case of wildfires, ash from the biomass burned in the Australian bush drifted over the Southern Hemisphere at lower altitudes, circumventing the planet in around one month, and caused Pacific cooling to occur by brightening the clouds.
Forecasters assessed limited probability of an impending La Niña as late as June 2020, just before the cooling phenomenon became apparent. Fasullo said this research helps explain why the likelihood was overlooked.
La Niña can produce ruinous weather conditions in contrasting ways. Meteorologists have linked La Niña with additional hurricanes in North America, droughts in the Horn of Africa, and crop failures in South America.
In Southeast Asia, extreme rainfall has triggered natural disasters, fatal landslides and flash floods. La Niña also impacts populations of marine species by shrinking phytoplankton, which forms the basis of the food chain.
The government of Tuvalu, an island country in the South Pacific, declared a state of emergency last November as some countries in the region began rationing water because of drought.
“I would describe these aspects in a more probabilistic sense,” Fasullo said. “That’s to say, that the Australian bushfires very likely increased the chances for La Niña to occur from 2020-22 (perhaps doubled them?). It is hard to be more precise than that because of the uncertainties involved.”
Impacts on land caused by fluctuations in the El Niño-Southern Oscillation cycle can be highly complex. Soil moisture in much of Indonesia and Malaysia, the world’s No. 1 and 2 producers of palm oil, is at the highest level in more than a decade after several years of sustained rain.
This has likely suppressed the fires and haze pollution that spiked during extended dry seasons in 2015, a strong El Niño year, and 2019, which was influenced by a positive Indian Ocean dipole (which is driven by sea temperatures in the Indian Ocean).
In March, NASA announced that La Niña had ended and been replaced by neutral conditions.
However, the latest assessment by the World Meteorological Organization notes a 60% probability of an El Niño emerging in May-July, and a 70-80% likelihood in the July-October period.
Indonesia’s Meteorology, Climatology, and Geophysics Agency (BMKG) has said the archipelagic country in 2023 is likely to experience its driest weather since 2019, caused by an El Niño forming in the coming months, increasing the risk of land and forest fires. Military and police personnel have been mobilized to confront fires ahead of what the government expects will be a challenging dry season.
Gaps remain in the understanding of wildfire emissions on climate.
“The future emissions scenarios used in most current climate projections depict a future reduction in total biomass emissions, a highly unlikely outcome in light of current trends,” the study noted.
Fasullo added, “As the climate changes, the emissions from wildfires will also change. But we don’t have that feedback in the model. It is the goal of our current work to incorporate these effects as realistically as possible.”
Banner image: An Eastern grey kangaroo and her joey who survived the forest fires in Mallacoota. Australia, 2020.
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