Wind How Earth Made Us


Wind

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Our planet is full of astonishing natural wonders.

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Look at that!

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Oh!

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It has immense power.

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And yet, that's rarely mentioned in our history books.

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I'm here to change that.

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I'm looking at four ways that the power of the planet has shaped our history.

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The power of fire,

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the source of great technological breakthroughs.

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Water...

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Oh, my gosh! You're getting all wet there.

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..our struggle to control it has directed human progress.

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The deep Earth...

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Blooming heck! That really is deep.

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..that provided the raw materials for our conquest of the planet.

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But this time I'm looking at the power of the wind.

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For thousands of years,

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the wind has shaped the destiny of peoples across the globe.

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It has built fortunes and brought ruin.

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Even today, we're still at the mercy of the wind.

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WIND WHISTLES

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People have exploited the wind for thousands of years,

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on land and, most of all, at sea.

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And to really experience its awesome force, this boat is the place to be.

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This is one of the fastest sailing boats ever built.

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It's capable of up to 50 miles an hour.

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And when you're down close to the water,

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you can really feel that phenomenal speed.

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But what makes this thing really special is when it starts to fly.

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Whoo!

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HE LAUGHS

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But the real key to this craft's phenomenal breakneck pace is up there.

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The sail. There's enough of it to actually cover a tennis court,

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every inch of it grabbing every bit of energy from the wind

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and converting it to pure power.

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This is the power of the wind, the atmosphere in motion,

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one of the most powerful and least understood forces on Earth.

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We tend to think of the wind as chaotic and difficult to predict.

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But when you look on a much bigger scale,

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at the global picture over time,

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a very different view emerges.

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Weather systems, and with them the winds,

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follow the same routes around the planet again and again.

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The discovery of these patterns,

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and sometimes the failure to understand them,

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lie at the heart of some of the greatest adventures in human history.

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To see a remarkable example of how powerful the wind can be

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in changing people's lives,

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I've come to a small town in the middle of the Sahara Desert called Chinguetti.

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Today, it's almost lost in a sea of shifting sand dunes,

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but once it was so much more.

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There's a timelessness about this.

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Some of the buildings are over 700 years old.

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There's only a few thousand people live here now,

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but in its heyday, this place heaved with 20,000 people.

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And twice as many camels!

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Hidden away down the back streets of this crumbling town,

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there's a reminder of Chinguetti's glorious past.

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-Bonjour.

-Ah, bonjour.

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-Ca va tres bien?

-Ca va, ca va.

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The Al Ahmad Mahmoud Library

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has been run by the same family for over 300 years

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and contains hundreds of ancient manuscripts.

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What is the oldest...? Plus ancien livre?

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Ah. Le plus ancien livre chez moi...

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-LAUGHS:

-It's in a shoebox!

-Ah.

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It's not hermetically sealed.

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-MAN SPEAKS FRENCH

-Oh, wow.

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Look at that.

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Ah. What is this?

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Ca, c'est le plus vieux Coran en Afrique de l'Ouest.

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It's the oldest Koran in West Africa?

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Dixieme siecle.

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It dates back to the 10th century.

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Oh, look, the writing's tiny.

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This priceless book is one of thousands stored in dozens of libraries

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throughout Chinguetti.

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Ca, c'est les arabesques.

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Arabesque, yeah, yeah. The colour is beautiful.

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Chinguetti's glory days were over 500 years ago,

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and it owed its existence as a thriving town to the wind.

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Chinguetti is in the heart of the Sahara.

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It's a barren, inhospitable wilderness.

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The largest desert on the planet.

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Ah.

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Look at that.

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It just goes on and on.

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The Sahara is so hostile that crossing it is dangerous and difficult.

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Searing heat, no water, immense distances.

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It's effectively a climate barrier.

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WIND HOWLING

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Well, there's another reason why deserts and dunes are so hard to cross,

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and that is, they simply don't stand still.

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They are constantly on the move.

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In fact, these are some of the most dynamic and rapidly changing landscapes

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on Earth.

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HE COUGHS

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There are few reliable landmarks,

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so following a route across the desert is incredibly hard.

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But it's not only the shifting sand that's controlled by the wind.

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The entire Sahara Desert itself was created by large-scale wind movements.

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These winds begin at the equator.

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This is where the sun is at its hottest, so the air is continually rising.

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As it spreads away from the equator, it cools,

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until between about 20 and 30 degrees latitude,

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the air sinks back to Earth, heating up again in the process.

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This pattern of winds creates a band of hot, dry deserts around the world

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on either side of the equator,

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including the Sahara and Arabian deserts.

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In an era when travelling was done by foot,

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the desert was a formidable barrier.

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For most of human history,

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different corners of the world have evolved as if in parallel universes,

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hemmed in not just by mountains and oceans,

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but by the desert that made climate a barrier too.

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But about 1,000 years ago, nomads were forging routes through the Sahara.

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Chinguetti was an oasis town along one of these routes.

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To the south was gold and ivory.

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To the north, the markets of Europe.

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Chinguetti's fortune was made

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because it was a gateway connecting two worlds

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that were separated by the power of the wind.

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But this city's great days didn't last.

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The winds that created the desert barrier had brought it riches.

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But ironically, its decline was also due to the wind.

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In one short period, about 500 years ago,

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the world was entirely remade,

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transforming the fate of people around the globe.

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And it was all down to a pivotal discovery about how the winds work.

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This is the Gold Coast in Ghana, on the west coast of Africa.

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Today, it's dominated by bustling fishing ports.

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Everyone's got piles of fish!

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But in the 15th century, it was an important centre for the gold trade.

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Europeans began to trade with the rich empires of West Africa,

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and the Portuguese built this fort, Elmina,

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to protect their commercial interests.

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And you could say it was here that the remaking of the world began.

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You know, if you'd been looking out from this spot in 1482,

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you'd have seen a Portuguese ship hove into view

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carrying materials to build this fort.

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On board was a man who would end up inadvertently changing the destiny

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of this whole region.

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And he did that not with swords and with cannons,

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but with a discovery about how the Earth's atmosphere worked.

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He also happened to discover a new continent.

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His name? Cristoforo Colombo.

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Christopher Columbus visited these shores

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at an important moment in European history.

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In the 15th century,

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the nations of Europe were competing to find quicker, easier routes

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to the riches of Asia.

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Christopher Columbus was a man with a plan,

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because he reckoned he knew a shortcut route to the Far East.

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As he'd been sailing up and down this coast,

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he'd been keeping a close eye on the winds.

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Now, the West African coast juts out into the Atlantic,

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so sailors here were sometimes forced into the open ocean.

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Columbus realised that out there, among the rolling waves,

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the winds seemed to be always blowing in the same direction -

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away from Africa.

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Columbus reckoned he could use that wind to blow him all the way round the world.

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Columbus had no way of knowing

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whether the wind he'd encountered along the West African coast would carry on

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or peter out, leaving him stranded in the middle of the ocean.

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But in 1492, he headed west into the apparently endless ocean

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in search of his new route to the Far East.

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It's hard to appreciate today

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just what an epic leap into the unknown this voyage was.

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It took five tough weeks,

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but as we all know, Columbus's hunch was right -

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there was a wind that blew right across the Atlantic.

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The thing is, his grasp of sailing was much better than his grasp of geography.

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It wasn't the Far East he'd landed in. It was the Bahamas.

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As far as Europeans were concerned, he'd discovered a new continent,

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and for that, his name is known throughout the world.

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Yet for me, America wasn't his greatest discovery.

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Columbus's real genius was his instinctive understanding

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of the way the winds blow across the Atlantic.

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He had discovered what we now call the trade winds -

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winds that blow steadily in a south-westerly direction.

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It was the trade winds that took him all the way from the African coast

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to the Bahamas.

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Getting across the Atlantic was all well and good,

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but now Columbus had to find his way back home.

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And that was going to be tricky,

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because if he just tried to retrace his steps east,

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then that would carry him straight into the wind

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that brought him here in the first place.

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Instead, Columbus headed north, along the American coast,

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and here he picked up another wind

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that blew consistently in the opposite direction, from west to east -

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what's known as a westerly.

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At the time, it must have seemed he was just outrageously lucky with the winds.

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But luck had nothing to do with it.

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To prove the point, Columbus sailed back to America three more times.

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Each time, he found the same winds.

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Between 20 and 30 degrees latitude, the wind blew east to west.

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Between 40 and 50 degrees, it blew in the opposite direction.

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You know, Columbus was wrong about the continent he'd discovered,

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but he was right about something far more important -

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how to repeatedly use the circulation of the atmosphere

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to cross the Atlantic Ocean and get safely home.

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Today, we know that the trade winds and westerlies that Columbus exploited

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are part of one system,

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the same atmospheric circulation that creates deserts over continents.

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At the surface, the descending air flows back towards the equator.

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These are the trade winds.

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They close the loop and form what's known as an atmospheric cell.

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It's the spin of the Earth that deflects these surface winds

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so that they move towards the Americas.

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Each hemisphere has three giant atmospheric cells

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which define the prevailing surface winds around the entire Earth.

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Once people knew about the prevailing wind patterns,

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it spurred them on to set sail for other new lands.

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The fate of nations now depended on where they lay in relation to the winds.

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The Dutch connected with the westerlies in the Southern Hemisphere

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to reach the Far East

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and ended up in control of the Dutch East Indies,

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or Indonesia, as it's now known.

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The trade winds took them home.

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In the Atlantic,

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Columbus's voyage formed the basis for a triangular trade route,

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connecting Europe, Africa and the Americas for the first time.

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The Spanish crossed the Pacific using the easterly trade winds,

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so their ships made landfall at the Philippines,

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which became a Spanish colony.

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To get home, the Spanish picked up the westerlies,

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bypassing Japan, which preserved its isolation,

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and landed in California.

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Now, you can still see the legacy of that distant Spanish influence

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in the names that are so familiar to us today.

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San Diego,

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Los Angeles

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and San Francisco.

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Within 150 years of Columbus's voyage,

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a network of trade routes had spread out across the world.

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It was the start of globalisation.

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For Europeans, the conquest of the winds and waves was a triumph.

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But there was a terrible price.

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Many other civilisations were devastated by European contact.

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Perhaps the biggest impact was here, back in Ghana.

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And you can trace those changing fortunes

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in the story of the Elmina fort.

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By the early 1500s, the function of this trading fort had changed dramatically.

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Gone was the bartering for ivory and gold,

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and instead the storerooms here

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were swollen with a very different kind of commodity.

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These dark cellars had once contained the stock for the gold trade.

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Now the fort of Elmina had become a staging post for the slave trade.

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You know, it's really ugly to think of this place

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as a storeroom for gold and ivory and all these beautiful riches

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and then, just within a few years, changed into a prison.

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While Europe boomed,

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Africa's place in the world had been changed for ever.

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It looks like a way out, and in a perverse kind of way, it was.

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Because after spending a couple of months locked up in the cells,

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you'd be taken down this long, low passageway to this -

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a gate barely one person wide.

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This was the door of no return,

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because when you left here, blinking into that sharp African light,

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probably completely unaware of what your fate was,

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you'd go onto a gangplank and you'd be shipped to the Americas as slaves.

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In the 400 years after Columbus made his epic voyage,

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nearly 12 million slaves were shipped across the Atlantic.

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The impact of new ocean trade routes even reached as far as Chinguetti,

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in the Sahara.

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Sailing ships now bypassed the old desert trade routes,

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so the town was eclipsed

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by human exploitation of the very winds that had made it great.

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The atmospheric cells are the framework for winds around the planet.

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But there's another global wind that influences the climate,

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and with it, the course of human history.

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High in the atmosphere are giant conductors

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that orchestrate weather patterns around the world.

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They're called jet streams.

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Jet streams are powerful currents of fast-moving wind

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that whip along the boundary between two cells.

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They're several hundred kilometres wide but only a few kilometres thick.

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They snake around the globe in wavy loops,

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directing the course of weather systems below.

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We're only really aware of their significance

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when they stray from their normal path.

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If the jet stream strays southward,

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it can send deadly tornadoes across Florida,

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far from their usual route to the north.

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In 1998, a jet stream wandered off course

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and sent a devastating ice storm across north-eastern America,

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leaving 45 people dead and forcing hundreds of thousands from their homes.

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But perhaps the most catastrophic example of the power of the jet stream

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was on the High Plains of the United States in the 1930s.

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Today, towns like Capa in South Dakota

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lie empty and abandoned.

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But in the early part of the century,

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farmers were rushing here to claim new land.

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Then, in the 1930s, disaster struck.

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Powerful winds, intense drought

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and dense, choking dust storms.

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It became known as the Dust Bowl.

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Millions of acres of farmland turned to wasteland.

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Half a million people were uprooted from their homes.

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Most never returned.

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At the time, it seemed like a freak accident,

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but we now know that the jet stream was the trigger.

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For several years, it had drifted hundreds of kilometres south

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from its normal course,

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taking the rains with it.

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The jet stream controls the short-term patterns of wind and weather

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across the world.

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But perhaps the most significant way that the wind has affected history

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is by defining the climate and character of entire continents

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over thousands of years,

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imposing limitations for people in some parts of the world,

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and for others, offering huge opportunities.

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Take China.

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Today, China has become a world superpower.

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But China's civilisation is one of the oldest in the world,

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and its success was built on something delivered by the wind.

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This is central China.

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It's known as the cradle of Chinese civilisation,

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because this is where

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the wealth and power of China's ancient dynasties began.

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High above the Yellow River is what made it all possible.

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A resource that was the key to China's earliest beginnings.

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This plateau was the foundation stone for China's ancient agriculture.

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But what made it that wasn't a stone at all.

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It's what's under my feet.

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It's soft and crumbly.

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When you crunch it, it just turns to dust,

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which is exactly what it is, except it's called loess.

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This dust is rich in minerals

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and combines with rotten plant matter to form a light, fertile soil.

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Chinese farmers settled here more than 10,000 years ago,

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and it was the first sites of rice cultivation in the world.

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And the reason all this loess is here is because of the winds.

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50 million years ago, India collided with Asia,

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and that pushed up the Himalayas.

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These mountains created a completely new pattern of winds.

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The Himalayas are so high that air is forced up, forming clouds and rain.

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But when the wind reaches the far side of the Himalayas,

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it's bone dry.

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It's called a rain shadow,

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and it forms some of the driest and dustiest places on Earth -

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the Taklamakan and the Gobi deserts.

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So China is surrounded by giant reserves of dust,

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and the prevailing winds act like a huge conveyor belt

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that blows it all the way to central China.

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Because the plateau is so vast,

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farming could develop here on an enormous scale.

0:30:060:30:09

That meant surplus food,

0:30:090:30:12

and surplus food is the first and most important prerequisite

0:30:120:30:16

for any self-respecting empire.

0:30:160:30:18

Over 3,000 years ago,

0:30:210:30:23

the first of China's famous dynastic empires was formed.

0:30:230:30:27

It was based in the centre of the loess plateau.

0:30:290:30:32

The Great Wall of China was built across the northern edge of the plateau

0:30:340:30:39

to safeguard the empire's heartland.

0:30:390:30:41

The importance of the loess plateau

0:31:030:31:06

has also shaped China's cultural heritage.

0:31:060:31:09

In the 5th century, they built these - the Buddhist temples at Yungang.

0:31:160:31:21

Carved into solid rock beneath the layer of loess

0:31:210:31:24

is a honeycomb of 250 man-made caves,

0:31:240:31:29

the walls covered with over 50,000 Buddhist statues.

0:31:290:31:34

But the crowning glory of the loess plateau is this.

0:31:420:31:46

The 8,000-strong Terracotta Army.

0:31:510:31:55

Not only are they buried in the loess,

0:31:580:32:01

the terracotta from which they were created

0:32:010:32:05

is itself made from loess.

0:32:050:32:07

So what began with loess led to empires and dynasties, art and religion,

0:32:140:32:20

and it was all made possible by the winds.

0:32:200:32:23

China was lucky.

0:32:300:32:32

It found itself at the end of a wind pattern

0:32:320:32:35

that delivered some of the finest-quality soil in the world.

0:32:350:32:38

Not everywhere was so fortunate.

0:32:450:32:47

Perhaps no continent on Earth has been more limited by the wind than Australia.

0:32:590:33:04

Nothing quite prepares you for the sheer scale of the Australian outback.

0:33:110:33:15

It's very, very barren.

0:33:150:33:17

I wouldn't like to be a farmer out here.

0:33:190:33:22

It's also amazingly dusty. I can feel it.

0:33:240:33:26

Bitter taste in my mouth.

0:33:260:33:29

Australia's Red Centre couldn't be a harsher place to live.

0:33:320:33:36

If it wasn't for the odd shrub,

0:33:360:33:38

it could be mistaken for the surface of Mars.

0:33:380:33:41

But at this watering hole

0:33:420:33:44

there are signs that people settled here a very long time ago.

0:33:440:33:48

Carvings up to 30,000 years old.

0:33:520:33:56

And well-crafted stone tools as well.

0:33:580:34:01

Flat, round stones like these

0:34:050:34:07

were used for grinding up millet seeds and tubers.

0:34:070:34:10

It's a very similar technology as that used by the first farmers

0:34:100:34:14

in Asia and the Middle East.

0:34:140:34:16

You know, it's fascinating to think why this didn't lead to the type of farming

0:34:160:34:20

that emerged elsewhere.

0:34:200:34:22

About 10,000 years ago,

0:34:240:34:26

the development of agriculture on other continents

0:34:260:34:29

led to complex, large-scale societies.

0:34:290:34:33

But here, farming never really took off.

0:34:330:34:37

You might think that's because it's parched and dry.

0:34:370:34:40

But it's just as much to do with the wind.

0:34:420:34:45

Here you can see the effects of the wind down at ground level.

0:34:520:34:56

Now, what you'd normally expect to find

0:34:560:34:58

is a kind of mixture of sand, gravel and clay,

0:34:580:35:00

all jumbled up with plant debris to give us soil.

0:35:000:35:03

Instead, here you get something that looks rather bizarre.

0:35:030:35:07

You can see a kind of mosaic of larger fragments,

0:35:070:35:12

where the finer stuff's just been blown away by the wind.

0:35:120:35:15

And what it produces is an armoured cap to the land surface -

0:35:150:35:18

what we call a desert pavement.

0:35:180:35:22

This crust makes it very difficult for plants to grow.

0:35:240:35:28

It isn't just a localised problem.

0:35:300:35:33

The winds strip dust and soil away across much of the continent.

0:35:330:35:38

So, what causes this stripping action?

0:35:380:35:41

To understand the answer, you need to be in the centre of the continent

0:35:430:35:49

and you need to get up high.

0:35:490:35:50

This tabletop mountain is called Attila, also known as Mount Conner.

0:36:010:36:07

It's a huge natural monument right in the centre of Australia.

0:36:070:36:11

HE CHUCKLES

0:36:270:36:29

Oh, that makes it all worth it.

0:36:290:36:31

Look at that.

0:36:310:36:33

That's a hell of a view.

0:36:330:36:35

Whoo!

0:36:350:36:37

You know, when you're down there, it's just so flat.

0:36:380:36:41

You don't get a sense of the sheer scale of this landscape.

0:36:410:36:46

It's only being up high that you can just see how...how big it is.

0:36:460:36:51

You also appreciate from here

0:36:530:36:55

that for the people that had this landscape, being so precious to them,

0:36:550:36:59

that being able to get up here,

0:36:590:37:01

and seeing the land laid out almost like a map,

0:37:010:37:04

must have made these high places just so special.

0:37:040:37:08

Mount Conner sits at the geographical and spiritual heart of Australia.

0:37:150:37:20

But it also lies at the centre of an amazing wind system.

0:37:220:37:26

The incredible thing about the atmosphere above central Australia

0:37:310:37:35

is that there's a giant circular wind pattern

0:37:350:37:38

thousands of feet above my head.

0:37:380:37:41

The prevailing winds swirl in a great anticlockwise spiral

0:38:000:38:04

around the continent.

0:38:040:38:06

They've been stripping the fertility from the soil

0:38:100:38:13

for hundreds of thousands of years.

0:38:130:38:15

In China, fertility was carried in by the wind.

0:38:210:38:24

But here in Australia, fertile dust and nutrients were simply blown away,

0:38:240:38:30

leaving sand and stones behind.

0:38:300:38:33

The sand has been shaped into vast fields of dunes,

0:38:350:38:39

which circle the centre of Australia, lined up with the path of the winds.

0:38:390:38:45

It's a process that continues to this day.

0:38:500:38:53

Giant dust storms regularly engulf eastern Australia.

0:38:550:38:59

In 2002, the largest ever recorded was more than 2,000 kilometres long.

0:39:030:39:09

Nearly 5 million tons of dust were removed in just this one storm.

0:39:130:39:19

Most of it ends up in the ocean, where its nutrients create huge algal blooms,

0:39:210:39:26

an essential part of the marine food chain.

0:39:260:39:29

So the climate and the winds dealt a tough hand

0:39:370:39:39

to the ancient Aboriginal peoples.

0:39:390:39:42

With large areas of the continent bare and arid,

0:39:450:39:49

continuing with the hunter-gatherer lifestyle made more sense

0:39:490:39:53

than taking up farming.

0:39:530:39:55

You know, you realise that the people here were ingenious and adaptable.

0:39:590:40:03

For a start, rather than relying on one or two intensive crops,

0:40:030:40:08

they instead diversified into a wide range of wild food sources.

0:40:080:40:13

And also, instead of living in permanent, settled communities,

0:40:130:40:17

they lived instead in small, mobile groups,

0:40:170:40:20

always able to move in search of food.

0:40:200:40:24

The differing fate of Australia and China

0:40:280:40:31

is down to large-scale wind patterns over continents

0:40:310:40:35

that are stable over thousands of years.

0:40:350:40:38

But the wind has had some of its most dramatic effects on human history

0:40:410:40:46

when it interacts with the energy of the oceans.

0:40:460:40:49

It's an interaction that can have major long-term consequences,

0:40:520:40:57

but it can also bring short-term disaster.

0:40:570:41:01

The sea acts as an immense store of the sun's heat.

0:41:010:41:05

There's more energy in the top three metres of the ocean

0:41:050:41:09

than the whole of the atmosphere - enough to power America for 50 years.

0:41:090:41:13

By pumping this energy into the air,

0:41:180:41:21

the ocean is constantly influencing the wind...

0:41:210:41:24

..a principle that is graphically demonstrated each year.

0:41:260:41:31

Hurricanes are the most extreme storms on Earth,

0:41:430:41:46

the ultimate example of the violent partnership

0:41:460:41:49

between the atmosphere and the ocean.

0:41:490:41:52

The hotter the ocean, the faster the air above rises,

0:41:520:41:56

drawing the wind inwards in a vicious spiral.

0:41:560:41:59

Each one degree rise in sea temperature

0:41:590:42:02

increases wind speeds by more than 20 kilometres per hour.

0:42:020:42:07

Around the eye of the hurricane,

0:42:070:42:10

the clouds build up like the inside of a stadium,

0:42:100:42:13

leaving a calm centre around which the winds rotate.

0:42:130:42:18

It's the spin of the Earth that gives a hurricane its distinctive spiral shape.

0:42:260:42:31

And as they move across the surface of the globe,

0:42:370:42:40

hurricanes are caught up in the same atmospheric circulation

0:42:400:42:43

that drives the trade winds and westerlies.

0:42:430:42:46

Their tracks cluster in bands of destruction

0:42:460:42:49

on either side of the equator.

0:42:490:42:52

Devastating as hurricanes are,

0:42:570:42:59

on a planetary scale, their effects are relatively minor and short-lived.

0:42:590:43:04

But it turns out that the ocean affects winds

0:43:070:43:10

over much larger areas and longer timescales,

0:43:100:43:13

and that discovery has answered a great puzzle

0:43:130:43:16

in the story of the human conquest of the globe.

0:43:160:43:20

The Pacific is the largest ocean on Earth.

0:43:240:43:28

The only land is a scattering of tiny islands,

0:43:280:43:31

some of the most inaccessible places on the planet.

0:43:310:43:34

Ever since modern humans left Africa several tens of thousands of years ago,

0:43:390:43:43

our distant ancestors have spread across the continents.

0:43:430:43:47

But there's always been a bit of a gap - the Pacific Ocean.

0:43:490:43:55

Long after the rest of the planet was colonised by humans,

0:43:570:44:01

the Pacific lay empty.

0:44:010:44:04

With its scattering of tiny islands,

0:44:060:44:09

it's little wonder that the Pacific remained unexplored for so long.

0:44:090:44:13

If you were a would-be explorer heading out into the unknown,

0:44:130:44:17

the chances are you'd run out of food or water

0:44:170:44:20

long before you reached the next tropical paradise.

0:44:200:44:24

Then, just over 3,000 years ago, sailors set off from Asia

0:44:320:44:37

and began to spread to nearly every island in this vast ocean,

0:44:370:44:41

ending up in the distant, far-flung islands

0:44:410:44:44

of Hawaii, New Zealand and Easter Island.

0:44:440:44:48

It was a journey that took them a quarter of the way around the world.

0:44:480:44:52

You know, it's not just the distances that people travelled that amazes me,

0:44:580:45:03

it's also the direction.

0:45:030:45:04

This is my crummy map of the Pacific.

0:45:040:45:07

Here's Asia over here, with Japan.

0:45:070:45:09

This is supposed to be the Americas here. Australia down here.

0:45:090:45:13

It's thought that this whole area was peopled by going from west to east,

0:45:130:45:17

but the thing is, in this region, the winds blow in the opposite direction -

0:45:170:45:20

from east to west.

0:45:200:45:22

Trying to sail into the wind from such long distances

0:45:220:45:25

would have taken a lifetime.

0:45:250:45:28

So quite how they did this has always been a big mystery.

0:45:280:45:31

The answer lies in that turbulent link between the atmosphere and the ocean,

0:45:340:45:40

and the best place to see it in action is in the middle of the Pacific.

0:45:400:45:44

An island like Yap.

0:45:480:45:50

A tiny dot of dense rainforest

0:45:510:45:54

over 1,000 kilometres from the nearest continent.

0:45:540:45:57

The question is, how did people get to islands like Yap

0:46:000:46:06

and then move on to the other islands of the Pacific

0:46:060:46:09

when they were heading into the prevailing winds

0:46:090:46:12

and all they had were these - wooden outrigger canoes?

0:46:120:46:17

TRUMPETS

0:46:190:46:21

These boats have barely changed

0:46:400:46:43

since the first sailors set off across the Pacific.

0:46:430:46:47

So how did they sail across the entire ocean against the wind?

0:46:520:46:57

Normally, sailing into the wind would involve taking a zigzag route

0:47:000:47:04

called tacking.

0:47:040:47:06

The problem with sailing into the wind is this -

0:47:090:47:12

you keep needing to tack all the time,

0:47:120:47:14

which means you need to move the sail from the front to the back

0:47:140:47:16

by swinging the mast and the boom round,

0:47:160:47:19

so that the front of the boat becomes the back.

0:47:190:47:22

And then... It's actually quite tricky and quite dangerous.

0:47:220:47:26

By moving this sail from the front of the boat to the back,

0:47:310:47:35

these canoes can indeed tack back and forth across the wind,

0:47:350:47:41

gradually moving forward.

0:47:410:47:43

But it's a slow and difficult process.

0:47:440:47:47

It's good? Yeah?

0:47:490:47:52

I always get slightly nervous.

0:47:520:47:53

For you, thousands of times. For me, this looks dangerous.

0:47:530:47:57

Ali Haleyalur is the chief navigator.

0:47:570:48:01

So in the past, when your predecessors made lots of long journeys,

0:48:030:48:08

how did they do that against the wind?

0:48:080:48:10

If it's really far, it's not safe to go east,

0:48:110:48:13

because within that four or five days that you tack in it,

0:48:130:48:19

you still cannot arrive,

0:48:190:48:21

and then another storm hits you there.

0:48:210:48:23

So it's better you have to wait when the westerly wind comes.

0:48:230:48:27

There are always short periods when the wind blows from the west

0:48:290:48:32

due to seasonal changes,

0:48:320:48:34

but not long enough to undertake long voyages.

0:48:340:48:38

But the ancient navigators realised

0:48:380:48:41

that there are certain times when the winds change direction

0:48:410:48:44

and blow consistently for long periods from west to east.

0:48:440:48:48

The secret of this change lies in the relationship

0:48:500:48:53

between the Pacific Ocean and the winds.

0:48:530:48:55

Every few years, warm water from the west Pacific

0:49:000:49:04

surges into the cooler waters of the east.

0:49:040:49:07

This warm water heats the air above, changing air pressure

0:49:070:49:11

and making the trade winds weaken or swap directions completely.

0:49:110:49:15

Today we know this phenomenon as El Nino.

0:49:190:49:24

These changes over the Pacific have a huge impact on the weather...

0:49:250:49:30

..causing flash floods on the American continent.

0:49:320:49:37

Meanwhile, in places as far apart as Australia and Africa,

0:49:390:49:44

temperatures soar, causing wildfires.

0:49:440:49:48

But for the ancient Pacific colonisers, it would have transformed their options.

0:49:550:50:00

With the wind blowing consistently from west to east,

0:50:000:50:04

the exploration of the Pacific would have been much easier.

0:50:040:50:07

So what happens to the winds during El Nino years?

0:50:080:50:11

I realised that during the El Nino years,

0:50:110:50:16

the wind is extended very long and very strong.

0:50:160:50:20

It remains coming from the west. That's what I see during that time.

0:50:200:50:26

So the westerlies stay for longer.

0:50:260:50:29

-Yeah, kind of stay for a longer time.

-Right.

0:50:290:50:31

And this may be the key to the mystery of how the Pacific was colonised.

0:50:350:50:40

El Ninos tend to come in phases.

0:50:400:50:44

It now seems that in the past,

0:50:440:50:46

each El Nino phase coincided with a wave of colonisation across the Pacific.

0:50:460:50:51

And so the most epic journeys in history,

0:50:540:50:58

journeys that took people to the most far-flung corners of the world,

0:50:580:51:02

were at least partly the result of how the ocean affects the winds.

0:51:020:51:06

It would be nice to think that the ocean and winds

0:51:110:51:14

always had positive effects on history. But the reality is more complex,

0:51:140:51:20

because El Nino is just one phase in a larger climatic system

0:51:200:51:25

called the Southern Oscillation.

0:51:250:51:27

This oscillation in the Pacific is so powerful

0:51:280:51:32

that it's had profound effects on civilisations across much of the planet.

0:51:320:51:38

Chaco Canyon in the south-west corner of the USA,

0:51:430:51:48

once home to a people who built a sophisticated civilisation.

0:51:480:51:52

Oh, wow! Look at that.

0:51:590:52:01

She's beautiful.

0:52:010:52:03

That is so big!

0:52:030:52:05

I mean, that's what really strikes you - this is a big landscape,

0:52:050:52:07

and still this jumps out at you.

0:52:070:52:09

You can just tell that this place was built to last.

0:52:090:52:14

It looks like the people here figured they'd be here for a very long time.

0:52:140:52:19

At the heart of the canyon are the remains of a structure

0:52:220:52:24

called a "great house".

0:52:240:52:26

Pueblo Bonito.

0:52:280:52:30

It was built by the Anasazi over 1,000 years ago.

0:52:380:52:43

Ooh!

0:52:500:52:52

Must have been a wee bit smaller than me!

0:52:520:52:55

Pueblo Bonito was the centre of the Anasazi civilisation.

0:52:550:52:59

Thousands of people lived nearby in the surrounding farms and villages.

0:52:590:53:05

You know, there's a good reason why the people at Chaco Canyon

0:53:100:53:12

built their settlements at the base of these massive cliffs,

0:53:120:53:15

and that's because the water is from up there.

0:53:150:53:18

There's hardly any rainfall around here,

0:53:180:53:21

but the rain that does fall lands on the mesa behind here, runs off into ravines

0:53:210:53:25

and then comes cascading down into the valley.

0:53:250:53:29

Rather than let it drain off into the river,

0:53:420:53:44

the Anasazi would build dams and channels to pool the water

0:53:440:53:48

or to divert it off to where it was needed.

0:53:480:53:50

But by 1300, this whole region had become effectively deserted,

0:53:570:54:02

and the big question was why.

0:54:020:54:05

The answer lay thousands of kilometres away.

0:54:120:54:16

Unknown to them, they were at the mercy of the Southern Oscillation

0:54:160:54:20

in the distant Pacific Ocean.

0:54:200:54:22

When unusually warm water moves to the west of the Pacific,

0:54:290:54:33

it changes the winds,

0:54:330:54:34

taking rain and storms away from the Americas

0:54:340:54:38

and leaving communities inland parched.

0:54:380:54:41

Normally, this isn't enough to have a lasting impact,

0:54:540:54:58

but around 1300 AD, the climate got stuck in this phase,

0:54:580:55:03

leading to a series of mega droughts lasting decades.

0:55:030:55:07

It wasn't just the Anasazi civilisation that was affected.

0:55:120:55:16

Each time the Southern Oscillation got stuck in this position,

0:55:160:55:19

the result was a similarly devastating mega drought.

0:55:190:55:23

The Fremont, Mogollon and Hohokam cultures

0:55:270:55:31

all declined at the same time as the Anasazi.

0:55:310:55:35

In South America, the Tiwanaku and the Sican,

0:55:360:55:41

and in Central America, the Toltecs and the Zapotecs

0:55:410:55:44

were all weakened or collapsed

0:55:440:55:46

because of changes in the Southern Oscillation.

0:55:460:55:49

And droughts caused by the Southern Oscillation

0:55:500:55:52

also brought to a close the first era of the mighty Mayan empire.

0:55:520:55:58

Severe droughts weren't the only factor

0:56:020:56:05

behind the collapse of these civilisations.

0:56:050:56:07

At Chaco Canyon, the people were living close to the limits of their resources,

0:56:100:56:16

so they were highly vulnerable to climatic changes.

0:56:160:56:20

For me, that's a message that still resonates today.

0:56:240:56:28

The impact of the winds on human history has been subtle and often unseen,

0:56:360:56:41

but extraordinarily powerful.

0:56:410:56:44

They define climate zones that, for thousands of years,

0:56:450:56:49

set the limits for human development over much of the world.

0:56:490:56:54

Then, paradoxically, the winds set us free from these limits.

0:57:010:57:07

Now, as our climate is changing,

0:57:090:57:13

we can expect significant changes in wind patterns,

0:57:130:57:17

altering the distribution of heat and moisture around the world.

0:57:170:57:22

How we cope will depend on how close we are to our own limits.

0:57:230:57:28

Whether it's on land or at sea,

0:57:340:57:36

we've gained so much by exploiting and adapting to the rhythms of the wind.

0:57:360:57:41

But we've never really mastered it.

0:57:410:57:44

We can only ever be one step behind.

0:57:440:57:46

I mean, even today,

0:57:460:57:48

when we can virtually track every twist and turn of the air above our head,

0:57:480:57:52

the atmosphere is still mysterious, still erratic

0:57:520:57:55

and ultimately still shapes our future.

0:57:550:57:59

Next time - fire.

0:58:010:58:03

Oh!

0:58:030:58:04

It's deadly and yet it's also the power behind human progress.

0:58:040:58:09

Our dependence on fire means that events deep in the Earth's past

0:58:090:58:14

have changed the course of human history.

0:58:140:58:17

Ah...

0:58:170:58:19

E-mail: [email protected]

0:58:450:58:48

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