Wind from the Sahara carries around 180 million tons of dust each year. And thousands of miles downwind, this fine dust shapes both the ecology and climate of the places it lands. Most of the dust that falls as it passes through Spain is less than 20 microns in diameter and is invisible to the human eye. Scientists have long known that inhaling these particles is not good for your lungs. And dust can cause significant harm to the health of communities as it is pushed around.

But it can also be good in many ways. On the other side of the world, in the Amazon, plants are getting stronger thanks to this phenomenon. The fog fertilizes plant and ocean life. It can also be a shield against climate change.

How does it work? The dry desert expanses of North Africa are the world’s largest sources of dust, no doubt about it. Under the right conditions, usually between spring and autumn, large quantities of dust are blown into the “Saharan air layer”, a mass of hot, dry winds one kilometer above the Earth’s surface.

When the coldest air masses from the ocean push it into the atmosphere, dust can float for days or even weeks in a phenomenon all Spaniards are already familiar with: haze. But even east-west winds sweep it from the Atlantic to the Caribbean or the USA in a matter of days. As the dust cloud moves, some of it falls into a steady shower of particles.

Fertilizer rain. A few years ago, a NASA satellite was able to measure how much dust this transatlantic journey created. The scientists not only measured the volume of the dust, but also calculated how much phosphorus and iron was transported in the ocean from one of the most desolate places on the planet to one of the most fertile: the Amazon. It turns out that phosphorus is an essential nutrient for protein and plant growth.

Phosphorus, which reaches about 22,000 tons per year from the Sahara dust to the Amazonian lands, is as much as the amount lost due to rain and flooding. Much of this soil is not sufficient to support the abundance of life growing on it, and rain, a key feature of rainforest habitats, washes away unused phosphorus very quickly.

cyclone destroyer. Many scientists think that traveling dust plays another role in the Atlantic: it helps suppress the formation of tropical cyclones. Layers of dusty air often dry out bones, and this spells the end of humid heat-fed tropical storms. So, if a developing storm hits the dust layer, dry air will help extinguish it. Imagine a flame without the oxygen it needs to keep burning.

Dust layers are often moved by strong winds, so they can cross the ocean in just a few days. And a storm that turns into a towering hurricane can be blown away by these winds, hindering its growth.

Climate Shield. It’s not entirely clear what impact an even dustier future will have on the climate, as dust could both warm and cool the planet. But it is true that the plumes flowing over the ocean reflect heat from the sun that would otherwise be absorbed by the dark surface of the ocean. Dust also changes the way different types of clouds form. It sometimes creates a series of reflective clouds that can deflect additional heat.

And there are more elaborate ways dust interacts with air. Under the right conditions, it can even fertilize photosynthetic organisms that can stimulate population explosions that result in the removal of carbon dioxide from the atmosphere. The fertilizing power of the dust may have caused at least a quarter of the change in carbon dioxide that brought Earth into the last ice age.

But let’s not forget that it is harmful to health. Despite the positive factors of haze, a study published in Nature Sustainability concluded that dust from depressions such as Chad’s Bodèle, one of the world’s largest and most important resources, makes it difficult to breathe.

The scientists examined 15 years of records of the impact of dust on air quality in downwind communities across the African continent. They found that how dense the dust-laden air was was devastatingly correlated with whether a newborn would survive a year. In West Africa, if the dust thickened the air by 25%, the baby’s chance of survival was reduced by 18%.

Picture: flickr