HKBU-led research identifies Arctic amplification as cause for dust reduction and suggests sustained anti-desertification measures

HONG KONG, March 26, 2024 /PRNewswire/ -- A research team led by Hong Kong Baptist University (HKBU) has discovered that intensified Arctic amplification associated with global warming, which led to changes in atmospheric circulation, is the underlying cause of the decline in dust levels across West and South Asia over the past two decades. However, this phenomenon is a reversible one, and with the ongoing worldwide efforts to fight against global warming, dust levels in the region may rise again in future, suggesting that sustained anti-desertification measures to mitigate dust emission are warranted in the long run.

The research findings have been published in the international academic journal Proceedings of the National Academy of Sciences (PNAS).

Dust impacts on health and economy

In arid regions, strong winds can create high levels of dust aerosols—a mixture of dust, salt, bacteria, and toxic metals—that pollute the environment. Dust aerosols can affect a wide region as large-scale atmospheric circulations transport them across the planet. They also have a negative impact on air quality, food security, energy supply, public health, as well as regional and global weather and climate.

Dust loading in West and South Asia, covering the Middle East and the Indian subcontinent, has been a major environmental issue created by strong local emission and long-distance transport by atmospheric circulations. According to the United Nations' Economic and Social Commission for Asia and the Pacific, sand and dust storms exposed more than 500 million people in India to medium and high levels of poor air quality, and over US$107 million in economic losses in 2019 alone. Yet, there is a lack of robust understanding of the recent changes and future projection of this phenomenon.

Arctic amplification causes decline in dust levels

A team researching on this topic was led by Professor Gao Meng, Professor of the Department of Geography at HKBU, and Professor Cheng Liu from University of Science and Technology of China, with Mr Fan Wang, a PhD student in the Department of Geography at HKBU, as a key member. The team used high-quality remote sensing data and the latest climate models, detected a consistent drop in dust levels in West and South Asia from 2008 to 2019. Previous studies have primarily attributed the drop to increased regional rainfall and suppressed emissions due to land management practices and anti-desertification measures. However, the research team's analysis suggested that atmospheric circulation changes related to Arctic amplification is the primary factor that accounts for this condition.

Arctic amplification refers to the phenomenon where the Arctic region experiences warming at a faster rate than the rest of the planet. The research team found that Arctic amplification weakened the polar jet stream, a belt of powerful upper-level winds that sits atop the polar front, allowing cold polar air to move further south. This disturbance to the mid-latitude atmospheric circulation resulted in easterly and southeasterly wind anomalies over the Middle East, South Asia, and the Indian Ocean. These anomalies have been observed to have reduced the dust transport from Northeast Africa to the Middle East.

The research team also observed a decreasing trend in zonal wind, winds circulating at the same latitude, in the main dust transport region of West and South Asia, which was coupled with the regional contrast in land-sea temperature. This temperature difference intensified a sea breeze-like circulation, partially contributing to the easterly wind anomaly and suppressing the transport of dust from the Middle East to South Asia.

Additionally, anomalies in atmospheric circulation could also disrupt hydrological cycles and surface winds, which in turn affect regional precipitation, soil moisture, near-surface wind speed, and atmospheric boundary layer stability. These disruptions reduce dust emission and facilitate its deposition processes in the region.

Sustainable plans to counter desertification needed

To conclude, the reduction in dust levels in West and South Asia is an inadvertent result of global warming. As the international community pools together efforts to curb global warming, the research team further utilised simulation models to predict the future scenario. They found that dust levels over West and South Asia are projected to decrease until around 2050. However, when carbon neutrality is achieved by 2050 and global warming is supposed to have improved, dust levels in the regions will increase towards the end of this century, and are at least 10% higher than those in the scenario without carbon neutrality by the 2100s.

Professor Gao stated: "The United Nations has called for carbon neutrality as the ultimate goal to combat global warming, with a 45% reduction in carbon emissions by 2030 and reaching net zero by 2050. Accompanying this development, our simulation models suggested that the trend of dropping dust levels in West and South Asia may reverse when environmental measures to fight global warming become fruitful.

"As the implementation of relevant measures against global warming is mandatory, our research results remind us not to overlook the risks of dust. Policy makers and related authorities should formulate long-term, sustainable plans to counter natural and urban-level desertification in West and South Asia, so that the goal to curb global warming will not be attained at the expense of intensifying the dust problem," he added.

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