Tag Archives: desert

What’s the largest desert in the world? (Hint: It’s not the Sahara)

When you hear the word desert, the mind usually drifts towards sun, sand, and dunes. But in truth, deserts are much more varied than you’d imagine. They come in all shapes and sizes and vary quite a lot from one part of the world to the next one.

You’ll probably be surprised to learn that the largest desert in the world is actually the Antarctic.

The Antarctica Desert. Credit Flickr

Deserts are far more than the desolate landscapes we often picture them as. They are biologically rich habitats with a wide array of animals and plants that have adapted to living there. Some deserts are among the last remaining areas of true wilderness on the planet, yet many people call them home: more than one billion people (a sixth of the global population) actually live in desert regions.

Deserts cover more than one-fifth of the Earth’s land area and can be found on every continent — and only 20% of them are covered in sand.

So what makes a desert?

A place that receives less than 25 centimeters (or 10 inches) of rain per year is considered a desert. They are part of a wider type of region called drylands, which are defined by a scarcity of water. Drylands can lose more moisture through evaporation than they obtain from precipitation.

Despite the usual misconceptions, deserts can be both hot and cold. The Sahara is the largest hot desert in the world and can reach temperatures of up to 122 degrees Fahrenheit (50 degrees Celsius) during the day.

But deserts can also be cold, such as the ones in the Antarctic and the Arctic — which also happen to be the largest two deserts overall. Cold deserts don’t necessarily need to be freezing: the Gobi desert in Asia is considered to be a cold desert since it is sometimes covered by snow and frost. However, winds can cause dramatic temperature shifts in the Gobi desert, shifting from −40 °C (−40 °F) in winter to 45 °C (113 °F) in summer. These rapid temperature shifts occur not only seasonally, but can even take place in the same day.

A Mongolian lady dressed for the Gobi desert. Image credits: Victor He.

The world’s driest deserts like the Atacama Desert in Chile have areas that get less than .08 inches (or two millimeters) of precipitation a year. They are such harsh environments that researchers have studied them to get a better idea about life on Mars. But every few years they a very rainy period called “super blooms.” The Atacama Desert may be the oldest desert on earth, being hyper-dry for over 3 million years.

The largest desert in the world

Purely in terms of size, the Antarctic Desert is the largest desert on the planet, measuring a total of 13.8 million square kilometers (or 5,500,000 square miles). Antarctica is not only the most isolated continent on Earth but also the coldest. It’s considered a desert as its annual precipitation is less than 51 millimeters (or two inches).

This is also a desert. Image in public domain.

To put that into perspective, much of the Sahara Desert gets twice as much rain as the Antarctic. The coastal regions of Antarctica receive more rain, but still average only 200 millimeters (or eight inches) per year. Unlike most desert regions, however, the rain doesn’t soak into the ground. Instead, the snow piles on top of itself.

Despite having so little rain, Antarctica still gets massive windstorms. Just like the sandstorms seen in hot deserts, the high winds pick up snow and turn into blizzards. The storms can reach speeds of up to 320 km an hour (200 mph) and are one of the reasons the continent is actually so cold.

The continent is covered by a permanent ice sheet that contains 90% of the Earth’s freshwater and averages 1.6 kilometers in thickness. Only 2% of Antarctica isn’t covered by ice, an area mainly located along the coasts where penguins, whales, birds, seals and other animals reside.

There aren’t permanent human residents in Antarctica, but between 1,000 and 5,000 researchers can be found at different times of the year in the research stations across the continent. The largest one is McMurdo Station, located on the tip of Ross Island and managed by the United States.

The Antarctic can also get freakishly cold. The coldest temperature ever recorded was taken at the Soviet Vostok Station on the Antarctic Plateau. It reached a historic low of -89.2°C (-129°F) on July 21st, 1983, and was obtained using ground-based measurements. Satellite data indicated a temperature of around -93.2 °C on August 10th, 2010 but the reading hasn’t been confirmed.

Other large deserts in the world

Curiously, the second-largest desert in the world is also cold. The Arctic Desert covers a total area of about 13,7 million square kilometers (5,29 million square miles). The total amount of precipitation is below 250mm (10 inches), which is predominantly in the form of snow.

The desert partially occupies parts of territories claimed or controlled by Canada, Denmark, Norway, Russia, Sweden, and the United States. The average temperature in the Arctic Desert is -20 °C, reaching as low as -50 °C in the winter. During summer, the sun doesn’t set for 60 days. Then, in winter, there are extended periods of darkness.

The Arctic Desert. Credit Wikipedia Commons

The third-largest desert in the world is the well-known Sahara, which is also the world’s largest hot desert. It has a total size of 9,4 million square kilometers (or 3,3 million square miles). It occupies most of the land in North Africa except for the regions of the Maghreb, the Atlas Mountains, and the coastal region next to the Mediterranean Sea.

The average annual rainfall ranges from very low in the northern and southern fringes of the desert to nearly non-existent over the central and eastern parts. Most of the Sahara receives less than 20 millimeters (or 0.79 inches). Temperatures are also quite intense in the Sahara, and can rise to more than 50 °C.

The Sahara Desert. Credit Flickr

Located in Western Asia, the Arabian desert is the fourth largest one on Earth. It covers an area of 2,3 million square kilometers (or 900,000 square miles). It encompasses much of Yemen, the Persian Gulf, Oman, Jordan, and Iraq. Its center, known as the empty quarters, forms the largest continuous body of sand in the world.

The climate of this area is very dry. Temperatures oscillate between regular, characteristically high heat on one end of the spectrum to seasonal nighttime freezes on the other. The annual rainfall is around 100mm on average, but the driest areas receive as little as 30 to 40 mm of rain a year.

Also in Asia, the Gobi Desert is known as the fifth-largest desert in the World. It has a total land area of 1.2 million square kilometers (or 500,000 square miles) and covers parts of northwestern and northern China, as well as southern Mongolia. It’s called the “rain shadow desert” as the Himalayan Mountains block the rainfall from the desert. It’s not a sandy desert and instead has exposed, bare rock.

The Gobi Desert. Credit Flickr

Desertification and environmental challenges

A significant number of the world’s semi-arid regions are turning into deserts at record speed through a process known as desertification. This isn’t caused by natural drought but rather by deforestation and demands from human populations that establish in the semi-arid lands.

For example, in northern China, the expansion of urbanization, which left the land unprotected against wind erosion, and the accumulation of sediment from a surrounding desert recently created a desertification problem. Replying to it, the government built a so-called great green wall to act as a border against the desert.

But that’s not the only challenge that deserts are dealing with. Species in existing deserts are threatened by a warmer world. Higher temperatures cause more wildfires that then change the desert landscapes, eliminating slow-growing trees and shrubs and replacing them with fast-growing grasses.

Scientists have warned that the iconic Joshua tree from California might not survive a hotter climate. If that’s actually the case, the effect would also be severe in other species such as the yucca moth, which deposits its eggs into the flower of the Joshua tree — and the effects could cascade down the food chain. Many desert birds could also be affected by dehydration and might not be able to survive in hotter deserts.

Deserts are a natural part of our ecosystem, but as it is so often the case, human intervention is changing the natural cycles. This change is often much quicker than natural change, which renders ecosystems incapable to adapt in time.+

Ripping the desert apart: Stunning images show Ridgecrest earthquakes shattering the ground

The 2019 Ridgecrest earthquakes struck California on the 4th and 5th of July, with magnitudes of 6.4, 5.4, and 7.1, respectively. Millions felt the shaking, and even more were frightened by a potentially devastating earthquake. Now, satellite images show just how powerful the earthquake was.

Before-and-after satellite images show rock displacement following the 7.1 magnitude earthquake. Image credits: Sotiris Valkaniotis / Google Earth / Digital Globe.

California is pierced by the San Andreas fault, which extends roughly 1,200 kilometers (750 mi). The fault poses great seismic threat, with many seismologists suspecting that the fault is overdue for a major earthquake.

The Ridgecrest earthquakes should also be understood in the context of the San Andreas fault. Although the earthquakes caused relatively minor damage, the effects were felt across much of Southern California, as well as Arizona and Nevada, and even Mexico. It’s estimated that some 30 million people experienced the main shock.

However, the desert satellite images help convey the full power of the earthquake.

A long scar produced along a geological fault in the aftermath of the Ridgecrest earthquake of July 5. The dark stain is water leaking from a pipeline that had ruptured. Image credits: Sotiris Valkaniotis / Google Earth / DigitalGlobe.

A geological fault is essentially a crack in the Earth’s crust. Typically, major faults are associated with, Earth’s tectonic plates, but smaller faults emerge all around the world. In an active fault, the two sides of the fault tend to move relative to each other over time — this movement can cause earthquakes.

A fault on the scale of San Andreas isn’t neatly carved through California. It produces many other faults that slice up in ribbons. These secondary faults can be ruptured by earthquakes, causing further temblors. When this happens, the effects can be severe.

Note the displacement on the two sides of the fault. Image credits: Sotiris Valkaniotis / Google Earth / DigitalGlobe.

These images are among the best of their kind. For starters, the earthquakes occurred in the desert, where displacements can be followed with relative ease. There’s no vegetation and nothing to obscure the geologists’ (or the satellites’) eyes.

“I like to think about the desert as an unpainted canvas,” said Ken Hudnut at the US Geological Survey. “And the earthquake tore a big rip through the desert canvas.”

These stunning visual effects have been produced using openly available satellite imagery from Google Earth and DigitalGlobe by earthquake geologist Sotiris Valkaniotis, who is based in Greece. It should be said that while the earthquake and faults are the main cause of the displacement, other causes such as landslides or liquefaction can also cause displacement.

Wax, water, and heat: how leaves survive in extremely hot environments

For plants, breathing is a balancing act between gathering what they need from the atmosphere and not losing too much water. A new study shows how some plants are able to regulate this mechanism and stay hydrated, even at very high temperatures.

The wax can make the surface of some leaves waterproof. Image credits: Rei.

In the 1950s, the German botanist Otto Ludwig Lange was studying plants in Mauritania — a country in western Africa that’s mostly covered by a desert. Lange noticed that leaves can heat up to temperatures as high as 56 degrees Celsius (133 Fahrenheit). He couldn’t figure out how they do it — how do plants get so hot without losing all their water?

In an attempt to solve that, botanists Markus Riederer and Amauri Bueno from Julius-Maximilians-Universität Würzburg in Germany, succeeded in revealing the secret studied the complex structure of a plant leaf.

Leaves are covered with a “skin” called a cuticle. The cuticle consists of lipids and polymers impregnated with tax, and it acts coherent outer covering of the plant. If you’ve ever seen droplets of water sitting on top of a leaf, it’s the wax-rich cuticle holding it in place.

This protective layer contains numerous pores (called stomata), which open and close according to the plant’s needs. The problem is that when these pores open up to allow the plant to breathe, they also allow water to evaporate. For desert plants, this is particularly troubling, but as Riederer and Bueno found, they have different ways of dealing with this.

Date palms have an innovative strategy to survive extreme heat.

For instance, a plant called a colocynth (Citrullus colocynthis), also called a bitter apple or a bitter cucumber opens up its pores when the heat gets going. This allows some of its water to evaporate as sweat, cooling down the leaves. This process is water-intensive, but the colocynth can afford it because it has a deep root which allows it to gather sufficient water. Decades ago, Otto Ludwig Lange noted that the plant can keep its leaves up to 15 degrees cooler than the surrounding air, and now the mechanism is better understood. However, the date palms have a radically different approach.

The date trees can’t afford to lose water, so they don’t “sweat”. As a result, their leaves get much hotter than the surrounding desert — up to 15 degrees hotter. The secret to its survival lies in the cuticle, specifically in the wax in the cuticle.

Unlike that of the colocynth and most other plants, the wax in the date palm’s skin is much more water-proof, due to its different water composition. While it’s not clear exactly what causes this different composition, the results are important because they could be used in agriculture, encouraging crop growers to select plants with certain cuticle waxes because they have better chance of survival in hot locations.

The study was published in the Journal of Experimental Botany.

A piece of Libyan desert glass that weighs 22 grams and is about 55 mm wide. Credit: Wikimedia Commons.

Scientists solve 100-year-old mystery of yellow desert glass prized by Egyptian pharaohs

A piece of Libyan desert glass that weighs 22 grams and is about 55 mm wide. Credit: Wikimedia Commons.

A piece of Libyan desert glass that weighs 22 grams and is about 55 mm wide. Credit: Wikimedia Commons.

An exotic and beautiful type of glass found in the Sahara desert has a cosmic origin, according to a new study. After analyzing the chemical makeup of Libyan desert glass — a naturally occurring glass whose striking yellow color made it a much-sought-after decorative material — researchers found that it was produced by ancient meteorite impacts.

Cosmic glass fit for kings

Breastplate found in King Tutankhamun’s tomb. The scarab is made out of Libyan desert glass. Credit: Wikimedia Commons.

Breastplate found in King Tutankhamun’s tomb. The scarab is made out of Libyan desert glass. Credit: Wikimedia Commons.

The rare Libyan desert glass has been prized for its beauty for thousands of years. The glass — the purest natural silica glass ever found on Earth — is generally yellow in color and can be very clear, although most pieces are milky and may even contain tiny bubbles, white wisps, and inky black swirls.

By one estimate, over a thousand tons of Libyan desert glass are strewn across the deserts of eastern Libya and western Egypt. Most are the size of pebbles, although some chunks can have a considerable size and weight — the biggest piece ever found weighs around 26 kg.

Local inhabitants in the Neolithic period made tools out of the glass, and later the Egyptians used it to fashion jewelry. In fact, the carved stone on the breastplate of the famous Egyptian pharaoh Tutankhamun was made of Libyan desert glass. But these piece of glass were created long before King Tut was born — about 29 million years by one estimate.

Silica glass at the Great Sand Sea. Credit: Mohamed El-Hebeishy.

Silica glass at the Great Sand Sea. Credit: Mohamed El-Hebeishy.


For more than a hundred years, scientists have debated what forces could have created the enchanting glasses. There are two major hypotheses that explain their formation: either a meteor impact or an airburst (an atmospheric explosion which happens when meteoroids explode in the lower atmosphere) was responsible. A recently published study supports the former theory.

In a new study, Aaron Cavosie from Curtin University in Australia and colleagues performed chemical analyses of Libyan desert glass samples that unequivocally supports the meteorite formation theory.

While they were examining zircon minerals embedded in the glasses, the researchers found traces of another mineral called reidite. This mineral only forms in high pressure and heat — so far, it hasn’t been found anywhere other than meteorite impact craters.

“Both meteorite impacts and airbursts can cause melting, however, only meteorite impacts create shock waves that form high-pressure minerals,” says Cavosie.

“So finding evidence of former reidite confirms it was created as the result of a meteorite impact.”

Whatever meteorite impacted the desert all those millions of years ago, it must have caused a gigantic explosion. It vitrified (glassified) a huge area, resulting in a broad range of glasses ranging from cloudy dark to stunningly luminous lemon yellow — all depending on the kind of contaminants that dissolved into the liquid silica created by the powerful impact.

A variety of Libyan Desert Glasses. Credit: Corning Museum of Glasses.

A variety of Libyan Desert Glasses. Credit: Corning Museum of Glasses.

The findings published in the journal Geology are useful for establishing how often near-Earth objects come in contact with our planet’s surface. The study seems to suggest that the kind of impacts that are powerful enough to create Libyan desert glass are, thankfully, quite rare.

“Meteorite impacts are catastrophic events, but they are not common,” says Cavosie.

“Airbursts happen more frequently, but we now know not to expect a Libyan desert glass-forming event in the near future, which is cause for some comfort.”

New Hadrosauroid.

New species of duck-billed dinosaur discovered in the Gobi Desert

A fossilized, nearly-intact dinosaur skeleton unearthed in Mongolia fills a gap in the evolution of hadrosaurs.

New Hadrosauroid.

Skeletal reconstructions of Gobihadros mongoliensis.
Image credits Tsogtbaatar et al,, (2019), PLOS ONE.

Researchers from the Mongolian Academy of Science and the Royal Ontario Museum, funded by the Hayashibara Museum of Natural Sciences, describe a new species closely related to Hadrosaurids, which they named Gobihadros mongoliensis. The new species will help us better understand the evolution and ecology of the dinosaur family Hadrosauridae, the ‘duck-billed’ dinosaurs.


“The article describes, for the first time, extraordinary well-preserved fossil material of hadrosauroid dinosaur as a new genus and species from the early Late Cretaceous in Mongolia. We hope that it will be very useful material for further study of the evolution of hadrosauroids, iguanodintians and ornithopods as well,” the authors write.

Duck-billed dinosaurs were quite successful during their day in the Late Cretaceous. They had a wide geographical range over the world as it was at the time and were important large herbivores in their ecosystem. But we don’t really know much about the species during its early days. Some partial fossils found previously are helping us piece together the duck-billed dinos’ family tree, but complete fossils remain few and far between.

Gobihadros mongoliensis was discovered at the Bayshin Tsav Site in the Gobi Desert, Mongolia. Several specimens were found at the site, including one “virtually complete” skeleton measuring almost three meters in length. Anatomical comparisons to Hadrosauridae fossils revealed that this species doesn’t quite fit into the family. The species, however, are very closely related. Gobihadros is the first hadrosaur-like dinosaur from the Late Cretaceous of central Asia known from complete remains.

The team also reports, based on comparisons to later Asian hadrosaurs, that Gobihadros would not make it through the natural-selection gauntlet. Later Asian hadrosaurs are related to species in today’s North America, and likely migrated from there during the Late Cretaceous. The authors caution that we need more fossils from this transition period in order to get a proper idea of what happened — and when. But, from the data we have now, Gobihadros seems to have disappeared from Asia and was soon followed by the hadrosaurs. This suggests that the hadrosaurs ultimately outcompeted species like Gobihadros.

“[…] the relationships of other taxa are well-resolved, and in combination with biostratigraphic data, suggest that hadrosaurids from the Maastricthian of Asia migrated from North America across Beringia in the Campanian, and replaced non-hadrosaurids such as Gobihadros,” the authors conclude.

The paper “A new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous Baynshire Formation of the Gobi Desert (Mongolia)” has been published in the journal PLoS ONE.

Tadrart Acacus desert in western Libya, part of the Sahara. Credit: Wikimedia Commons.

The Sahara swings between ‘lush’ and ‘desert’ every 20,000 years, in sync with the Earth’s tilt

Few places on this planet are as inhospitable as the Sahara desert. This is why it’s so intriguing to learn that the Sahara, and most of North Africa for that matter, used to be a lush region filled with a diversity of plants and wild animals. What’s more, this transition occurred relatively recently, in the order of thousands of years, judging from fossils and even rock paintings made by artists who lived in now abandoned settlements.

Now, MIT researchers claim that the region may be swinging between desert and lush conditions every approximately 20,000 years due to changes in the Earth’s axial tilt.

Tadrart Acacus desert in western Libya, part of the Sahara. Credit: Wikimedia Commons.

Tadrart Acacus desert in western Libya, part of the Sahara. Credit: Wikimedia Commons.

Each year, tons and tons of Saharan dust are swept by northeastern winds into the Atlantic Ocean forming thick sediment deposits on the ocean floor. By analyzing these dust layers, it’s possible to infer many qualities about the climate they originate from. For instance, thick dust layers indicate arid times, whereas thinner layers are a sign of a wetter climate.

Some of the sediment core samples retrieved off the coast of West Africa can trace back Sahara’s climate history over millions of years. Previously, such analyses suggested that the Sahara oscillated between wet and dry climates every 100,000 years or so — something which scientists had pinned down to ice age cycles. Thick layers of dust seemed to coincide with periods when the Earth was more covered in ice, wheres less dusty layers corresponded to interglacial periods.

This correlation, however, does not bode well with our present understanding of the Saharan climate, which ought to be mainly driven by the region’s monsoon season. A periodic change in precipitation is determined by the tilt of the planet’s axis, which exposes some regions of Earth to more sunlight than others.

“We were puzzled by the fact that this 20,000-year beat of local summer insolation seems like it should be the dominant thing controlling monsoon strength, and yet in dust records you see ice age cycles of 100,000 years,” David McGee, an associate professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences, said in a statement.

McGee and colleagues devised a new technique which reinterprets the values of Saharan dust cores deposited over the last 240,000 years. The new method hinges on the measurement of the concentration of a rare isotope of thorium.

Thorium is produced in the ocean when small amounts of radioactive uranium dissolve in seawater, then quickly attaches itself to sinking sediments, i.e. Saharan dust. This way, it’s possible to infer how much dust was accumulating during a particular era by studying the concentration of thorium in a particular sediment layer. The slow accumulation of sediment is associated with a higher concentration of thorium, and vice-versa.

Using thorium as their proxy for dust deposition (and, hence, Sahara’s historical climate), the MIT research team found that some peaks of dust in the cores may be false positives due to carbonate dissolution. With the confounding effect removed, the researchers found that the Sahara shifted from wet to dry climates every 20,000 years, in sync with monsoon activity and the planet’s periodic tilting of its axis.

This time series could be useful not only for understanding the history of the Sahara Desert (or luxurious plains, alternatively) but also that of our species. Humans emerged out of multiple hotspots in Africa and migrated towards the Middle East, and from there to Europe, Asia, and the rest of the world. These migrations may have been facilitated by the Sahara’s periodical mood swings.

“We can now produce a record that sees through the biases of these older records, and so doing, tells a different story,” McGee says. “We’ve assumed that ice ages have been the key thing in making the Sahara dry versus wet. Now we show that it’s primarily these cyclic changes in Earth’s orbit that have driven wet versus dry periods. It seems like such an impenetrable, inhospitable landscape, and yet it’s come and gone many times, and shifted between grasslands and a much wetter environment, and back to dry climates, even over the last quarter million years.”

That being said, the Sahara is also influenced by the global climate. According to a 2018 study, human-induced climate change contributed to a 10% expansion of the Sahara desert’s surface over the past hundred years.

And, of course, some of you might be wondering: when will the Sahara’s climate revert back to lush conditions? Scientists believe that up until 10,000-11,000 years ago, the Sahara looked more like today’s African savannah. This means that we still have another 10,000 years before North Africa becomes a giant oasis again.

The MIT study was published in the journal Science Advances. 

MOF-303 crystals.

New material harvests water from thin air without using energy — even in dry, arid Arizona

One kilogram of the new metal-organic framework (MOF) material can produce 0.2 liters (7 ounces) of water every 24 hours — even in dry Arizona.

Device prototype.

The team’s prototype water harvester.
Image credits: Wang Laboratory / MIT.

Us reading this probably take it for granted that if you turn a tap in your kitchen freshwater flows out. However, many people make their homes in arid areas where that is just a pipe dream — but they still need a reliable source of water. A new material developed by a team at the University of California, Berkley, might be just what provides that hydration. One kilogram of the material, a metal-organic framework (MOF), produced 0.2 liters (7 ounces) of water during a 24-hour trial in Arizona — without using any energy.

Water from thin air

The team first built a prototype water harvester last year — it used solar heat to capture water vapor from the air. Now, they’ve scaled up their device, plopped it down in the backyard of a tract home in Arizona, and waited for it to complete a full 24-hour cycle. The results are consistent with what the team predicted in 2017, after running their prototype through field trials: the new, larger device can produce drinkable water at very low humidity for almost no cost.

“There is nothing like this,” said Omar Yaghi, paper co-author. “It operates at ambient temperature with ambient sunlight, and with no additional energy input you can collect water in the desert. This laboratory-to-desert journey allowed us to really turn water harvesting from an interesting phenomenon into a science.”

The trial was carried out in Scottsdale. Relative humidity here drops from 40% at night to 8% during the day, the team reports. Despite this, the harvester worked — and, according to the team, it can easily be scaled up by simply adding more MOF. This highly porous material, MOF-801, was produced from metal zirconium. The researchers calculate that one kilogram of this material (2.2 pounds) can harvest about 200 milliliters (about 7 ounces) of water per kilogram (2.2 pounds) of MOF.

MOF-303 crystals.

Optical microscope images of MOF-303 crystals.
Image credits Omar Yaghi laboratory, UC Berkeley

However, Yahgi says the team has also been working on a new MOF, dubbed MOF-303, based on aluminum. This should be much cheaper than MOF-801 — the team estimates it will be at least 150 times cheaper — and twice as effective. Lab tests showed that MOF-303 could produce over 400 milliliters (14 ounces) of water per day per kilogram of MOF — equivalent to about 3 cups.

“There has been tremendous interest in commercializing this, and there are several startups already engaged in developing a commercial water-harvesting device,” Yaghi said. “The aluminum MOF is making this practical for water production, because it is cheap.”

MOFs are solids, but they’re mostly hollow. They’re crisscrossed with an immense number of internal channels or holes, giving them a huge equivalent surface area: one sugar-cube-sized piece of MOF has the internal surface of roughly six football fields, the team notes.

Because of all of this surface area, MOFs easily trap gases or liquids. When heated, they release the fluids, allowing for easy retrieval.

The team’s harvester is essentially a box placed within another box. The inner structure packs a 2-square-foot bed of MOF pallets, open to the air, to absorb moisture. The outer box is a 2-foot cube, constructed out of transparent plastic. The top is left open at night to let moist air flow in and come into contact with the MOF, and replaced during the night to heat the material so it releases stored water. This water then condenses on the insides of the outer box, drips to the bottom, and gets collected.

While not yet suited for commercial applications (for example, the team had to harvest the water with a pipette), it does marvelously as a proof-of-concept device. It could lead the way to cheap and reliable water harvesters for use in arid areas. It will also capture water at sub-zero dew points, the team notes.

The team plans to test their aluminum-based MOF later this summer in the Death Valley National Park, to see how it performs in these higher average temperatures.

The paper “Practical water production from desert air” has been published in the journal Science Advances.

The Sahara desert expanded by 10% in the last century

Tadrart Acacus desert in western Libya, part of the Sahara. Credit: Wikimedia Commons.

Tadrart Acacus desert in western Libya, part of the Sahara. Credit: Wikimedia Commons.

In almost a hundred years, the Sahara Desert has expanded by 10%, according to a new study. The authors say that both natural climate cycles and human-induced climate change have contributed to this worrisome expansion threatening the livelihoods of agricultural-based communities.

A continent turning to sand and dust

The Sahara is the largest hot desert in the world, and the third largest desert after Antarctica and the Arctic. Scientists typically classify a region as a desert if it receives less than 100 millimeters (4 in.) of rainfall annually.

This is not the first study to report an expansion of the Sahara, and therefore the report in and of itself is not that surprising. However, the new research carried out at the University of Maryland is unique because it analyzed trends to infer changes in the desert expanse on the century timescale.

The researchers learned by studying the rainfall data recorded throughout Africa from 1920 to 2013 that the Sahara, which occupies much of North Africa, expanded by 10%. You might not notice it by looking at a Mercator world map (notorious for its distortions), but the Sahara is actually as large as the contiguous United States.

“Our results are specific to the Sahara, but they likely have implications for the world’s other deserts,” said Sumant Nigam, a professor of atmospheric and oceanic science at UMD and the senior author of the study.

According to Nigam and colleagues, the Atlantic Multidecadal Oscillation (AMO) is one of the primary drivers of the Sahara’s rapid expansion. This is a climate cycle that affects the sea surface temperature (SST) of the North Atlantic Ocean with an estimated period of 60-80 years. There is also seasonal variability: the desert expands in the dry winter and contracts during the wetter summer, with the most notable differences occurring along the northern and southern boundaries of the Sahara.

Between the barren Sahara and the fertile savannas further south lies a semi-arid transition region called the Sahel. When the Sahara expands, the Sahel inevitably contracts, with serious repercussions for its largely agrarian human society and local grassland ecosystems.

Warm phases of the AMO are linked to increased rainfall in the Sahel, while the opposite is true during the cold phase. We’ve seen the effects of such a cold phase first hand when the Sahel dramatically dried up from the 1950s well into the 1980s. According to the researchers, another natural cycle called the Pacific Decadal Oscillation (PDO), which is characterized by temperature fluctuations in the northern Pacific Ocean on a scale of 40 to 60 years, also played a major role in the desert’s expansion.

“Deserts generally form in the subtropics because of the Hadley circulation, through which air rises at the equator and descends in the subtropics,” Nigam said. “Climate change is likely to widen the Hadley circulation, causing northward advance of the subtropical deserts. The southward creep of the Sahara, however, suggests that additional mechanisms are at work as well, including climate cycles such as the AMO.”

Lake Chad, which sits in the center of this climatologically conflicted transition zone, serves as a bellwether for changing conditions in the Sahel.

“The Chad Basin falls in the region where the Sahara has crept southward. And the lake is drying out,” Nigam explained. “It’s a very visible footprint of reduced rainfall not just locally, but across the whole region. It’s an integrator of declining water arrivals in the expansive Chad Basin.”

Besides AMO and PDO, human-induced climate change also impacted rainfall variability during the last century. The two natural cycles accounted for about two-thirds of the desert’s total expansion. The remaining third can be attributed to climate change, although the researchers caution that longer climate records which extend over numerous climate cycles would helpful in reaching a more definite conclusion.

This pair of images shows the change in the boundaries of the Sahara Desert during the period 1920-2013, broken down by season. Dotted lines show the boundary as it existed in 1920, while solid lines show the boundary in 2013; both boundaries are averaged across the three months of each season. (Winter = Dec-Feb; Summer = Jun- Aug). Brown shaded regions indicate desert advance while green shaded regions indicate desert retreat. Credit: Natalie Thomas/Sumant Nigam/University of Maryland.

This pair of images shows the change in the boundaries of the Sahara Desert during the period 1920-2013, broken down by season. Dotted lines show the boundary as it existed in 1920, while solid lines show the boundary in 2013; both boundaries are averaged across the three months of each season. (Winter = Dec-Feb; Summer = Jun- Aug). Brown shaded regions indicate desert advance while green shaded regions indicate desert retreat. Credit: Natalie Thomas/Sumant Nigam/University of Maryland.

Obviously, an expanding Sahara — which was already huge, to begin with — means very worrisome news. As Nigam mentioned earlier, other deserts around the world are likely expanding as well. Over 45,000 square miles of arable land are lost to desertification each year, by one estimate — that’s while the world’s population continues to grow, driving food demand up. The United Nations warns that desertification could drive up to 50 million people from their homes, unless humanity cuts back on greenhouse gas emissions.

“The trends in Africa of hot summers getting hotter and rainy seasons drying out are linked with factors that include increasing greenhouse gases and aerosols in the atmosphere,” said Ming Cai, a program director in the National Science Foundation’s Division of Atmospheric and Geospace Sciences, which funded the research. “These trends also have a devastating effect on the lives of African people, who depend on agriculture-based economies.”

In the future, the researchers plan on learning more about what drives desert expansion not only in the Sahara, but in other deserts around the world as well.

“With this study, our priority was to document the long-term trends in rainfall and temperature in the Sahara. Our next step will be to look at what is driving these trends, for the Sahara and elsewhere,” said Natalie Thomas, a graduate student in atmospheric and oceanic science at UMD and lead author of the research paper. “We have already started looking at seasonal temperature trends over North America, for example. Here, winters are getting warmer but summers are about the same. In Africa, it’s the opposite–winters are holding steady but summers are getting warmer. So the stresses in Africa are already more severe.”

Scientific reference: “20th-Century Climate Change over Africa: Seasonal Hydroclimate Trends and Sahara Desert Expansion,” Natalie Thomas and Sumant Nigam, was published online March 29, 2018, in the Journal of Climate.

Southern Europe might become a desert by 2100, which is really bad news

Southern Europe may become a desert by the end of the century if we don’t move to reduce emissions, warns a newly published paper.

Image credits Ed Gregory / Pexels.

The Mediterranean coast is a touristic powerhouse, drawing tourists from around the world with its mild climate, good food, and clear waters. But this may well change by the end of the century, warn Joel Guiot, a palaeoclimatologist at the European Centre for Geoscience Research and Education in Aix-en-Provence, France and Wolfgang Cramer, of the Mediterranean Institute for Biodiversity and Ecology. The whole of Southern Europe could become a desert, according to their study, if the climate continues to warm up.

“With 2 degrees of warming, for the Mediterranean we will have a change in the vegetation which has never been known in the past 10,000 years,” said lead author of the study Joel Guiot.

The duo studied pollen cores retrieved from lake mud sediments deposited over the last 100 centuries (roughly equivalent to the Holocene, the geological epoch we’re living in). Because vegetation is closely tied to environmental conditions, they could use pollen to get an idea of how climate shifted over the investigated period. More oak pollen, for example, suggest periods of humid and mild climate, while finding more fir or spruce would point to chillier conditions.

With this data, they built a model of past vegetation (and climate) in the Mediterranean, which they then ran through four predictions taken from the UN’s climate change panel, the IPCC. They found that under a business-as-usual model, the Med’s ecosystems would change beyond anything they’ve been like in the Holocene. Barring a dramatic reduction in emissions, which the team believes is “extremely ambitious and politically unlikely”, Southern Europe will see a dramatic increase in desert areas. Even if the Paris pledge of keeping climate change under 1,5 degrees Celsius is met, the region will experience a “substantial” expansion of deserts.

“Everything is moving in parallel,” Guiot told Nature. “Shrubby vegetation will move into the deciduous forests, while the forests move to higher elevation in the mountains.”

Needless to say, propelling your flora and fauna some 10 millennia back into the past is a pretty bad move. It would take ecosystems back to the state they were before the start of Western Civilization in less than a hundred years. This change will have far-reaching impacts, starting with an unprecedented economic downturn.

Much of Southern Europe relies on the Mediterranean for tourism. Cities like Lisbon, Portugal, or Seville, Spain see millions of tourists per year — who come for the food, the scenery, the history but most of all, the climate. Both these cities have distinct wet and dry seasons (like the coast of California), and the dry summer is the height of the tourist season. But as temperatures push into uncomfortable figures, fewer and fewer tourists are going to come visit.

That’s bad for the economy but not devastating. However, with warmer climates crops will dry out, water systems will be put under huge strain, and as we’ve seen in California, the lack of precipitation during the wet season will cause drought and promote wildfires. Guiot said that these fires, along with the drought and heat will lead to food shortages and, like in Syria in 1998 and 2010, political upheaval and civil war.

“It’s not just climate — political organization is important as well,” Guiot told Inside Climate News.

“But if you amplify a problem of war with the problem of climate, the consequence can be more important.”

The full paper “Climate change: The 2015 Paris Agreement thresholds and Mediterranean basin ecosystems” has been published in the journal Science.

The solar system brought down to scale in Nevada desert

The solar system is a mind boggingly vast thing. And while we all kinda know and agree on that, it’s still hard to wrap your head around the sheer scale we’re talking about here. The distances involved are much more immense than anything our brains are used to handling.

Image via ytimg

And there are no proportional models of the solar system on the Internet. The fact that every picture you’re likely to see of it shows planets and moons too close together prevents you from getting a feel of the size of our solar system. A group of friends plans to change that, however. Wylie Overstreet, Alex Rowe Gorosh and some of their friends decided to build a proportional model of the solar system. And the only place they found enough room to do so was on a dry lakebed in Nevada.

Starting with a 1.5 meter sun and a marble-sized Earth, the team drew circles to represent the orbit of each planet. And when the sun set, their work came alive in a stunning display…Well, I’ll let you see for yourselves.




Condensing towers could make water from thin air in the driest places on Earth


Artist impression of how two such tower might look like in a desert community. Photo: Architecture and Vision

The Namib desert is one of the vastest and driest deserts in the world. There is little water to be found here, so the few critters calling the desert home had to learn to adapt in order to survive. One particular beetle species stands out through the ingenuity with which it manages to quench its thirst – it doesn’t need to find water, it gathers it. Because temperature variations are very high in the Namib (the day time is scorching how, while nights can be freezing), the beetle condenses water on its back until drops roll down into the insect’s mouth. Remarkably simple and effective.

What can remote communities with little access to clean water learn from the Namib beetle? Clearly, humans need more than a few drops of water to survive, but Arturo Vittori, an industrial designer, and his colleague Andreas Vogle claim that they have designed a water condensing tower that is cheap, easy to build and potentially effective at gathering water. Called the Warka Tower, The 9 meter tall construction could potentially gather as much as 100 liters of water during the night, depending on temperature variations and humidity. Nothing less of a godsend for some of the one billion water-deprived people living in the world.

The invention doesn’t involve any complicated gadgetry. Heck, it doesn’t even need electricity to power anything inside. Instead, it lets nature do all the work for it, while the design, carefully chosen to the last curve and bit of material, ensures a steady collection of water.

The self condensing water tower

The rigid outer housing of each tower is comprised of lightweight and elastic juncus stalks, woven in a pattern that offers stability in the face of strong wind gusts while still allowing air to flow through. A mesh net made of nylon or  polypropylene, which calls to mind a large Chinese lantern, hangs inside, collecting droplets of dew that form along the surface. As cold air condenses, the droplets roll down into a container at the bottom of the tower. The water in the container then passes through a tube that functions as a faucet, carrying the water to those waiting on the ground.

Now, I don’t want to get any one’s hope up right away, since the project has yet to be practically proven and considering it’s not the first project to promise great results, only to perform poorly. Millions have poured into research and development in hopes that a solution or series of complementing solutions might help people living without access to clean water  in the world. Results have been mixed: some were effective, others less so. Matt Damon and Bill Gates are one of the many wealthy personalities currently pledging solid cash to such projects, like the “Re-invent the Toilet Challenge,” which we’ve written about in the past.

What most of these proposed solutions do, however, is either recycle, filter or improve extraction of water from readily available liquid sources. To drill for water, in places like Etiopia for instances – one of the driest countries on Earth – you need to go as deep as 1,600 feet, if you can find a water basin in the first place. This means money and, sometimes, technology that these people don’t have. This is why the Warka Tower may be a big deal, because it can collect water virtually anywhere, only at the cost of raising the structure.

In all, it costs about $500 to set up a tower—less than a quarter of the cost of something like the Gates toilet, which costs about $2,200 to install and more to maintain.  Vittori and Vogle hope to instal two Warka Towers in Ethiopia this year, but not until they can find a sponsor the financially aid this prospect. If you find interesting and would like to pledge your support, feel free to contact them.