RESEARCH NEWS STORY
August 8, 2024
Chiba University

Detecting Climate Change Using Aerosols
Researchers propose a new metric using aerosols to understand changes in transboundary
air pollution pathways due to climate changes
Researchers analyzed long-term aerosol satellite observation big data focusing on thePacific Ocean downwind of China. Using a newly developed metric that considered aerosols
as tracers, they detected altered atmospheric transport patterns associated with climatechange. They observed that the distance of transboundary air pollution moving east fromChina had shortened. Thus, long-term satellite-based Earth observations are crucial forearly climate change detection and accurate evaluation of this trend.

Image title: The image depicting transboundary air pollution pathways of aerosols, such as
PM2.5
Image caption: By analyzing long-term satellite observation data and using a new methodthat treats aerosols as tracers, researchers found that these pathways from China areshifting slightly northward due to global warming
Image credit: Shinichiro Kinoshita
Image license: Original Content
Usage restrictions: Cannot be reused without permission
Climate change is one of the most significant environmental challenges of present times,
leading to extreme weather events, including droughts, forest fires, and floods. The primary
driver for climate change is the release of greenhouse gases into the atmosphere due tohuman activities, which trap heat and raise Earth’s temperature. Aerosols (such as particulatematter, PM2.5) not only affect public health but also influence the Earth's climate by absorbing
and scattering sunlight and altering cloud properties. Although future climate changepredictions are being reported, it is possible that the impacts of climate change could be more
severe than predicted. Therefore, it is necessary to detect climate change accurately and as
early as possible.
Building on these insights, a research team from Japan, led by Professor Hitoshi Irie from theCenter for Environmental Remote Sensing at Chiba University, utilized long-term
observational data to study the effect of climate change on transboundary air pollution in thedownwind area of China by using aerosols. They utilized a completely unique perspective on
how aerosols impact climate and developed a new metric to detect climate change byconsidering aerosols as tracers.
“The significance of this study lies in the fact that most of its results are derived fromobservational data. In natural sciences focused on Earth studies, the ultimate goal is to piece
together highly accurate data obtained from observations to quantitatively understand theprocesses occurring on Earth and to pursue immutable truths. Therefore, the more
observational data we have, the better. With the continued Earth observations by Japan'smajor Earth observation satellites (such as the GCOM series, GOSAT series, Himawari series,and ALOS series), we aim to complement these efforts with numerical simulations and data
science methodologies to achieve a safe and secure global environment that mitigates theimpacts of the climate crisis.” explains Prof. Irie.
The research team included Ms. Ying Cai from the Graduate School of Science and Engineering,
Chiba University, Dr. Alessandro Damiani from the Center for Climate Change Adaptation,
National Institute for Environmental Studies, Dr. Syuichi Itahashi and Professor Toshihiko
Takemura from the Research Institute for Applied Mechanics, Kyushu University, and Dr.
Pradeep Khatri from Faculty of Science and Engineering, Soka University. Their study was
made available online on May 23, 2024, and published in Science of The Total Environment on
August 20, 2024.
China is a major contributor to air pollution in East Asia. The downwind area of China analyzed
in this study is a unique open ocean area with minimal human interference yet an important
zone of transboundary air pollution pathways, making it an ideal location for studying
meteorological variations due to climate change.
In their study, the researchers analyzed aerosol optical depth (AOD) datasets derived fromsatellites, reanalysis datasets, and numerical simulations focused on the Pacific Ocean in thedownwind area of China, over 19 years from 2003 to 2021. AOD, a measure of the amount ofsunlight blocked by aerosols, is a key factor is analyzing aerosols and their impact on climatechange.
The researchers developed a new metric called RAOD which utilized the potential of aerosols
as tracers to evaluate the impact of climate change on transboundary air pollution pathways.
Using RAOD the researchers were able to quantify significant temporal variations in aerosol
transport. They discovered that long-term changes in RAOD due to climate change wereoutweighed by larger year-to-year variations in the meteorological field. Moreover, seasonal
trends showed that aerosols moved west to east during spring and winter, and northward insummer. They concluded that the probability of aerosols from China to be transported far

eastward was low, highlighting a shift in transboundary pollution pathways due to global
warming. In this study the authors successfully detected climate change using long-term
satellite observational data, in contrast to most existing studies that tracked transboundary
air pollution using model simulations.
“These results suggest that RAOD is a valuable metric for quantifying the long-term changes intransboundary air pollution pathways due to climate change. These results are particularly
significant because most of them are derived from observational data,” says Prof. Irie,
highlighting the importance of the study. Sharing the future implications of their study heconcludes, “The effects of climate change could be more severe than currently predicted. This
study will help verify climate change predictions from an unconventional perspective of‘aerosol observation,’ enabling a more accurate understanding of climate change progression
and implementation of rational countermeasures.”In summary, this study demonstrates an innovative use of aerosols as climate change tracers,
marking a significant step forward in the global effort to tackle the pressing issue of climatechange.
About Professor Hitoshi Irie
Hitoshi Irie is currently a Professor at the Center for Environmental Remote Sensing (CEReS)
at Chiba University. He obtained his M.S. and Ph.D. degrees from Nagoya University, Japan in1999 and 2002, respectively. He has over 230 publications with over 6400 citations. At ChibaUniversity, he also leads the Irie lab, which focuses on studying the effects of climate change.
His research focuses on understanding the evolution of air pollution and climate change on aglobal scale.
Funding:
This research was supported by the Environment Research and Technology Development
Fund (grant number JPMEERF20215005) of the Environmental Restoration and Conservation
Agency of Japan, JSPS KAKENHI (grant numbers JP20H04320, JP21K12227, JP22H03727, andJP22H05004), the JAXA 3rd research announcement on the Earth Observations (grant number19RT000351), and the Virtual Laboratory (VL) project by the Ministry of Education, Culture,Sports, Science and Technology (MEXT), Japan.
Reference:Title of original paper: Detectability of the potential climate change effect on transboundary
air pollution pathways in the downwind area of ChinaAuthors: Ying Cai a, Hitoshi Irie a, Alessandro Damiani b, Syuichi Itahashi c, Toshihiko
Takemura c, Pradeep Khatri dAffiliations: a Center for Environmental Remote Sensing (CEReS), Chiba University, Japanb Center for Climate Change Adaptation, National Institute for Environmental Studies, Japanc Research Institute for Applied Mechanics, Kyushu University, Japand Department of Science and Engineering for Sustainable Innovation, Faculty of Science andEngineering, Soka University, Japan
Journal: Science of the Total Environment
DOI: 10.1016/j.scitotenv.2024.173490

Contact: Hitoshi Irie
Center for Environmental Remote Sensing (CEReS), Chiba University
Email: hitoshi.irie@chiba-u.jp
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