Bushfires, not pandemic lockdowns, had biggest impact on global climate
in 2020
Smoke from Australian fires affected temperatures, storm tracks

Date:
July 27, 2021
Source:
National Center for Atmospheric Research/University Corporation
for Atmospheric Research
Summary:
The devastating bushfires in Australia had a larger impact on
the world's 2020 climate than the pandemic-related lockdowns,
as plumes of smoke cooled global temperatures and pushed tropical
thunderstorms northward.

New research indicates that regional wildfires can have far-reaching
climatic effects that are comparable to a major volcanic eruption.



FULL STORY ==========================================================================
When a team of scientists began analyzing events that influenced the
world's climate in 2020, they made sure to consider the pandemic-related lockdowns that reduced emissions and led to clearer skies over many
cities.


==========================================================================
But their research found that an entirely different event had a more
immediate impact on global climate: the devastating bushfires that burned through Australia from late 2019 to 2020, pumping plumes of smoke that
reached the stratosphere and circled much of the southern hemisphere.

"The main climate forcing of 2020 wasn't COVID-19 at all," said John
Fasullo, a scientist at the National Center for Atmospheric Research
(NCAR) and the lead author of the new study. "It was the explosion of
wildfires in Australia." The study is being published online today in Geophysical Research Letters, an American Geophysical Union journal.

Fasullo and his NCAR co-authors used advanced computer modeling techniques
to quantify the climatic influence of the reductions in traffic and
industrial activity related to COVID-19, as well as the smoke emitted
by the fires. They found that the pandemic-related lockdowns of 2020
had a relatively modest and gradual influence that will result in an
average warming worldwide of about .05 degrees Celsius by the end of
2022. In contrast, the fires had a briefer but more significant impact,
cooling the planet within months by about .06 degrees Celsius.

The study illuminates the surprisingly wide-ranging effects of
major wildfires on the world's climate system. Although it may seem counterintuitive that fires, which are associated with hot weather, can
have a temporary cooling influence, their smoke tends to block sunlight
and modify clouds.



========================================================================== Scientists have conducted a number of studies into the potential effects
of warming temperatures on wildfires, which have become increasingly destructive in recent years, as well as the localized impacts of fires
on weather. But they have devoted less research into what the blazes
may portend for large-scale temperature and precipitation patterns.

The NCAR research indicates that major fires inject so many sulfates
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 tropical
Pacific Ocean waters known as El Nin~o and La Nin~a.

"What this research shows is that the impact of regional wildfire on
global climate can be substantial," Fasullo said. "There are large-scale fingerprints from the fires in both the atmosphere and ocean. The
climate response was on par with a major volcanic eruption." He and his co-authors cautioned that a range of caveats applies 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.

The research was funded by the National Science Foundation, which is
NCAR's sponsor, as well as by NASA and the U.S. Department of Energy.



========================================================================== Disparity between hemispheric temperatures To detect the climatic
influence of the pandemic and 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 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 Center.

As they expected, Fasullo and his co-authors found that the lockdowns associated with COVID-19 had a slight warming influence on global
climate. This effect, which other scientific studies have shown on a
regional level, has to do with the clearer skies that resulted from fewer emissions, which enabled more of the Sun's heat to reach Earth's surface.

In contrast, the Australian bushfires cooled the Southern
Hemisphere to such an extent that they lowered Earth's average surface temperatures. This is because sulfates and other smoke particles interact
with clouds to make their droplets smaller and reflect more incoming
solar radiation back to space, reducing the absorption of sunlight at
the surface.

At their peak, the pandemic-related lockdowns led to an increase of solar energy at the top of the atmosphere of about 0.23 watts per square meter,
which is a measure used by climate scientists to quantify the amount
of solar heat entering and leaving Earth's atmosphere. In contrast,
the Australian fires temporarily cooled the globe by almost a watt per
square meter. (For perspective, the average intensity of solar energy at
the top of the atmosphere directly facing the Sun is about 1,360 watts
per square meter.) By circling the Southern Hemisphere and lingering
in the atmosphere for months, the smoke particles disproportionately
cooled the southern half of the planet.

As a result, the disparity between hemispheric temperatures displaced
tropical thunderstorms farther to the north than usual. Fasullo said
that further research is needed to determine if the smoke had additional impacts, such as affecting El Nin~o and La Nin~a.

"We've theorized that the climate system responds this way to
major volcanic eruptions," Fasullo said. "But those tend to happen
every 30 years or so. In contrast, major wildfires can occur every
couple of years and therefore have more recurring impacts. We
clearly need to learn more about how they affect global climate." ========================================================================== Story Source: Materials provided by National_Center_for_Atmospheric_Research/University Corporation_for_Atmospheric_Research. Original written by David
Hosansky. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. J. T. Fasullo, N. Rosenbloom, R. R. Buchholz, G. Danabasoglu, D. M.

Lawrence, J.‐F. Lamarque. Coupled Climate Responses to
Recent Australian Wildfire and COVID‐19 Emissions Anomalies
Estimated in CESM2. Geophysical Research Letters, 2021; DOI:
10.1029/2021GL093841 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210727171604.htm

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