The devastating southeastern Australian bushfires that started last September spewed smoke and aerosols higher into the atmosphere than some Earth-observing instruments have ever measured.
After months of hot and dry weather, the fires erupted in the heavily populated areas of New South Wales and Victoria burning millions of acres of land, destroying thousands of homes, and taking dozens of lives across the country. Now that the fires have been extinguished, NASA scientists are still seeing lingering effects of this natural disaster.
NASA’s fleet of space-based instruments help scientists and researchers understand how these fires can effect the Earth. Working collaboratively, these NASA systems can detect actively burning fires, track smoke and aerosol transport, help to create air quality forecasts, and observe long-term impacts to wildlife and ecosystems.
Between November 2019 and the end of January 2020, the Stratospheric Aerosol and Gas Experiment (SAGE) III instrument, mounted on the International Space Station (ISS), saw a dramatic increase in the amount of stratospheric aerosols above Australia.
Aerosols are tiny, airborne, solid and liquid particles in the atmosphere. Most aerosols are naturally occurring, including windblown dust from deserts, sea salt, smoke from wildfires, and ash from volcanic eruptions. Stratospheric aerosols can play a role in the destruction of ozone, which acts as Earth’s sunscreen to protect humans from harmful ultraviolet rays from the Sun. In addition, depending upon their size, type, and location, stratospheric aerosols can also either cool Earth’s surface, or warm the atmosphere, contributing to variability in the climate record.
In November, SAGE III saw increased amounts of aerosol in the upper part of the troposphere (approximately below 12 km for mid-latitudes), but the loading in the stratosphere, just above the troposphere, remained normal. At the end of December and into early January, the intrusions of aerosols into the stratosphere became more consistent in the SAGE III science data due to pyrocumulonimbus storms, or pyroCbs. These pyroCbs occur when fires loft enough heat and moisture into Earth’s atmosphere, creating powerful clouds that cause dangerous smoke-infused thunderstorms.
“Different from typical stratospheric sulfate aerosol, pyroCb injected aerosols are of larger size, according to SAGE III/ISS data, and most likely carbonaceous (soot), based on the context,” said David Flittner, SAGE III project scientist at NASA’s Langley Research Center in Hampton, Virginia.
Approximately once a month, the orbit of the ISS allows SAGE III to make high-resolution, vertical observations of the stratosphere within a specific latitude region. Visiting latitudes south of Australia for this regular monthly check-up, SAGE observed the increased aerosol loading at successively higher altitudes: 15 km in early January, 20 km in late January/early February, 25 km in early March, 30 km in late March, and just over 30 km in May.
“A process called the diabatic heating effect causes the aerosols resulting from the wildfires to absorb sunlight and heat the air around them, and rise higher into the stratosphere. This process causes the aerosols to remain in the atmosphere longer before slowly falling back to the Earth’s surface, than if there was no substantial diabatic heating,” said Kevin Leavor, SAGE III scientist.
Initially, SAGE III scientists saw the aerosols from the fires drift east toward South America, as well as towards the southern extent of the SAGE III observation range (70°S). In more recent observations, aerosols have been drifting towards the tropics. Based on events in the past that produced large amounts of stratospheric aerosols, such as the Pacific Northwest wildfires in 2017, scientists expect the effects of the Australian wildfires to stick around for at least a year.
Possible effects on ozone
Aerosols from wildfires, as well as volcanic eruptions, can have an effect on Earth’s Antarctic stratospheric ozone hole.
During winter in the polar regions, aerosols grow to form polar stratospheric clouds (PSCs). The large surface areas of these cloud particles provide sites for chemical reactions to take place. These reactions lead to the formation of large amounts of reactive chlorine and, ultimately, to the depletion of ozone in the stratosphere.
“The increased aerosol content in the south polar stratosphere resulting from the Australian wildfires might have an effect on the 2020 ozone hole by altering the number of PSC particles and the timing of the processes involved in ozone hole chemistry,” said Flittner. Scientists observed enhanced ozone destruction occur after the April 2015 eruption of the Calbuco volcano in Southern Chile.
“Although the timing is slightly different (January for the peak of the fires vs. April for the volcanic eruption) and the composition of the enhanced aerosol is different (carbonaceous vs. sulfate), in light of the response to Calbuco, I am interested to see if the Australian wildfires will influence the 2020 Antarctic ozone hole season,” said Flittner.
Because the fires could have a potential impact on ozone levels at the pole, areas of low ozone could sweep out over regions in the southern hemisphere. New Zealand and parts of South America, such as Argentina and Chile, have been affected in the past by areas of low ozone moving overhead. With reduced amounts of ozone, which acts as Earth’s protective sunscreen, there could be an increase in sunburns, skin cancer and cataracts in humans and reduced crop yield in plants.
“SAGE III is helping to contribute science data to the models that will give a better understanding to what is happening to the ozone in those regions,” said Marilee Roell, SAGE III science manager.
Monitoring fires and eruptions
In addition to the Australian wildfires, SAGE III has seen numerous other notable stratospheric aerosol events throughout its three years in orbit on the International Space Station.
SAGE III saw significant stratospheric aerosol loading events in the Northern Hemisphere resulting from large wildfires in the Pacific Northwest in 2017 and in Alberta, Canada and Siberia, Russia in mid to late 2019.
In addition to the wildfire events, volcanic emissions from the eruptions of Ambae on the south Pacific island of Vanuatu in mid-2018, and Ulawun in Papua New Guinea in mid-2019, introduced significant amounts of aerosols into the stratosphere and greatly increased the concentration of aerosols measured at altitudes observed by the SAGE III instrument. Additionally, the Raikoke volcano on the northwest Pacific Kuril Islands erupted in June 2019 emitting the largest amount of sulfur dioxide into the atmosphere in the past decade. The resulting plume quickly moved toward the equator and was observed at high stratospheric altitudes for several months afterward.
Stratospheric aerosol particles can block sunlight from reaching the ground by absorbing or scattering light, which can then exert a cooling effect on the Earth’s surface. A data measurement called the stratospheric aerosol optical depth tells scientists how much direct sunlight is prevented from reaching the ground by the concentration of aerosol particles in the stratosphere. Since the SAGE III/ISS record began in June 2017, the stratospheric aerosol optical depth record has increased globally by a factor of 2 or 3 due to the various wildfires and volcanic eruptions observed in the past three years. To put this in perspective, the current optical depth record remains a factor of 20 less than after the Mt. Pinatubo eruption in 1991. The Mt. Pinatubo eruption had the most major stratospheric impact in the last 50 years and caused the global troposphere to cool by approximately 1 degree F.
“There has been a significant amount of variability in stratospheric aerosol loading across the globe. Typically, we associate dramatic changes in stratospheric aerosols with volcanic eruptions, but these wildfire events mimic minor volcanic eruptions,” said Flittner. “We have seen major wildfire events three times now in less than three years. This has been unique for historical SAGE observations stretching back to the mid-1980s.”
The SAGE III/ISS stratospheric data complements observations from other NASA satellites such as trace gas data from the Microwave Limb Sounder (MLS) showing record amounts of carbon monoxide (CO), a by-product of wildfires, and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) sightings of stratospheric aerosol plumes. Using these data sources, NASA scientists will continue to monitor the effects of the Australian wildfires on Earth’s atmosphere for the months to come.