Aerosols used to monitor climate change

Japanese researchers have used aerosols to detect altered atmospheric transport patterns associated with climate change, observing that the distance of transboundary air pollution moving east from China has shortened. Their findings indicate that long-term, satellite-based Earth observations are crucial for early climate change detection and accurate evaluation of this trend.

Climate change is one of the most significant environmental challenges of present times, leading to extreme weather events including droughts, bushfires and floods. But 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 as accurately and as early as possible.

With this in mind, a research team led by Professor Hitoshi Irie, from the Center for Environmental Remote Sensing at Chiba University, utilised long-term observational data to study the effect of climate change on transboundary air pollution in the downwind area of China by using aerosols, which influence the Earth’s climate by absorbing and scattering sunlight and altering cloud properties. With a new perspective on how aerosols impact climate, they developed a metric to detect climate change by considering aerosols as tracers. Their results were published in Science of The Total Environment.

“The significance of this study lies in the fact that most of its results are derived from observational data,” Irie said. “In natural sciences focused on Earth studies, the ultimate goal is to piece together highly accurate data obtained from observations to quantitatively understand the processes occurring on Earth and to pursue immutable truths. Therefore, the more observational data we have, the better.

“With the continued Earth observations by Japan’s major 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 the impacts of the climate crisis.”

In their study, the researchers analysed aerosol optical depth (AOD) datasets derived from satellites, reanalysis datasets and numerical simulations focused on the Pacific Ocean in the downwind area of China, over 19 years from 2003 to 2021. AOD, a measure of the amount of sunlight blocked by aerosols, is a key factor is analysing aerosols and their impact on climate change. Meanwhile, the location examined is an 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.

Using a new metric called R_AOD, which utilised the potential of aerosols as tracers to evaluate the impact of climate change on transboundary air pollution pathways, the researchers were able to quantify significant temporal variations in aerosol transport. They discovered that long-term changes in R_AOD due to climate change were outweighed 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 in summer.

The team 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. They thus 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 R_AOD is a valuable metric for quantifying the long-term changes in transboundary air pollution pathways due to climate change,” Irie said. “These results are particularly significant because most of them are derived from observational data.

“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.”

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