- 15 hours ago
The Sahara Desert is changing in ways scientists didn’t expect. Recent heavy rains have turned parts of this vast desert green again, filling lakes and rivers that have been dry for decades. Experts are watching closely, worried about what these unusual changes could mean for the region and the planet. From shifting weather patterns to potential impacts on local communities, the Sahara’s transformation raises urgent questions about the future. Animation is created by Bright Side.
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00:00Now, if you were to check out the Sahara from space right now, instead of a barren wasteland, you'd spot
00:06a surprising sight.
00:08Dry land sprinkled with some lakes and rivers in Morocco and Algeria, all thanks to some heavy rains in early
00:15September 2024.
00:17These aren't oases. This is just the Sahara going back to the factory settings.
00:22Believe it or not, eons ago, one of the biggest deserts on Earth was actually a lush paradise full of
00:28greenery.
00:30Let's first see how the Sahara turned into a desert.
00:32During the last ice age, Earth was much colder, and big ice sheets covered a lot of the land.
00:38At that time, the Sahara desert was significantly bigger than it is today, and on our planet, there were fewer
00:45tropical forests.
00:46And the cooler temperatures changed how rain was distributed in the tropics.
00:51Normally, warm air rises in the tropics, which helps create rain.
00:55Since it was colder during the ice age, this system got, well, messed up.
01:00And less rain fell in some areas.
01:01This caused more dry and desert-like conditions in places that are usually wetter.
01:07There was also a lot of dust blowing around in the Sahara desert, which scientists found in old ocean sediments.
01:15But about 12,500 years ago, something surprising happened.
01:19The dust levels went way down.
01:22This meant that the Sahara got a lot wetter, which is a sign that the climate suddenly warmed up for
01:27a while before cooling down again.
01:30After 12,500 years ago, the Sahara became a much greener place, like a savannah.
01:36Because a weather pattern called the Intertropical Convergence Zone, a mouthful indeed, moved north during summer.
01:43This wet period was at its best around 4,000 years ago, when temperatures were a bit warmer than today.
01:49At that time, more rain fell in the Ethiopian highlands, which made the Nile River carry more sediment.
01:56However, there was another big change called a Heinrich event, which caused the Intertropical Convergence Zone to move back south.
02:04This led to the Sahara and Arabian regions drying out quickly.
02:08Because of this, the Nile River had much less flooding between 2700 and 2100 BCE.
02:15Long story short, well, too late for that, the Sahara has gone through wet and dry cycles due to changes
02:22in the climate and weather patterns over thousands of years.
02:26Up until recently, we've known about the Sahara in its dry era.
02:30But in September 2024, an unusual cyclone rolled through.
02:35It hit Morocco, Algeria, Tunisia, and Libya, and filled those dry lakes and rivers.
02:41The satellite images from NASA of before and after the rains are stunning.
02:45It's like the Sahara has had a makeover.
02:49Some areas in North Africa received up to 8 inches of rain.
02:53For comparison, Seattle gets about 40 inches per year, only 5 times what the Sahara received.
03:00I say only for one simple reason.
03:02Seattle has a reputation for being quite rainy, while the Sahara does not.
03:08The tricky part is those 8 inches.
03:10Essentially, the entire yearly quota for this area fell in a matter of moments.
03:15So, in a way, it might have felt rainier in the Sahara than in Seattle.
03:20The mountains funnel the water into ephemeral lakes in northern Algeria, which recently expanded to over 70 square miles and
03:28reached depths of more than 7 feet.
03:30That's enough water to sustain it for a year.
03:33So, what exactly are these ephemeral lakes?
03:36Well, they're basins that fill up for a short time each year, but might stay dry for several years if
03:42the rain doesn't cooperate.
03:44Sometimes, water flows into them from a small surrounding area.
03:48Or, it can just be good old-fashioned rain.
03:51Now, a big question arises.
03:53How come these lakes exist in the first place?
03:56Well, generally, they form because there's excess water trapped on the surface.
04:00But the soil in the Sahara is incredibly dry.
04:04Shouldn't it act like a sponge?
04:05It must be thirsting for moisture.
04:07Well, think about how eagerly your potted plant drinks up water when you return home from a vacation.
04:13However, no matter how parched it is, dry soil can only absorb a limited amount of water, which is often
04:20quite small.
04:21And, just like your potted plant, it doesn't necessarily drink at all.
04:25You might simply be over-watering.
04:27Or, if you check the saucer below, you could find a mini-flood.
04:32Another significant factor preventing the soil from absorbing water is the lack of vegetation.
04:38Under normal conditions, trees, shrubs, and various plants help retain moisture.
04:43In the desert, however, it's nearly impossible.
04:46There may be a few palm trees, but that's about it.
04:49This also explains the formation of those temporary lakes.
04:53Precipitation, that isn't held by plants, accumulates in low-lying valleys and depressions, creating these fleeting bodies of water.
05:03These lakes may only last for a limited time.
05:06But that doesn't mean they shouldn't have names.
05:08For instance, the beautiful lake adorned with swaying palms that you see is called Lake Yasmina, located in the oasis
05:16town of Myrtsoga.
05:17In certain areas of the desert, where the dunes rise, it may appear as though you're looking at a mirage.
05:24But it's not.
05:25The sand dunes are partially covered by water.
05:28Remember how I mentioned 8 inches?
05:31Well, that's not entirely accurate for some regions.
05:34In fact, there are places where the flooding is so extensive that the palms are submerged up to their crowns.
05:41Now, the last time we saw a downpour this intensive was 30 to 50 years ago.
05:46But this rain is more than welcome.
05:48After 6 consecutive years of drought, Morocco really needed it.
05:53Lakes that had been dry for decades, like Lake Ariki, are finally getting some much-needed water.
05:59A recent analysis revealed that out of the hundreds of storms that have hit the region since 2000,
06:06only 6 brought enough rain to start filling up this lake.
06:09And of those, only 2 resulted in a lake level higher than what we saw in September 2024.
06:16So while this torrential rain seems like a blessing, the big question is, will it last?
06:22The answer is yes.
06:24When humid air from near the equator meets the hot dry air from the north,
06:28the Sahara Desert tends to get more rain.
06:32Scientists say this collision zone is shifting further north as the planet warms.
06:36And it warms.
06:37So it's likely to keep moving that way over the next couple of decades.
06:42So I seem a bit overly optimistic about this.
06:45And the truth is, the news isn't entirely positive.
06:49The reality is that no one was truly prepared for a flood situation like this.
06:54Moreover, remember that this isn't some Southeast Asian country where people are accustomed to dealing with water.
07:00This is the bone-dry Sahara.
07:03That said, I think you know what I'm getting at.
07:06Tragically, at least 18 people lost their lives to the intense rains in southern Morocco.
07:12The authorities are gearing up for even more heavy rain in the region.
07:16But if that's the case, could it mean the Sahara is facing extinction?
07:20And what would that even mean for us?
07:23It might sound a bit strange, but our planet actually relies on deserts, and the Sahara is no different.
07:30At first glance, it may seem like a barren wasteland, and it's nothing to write home about.
07:35But deserts play a crucial role in our ecosystem.
07:38They act as major carbon storage sites and are considered net carbon sinks,
07:44with the Sahara alone holding an estimated 1 trillion metric tons of carbon.
07:49In the fight against climate change, these existing deserts are like a buffer,
07:54helping to keep the temperatures within acceptable levels.
07:57Yeah, deserts are scorching hot, but they act as the world's air conditioning.
08:02Plus, desert sands are an unexpected source of nutrients for lush areas like tropical rainforests.
08:09Believe it or not, scientists have found that the sand particles from the Sahara
08:13have a hand in nurturing the Amazon rainforest.
08:16These particles travel across the Atlantic Ocean, riding the winds all the way to South America,
08:23where they enrich the soil in the Amazon basin.
08:25Without the Sahara, experts believe the Amazon rainforest could face serious collapse.
08:36Name a desert.
08:37Let me guess, Sahara?
08:39Well, actually, no matter which one you thought of, I'm sure of one thing.
08:43It's located somewhere below this line.
08:48See, when we hear the word deserts, we usually picture dry, sandy, blazing hot places.
08:54And there's not a single one of those above 45 degrees north latitude, or below 45 degrees south.
09:02In the south, that kind of makes sense.
09:05I mean, if you leave out Antarctica, there's not a whole lot of land down there.
09:09But things are different above 45 degrees north.
09:13There are tons of land.
09:14Countries like Canada, France, the United Kingdom, and a bunch of others.
09:18And still, not a single desert.
09:21Actually, not a hot desert.
09:25Most of the major hot deserts are up in the northern hemisphere, near the tropics of Cancer and Capricorn.
09:31And the hottest ones are usually found between 15 and 30 degrees north or south of the equator.
09:37Just like the Sahara, where average high temperatures can reach up to 104 degrees Fahrenheit.
09:43Together, hot deserts cover almost 15% of the Earth's land area.
09:48But if our planet is packed with them, why doesn't a single one appear above this line?
09:54I mean, the 45 degrees north latitude.
09:58I'll explain.
09:59Let's divide Earth into five main zones.
10:02The polar regions are located at both ends, north and south.
10:07Right here, we have the two temperate zones.
10:09And finally, right in the middle of the globe, is the tropical zone.
10:14Now, the line we're talking about sits in the temperate zone, in a colder area.
10:19Because the farther you go away from the equator, the colder it gets.
10:23Actually, the average annual temperature drops about 1.2 degrees Fahrenheit
10:28for every degree of latitude you move north in the northern hemisphere.
10:32And cold weather is the main reason hot deserts don't form above this line.
10:38It turns out that as you move farther north from the equator,
10:42the sun's rays hit the Earth at a more slanted angle.
10:46That spreads the solar energy over a larger area,
10:49which means less heat is concentrated in one spot.
10:52Basically, these regions just don't get as hot.
10:55And it's one of the reasons why countries like Finland
10:58are much colder than Colombia, for example.
11:02Another reason temperatures are lower in this zone
11:04has to do with something called albedo.
11:07Basically, this term refers to the amount of sunlight
11:10that a surface reflects back.
11:12Let me give you an example.
11:14Every surface on Earth both reflects and absorbs sunlight,
11:18but in different amounts.
11:20Take snow, for example.
11:22It can reflect up to 90% of the sunlight that hits it
11:25and only absorbs about 10%.
11:27That's what gives snow a high albedo.
11:30And it's totally different with sand,
11:32which has a lower albedo.
11:34In places like the Kalahari Desert,
11:36down in southern Africa,
11:38it's about a 50-50 situation.
11:40Most of the year,
11:42roughly 50% of the sunlight gets reflected around there,
11:45and the other 50% is absorbed.
11:47The heat absorbed by the sand
11:49is part of why it gets so hot in dry places like deserts.
11:54I mean, hot deserts.
11:56Simply put,
11:58sand soaks up more heat,
11:59while snow reflects most of it.
12:02This is one of the reasons
12:03why snowy areas stay much cooler.
12:06So the closer you get to the polar zones,
12:08the easier it is for sunlight to be reflected
12:10instead of absorbed.
12:12And that helps explain
12:14why there aren't any hot deserts around those parts.
12:18Then, we also have atmospheric patterns.
12:22Let's just say that the air patterns change a lot
12:24once you go above that 45-degree line.
12:27That's because this region is controlled by a wind belt
12:29known as the feral cell.
12:32Okay, so Earth has three main convection cells.
12:35You can think of them as big loops of moving air.
12:38Warm air rises,
12:40cools down,
12:41sinks,
12:41and then the cycle repeats.
12:43At the top and bottom of the planet,
12:46we have the polar cells.
12:47Right in the middle are the Hadley cells,
12:50and sandwiched between those two
12:51are the feral cells.
12:54Now, everything that happens
12:55between these three cells
12:56can get a little complicated.
12:58But for today,
12:59the main thing to know is this.
13:01In those middle zones,
13:03the warm air that comes from the tropics
13:05meets the cold air from the polar regions.
13:08So, feral cells play a big role
13:10in moving heat from the equator
13:12up toward the poles.
13:13This flow of warm air
13:15helps smooth out the temperature differences
13:17between the tropics and the polar regions.
13:19And that's what shapes the weather
13:21in places like North America,
13:23Europe,
13:23and parts of Asia.
13:25In the mid-latitudes,
13:27the feral cell keeps the air moving around so much
13:30that hot, dry air
13:31doesn't really get a chance to settle.
13:33So, those regions end up with more moisture,
13:36more clouds,
13:37and even storms,
13:38rather than dry, desert-like weather.
13:41That's why you don't usually see hot deserts
13:43around 45 degrees latitude.
13:46Basically, what I'm trying to say
13:48is that the feral cell
13:49makes the weather less stable.
13:51And that's very different
13:52from what happens in the Sahara Desert,
13:54for example.
13:55Over there,
13:56temperatures don't change all that much
13:57throughout the year.
13:58Just expect it to be hot.
14:01When you put all these factors together,
14:03it helps explain
14:03why hot deserts are mostly limited
14:05to the middle parts of the Earth,
14:07and why you'll never find a Sahara
14:09or Kalahari-style desert
14:10in places like Canada or Sweden.
14:12But that doesn't mean
14:14we don't have any deserts
14:15above the 45-degree line.
14:18Turns out,
14:19deserts don't always have to be hot and sandy.
14:22In fact,
14:23they can look like this.
14:25Yep,
14:26I'm talking about the Arctic.
14:28Because the actual definition of a desert
14:30isn't just some hot, dry, sandy place,
14:33it's really any area
14:34that gets very little precipitation.
14:37In other words,
14:38an area where it doesn't rain much.
14:39And it usually gets no more than 10 inches
14:42of precipitation per year.
14:44So,
14:44no matter if the weather is hot or cold,
14:47deserts are really dry places
14:49with hardly any vegetation around.
14:51That makes it pretty tough
14:52for animals and plants
14:53to live in those environments.
14:55If you think about it,
14:57that means the biggest desert on Earth
14:58is Antarctica.
15:00It covers about 5.5 million square miles,
15:03just endless ice flats
15:05as far as the eye can see.
15:06It's also the coldest desert on the planet,
15:09even colder than the Arctic,
15:11which is the other polar desert.
15:13Temperatures there can drop as low
15:15as minus 128.2 degrees Fahrenheit.
15:20If you look at the Earth,
15:21about 33% of its land is desert.
15:24Now,
15:25pay close attention to the ones
15:27located between 15 and 30 degrees latitude.
15:30These are called tropical deserts.
15:33But can you notice something curious
15:35about their locations?
15:37Most of them are found
15:38on the western edges of continents.
15:40And there's a reason for that.
15:42Actually,
15:43four main reasons.
15:44First,
15:45the winds that bring rain
15:46usually blow from the east.
15:48When they move across the land,
15:50they drop most of the rain early on.
15:52By the time these winds
15:53reach the west side,
15:55they're dry,
15:56so there's no rain left
15:57for those areas.
15:59That already makes things pretty dry.
16:01Second,
16:02in the western margins of continents,
16:04the air usually goes down
16:06instead of up.
16:07When air goes down,
16:08it gets warmer
16:09and can't form clouds.
16:10So again,
16:11no rain.
16:14Third,
16:14if there are mountains nearby,
16:16they can block the rain too.
16:18One side of the mountain
16:19gets all the moisture,
16:21and the other side,
16:22called the rain shadow,
16:24stays dry.
16:25And lastly,
16:26the ocean near these places
16:28often has cold water.
16:29Cold water cools the air above it
16:32and makes it calm,
16:33so clouds don't form easily.
16:35No clouds means no rain.
16:38So when you put all of that together,
16:40it helps explain
16:40why those tropical deserts
16:42seem to prefer
16:43one side of the continent
16:44more than the other.
16:48That's it for today.
16:49So hey,
16:50if you pacified your curiosity,
16:52then give the video a like
16:53and share it with your friends.
16:54Or if you want more,
16:55just click on these videos
16:57and stay on the bright side.
16:58So let's get started.
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