The Earth’s Furies: When Earth Will Be a Desert

The deserts occupy almost a third of the surface of the planet and are increasing. It is one of the biggest problems of the 21st century and gains ground everywhere. The deserts are dynamic objects that are evolving and we constantly have to deal with their progress. That is why they are a force of nature. Desertification threatens 40% of the Earth's surface. Experts from all over the world are striving to understand this devastating phenomenon. Because of this desertification, we sometimes see dunes, a clear sign that the desert is approaching. Thanks to science, we now know how a desert is born and how the sand dunes move. While experts have made some progress in the mysteries of desertification, they still cannot intervene in the development of the dunes. Among the most mobile dunes, the largest advance by generally one meter per year and the smallest between 30 and 50. As a result, entire regions are surrounded by sand like the south of the Sahara. If nothing is done, the 44 million inhabitants of the area will be forced to leave their homes. Here, many people have had to leave their homes due to the invasion of the sand that has completely covered them. The region lives with the days counted. You may wonder why. We will see how desertification is capable of taking even more extreme forms. Sandstorms are a phenomenon that was rarely seen a few decades ago, but is now striking the world. We thought it was fog, but it's actually sand. It's incredible. In September 2015, a wall of sand shook several countries in the Middle East and submerged them in a huge cloud of desert dust. Scientists study this phenomenon closely, which is clearly capable of starting disasters. It acts like a vacuum cleaner, which then forms this wall, which is several hundred meters thick. With the help of avant-garde satellite images, experts follow its movement over thousands of kilometers. Why are these storms more and more frequent and increasingly intense? Capable of the highest levels of destruction, we will see exactly how they cause chaos and even, in certain circumstances, death. If we observe the areas of the world where sandstorms occur in particular, it is almost always associated with a strong pollution. We will discover a force of nature underestimated by many. Fierce land. Desertification. The desert gains ground. In the last 50 years around the world, its movement has increased. A phenomenon that consists of arid and semi-arid lands. That is, almost half of the surface of our planet, where almost a third of the population lives. Scientists estimate that if nothing is done to combat desertification, every year 10 million hectares of fertile land, a fifth of France, will be lost. Each continent is affected by this catastrophe, but one in particular is the most affected. Africa. Here lies the largest desert in the world, with 9 million square kilometers, the Sahara Desert. In a century, it has grown by more than 10%. Towns, roads and rivers are buried under the sand. Fertile lands disappear, like Mauritania, a country where two-thirds of the land is desert. Its capital, Nouakchott, was built at the entrance of the Sahara in the 1960s. Today, several districts are threatened by erosion and sedimentation. Only 40 kilometers east, the town of Erebin has almost been erased from the map. To get to the entrance of his home, this woman must now cross a dune. I'm afraid because the sand comes in from everywhere. From the house and even above us. It comes through the doors and also through the windows. It's dangerous. There are four of us who live here. And it's just like the other houses and families that inhabit the town. In this country, the problem seems to worsen every year. Government data show that the dunes advance 6 to 10 kilometers every year. So how is this progress possible? Scientists have managed to identify the dynamics of these sand hills. To understand it, we must first go to their origins. In the Sahara, these dunes accumulate in large basins, huge sands of sand that look like waves and oceans. They cover almost 20% of the desert's surface. We call them ercs. The great ercs, Oriental and Western, or the sandy sea of Libya, are among the most famous and were not formed by chance. The sandy seas are found more often where the winds converge. Once this happens, their intensity decreases, so that the sand accumulates on geological time scales. These large accumulations of sand are created like this. The sand has been eroded from the mountains and then dragged out of these to the region. The sand comes from the process of erosion of the rock. At first it is a large stone. This large stone is eroded and transported by the rivers and the wind. The chemical deterioration operates systematically and we end up with a grain of sand that is the size of a tenth of a millimeter. This material is a nightmare for specialists because its physical properties challenge the laws of nature. In the Complex Matter and Systems Laboratory, scientists study each aspect of the sand. The sand is always a little surprising because it is both liquid and solid. It is liquid because it fills a container, which is the definition of liquid, but at the same time it is solid because gravity or force can be applied to it and it resists. This transits with enough force or not, so if it exceeds a threshold of force, it begins to flow like a liquid, and if there is not enough, it begins to flow like a solid. The sand is the raw material from which the dunes are composed. To move, they need a second ingredient, the wind. It is created when atmospheric pressure differs from one place to another. The air in the high-pressure zone, an anticyclone, will rush to the low-pressure zone, the fall, producing wind. In the desert, it begins to interact with the sand, which becomes its toy. They move in different ways. We can illustrate it by blowing on sugar. You can see that when they blow, they will make the grains drag on top of each other and roll. That is why we call it reptile. The nature of the movement of sand grains varies according to size. The larger particles are the ones that erupt. As for the smaller ones, another phenomenon occurs. If you start blowing harder, you will see that there will be some grains that can be expelled. This is called jumping. Therefore, the grain is expelled, flies, and eventually falls under the effect of its own weight. The fact of falling again and impacting the sedimentary bed Jumping and reptile are the two main modes of movement of sand grains that result in the creation of a dune. The dunes are an interaction between the wind and an erosible surface. So, if we imagine that there is a small bulge on this surface and that this bulge modifies the wind, making the wind go a little faster up and a little slower down, this wind will be at its maximum speed a little before reaching the top, but the speed of the wind will decrease at the top, because if the speed decreases, it means that it can transport less sand and therefore the sand will be deposited at the top of the bulge. This interaction between the topography and the wind means that a small bulge will increase in height and form a dune. However, contrary to popular belief, the dunes also form outside the desert. This is one of the consequences of desertification that affects humanity the most. The result of a series of recurring effects. This process of degradation of the earth begins with the gradual disappearance of the vegetal cover. Without the cover, the winds damage the soil and turn it into dust. Then the rain flows and evaporates instead of infiltrating the soil. These phenomena of erosion carry with them the nutrients and organic matters contained within the earth. If it does not rain for a long time, the surface cracks and in the final stage the rock, stripped of its sand, appears. Desertification is irreversible. As a result of desertification, sometimes we see dunes appear in the fields when the soil is already sandy. Under the action of the wind, dunes will form and this tells us that the desert has arrived. In fact, that sand does not come from the Sahara. It formed in that place. A desert is forming. Several factors can trigger such a disaster. The first are related to the climate. First of all, droughts. An occasional lack of water, but enough for the environment to be affected. Its consequences can be devastating. It is true that desertification did not begin yesterday, but we began to take it seriously after the great droughts that affected the Sahel, especially in the 1970s. It was an unprecedented humanitarian catastrophe and provoked an awareness that made this issue become an international issue. The Sahel, a semi-arid strip that borders the south of the Sahara, houses a fragile ecosystem. The people who live there depend on cultivation and agriculture, but within 25 years, 135 million people will have to emigrate. The Sahel area will be the most affected by desertification. To explain this phenomenon, we must take into account the variations in the earth's climate cycles. The desert borders are changing. For example, the Sahara has not always been a desolate landscape. A thousand years ago, the region even experienced a rainy season. The Sahara is in perpetual evolution. The Sahara has been green, it has been covered with lakes, it has been covered with rivers, and it will become green again during the climate cycles. So we should not be surprised. It really is an ever-evolving system. Today, the desert reigns in this entire region. Scientists attribute it to humanity. Deforestation, overgrazing, and poor water management are both indirect and intense causes of agriculture. In other places, deserts have turned into green fields, but this industrial agriculture sometimes damages the soil and can turn fertile land into dunes. The sand hills, once formed, evolve under the action of the wind. The dunes form, then develop, move, and migrate with speed. In fact, it is inherent to the dune to be alive, because if a dune does not move, there will be a soil that will develop and stabilize completely. It will lose its characteristic of a dune. A dune, by definition, is an object in motion on which sediment is transported. Researchers have been able to identify the mechanism that allows them to move. A dune moves because the sand slides from the back, is deposited again at the top, and is deposited in the form of an avalanche. So when it moves, it makes a movement of caterpillar. Among the most mobile dunes, the largest usually move one meter per year, and the smallest between 30 and 50. The speed of this movement varies a lot depending on the size, the shape, the moisture content of the sand, and the speed of the wind. Essentially, the dunes are almost always immobile, but when there is a very strong wind, they move a lot, so they advance when the speed is at its maximum. For example, in Morocco, there are warning signs for the dunes along the main roads. We believe it is rare, but when there is a storm, the dune is capable of moving one or two meters, so being in the middle of the road is dangerous. Despite the risks involved, man has learned to live with the desert. In the past, the inhabitants of the Sahara even made good use of mobile dunes. The people who lived in the desert areas knew that the dunes moved, that is, they knew that if they put their grain reserve at a certain height of the dune at a certain time, this grain was going to be covered with sand, stored for a while, and that it would come out at the other end due to the migration of the dunes. It was not until the mid-20th century that the experts were able to identify the factors that control the morphology of the dunes. Scientists have realized that in the deserts, not all dunes evolve in the same way. What is beautiful in the sands and dunes is to see the diversity of these objects. There are two factors that control the shape of the dunes. The first factor is the amount of sand available to generate the dunes, and the second factor is the conditions of the wind. In some areas, the wind almost always blows in the same direction. These are dominant winds, like the winds of the Alices. In this case, the fastest way for a dune to emerge from a desert is like a barge. This model, carried out by scientists, fully represents its evolution. By recreating a miniature field of dunes in the laboratory, this specialist and his team have managed to highlight how these famous barges become true invaders. In this experiment, the dunes are made underwater. Instead of wind over the dunes, what we do is move the dunes in the water, which stimulates a unidirectional wind. So we can see a field of barges, which are these half-moon-shaped dunes that extend in the direction of the wind. So these are the dunes that we see when there is only one direction of wind and there is no sand between the dunes. The dunes do not move at the same speed. They collide and exchange sand, and this interaction determines the size of the barges on the ground. Capable of traveling several hundred meters per year, the barges are known to be the fastest dunes, so it is difficult to protect yourself from them. While the ground is completely covered in sand, long barges begin to grow perpendicularly to the air flow for several dozen kilometers. They are known as transversal dunes. But when the winds vary from one station to another, these sand mountains acquire a completely different look when they place their barge parallel to the air flow. They become longitudinal and reach several hundred kilometers in length, as in the Runa Al-Khali, located in the Arabian Peninsula. Named the desert of all deserts, it is as large as France and has the record for the largest uninterrupted sand extension in the world. A hell for humanity, it is also the home of the last type of dune born from a particular climatic phenomenon. When there are winds that move in each direction, the sand remains in place, accumulates, so it creates shapes that are called star dunes, because seen from above, they look like sea stars and are the largest dunes. In the Badain Haran desert in China, sometimes several hundred meters are raised. Scientists call them giant dunes. These giants can remain in place for decades. Their peaks only evolve a few meters with strong winds. It is said that the dunes smoke. Although they adopt various shapes, these sand hills have one thing in common. The angle of their slopes is always 30 degrees. As they grow in height, they will become more and more inclined. And then, as these objects become more and more inclined, there is a point when we go beyond the angle of the avalanche. Entire sections of the dune collapse, taking everything in its path. During these avalanches, sometimes a magical sound is released. It is the song of the dunes. A mysterious sound reported for the first time almost a millennium ago by the explorers of the Silk Road. This natural phenomenon has been tested in the field by specialists. It is a magical sound because it is very powerful and it completely envelops us. We notice that it is really the avalanche that sinks that makes this sound. Typically, this is a pile of two-dimensional sand and an avalanche reduced to a grain. What happens is that when it flows, it is forced to climb on the grains to fall back. All the grains of sand begin to rise and fall at the same time and fall again and that is enough to make a huge sound and therefore it makes a wave on the ground. In fact, it is a seismic wave that extends over the surface of the dune and can be heard from far away. To hear it, it is necessary that these grains of sand have a particular nature. They must be dry, rounded, of identical size, but in particular they must be covered with a layer of iron and clay. This cover favors the adhesion between the particles. Thanks to it, the collisions are synchronized during the avalanche and therefore produce a fairly audible sound. Scientists have numbered around 100 areas in the world where the dunes make this noise. These hills of sand that surround the deserts are under constant surveillance. Deserts are dynamic objects that are evolving and we constantly have to deal with their progress. That is why they are a force of nature. A force of nature that can turn into real storms that sweep everything in its path. Now we know that the dunes are created under the action of the wind thanks to the reaction mechanism that causes the grains of sand to roll to the level of the ground and also the jumping that moves them in short jumps. The finest particles of the desert can fly in the air. There is a third mode of transport known as suspension. That is, the grains can be transported at great heights at great distances and sometimes we observe the suspension during sandstorms. March 2018, Sudan. A wall of sand hits its capital, Khartoum. This scene occurs more and more often in Africa and even in the Middle East, like here in Kuwait. Entire regions are taken unannounced by an apocalypse. April 2015, Dubai, around 3 p.m. The emirates are dyed orange. Visibility is limited to less than 500 meters. Tourists cannot do anything in the face of such a phenomenon. We just arrived this morning from England and we are surprised. We have never seen this before. We were expecting blue skies. We thought it was fog, but it's actually sand. It's incredible. An event that can have devastating consequences. February of the same year. A Sahara storm sweeps Alexandria in Egypt. It leaves behind a landscape of desolation. Its sandstorms cause great damage, covering the streets with a thick, dark cover. We couldn't leave the house yesterday due to the weather conditions. We expected them to improve, but they didn't. Both Alexandria and Cairo are paralyzed. These huge clouds are capable of damaging the economies of entire countries. March 2010. Tons of sand from the Chinese deserts cover Beijing in a matter of seconds. Authorities issue a pollution alert. I saw the sky turn yellow and the air filled with sand. I'm worried that my lungs have been affected. The dust from the desert threatens the health of more and more people. In China alone, the event has affected almost 270 million people, spreading in an area larger than France. How do we explain these gigantic sandstorms that seem to be multiplying all over the world? You need two ingredients. Sand, of course, to transport it at great distances. The grain size must be less than 100 microns. The second component is the winds that move at more than 30 kilometers per hour. Several meteorological phenomena are capable of creating such winds. One of them we know well. It is the result of air depressions and we call it a storm. Sandstorms are a meteorological phenomenon very similar to those found in Europe. However, these climate systems move on bare surfaces and in motion. And when the wind is strong enough, it mobilizes dust particles and moves them at great distances. These large sand clusters are easily recognizable as sandstorms instead of conventional storms. These storms form over arid and semi-arid areas like Central Asia, China, the Arabian Peninsula, and even North Africa. These are the main desert dust sources in the world. When two air masses meet above these regions, the warmest and lightest air rises above the cold air through the suction effect. During this rise, the water vapor condenses little by little and forms clouds. Due to the rotation of the Earth, this system begins to rotate. Its diameter can extend over thousands of kilometers and thus cover several countries. On the outskirts of these giants, the winds can blow for almost a week at more than 100 kilometers per hour. Then large amounts of material rise and a sandstorm is created. The way scientists classify sandstorms is by observing the obstruction and the reduction of visibility. This allows us to see a scale that can oscillate between 1 and 5 in extreme cases. And between this scale we have 1, which is hundreds of meters of visibility, almost kilometers, and at the other end we have 5, which is a few dozen meters of visibility, almost none at all. At this stage, the night immediately turns into day. These brutal desertification manifestations worry the scientists who constantly monitor the phenomenon. They carefully examine a specific sign that is likely to accentuate these storms. The aridity. Because it is above all the lack of water that gives rise to a desert. A desert is typically an area of land where there is a water deficit. Deserts are extreme places because life on earth is accompanied by water and therefore, as soon as there is a water deficit, there is no vegetation. And so we end up in an extreme environment where life cannot develop. Even if there is life, it is still extremely localized and in very precarious conditions. In all parts of our planet, water is life. Without it, we get what specialists call aridity. These different deserts are classified according to their levels of aridity and these levels are measured in terms of annual precipitation height. That is, the height of the water is what determines if we are in a hyperarid, semi-arid or arid system. The region is defined as semi-arid when it rains between 25 and 50 centimeters per year. This is the case, for example, in the Sahel in Africa. Certain areas are, against all odds, soaked in rain in concentrated periods of the year. Let's take, for example, Niamey, which is located in the south of Niger, in the extreme south of the Sahara. And in it, it rains as much as in Brussels. It rains approximately 700 millimeters per year, except that in Niamey, this rain falls in 10 days. Unfortunately, these rains usually occur abruptly on soils with a very low water absorption capacity. As a result, the rain flows, which can lead to the sudden flooding of the dry water courses and little help to the vegetation. When the precipitation decreases again between 5 and 25 centimeters, it is an arid climate. This is the case in most deserts. Below 5 centimeters per year, hyperaridity is created. For example, in some parts of the Atacama Desert in Chile, not a single drop of water has fallen for half a century. It is uninhabitable for humans, and to understand the water shortage in the deserts, we must first know where the rain comes from and what are the reasons that prevent it from falling. Air stores moisture in the form of invisible water vapor. Clouds are formed when the vapor condenses enough in drops that increase in size. This is rain, but it does not always reach the ground, since during its fall, the air can absorb it, since it contains less water. In most deserts, this dry air comes from atmospheric circulation, and more precisely, from what scientists call Hadley cell. Hadley cell is the large-scale movement of the atmosphere. Most of the energy that comes from the sun reaches the equator, where the air heats up and is charged with moisture. With this moisture, the air will begin to rise, the moisture will condense, the heat will release, and the air will continue to increase. At 10 to 12 kilometers, the air will lose all its moisture, it will move towards the two poles, and after a while, it will become unstable and the surface will descend completely dry and very hot. And it is really this large-scale circulation that characterizes the deserts and explains why all the deserts are located in the same latitude. The most uninhabitable areas for humans are located in two wide bands located on both sides of the equator, in the tropics, the desert belt. Since the beginning of time, these vast and desolate extensions have contributed to the global balance of the Earth's climate. From the moment we have a living planet, a dynamic planet, the humidity must be compensated by dry areas. The desert areas are part of the dynamic balance of the planet, so it is logical for it to evolve. Otherwise, the planet would no longer be alive. These territories are increasingly exposed to the formation of exceptional sand storms and powerful forces of nature. One of them reached the headlines in the Middle East in September 2015. It was an unprecedented event that scientists have called the storm of the century. We obtained record measurements, an optical thickness of 5. This literally means that if you put your hand in front of you, you will hardly see it. We had never seen such a measure before. Sand storms are common in the region, but the episode is surprising in both intensity and size. Coming from northern Iraq, the storm of the century is of such magnitude that it extends to Syria, Gaza, Israel, Lebanon, and even Cyprus. It is a very particular meteorological phenomenon that generated this monster. Specialists call it Habu, which means strong wind in Arabic. The term Habu refers to sand storms of convective origin. The term convective may require a small explanation. It corresponds to storms. A storm is born when the atmosphere is unstable. The air heated by the sun's radiation on the surface of the earth expands and becomes lighter than the layer of air above it. It rises like an aerostatic balloon. If this air is humid enough, the water vapor contained in it condenses, creating a cloud in the shape of a giant yunkee, a cumulonimbus. But the power of a single storm cloud is not enough to form a Habu. Such a phenomenon is born when several cumulonimbus align. This is what meteorologists call a flanking line. Once these clouds are saturated with humidity, the movements of the air inside are reversed and the cold air sinks to the ground. The temperature drops rapidly by about 10 degrees. The sand wall gives a tangible shape to the cold air created by the storm, which crashes against the ground and causes gusts of wind. These gusts raise the sand and the dome of the cold air. It crashes against the ground and becomes visible by the dust. The gusts of wind can exceed 100 kilometers per hour. A rare and violent phenomenon. What is unique about the Habu is that it not only has these violent horizontal winds, but also turbulences. This means that there are impressive vertical movements. It's a kind of vacuum. And this vacuum becomes a wall that is several hundred meters wide and very dense. We see that there are waves because the speeds are different. It is the beginning of turbulence. Everything is different and everything covers us. The main Habu can extend over almost 1,000 kilometers and travel the same distance. These are real giants. What you see is a wall of several hundred meters of dust that will fall on you. So what is impressive is that you will see it approaching. You realize that at a certain moment when the front passes, you will not have visibility. You will not be able to see a car that is five meters, or a house that is two meters, or a person that is ten meters. All reference points are lost. They are completely disoriented and this continues for many hours. Once in this cloud of dust of the desert, the conditions become extremely dangerous, especially traffic. The loss of visibility affects many, and that's not all. The sand makes the surface of the road very slippery, as slippery as the snow when large quantities fall. So the braking distances are longer, and often take the drivers by surprise. As a result, there are large collisions like on this road in Dubai in February 2018. And the danger is even more serious in the Middle East. In 2015, in the face of the danger of a hijab for flying aircraft, several airports had to close the runway. Composed of fragments of sand, the dust of the desert can damage the turbines. Some engines reach 1,200 degrees Celsius. When these engines suck this dust from the desert, they pass over the liquefaction temperature of this solid and it's like melted glass. Melted glass affects the engines and this can be worrying. There are other consequences, this time in people's health. When inhaled, particles of less than 10 microns can cause heart and lung problems. These tiny grains of sand become even more dangerous when loaded with toxic gases trapped when flying over industrial sites. If we observe the areas of the world where sand storms occur, in particular, it is almost always associated with a strong contamination. Why? Because for some, the polluting gases tend to adhere to the surface of the dust and the dust is the vector that allows these toxic gases to enter the pulmonary alveoli. This storm, known as the century storm, produced a large number of deaths. Twelve people lost their lives and another four days will pass before the dust of the desert begins to dissipate. In September 2015, a huge sand storm crosses the Middle East. Unanticipated in this event, this devastating episode has disconcerted meteorologists around the world. The recurrence of HABOOBS varies considerably depending on the seasons. In Africa, for example, a particular period triggers these extreme events. When reconstructing the trajectory of the century storm, scientists noticed that it extended from the north to the south of Syria, where the war had been particularly intense in the months prior to the event. It seems that the regular passage of tanks throughout the region led to the creation of large areas of dust, which made the earth extremely volatile. The war seems to have intensified the phenomena of the sand storm and experts are not optimistic. According to the UN, in the course of a decade, some countries like Iraq could face 300 days of sand storms a year, which makes the region almost uninhabitable. The desertification that occurs currently in the Middle East is also responsible. In 15 years, the vegetation has decreased by an average of 30%. The rush to build dams throughout the region and divert water resources for agriculture is considered one of the main factors. Humidity acts as an adhesive to the ground. When it dries, dust storms are overwhelmed by the winds. It seems that humanity has not learned from the past. We can also see the creation of susceptible areas, for example, in areas where lakes are going to dry. This is the case of the Aral Sea, where we believe that storms have become increasingly frequent because they are drying up. But we have already observed this type of phenomenon in smaller lakes. Where the Aral Sea used to be, a new desert has emerged in the heart of Central Asia. In the last 50 years, this huge stretch of water, which is twice the size of Belgium, has lost three quarters of its surface. It is one of the worst environmental disasters of the 20th century. Thousands of fishermen lost their jobs and had to leave their villages. The reason is that the Soviet Union decided on the intensive irrigation of cotton fields during the 1960s, irrigation that has been draining the Aral Sea for half a century. Since then, every three days the Aral Sea has been swept away by sand storms, throwing enormous amounts of dust from this new desert into the atmosphere. We have between 10 and 25 percent of the dust mass in the atmosphere caused by agricultural activities. For example, in southern Spain, there is currently a massive greenhouse crop that requires a large amount of water. This is draining the soil and is only contributing to the appearance of semi-arid areas. Understanding whether these areas are prone to dust is, therefore, a very active field of study in the Mediterranean region. In arid areas, plowing the cultivated land too frequently and deeply leaves the soil exposed and the wind then raises fine particles. Since 1900, the fugitive dust has increased from 25 percent to 50 percent on a global scale according to scientific tests. We have been aware of these events for a long time due to the Dust Bowl phenomenon which coincided with the largest economic crisis in modern U.S. history in 1929. Scientists quickly realized that deep plowing had released dust and, combining this with several years of very strong winds, created the Dust Bowl. The name Dust Bowl requires little explanation. Dust storms devastated the great plains of the United States for 10 years, completely altering the landscape until, in 1932, 14 sandstorms swept the region. The following year, 38 of them were recorded. This phenomenon was completely unheard of and, given the magnitude of this disaster, the U.S. authorities were forced to take measures. After the crisis, the government took things into their own hands, created adequate surfaces, and restored the soil. Today, we can see that this soil has been restored, that it is agricultural land, and that it is handled correctly. In other words, the impacts of land degradation, although considerable, are not necessarily irreversible. The restoration of the soil was possible thanks to the considerable financial resources deployed by the United States. The Dust Bowl was strange at the time, but today the sandstorms are increasingly frequent and increasingly impressive. With global warming, the phenomenon is likely to intensify, even expanding to new areas. We have the possibility, in a context of climate change, to see an increase in dry conditions, for example, in southern Europe or in the United States. This would lead to a drier soil, which at certain wind speeds would emit dust, and then there is the possibility of a change in wind speed that could intensify. But in general, the occurrence of more extreme events suggests that we could have events with stronger winds, and therefore storms with more dust. Fortunately, the accuracy of sandstorm forecasts has improved, mainly thanks to Vanguardia's technology. Today there are two types of tools used in the observation of these storms. First, there is the observation satellite that allows us to see the creation of dust clusters and their dispersion in the atmosphere, and then the modeling. In the same way that we make the weather forecast, now we also have the possibility of predicting sandstorms and the movement of dust clusters in the atmosphere, from their origin to their different transport zones. In the face of this global threat, the World Meteorological Organization has established an alert system for dust storms around the world. It is based mainly on a supercomputing center based in Barcelona, Spain. A fact, however, remains difficult to understand. The uncertainty has to do with the quantities emitted and transported and the ability to predict what concentration of dust we would be exposed to during transport, in Europe, for example. And sandstorms not only affect river communities. A fraction of the dust mobilized during such events can rise to a height of 5 kilometers. Then they form what specialists call an aerosol, a huge cloud that can be observed from space. A single event can transport to the atmosphere tens of millions of tons of substance in the form of very small particles that are one-tenth the size of a millimeter. This is just one-tenth the width of a human hair. That is why they are light to follow the movements of the air masses. So if these air masses combine with strong winds, they can transport the particles very far. A desert dust aerosol can travel hundreds, even thousands of kilometers as shown in these remarkable satellite images. It forms a dense layer of clouds that is capable of absorbing sunlight. By blocking this exposure to the sun, what do these fine particles do? Well, they reduce the radiation that reaches the surface, and in this way they reduce the temperature of this surface. Therefore, in the space of a day, the temperature of the surface can drop from 2 to 3 degrees during a severe storm. Surprisingly, sandstorms contribute to cooling the planet. The useful life of desert dust in the atmosphere varies from a few hours to more than 10 days. When the winds at altitude weaken, they spread over the surface of the Earth. The aerosols produced in the Asian deserts can be transported beyond the Pacific. We can even find traces of these particles in the poles of the Earth, so they are transported at great distances. And the further they travel, the fewer particles there will be. The aerosols make up 40% of the particles emitted into the atmosphere every year. In a similar way, the sand from the Sahara, which is transported by the depressions, can reach Europe, which changes our climate. When this sand is deposited again, an unwanted variety of consequences occurs. These aerosols can accumulate as dry matter, and sometimes we can see it in vehicles, especially in southern France. But it can also be deposited by precipitation, what we call blood rain, which is when normal rain changes the color of the dust. Another example of the particle deposit can also be seen on very light colored surfaces. This was the case a few years ago in the Pyrenees, where the snow was covered by a layer of Saharan aerosol that caused a slight impact on the skiers. Another impact is the one In October 2017, a sunset seemed to appear in the middle of the day. Why did this happen? Due to the Ophelia storm that passed through the west coast of France and left a trail of sand in the Sahara. In total, 182 million tons of sand leave Africa every year. It is the largest source of dust in the desert on our planet, sometimes creating beneficial effects. NASA scientists have discovered that about 28 million tons reach the Amazon jungle, enough to fill more than 100,000 reeds. Dust particles contain essential nutrients for plants, including 22,000 tons of phosphorus. The thousands of tons of phosphorus deposited in the Amazon help certain plants grow and could be beneficial if they are integrated into the vegetation of the Amazon. The amount of sand transported to the Amazon varies from year to year. This fluctuation is closely related to the precipitation that occurs in the Sahel, a strip of land that consists of semi-arid areas in the southern Sahara. The more it costs, the more sand is transported to the Amazon the following year. It is one of the direct consequences of desertification. China is another part of the world that is affected by these effects. The Gobi Desert and the Taklamakan, among many others, occupy almost a quarter of the country and are expanding to Beijing at an alarming rate. Every spring, storms carry about one million tons of sand to the east. The first dunes are located less than 80 kilometers from the north of the capital, a threat so great that the people of China have even called it the Yellow Dragon. How did the country get to this? It all started in the 1950s. The reason for this desertification is quite well known. We know that there was an excessive amount of deforestation during the industrial development boom under Mao Zedong's government. Intense agriculture and massive urbanization are responsible for the rest. Together with this, temperatures have increased two degrees in the space of 50 years to the north of China. The result is that the arid and semi-arid areas now cover almost half of the country and every year the desert continues to consume 260,000 hectares of land, that is, the surface of Luxembourg. Today the country has almost 350,000 climate refugees. Given the expansion of the desert, Chinese authorities have declared a total war. The solution that has been found to solve this problem is to build a new Great Wall, but this time made of plants. An immense project that began almost 40 years ago. The Great Green Wall of China is basically to protect the east of China from the greatest sand storms and to maintain the presence of an oasis that renews the entire western border of traditional China, that is, the non-mountainous regions of China. By 2050, China expects to have planted more than 35 million hectares of trees and thus form a green belt of approximately 1,500 kilometers wide and 4,500 kilometers long. The first stage of this mega-project is to stabilize the sand with plant partitions. The goal of organizing plant partitions to stabilize the dunes is to reduce the speed of the wind on the surface. The sand dune moves due to the wind that runs along its surface, which drags the sand particles or grains of sand and deposits them a little further at the foot of the dune, so the dune will change gradually. Due to the plant partitions, the wind will decelerate, which will stabilize the sand and it will practically no longer move and from there we will be able to grow more plants. Thanks to its root system, the trees or shrubs will be attached to the interior of the dune. The soil will grow, allowing biodiversity to return. A virtuous circle has been formed. Since the project began, nearly 66 billion trees However, some scientists have raised doubts about the need of this large company. It's not just about creating a great wall, but about establishing a rural landscape in which the trees will play a key role. And at this moment, we have a mosaic. A mosaic of cultivated lands in the forestation and the continuous list. And that is what will be effective in the fight against desertification. But in the urgency of the 1980s, the Chinese government selected the species of trees with the fastest growth without taking into account their abilities to survive in arid areas. The intensively used alam trees, which became mass-produced in the region, are rarely resistant. Fortunately, the procedures were able to evolve. The species of native trees have been favored, and since then it has been scientifically proven that they are resistant to drought. In this way, according to the authorities, thousands of hectares of desert are in the process of stabilization and the number of storms has decreased by 20% in recent years. Faced with desertification, it is now the turn of Africa to get involved. No less than 10 countries expect to erect a huge green barrier in the Sahara del Sur. It would connect Senegal to the West, to Djibouti in the East, that is, 15 kilometers wide and 7,600 kilometers long. An ambitious plan was launched in 2008, and even today it is in its early stages. For now, only Senegal has embarked on this exceptional enterprise. However, the fight against this force of nature is everyone's concern. Desertification is an important problem for the planet as 2 billion people live in a desert region. We can say that with desertification and the constant growth of the population, especially in the poorest areas, more and more people will need food to eat. We must fight the problem and improve the function of ecosystems. Despite the threat of desertification, there is still time to act. For scientists, the fight against this burden is underway thanks to the organization of sustainable agriculture, a good soil irrigation, and the conservation of forests. The battle against deserts and sandstorms has just begun.