Biomass burning increases low clouds over southeastern Asia

Date:
January 11, 2022
Source:
Max Planck Institute for Chemistry
Summary:
Clouds have significant impact on the energy balance of the
Earth system.

Low clouds such as Stratocumulus, Cumulus and Stratus cover
about 30 percent of the Earth surface and have a net cooling
effect on our climate. What counteracts global warming, can have
economic consequences: a persistently dense and low cloud cover
over land can reduce agricultural production and the solar-power
generation. Understanding the factors governing low cloud cover
is not only important for regional weather forecasting and global
climate prediction but also for their socioeconomic effects.



FULL STORY ========================================================================== Clouds have significant impact on the energy balance of the Earth
system. Low clouds such as Stratocumulus, Cumulus and Stratus cover about
30 percent of the Earth surface and have a net cooling effect on our
climate. What counteracts global warming, can have economic consequences:
a persistently dense and low cloud cover over land can reduce agricultural production and the solar-power generation. Understanding the factors
governing low cloud cover is not only important for regional weather forecasting and global climate prediction but also for their socioeconomic effects.


========================================================================== Aerosol effects on cloud formation are key to understand climate forcing
in the Anthropocene. Wildfires inject large amounts of biomass burning
aerosol particles into the atmosphere, which by interacting with clouds, strongly enhance the formation of marine stratocumulus cloud. But
their role in regions with strong human activities and complex monsoon circulation remains unclear.

An international team led by Yafang Cheng from the Max Planck Institute
for Chemistry (MPIC) and Aijun Ding from Nanjing University have now investigated the role of wildfires in the formation of low clouds in
southern Asia, a region that covers a land area about 500,000 km2
with approximately 270 million inhabitants. The researchers used
a comprehensive approach combining model simulations with multiple
information from weather observations, biomass burning emissions and
satellites data.

"We discovered a particular strong impact of biomass burning aerosols
on cloud formation in southeastern Asia," says the first author of the
recently published study, Ke Ding. "The degree of cloud enhancements over continent in this region are comparable to those in the Southeast Atlantic induced by biomass burning in Southern Africa, a well-known wildfire
hotspot, even though the total biomass burning emissions in Southeast
Asia are much lower." According to Ding, who was an exchange PhD student
in Cheng's Group, supported by the Chinese Scholarship Council, and is
now an assistant professor in Nanjing University, the biomass burning
emission in this region is about one- fifth of Southern Africa.

Aerosol-radiation interactions continue to increase whereas aerosol-cloud interactions tend to saturate at high aerosol loading "Our analysis shows
that the main reason for the amplified aerosol effect and enhanced cloud formation is the synergetic effect of large-scale monsoon circulation
and aerosol-cloud-boundary layer interactions in southeastern Asia,"
explains Yafang Cheng, the head of a Minerva Research Group at the MPIC
and corresponding author of this study. Aerosols can influence cloud
formation directly by serving as cloud condensation nuclei (aerosol-cloud interaction) or indirectly by absorbing and scattering solar radiation (aerosol-radiation interaction). "Though many studies have focused on
the aerosol-cloud interaction effect, we find that the aerosol-radiation interaction effect, especially that of the absorbing soot particles,
play a dominant role on the low-cloud enhancement in southeastern
Asia. This further supports our recent hypothesis that aerosol-cloud interactions tend to saturate at high aerosol loading, whereas the
strength of aerosol-radiation interactions continues to increase and
plays a more important role in highly polluted episodes and regions,"
the atmospheric scientist adds.

The results further demonstrate that aerosol-radiation interaction caused
by biomass-burning smoke from wildfire dominates the springtime low-cloud enhancement in southeastern Asia, and hence influence the regional climate
and weather. Given the direct impacts the clouds over land have on human activities, such as agricultural production, solar-energy generation,
and regional climate, the mechanism reported in this study is important
for regional sustainability. It thus needs to be included in future
forecast and assessment models.

Moreover, climate change is expected to increase the frequency and spread
of wildfires. "Thus, recording a present-day baseline with extensive
and long-term measurements such as our ongoing project CARIBIC-SP2
should help to constrain model estimations of the climate impact of
wildfire and foster our fundamental understanding of future climate
change." summarized Yafang Cheng.

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========================================================================== Journal Reference:
1. Ke Ding, Xin Huang, Aijun Ding, Minghuai Wang, Hang Su, Veli-Matti
Kerminen, Tuukka Peta"ja", Zhemin Tan, Zilin Wang, Derong
Zhou, Jianning Sun, Hong Liao, Huijun Wang, Ken Carslaw,
Robert Wood, Paquita Zuidema, Daniel Rosenfeld, Markku
Kulmala, Congbin Fu, Ulrich Po"schl, Yafang Cheng, Meinrat
O. Andreae. Aerosol-boundary-layer-monsoon interactions amplify
semi-direct effect of biomass smoke on low cloud formation
in Southeast Asia. Nature Communications, 2021; 12 (1) DOI:
10.1038/s41467- 021-26728-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220111112004.htm

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