Australia’s wildfires had a greater impact on Earth’s climate than the reduction in emissions caused by the Covid-19 pandemic, according to a new computer-modelled study.
Scientists at the National Centre for Atmospheric Research (NCAR) in Colorado analysed the events that influenced climate across the globe over the past year. They found that the smoke emitted from the fires that ravaged Australia from late 2019 to 2020 had a bigger impact on the climate than Covid-related restrictions.
Over the past 12 months, countries around the world have gone into lockdown to help limit the spread of the virus. With people staying at home, and domestic and international travel ground to a halt, fewer emissions were released into the atmosphere.
“The main climate forcing of 2020 wasn’t Covid-19 at all,” said John Fasullo, a scientist at the NCAR and the lead author of the new study. “It was the explosion of wildfires in Australia.”
Experts estimate that more than 10 million hectares of land were scorched during months of fires, which hit several states in the southern hemisphere country. This sent plumes of smoke – similar to those emitted by a powerful volcano, one study said – billowing into the stratosphere, causing temperatures to cool.
According to the computer-modelled study, published in Geophysical Research Letters, an American Geophysical Union journal, on Tuesday, this caused the planet to cool by about 0.06C in the months following the fires.
The smoke caused by fires blocks sunlight from reaching the Earth and modifies clouds, impacting temperatures, the researchers said.
Meanwhile, reductions in traffic and industrial activity will result in an average warming worldwide of about 0.05C by the middle of 2022, the study said.
The researchers suggested the lockdown-related heating, which they said they had been expecting, was caused by clearer skies resulting from fewer emissions, enabling more of the sun's heat to reach the Earth’s surface.
The NCAR says its research adds to work showing that major fires inject so many sulphates and other particles into the atmosphere that they can disrupt the climate system, push tropical thunderstorms northward from the equator, and potentially influence the periodic warming and cooling of the tropical Pacific Ocean waters known as El Niño and La Niña.
“What this research shows is that the impact of regional wildfire on global climate can be substantial,” Mr Fasullo said.
“There are large-scale fingerprints from the fires in both the atmosphere and ocean. The climate response was on a par with a major volcanic eruption.”
He and his co-authors cautioned that a range of caveats should be applied to the study, largely because of uncertainties about the full extent of emission reductions during the lockdown and the exact climatic effects of wildfire smoke.
To detect the climatic influence of the pandemic and the wildfires, the research team turned to estimates of emissions from both these events.
They then used the NCAR-based Community Earth System Model to run a series of simulations to recreate the global climate – both with the actual emissions and without them – as well as under various atmospheric conditions, and over a time period from 2015 to 2024.
This allowed them to capture the difference that the emissions made to the world’s climate, and to glean more insights than would be possible from observations alone.
The intensive simulations, more than 100 in all, were performed on the Cheyenne supercomputer at the NCAR-Wyoming Supercomputing Centre.
The research was funded by the National Science Foundation, which is NCAR’s sponsor, as well as by NASA and the US Department of Energy.