Why we need to rethink what we know about dust

<span rang=Current models have overestimated the role of northern Africa as the main source of global dust emissions for nearly 30 years. GizemG/Shutterstock” src=”https://s.yimg.com/ny/api/res/1.2/0zLUokJvc6d66vthhSlgow–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTYzMw–/https://media.zenfs.com/en/the_conversation_464/468800f730419a5f2b6fcaee188c312e” data- src= “https://s.yimg.com/ny/api/res/1.2/0zLUokJvc6d66vthhSlgow–/YXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTYzMw–/https://media.zenfs.com/en/the_conversation_464/468800f730419a5f2b6fcaee188c312e”/>

You might think of dust as an annoyance to be vacuumed and disposed of, but in reality, on a grander scale, it is much more important than most people realize. All over the world, dust plays a vital role in controlling our climate, radiation balance, nutrient cycles, soil formation, air quality and even human health.

But our understanding of it is hampered by the limitations of current mathematical models. These models, built on methods developed decades ago, struggle to accurately simulate the properties and quantities of dust.

The latest research by my colleagues and I sheds light on these limitations and suggests a more detailed picture of dust. Our results show that dust emissions are not constant but vary seasonally and between hemispheres, across deserts and bushlands. This challenges the long-held notion that northern Africa and the Middle East are the main sources of global dust.

Using two types of satellite data, our research suggests that dust emissions during dust storms are rare and localized, like lightning strikes, and occur in ever-changing locations.

Dust complexity

The cycle of dust emissions, transport and deposition has both positive and negative effects on our environment. Nutrients in settled dust fertilize our oceans and rainforests. But dust from eroded sediments can damage plants and trees and interfere with photosynthesis, and dust that deposits on ice increases the rate at which it melts.

Variations in dust composition, such as mineral type and color, create a complex mix of particles injected into the atmosphere. This, in turn, interacts with clouds to influence how sunlight is reflected or absorbed, ultimately controlling Earth’s temperature.

Therefore, it is vital that we have an accurate understanding of where dust emissions come from, in what amounts, how dust is transported around the planet and where it originates.

Dust emission models were developed almost 30 years ago when much less data was available. As a result, those classic dust cycle models made several assumptions. One important assumption was that the Earth’s land surface was uniformly covered in permanently loose and dry material that was constantly available and gave rise to dust emissions.

However, we now know from field measurements that soils are often crusted or covered with various types of gravel. It was also assumed that the threshold for the wind to lift the soil and release it to the atmosphere was constant and did not change over time.

We also now know that sediment moves around the landscape and may not always be available. Vegetation that covers the soil reduces the speed of wind reaching the soil surface, which reduces dust emission. Dust models still assume that “greenness” indicates the presence of vegetation. However, in dry lands where most dust emissions occur, the vegetation is often brown, but its roughness still reduces wind speed and shelters the soil from dust emission.

Therefore, classical dust cycle models have overestimated the amount of dust emission. These weaknesses have persisted since the development of models. This is mainly because modeling assumes that they overcome any weaknesses in dust emission modeling by adjusting their dust cycle models to atmospheric dust measurements.

A new approach

Almost ten years ago we developed a new approach using shadow to estimate the amount of wind speed that is reduced by roughness, such as vegetation, on the Earth’s surface. This approach was still limited by the previous model assumptions described.

However, during the pandemic, traditional field studies were impossible. So we took a new approach. Using satellites, we have provided a global collection of dust emission points. This provided valuable data and paved the way for further research.

We found that current models overestimated the role of North Africa as a major source of global dust emissions. Our research shows that dust emissions vary seasonally and between hemispheres, from deserts in eastern Asia, the Middle East and northern Africa as well as bushlands in Australia and North America.

Current models based on atmospheric dust over northern Africa and the Middle East provide only a small part of the story. Little dust emission was predicted in the southern hemisphere. But this contrasts with field observations and experiences of people in those regions.

These new results are crucial for large-scale models because the properties of dust vary depending on where it comes from. Not only that, but dust may change as it is transported within a hemisphere to different destinations where it settles on land, in our oceans and on ice caps.

Our new understanding of dust distribution, quantity and seasonal changes has significant implications. Historical reconstructions that explain past climate changes will require revisions. Our findings will also have implications for future climate projections and how the dust cycle interacts with the carbon, energy and water cycles of the Earth’s systems.

This article from The Conversation is republished under a Creative Commons license. Read the original article.

The conversation

The conversation

Adrian Chappell receives funding from the Natural Environment Research Council (NERC) in the UK.

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