Why Does Earth Have Deserts?

Deserts History

The deserts of today were not deserts in the past Earth. About 8,000 years ago, deserts were moister and a more livable place. The fossilized bones of hippopotamus and elephants have been discovered in the Sahara Desert! There are two kinds of deserts: Hot deserts and Cold deserts. The cold deserts like the Atacama are desert plateaus located in South America. The largest desert in the world is located in Africa.

Planet Earth is a constantly shifting landscape of 8 biomes, ranging from rainforest to grassland and desert to taiga. Twenty-two thousand years ago, the Sahara was uninhabited, except for the area around the Nile Valley. Then, about 10,500 years ago, monsoon rains rolled in to get it up. Climates change. It happens, and sometimes they change dramatically, like when whole deserts completely shift their borders.

Why does Earth have deserts?

Deserts exist on Earth due to a combination of factors related to climate, geography, and atmospheric circulation patterns. The primary reasons why deserts form and persist are as follows:

Rain Shadow Effect: Deserts occur on the leeward side of mountain ranges. As moist air approaches a mountain range, it is forced to rise, cool, and condense, leading to precipitation on the windward side. As the air descends on the other side of the mountains, it becomes drier and warmer, resulting in reduced cloud formation and limited rainfall. This phenomenon is known as the rain shadow effect and is a common cause of desert formation.

Subtropical High-Pressure Zones: Deserts are commonly found in regions where persistent high-pressure systems dominate. In areas like the Sahara Desert or the Australian Outback, the sinking air associated with high-pressure zones inhibits cloud formation and suppresses rainfall. The descending air warms and dries out, leading to arid conditions.

Cold Ocean Currents: In some cases, cold ocean currents can contribute to the formation of deserts. Cold currents flowing along coastlines can lower air temperatures and reduce the moisture-holding capacity of the air, leading to drier conditions and limited precipitation. Examples include the coastal deserts of Peru and Namibia, influenced by the Humboldt Current and the Benguela Current, respectively.

Distance from Moisture Sources: The distance from major moisture sources can also contribute to desert formation. Landlocked deserts, such as the Gobi Desert in Central Asia, are far from major bodies of water, making it more difficult for moist air to reach these areas. As a result, the limited moisture available in these regions contributes to aridity.

Atmospheric Circulation Patterns: Global atmospheric circulation patterns, such as the Hadley Cell circulation, shape desert distribution. As air rises near the equator and moves toward the poles, it loses moisture through precipitation. By the time the air descends in the subtropics, it has become dry, contributing to desert conditions in those regions.

Deserts are defined as areas of land that receive less than 10 inches of rainfall yearly. These regions are low in humidity and can even be moisture-deficient, evaporating faster than received. While most deserts are found in the mid-latitudes, these diverse ecosystems occur on all seven continents. Also, these make up nearly one-third of Earth’s total landmass.

Deserts are sometimes classified into four major types: subtropical, semiarid, coastal, and polar.

Subtropical: These deserts are found along the equator, the Tropic of Cancer, and the Tropic of Capricorn. They are the hottest deserts on Earth, with daytime temperatures reaching 120 degrees Fahrenheit.

Semiarid: Semiarid deserts are in Asia, Europe, and North America. These cold-winter deserts often form when tall mountain ranges block moisture through the rain-shadow effect.

Coastal: Coastal deserts form alongside the tropical western edges of specific continents. Despite their proximity to water, coastal deserts remain dry.

Polar: Polar deserts are found in the Arctic and Antarctic—the other end of the extreme, winter temperatures in the Antarctic Desert average around 50 degrees Fahrenheit.

Only a few thousand years ago, the Sahara was green and lush. Research has found the Sahara’s shifting sands are expanding, causing die-offs of vegetation, failure of agriculture, and increased erosion without plants to hold the soil in place. But this wasn’t always the case.

Scientists hypothesized that an ancient river ran through Western Sahara, feeding the land and securing it with vegetation. Clues were left off the coast of Mauritania, where researchers found sediment resembling that of a vast river. But there was no river around, only arid sands. They called this ancient waterway the Tamanrasset.

A recent Japanese Advanced Land Observing Satellite study says it’s real! It was confirmed recently using microwave radar. If it were still there, the Tamanrassat River would be the 12th largest on Earth, winding 300 miles inland (500km) to the Mauritanian coast.

As the researchers point out, climate change happens fast. For example, a study in Earth and Planetary Science Letters looked at 30,000 years of dust blown from Africa into the Atlantic. Over the millennia, the amount of blown dust rose and fell in lockstep with moisture on the continent.

  • Less moisture, more dust, more moisture, less dust.

As dryness, most of the sediment in the Atlantic is from Saharan dust! Therefore, it can reach North America! By looking at this dust, they knew about 6,000 years ago, the African Humid Period ended suddenly, coinciding with an axial change in the Earth’s orbit.

  • According to NASA and climate scientists’ research, the deserts exist because the Earth’s spin changed, decreasing Northern Hemisphere monsoons.
  • Vegetation died very quickly, and the third-largest desert in the world took over North Africa, all in less than 300 years!

In a separate study in Science, one jet stream moves hot, dry air across the planet’s Equator. As a result, it has shifted northward, causing the tropics to expand 140 miles northward in the last 26 years. With it, the deserts of Earth occur.

Deserts formation

Deserts usually form between 15 and 30 degrees north and south of the equator.

  • In the interior of continents.
  • In rain shadows of large mountain belts.

The Hadley cell is a large-scale atmospheric convection cell with air rising near the equator and flowing poleward 10 to 15 kilometers above the Earth’s surface. It descends into the subtropics and returns to the equator near the surface. This process starts because the equator region receives more solar radiation.

So there have warmer air and lots of evaporation. The region is usually humid because warm air can hold more moisture than cool air. Warmer air tends to rise, and it will do so until it reaches about 10 to 15 kilometers high. As the air rises, the temperature decreases.

So there will be many precipitation events as the air masses rise and trip toward the north and south. Air masses will continue flowing southward and northward. But they will get drier and drier because of the rain events and colder since they leave the equator and go towards the poles.

At around 30 degrees south and 30 degrees north, air masses tend to descend toward the planet’s surface. So these regions will be dominated by dry air without much precipitation, which creates the perfect environment for deserts to form.

Some deserts are also located in the interior of continents. In a very simplistic way, they may be farther from the main sources of moist air. The primary source of moist air that promotes rain is the ocean, far from the interior of continents.

So there is usually more rain near the coasts, and once the air masses reach the interior of continents, they are already dry. But this effect includes many other factors, including the rain shadow effect. So rainshadow regions are perfect settings for deserts to form.

One example of rain shadow is the Tibetan Plateau north of the Himalayas. This is because the winds mainly come from the south. So when they encountered the Himalayas, the air masses tended to rise, and much precipitation tended over there. However, when the air masses cross the Himalayas towards the Tibetan Plateau, they are already very dry. So this region is much arider.

Desert existence

According to NASA’s Jet Propulsion Laboratory, the melting of Greenland ice is changing how the Earth spins. It is changing the tilt of Earth’s axis by 2.6 centimeters per year, increasing that tilt on the horizon!

As the planet’s ice and water distribution changes, the Earth’s axis changes in precession. Thus, the sun will hit different earth’s latitudes at different intensities than before, drastically changing the weather systems.

The jetstream is already shifting, causing the tropical deserts to expand into a previously lush territory. But scientists don’t believe this is a natural phenomenon. It is happening way too fast, and the rates are increasing.

As desertification hits the American plains, South Asia, and the Mediterranean, humans feel the effects of drought, climate change, and economics. In a 2005 report about desertification by United Nations University, 10 to 20 percent of these “drylands” have been negatively impacted by losing farmland and biodiversity.

That was a decade ago, and at the time, 2.1 billion people lived in the drylands of our planet. It’s clear the deserts have and will expand. As they continue to do so, farmland will dry, vegetation will disappear, and people will have to move or completely alter their lifestyles.

Desert ecosystems

While deserts experience extreme temperatures and receive very little precipitation, they are still essential habitats for plants and animals. They have evolved to withstand harsh desert conditions by burrowing into the excellent ground and emerging at night when desert temperatures drop. In addition, many desert plants, including the saguaro cactus, have established long and shallow root systems to absorb minimal moisture in the ground better.

Desert wildlife is particularly vulnerable to ecological changes and is highly specialized in surviving in harsh environments. Existing deserts have become less habitable because of rising temperatures. That drier up scarce water resources and increase the risk of wildfires.

Additionally, new desert areas are beginning to form through desertification. This phenomenon occurs when deforestation, climate change, and resource mismanagement degrade biological productivity, creating a desert.

For instance, poor irrigation practices and excessive water usage in Central Asia dried up the Aral Sea and formed the youngest desert on the planet. Thus, it may be possible to curb desertification while protecting our surprisingly rich desert ecosystems.

  • By practicing responsible agriculture, better management of limited water resources, and limiting further development.

Frequently asked questions

Why is the desert dry?

The first reason is deserts are located in the ‘rain Shadow area.’ These are areas that have a mountain range between them and the sea. The air that rises from the sea has moisture and reaches the deserts. Therefore, they must travel over the mountain ranges. In doing so, the moisture in the airdrops over the mountains is rain and snow. When it reaches the deserts, the air has no water or rain!

The deserts are situated on the western coasts of the continents. Here the ocean currents are cold. Hence they don’t carry much moisture and are relatively dry. An example of a rain shadow area desert is the Atacama Desert In Chile caused by the Andes Mountains.

Another reason deserts are dry is that they are located in areas with high air pressure. The air travels in the upper atmosphere and sinks at approximately 30° north and 30° south of the Equator. When the air sinks, it creates an area of high pressure. These high-pressure areas experience very dry and warm conditions. As a result, these areas have calmer and dryer weather, resulting in a hot desert climate like the Sahara Desert.

Why are deserts so cold at night?

During the day, there’s little moisture in the air. So when the sun’s beating down, it gets hot. Very little moisture when the sun starts to set, so it only holds very little heat. It starts to cool dramatically, and most deserts have clear cloudless skies. So there’s nothing to keep the heat in. The result is that most efforts have very low temperatures at night. Even the summer’s hottest days can have the coldest nights.

More Articles:

Why Does The Sahara Desert Exist On Earth?

Why Europe Has No Desert?

What Happened To Camels In North American Region?

Why Can Not You Visit Antarctica?

Julia Rose

My name is Julia Rose. I'm a registered clinical therapist, researcher, and coach. I'm the author of this blog. There are also two authors: Dr. Monica Ciagne, a registered psychologist and motivational coach, and Douglas Jones, a university lecturer & science researcher.I would love to hear your opinion, question, suggestions, please let me know. We will try to help you.

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