0:00:05 > 0:00:10Our planet is full of astonishing natural wonders.
0:00:10 > 0:00:11Look at that!
0:00:13 > 0:00:15Oh!
0:00:15 > 0:00:18It has immense power.
0:00:20 > 0:00:25And yet, that's rarely mentioned in our history books.
0:00:27 > 0:00:29I'm here to change that.
0:00:33 > 0:00:40I'm looking at four ways that the power of the planet has shaped our history.
0:00:45 > 0:00:47The power of fire,
0:00:47 > 0:00:52the source of great technological breakthroughs.
0:00:55 > 0:00:56Water...
0:00:57 > 0:01:00Oh, my gosh! You're getting all wet there.
0:01:00 > 0:01:05..our struggle to control it has directed human progress.
0:01:07 > 0:01:10The deep Earth...
0:01:10 > 0:01:12Blooming heck! That really is deep.
0:01:12 > 0:01:17..that provided the raw materials for our conquest of the planet.
0:01:19 > 0:01:23But this time I'm looking at the power of the wind.
0:01:24 > 0:01:26For thousands of years,
0:01:26 > 0:01:30the wind has shaped the destiny of peoples across the globe.
0:01:30 > 0:01:33It has built fortunes and brought ruin.
0:01:33 > 0:01:36Even today, we're still at the mercy of the wind.
0:01:48 > 0:01:50WIND WHISTLES
0:02:07 > 0:02:10People have exploited the wind for thousands of years,
0:02:10 > 0:02:13on land and, most of all, at sea.
0:02:18 > 0:02:23And to really experience its awesome force, this boat is the place to be.
0:02:31 > 0:02:34This is one of the fastest sailing boats ever built.
0:02:34 > 0:02:37It's capable of up to 50 miles an hour.
0:02:37 > 0:02:39And when you're down close to the water,
0:02:39 > 0:02:41you can really feel that phenomenal speed.
0:02:43 > 0:02:47But what makes this thing really special is when it starts to fly.
0:03:05 > 0:03:07Whoo!
0:03:07 > 0:03:09HE LAUGHS
0:03:10 > 0:03:15But the real key to this craft's phenomenal breakneck pace is up there.
0:03:15 > 0:03:20The sail. There's enough of it to actually cover a tennis court,
0:03:20 > 0:03:23every inch of it grabbing every bit of energy from the wind
0:03:23 > 0:03:26and converting it to pure power.
0:03:30 > 0:03:34This is the power of the wind, the atmosphere in motion,
0:03:34 > 0:03:37one of the most powerful and least understood forces on Earth.
0:03:43 > 0:03:48We tend to think of the wind as chaotic and difficult to predict.
0:03:48 > 0:03:50But when you look on a much bigger scale,
0:03:50 > 0:03:52at the global picture over time,
0:03:52 > 0:03:55a very different view emerges.
0:03:55 > 0:03:57Weather systems, and with them the winds,
0:03:57 > 0:04:00follow the same routes around the planet again and again.
0:04:02 > 0:04:04The discovery of these patterns,
0:04:04 > 0:04:07and sometimes the failure to understand them,
0:04:07 > 0:04:12lie at the heart of some of the greatest adventures in human history.
0:04:27 > 0:04:31To see a remarkable example of how powerful the wind can be
0:04:31 > 0:04:34in changing people's lives,
0:04:34 > 0:04:39I've come to a small town in the middle of the Sahara Desert called Chinguetti.
0:04:53 > 0:04:57Today, it's almost lost in a sea of shifting sand dunes,
0:04:57 > 0:05:01but once it was so much more.
0:05:21 > 0:05:22There's a timelessness about this.
0:05:22 > 0:05:25Some of the buildings are over 700 years old.
0:05:27 > 0:05:29There's only a few thousand people live here now,
0:05:29 > 0:05:34but in its heyday, this place heaved with 20,000 people.
0:05:34 > 0:05:37And twice as many camels!
0:05:44 > 0:05:48Hidden away down the back streets of this crumbling town,
0:05:48 > 0:05:51there's a reminder of Chinguetti's glorious past.
0:05:57 > 0:06:00- Bonjour.- Ah, bonjour.
0:06:00 > 0:06:03- Ca va tres bien?- Ca va, ca va.
0:06:03 > 0:06:05The Al Ahmad Mahmoud Library
0:06:05 > 0:06:09has been run by the same family for over 300 years
0:06:09 > 0:06:14and contains hundreds of ancient manuscripts.
0:06:14 > 0:06:17What is the oldest...? Plus ancien livre?
0:06:17 > 0:06:20Ah. Le plus ancien livre chez moi...
0:06:20 > 0:06:23- LAUGHS:- It's in a shoebox!- Ah.
0:06:23 > 0:06:25It's not hermetically sealed.
0:06:25 > 0:06:27- MAN SPEAKS FRENCH - Oh, wow.
0:06:27 > 0:06:29Look at that.
0:06:33 > 0:06:35Ah. What is this?
0:06:35 > 0:06:40Ca, c'est le plus vieux Coran en Afrique de l'Ouest.
0:06:40 > 0:06:42It's the oldest Koran in West Africa?
0:06:42 > 0:06:45Dixieme siecle.
0:06:45 > 0:06:48It dates back to the 10th century.
0:06:49 > 0:06:52Oh, look, the writing's tiny.
0:06:52 > 0:06:57This priceless book is one of thousands stored in dozens of libraries
0:06:57 > 0:06:59throughout Chinguetti.
0:07:01 > 0:07:03Ca, c'est les arabesques.
0:07:03 > 0:07:06Arabesque, yeah, yeah. The colour is beautiful.
0:07:08 > 0:07:12Chinguetti's glory days were over 500 years ago,
0:07:12 > 0:07:17and it owed its existence as a thriving town to the wind.
0:07:20 > 0:07:23Chinguetti is in the heart of the Sahara.
0:07:28 > 0:07:31It's a barren, inhospitable wilderness.
0:07:33 > 0:07:36The largest desert on the planet.
0:07:43 > 0:07:45Ah.
0:07:45 > 0:07:47Look at that.
0:07:48 > 0:07:51It just goes on and on.
0:08:04 > 0:08:10The Sahara is so hostile that crossing it is dangerous and difficult.
0:08:10 > 0:08:15Searing heat, no water, immense distances.
0:08:17 > 0:08:20It's effectively a climate barrier.
0:08:20 > 0:08:23WIND HOWLING
0:08:30 > 0:08:35Well, there's another reason why deserts and dunes are so hard to cross,
0:08:35 > 0:08:38and that is, they simply don't stand still.
0:08:38 > 0:08:41They are constantly on the move.
0:08:41 > 0:08:46In fact, these are some of the most dynamic and rapidly changing landscapes
0:08:46 > 0:08:48on Earth.
0:08:48 > 0:08:49HE COUGHS
0:08:57 > 0:09:00There are few reliable landmarks,
0:09:00 > 0:09:05so following a route across the desert is incredibly hard.
0:09:08 > 0:09:12But it's not only the shifting sand that's controlled by the wind.
0:09:15 > 0:09:21The entire Sahara Desert itself was created by large-scale wind movements.
0:09:32 > 0:09:35These winds begin at the equator.
0:09:35 > 0:09:40This is where the sun is at its hottest, so the air is continually rising.
0:09:40 > 0:09:44As it spreads away from the equator, it cools,
0:09:44 > 0:09:47until between about 20 and 30 degrees latitude,
0:09:47 > 0:09:52the air sinks back to Earth, heating up again in the process.
0:09:53 > 0:10:00This pattern of winds creates a band of hot, dry deserts around the world
0:10:00 > 0:10:02on either side of the equator,
0:10:02 > 0:10:05including the Sahara and Arabian deserts.
0:10:07 > 0:10:11In an era when travelling was done by foot,
0:10:11 > 0:10:14the desert was a formidable barrier.
0:10:17 > 0:10:19For most of human history,
0:10:19 > 0:10:24different corners of the world have evolved as if in parallel universes,
0:10:24 > 0:10:26hemmed in not just by mountains and oceans,
0:10:26 > 0:10:29but by the desert that made climate a barrier too.
0:10:33 > 0:10:39But about 1,000 years ago, nomads were forging routes through the Sahara.
0:10:54 > 0:10:58Chinguetti was an oasis town along one of these routes.
0:10:58 > 0:11:02To the south was gold and ivory.
0:11:02 > 0:11:05To the north, the markets of Europe.
0:11:07 > 0:11:09Chinguetti's fortune was made
0:11:09 > 0:11:12because it was a gateway connecting two worlds
0:11:12 > 0:11:16that were separated by the power of the wind.
0:11:23 > 0:11:26But this city's great days didn't last.
0:11:26 > 0:11:30The winds that created the desert barrier had brought it riches.
0:11:30 > 0:11:34But ironically, its decline was also due to the wind.
0:11:42 > 0:11:45In one short period, about 500 years ago,
0:11:45 > 0:11:48the world was entirely remade,
0:11:48 > 0:11:52transforming the fate of people around the globe.
0:11:52 > 0:11:57And it was all down to a pivotal discovery about how the winds work.
0:12:12 > 0:12:17This is the Gold Coast in Ghana, on the west coast of Africa.
0:12:18 > 0:12:23Today, it's dominated by bustling fishing ports.
0:12:23 > 0:12:25Everyone's got piles of fish!
0:12:28 > 0:12:33But in the 15th century, it was an important centre for the gold trade.
0:12:33 > 0:12:38Europeans began to trade with the rich empires of West Africa,
0:12:38 > 0:12:41and the Portuguese built this fort, Elmina,
0:12:41 > 0:12:44to protect their commercial interests.
0:12:49 > 0:12:54And you could say it was here that the remaking of the world began.
0:12:56 > 0:13:00You know, if you'd been looking out from this spot in 1482,
0:13:00 > 0:13:02you'd have seen a Portuguese ship hove into view
0:13:02 > 0:13:05carrying materials to build this fort.
0:13:05 > 0:13:09On board was a man who would end up inadvertently changing the destiny
0:13:09 > 0:13:11of this whole region.
0:13:11 > 0:13:13And he did that not with swords and with cannons,
0:13:13 > 0:13:17but with a discovery about how the Earth's atmosphere worked.
0:13:17 > 0:13:19He also happened to discover a new continent.
0:13:19 > 0:13:23His name? Cristoforo Colombo.
0:13:31 > 0:13:34Christopher Columbus visited these shores
0:13:34 > 0:13:37at an important moment in European history.
0:13:37 > 0:13:40In the 15th century,
0:13:40 > 0:13:44the nations of Europe were competing to find quicker, easier routes
0:13:44 > 0:13:45to the riches of Asia.
0:13:48 > 0:13:51Christopher Columbus was a man with a plan,
0:13:51 > 0:13:55because he reckoned he knew a shortcut route to the Far East.
0:13:55 > 0:13:57As he'd been sailing up and down this coast,
0:13:57 > 0:14:00he'd been keeping a close eye on the winds.
0:14:00 > 0:14:03Now, the West African coast juts out into the Atlantic,
0:14:03 > 0:14:07so sailors here were sometimes forced into the open ocean.
0:14:07 > 0:14:10Columbus realised that out there, among the rolling waves,
0:14:10 > 0:14:14the winds seemed to be always blowing in the same direction -
0:14:14 > 0:14:16away from Africa.
0:14:16 > 0:14:21Columbus reckoned he could use that wind to blow him all the way round the world.
0:14:26 > 0:14:28Columbus had no way of knowing
0:14:28 > 0:14:32whether the wind he'd encountered along the West African coast would carry on
0:14:32 > 0:14:37or peter out, leaving him stranded in the middle of the ocean.
0:14:43 > 0:14:50But in 1492, he headed west into the apparently endless ocean
0:14:50 > 0:14:52in search of his new route to the Far East.
0:14:58 > 0:15:00It's hard to appreciate today
0:15:00 > 0:15:04just what an epic leap into the unknown this voyage was.
0:15:05 > 0:15:08It took five tough weeks,
0:15:08 > 0:15:10but as we all know, Columbus's hunch was right -
0:15:10 > 0:15:14there was a wind that blew right across the Atlantic.
0:15:14 > 0:15:19The thing is, his grasp of sailing was much better than his grasp of geography.
0:15:19 > 0:15:24It wasn't the Far East he'd landed in. It was the Bahamas.
0:15:30 > 0:15:36As far as Europeans were concerned, he'd discovered a new continent,
0:15:36 > 0:15:40and for that, his name is known throughout the world.
0:15:43 > 0:15:48Yet for me, America wasn't his greatest discovery.
0:15:48 > 0:15:53Columbus's real genius was his instinctive understanding
0:15:53 > 0:15:56of the way the winds blow across the Atlantic.
0:15:59 > 0:16:02He had discovered what we now call the trade winds -
0:16:02 > 0:16:06winds that blow steadily in a south-westerly direction.
0:16:06 > 0:16:10It was the trade winds that took him all the way from the African coast
0:16:10 > 0:16:12to the Bahamas.
0:16:16 > 0:16:19Getting across the Atlantic was all well and good,
0:16:19 > 0:16:22but now Columbus had to find his way back home.
0:16:22 > 0:16:24And that was going to be tricky,
0:16:24 > 0:16:27because if he just tried to retrace his steps east,
0:16:27 > 0:16:29then that would carry him straight into the wind
0:16:29 > 0:16:31that brought him here in the first place.
0:16:35 > 0:16:38Instead, Columbus headed north, along the American coast,
0:16:38 > 0:16:40and here he picked up another wind
0:16:40 > 0:16:45that blew consistently in the opposite direction, from west to east -
0:16:45 > 0:16:49what's known as a westerly.
0:16:51 > 0:16:56At the time, it must have seemed he was just outrageously lucky with the winds.
0:16:56 > 0:16:59But luck had nothing to do with it.
0:16:59 > 0:17:04To prove the point, Columbus sailed back to America three more times.
0:17:04 > 0:17:06Each time, he found the same winds.
0:17:06 > 0:17:12Between 20 and 30 degrees latitude, the wind blew east to west.
0:17:12 > 0:17:17Between 40 and 50 degrees, it blew in the opposite direction.
0:17:17 > 0:17:22You know, Columbus was wrong about the continent he'd discovered,
0:17:22 > 0:17:25but he was right about something far more important -
0:17:25 > 0:17:28how to repeatedly use the circulation of the atmosphere
0:17:28 > 0:17:32to cross the Atlantic Ocean and get safely home.
0:17:36 > 0:17:40Today, we know that the trade winds and westerlies that Columbus exploited
0:17:40 > 0:17:43are part of one system,
0:17:43 > 0:17:49the same atmospheric circulation that creates deserts over continents.
0:17:49 > 0:17:54At the surface, the descending air flows back towards the equator.
0:17:54 > 0:17:57These are the trade winds.
0:17:57 > 0:18:03They close the loop and form what's known as an atmospheric cell.
0:18:03 > 0:18:06It's the spin of the Earth that deflects these surface winds
0:18:06 > 0:18:08so that they move towards the Americas.
0:18:10 > 0:18:15Each hemisphere has three giant atmospheric cells
0:18:15 > 0:18:19which define the prevailing surface winds around the entire Earth.
0:18:25 > 0:18:29Once people knew about the prevailing wind patterns,
0:18:29 > 0:18:33it spurred them on to set sail for other new lands.
0:18:35 > 0:18:41The fate of nations now depended on where they lay in relation to the winds.
0:18:43 > 0:18:46The Dutch connected with the westerlies in the Southern Hemisphere
0:18:46 > 0:18:48to reach the Far East
0:18:48 > 0:18:50and ended up in control of the Dutch East Indies,
0:18:50 > 0:18:53or Indonesia, as it's now known.
0:18:53 > 0:18:56The trade winds took them home.
0:18:58 > 0:18:59In the Atlantic,
0:18:59 > 0:19:03Columbus's voyage formed the basis for a triangular trade route,
0:19:03 > 0:19:08connecting Europe, Africa and the Americas for the first time.
0:19:10 > 0:19:13The Spanish crossed the Pacific using the easterly trade winds,
0:19:13 > 0:19:16so their ships made landfall at the Philippines,
0:19:16 > 0:19:19which became a Spanish colony.
0:19:19 > 0:19:22To get home, the Spanish picked up the westerlies,
0:19:22 > 0:19:27bypassing Japan, which preserved its isolation,
0:19:27 > 0:19:30and landed in California.
0:19:33 > 0:19:37Now, you can still see the legacy of that distant Spanish influence
0:19:37 > 0:19:40in the names that are so familiar to us today.
0:19:43 > 0:19:44San Diego,
0:19:44 > 0:19:47Los Angeles
0:19:47 > 0:19:48and San Francisco.
0:19:51 > 0:19:55Within 150 years of Columbus's voyage,
0:19:55 > 0:19:59a network of trade routes had spread out across the world.
0:19:59 > 0:20:02It was the start of globalisation.
0:20:07 > 0:20:13For Europeans, the conquest of the winds and waves was a triumph.
0:20:13 > 0:20:15But there was a terrible price.
0:20:15 > 0:20:20Many other civilisations were devastated by European contact.
0:20:22 > 0:20:27Perhaps the biggest impact was here, back in Ghana.
0:20:27 > 0:20:30And you can trace those changing fortunes
0:20:30 > 0:20:32in the story of the Elmina fort.
0:20:37 > 0:20:42By the early 1500s, the function of this trading fort had changed dramatically.
0:20:42 > 0:20:45Gone was the bartering for ivory and gold,
0:20:45 > 0:20:48and instead the storerooms here
0:20:48 > 0:20:51were swollen with a very different kind of commodity.
0:20:56 > 0:21:01These dark cellars had once contained the stock for the gold trade.
0:21:07 > 0:21:13Now the fort of Elmina had become a staging post for the slave trade.
0:21:16 > 0:21:18You know, it's really ugly to think of this place
0:21:18 > 0:21:21as a storeroom for gold and ivory and all these beautiful riches
0:21:21 > 0:21:27and then, just within a few years, changed into a prison.
0:21:34 > 0:21:35While Europe boomed,
0:21:35 > 0:21:39Africa's place in the world had been changed for ever.
0:21:48 > 0:21:51It looks like a way out, and in a perverse kind of way, it was.
0:21:51 > 0:21:54Because after spending a couple of months locked up in the cells,
0:21:54 > 0:21:58you'd be taken down this long, low passageway to this -
0:21:58 > 0:22:02a gate barely one person wide.
0:22:02 > 0:22:05This was the door of no return,
0:22:05 > 0:22:10because when you left here, blinking into that sharp African light,
0:22:10 > 0:22:13probably completely unaware of what your fate was,
0:22:13 > 0:22:19you'd go onto a gangplank and you'd be shipped to the Americas as slaves.
0:22:29 > 0:22:32In the 400 years after Columbus made his epic voyage,
0:22:32 > 0:22:37nearly 12 million slaves were shipped across the Atlantic.
0:22:42 > 0:22:47The impact of new ocean trade routes even reached as far as Chinguetti,
0:22:47 > 0:22:49in the Sahara.
0:22:49 > 0:22:53Sailing ships now bypassed the old desert trade routes,
0:22:53 > 0:22:55so the town was eclipsed
0:22:55 > 0:23:01by human exploitation of the very winds that had made it great.
0:23:13 > 0:23:17The atmospheric cells are the framework for winds around the planet.
0:23:17 > 0:23:21But there's another global wind that influences the climate,
0:23:21 > 0:23:24and with it, the course of human history.
0:23:24 > 0:23:28High in the atmosphere are giant conductors
0:23:28 > 0:23:32that orchestrate weather patterns around the world.
0:23:32 > 0:23:34They're called jet streams.
0:23:37 > 0:23:40Jet streams are powerful currents of fast-moving wind
0:23:40 > 0:23:43that whip along the boundary between two cells.
0:23:45 > 0:23:50They're several hundred kilometres wide but only a few kilometres thick.
0:23:53 > 0:23:56They snake around the globe in wavy loops,
0:23:56 > 0:23:59directing the course of weather systems below.
0:24:03 > 0:24:06We're only really aware of their significance
0:24:06 > 0:24:08when they stray from their normal path.
0:24:10 > 0:24:13If the jet stream strays southward,
0:24:13 > 0:24:16it can send deadly tornadoes across Florida,
0:24:16 > 0:24:18far from their usual route to the north.
0:24:18 > 0:24:23In 1998, a jet stream wandered off course
0:24:23 > 0:24:28and sent a devastating ice storm across north-eastern America,
0:24:28 > 0:24:33leaving 45 people dead and forcing hundreds of thousands from their homes.
0:24:38 > 0:24:43But perhaps the most catastrophic example of the power of the jet stream
0:24:43 > 0:24:48was on the High Plains of the United States in the 1930s.
0:24:49 > 0:24:53Today, towns like Capa in South Dakota
0:24:53 > 0:24:55lie empty and abandoned.
0:25:00 > 0:25:04But in the early part of the century,
0:25:04 > 0:25:06farmers were rushing here to claim new land.
0:25:09 > 0:25:13Then, in the 1930s, disaster struck.
0:25:20 > 0:25:23Powerful winds, intense drought
0:25:23 > 0:25:26and dense, choking dust storms.
0:25:26 > 0:25:30It became known as the Dust Bowl.
0:25:38 > 0:25:42Millions of acres of farmland turned to wasteland.
0:25:43 > 0:25:47Half a million people were uprooted from their homes.
0:25:49 > 0:25:51Most never returned.
0:25:53 > 0:25:56At the time, it seemed like a freak accident,
0:25:56 > 0:25:59but we now know that the jet stream was the trigger.
0:25:59 > 0:26:02For several years, it had drifted hundreds of kilometres south
0:26:02 > 0:26:04from its normal course,
0:26:04 > 0:26:06taking the rains with it.
0:26:18 > 0:26:22The jet stream controls the short-term patterns of wind and weather
0:26:22 > 0:26:24across the world.
0:26:34 > 0:26:37But perhaps the most significant way that the wind has affected history
0:26:37 > 0:26:41is by defining the climate and character of entire continents
0:26:41 > 0:26:44over thousands of years,
0:26:44 > 0:26:47imposing limitations for people in some parts of the world,
0:26:47 > 0:26:51and for others, offering huge opportunities.
0:26:53 > 0:26:54Take China.
0:27:07 > 0:27:10Today, China has become a world superpower.
0:27:14 > 0:27:19But China's civilisation is one of the oldest in the world,
0:27:19 > 0:27:23and its success was built on something delivered by the wind.
0:27:29 > 0:27:31This is central China.
0:27:31 > 0:27:34It's known as the cradle of Chinese civilisation,
0:27:34 > 0:27:37because this is where
0:27:37 > 0:27:39the wealth and power of China's ancient dynasties began.
0:27:44 > 0:27:49High above the Yellow River is what made it all possible.
0:27:58 > 0:28:02A resource that was the key to China's earliest beginnings.
0:28:10 > 0:28:14This plateau was the foundation stone for China's ancient agriculture.
0:28:14 > 0:28:17But what made it that wasn't a stone at all.
0:28:17 > 0:28:19It's what's under my feet.
0:28:19 > 0:28:22It's soft and crumbly.
0:28:22 > 0:28:24When you crunch it, it just turns to dust,
0:28:24 > 0:28:29which is exactly what it is, except it's called loess.
0:28:32 > 0:28:34This dust is rich in minerals
0:28:34 > 0:28:39and combines with rotten plant matter to form a light, fertile soil.
0:28:43 > 0:28:46Chinese farmers settled here more than 10,000 years ago,
0:28:46 > 0:28:50and it was the first sites of rice cultivation in the world.
0:28:53 > 0:28:58And the reason all this loess is here is because of the winds.
0:29:02 > 0:29:0750 million years ago, India collided with Asia,
0:29:07 > 0:29:11and that pushed up the Himalayas.
0:29:11 > 0:29:16These mountains created a completely new pattern of winds.
0:29:16 > 0:29:22The Himalayas are so high that air is forced up, forming clouds and rain.
0:29:22 > 0:29:26But when the wind reaches the far side of the Himalayas,
0:29:26 > 0:29:27it's bone dry.
0:29:31 > 0:29:34It's called a rain shadow,
0:29:34 > 0:29:38and it forms some of the driest and dustiest places on Earth -
0:29:38 > 0:29:42the Taklamakan and the Gobi deserts.
0:29:48 > 0:29:52So China is surrounded by giant reserves of dust,
0:29:52 > 0:29:56and the prevailing winds act like a huge conveyor belt
0:29:56 > 0:29:59that blows it all the way to central China.
0:30:03 > 0:30:06Because the plateau is so vast,
0:30:06 > 0:30:09farming could develop here on an enormous scale.
0:30:09 > 0:30:12That meant surplus food,
0:30:12 > 0:30:16and surplus food is the first and most important prerequisite
0:30:16 > 0:30:18for any self-respecting empire.
0:30:21 > 0:30:23Over 3,000 years ago,
0:30:23 > 0:30:27the first of China's famous dynastic empires was formed.
0:30:29 > 0:30:32It was based in the centre of the loess plateau.
0:30:34 > 0:30:39The Great Wall of China was built across the northern edge of the plateau
0:30:39 > 0:30:41to safeguard the empire's heartland.
0:31:03 > 0:31:06The importance of the loess plateau
0:31:06 > 0:31:09has also shaped China's cultural heritage.
0:31:16 > 0:31:21In the 5th century, they built these - the Buddhist temples at Yungang.
0:31:21 > 0:31:24Carved into solid rock beneath the layer of loess
0:31:24 > 0:31:29is a honeycomb of 250 man-made caves,
0:31:29 > 0:31:34the walls covered with over 50,000 Buddhist statues.
0:31:42 > 0:31:46But the crowning glory of the loess plateau is this.
0:31:51 > 0:31:55The 8,000-strong Terracotta Army.
0:31:58 > 0:32:01Not only are they buried in the loess,
0:32:01 > 0:32:05the terracotta from which they were created
0:32:05 > 0:32:07is itself made from loess.
0:32:14 > 0:32:20So what began with loess led to empires and dynasties, art and religion,
0:32:20 > 0:32:23and it was all made possible by the winds.
0:32:30 > 0:32:32China was lucky.
0:32:32 > 0:32:35It found itself at the end of a wind pattern
0:32:35 > 0:32:38that delivered some of the finest-quality soil in the world.
0:32:45 > 0:32:47Not everywhere was so fortunate.
0:32:59 > 0:33:04Perhaps no continent on Earth has been more limited by the wind than Australia.
0:33:11 > 0:33:15Nothing quite prepares you for the sheer scale of the Australian outback.
0:33:15 > 0:33:17It's very, very barren.
0:33:19 > 0:33:22I wouldn't like to be a farmer out here.
0:33:24 > 0:33:26It's also amazingly dusty. I can feel it.
0:33:26 > 0:33:29Bitter taste in my mouth.
0:33:32 > 0:33:36Australia's Red Centre couldn't be a harsher place to live.
0:33:36 > 0:33:38If it wasn't for the odd shrub,
0:33:38 > 0:33:41it could be mistaken for the surface of Mars.
0:33:42 > 0:33:44But at this watering hole
0:33:44 > 0:33:48there are signs that people settled here a very long time ago.
0:33:52 > 0:33:56Carvings up to 30,000 years old.
0:33:58 > 0:34:01And well-crafted stone tools as well.
0:34:05 > 0:34:07Flat, round stones like these
0:34:07 > 0:34:10were used for grinding up millet seeds and tubers.
0:34:10 > 0:34:14It's a very similar technology as that used by the first farmers
0:34:14 > 0:34:16in Asia and the Middle East.
0:34:16 > 0:34:20You know, it's fascinating to think why this didn't lead to the type of farming
0:34:20 > 0:34:22that emerged elsewhere.
0:34:24 > 0:34:26About 10,000 years ago,
0:34:26 > 0:34:29the development of agriculture on other continents
0:34:29 > 0:34:33led to complex, large-scale societies.
0:34:33 > 0:34:37But here, farming never really took off.
0:34:37 > 0:34:40You might think that's because it's parched and dry.
0:34:42 > 0:34:45But it's just as much to do with the wind.
0:34:52 > 0:34:56Here you can see the effects of the wind down at ground level.
0:34:56 > 0:34:58Now, what you'd normally expect to find
0:34:58 > 0:35:00is a kind of mixture of sand, gravel and clay,
0:35:00 > 0:35:03all jumbled up with plant debris to give us soil.
0:35:03 > 0:35:07Instead, here you get something that looks rather bizarre.
0:35:07 > 0:35:12You can see a kind of mosaic of larger fragments,
0:35:12 > 0:35:15where the finer stuff's just been blown away by the wind.
0:35:15 > 0:35:18And what it produces is an armoured cap to the land surface -
0:35:18 > 0:35:22what we call a desert pavement.
0:35:24 > 0:35:28This crust makes it very difficult for plants to grow.
0:35:30 > 0:35:33It isn't just a localised problem.
0:35:33 > 0:35:38The winds strip dust and soil away across much of the continent.
0:35:38 > 0:35:41So, what causes this stripping action?
0:35:43 > 0:35:49To understand the answer, you need to be in the centre of the continent
0:35:49 > 0:35:50and you need to get up high.
0:36:01 > 0:36:07This tabletop mountain is called Attila, also known as Mount Conner.
0:36:07 > 0:36:11It's a huge natural monument right in the centre of Australia.
0:36:27 > 0:36:29HE CHUCKLES
0:36:29 > 0:36:31Oh, that makes it all worth it.
0:36:31 > 0:36:33Look at that.
0:36:33 > 0:36:35That's a hell of a view.
0:36:35 > 0:36:37Whoo!
0:36:38 > 0:36:41You know, when you're down there, it's just so flat.
0:36:41 > 0:36:46You don't get a sense of the sheer scale of this landscape.
0:36:46 > 0:36:51It's only being up high that you can just see how...how big it is.
0:36:53 > 0:36:55You also appreciate from here
0:36:55 > 0:36:59that for the people that had this landscape, being so precious to them,
0:36:59 > 0:37:01that being able to get up here,
0:37:01 > 0:37:04and seeing the land laid out almost like a map,
0:37:04 > 0:37:08must have made these high places just so special.
0:37:15 > 0:37:20Mount Conner sits at the geographical and spiritual heart of Australia.
0:37:22 > 0:37:26But it also lies at the centre of an amazing wind system.
0:37:31 > 0:37:35The incredible thing about the atmosphere above central Australia
0:37:35 > 0:37:38is that there's a giant circular wind pattern
0:37:38 > 0:37:41thousands of feet above my head.
0:38:00 > 0:38:04The prevailing winds swirl in a great anticlockwise spiral
0:38:04 > 0:38:06around the continent.
0:38:10 > 0:38:13They've been stripping the fertility from the soil
0:38:13 > 0:38:15for hundreds of thousands of years.
0:38:21 > 0:38:24In China, fertility was carried in by the wind.
0:38:24 > 0:38:30But here in Australia, fertile dust and nutrients were simply blown away,
0:38:30 > 0:38:33leaving sand and stones behind.
0:38:35 > 0:38:39The sand has been shaped into vast fields of dunes,
0:38:39 > 0:38:45which circle the centre of Australia, lined up with the path of the winds.
0:38:50 > 0:38:53It's a process that continues to this day.
0:38:55 > 0:38:59Giant dust storms regularly engulf eastern Australia.
0:39:03 > 0:39:09In 2002, the largest ever recorded was more than 2,000 kilometres long.
0:39:13 > 0:39:19Nearly 5 million tons of dust were removed in just this one storm.
0:39:21 > 0:39:26Most of it ends up in the ocean, where its nutrients create huge algal blooms,
0:39:26 > 0:39:29an essential part of the marine food chain.
0:39:37 > 0:39:39So the climate and the winds dealt a tough hand
0:39:39 > 0:39:42to the ancient Aboriginal peoples.
0:39:45 > 0:39:49With large areas of the continent bare and arid,
0:39:49 > 0:39:53continuing with the hunter-gatherer lifestyle made more sense
0:39:53 > 0:39:55than taking up farming.
0:39:59 > 0:40:03You know, you realise that the people here were ingenious and adaptable.
0:40:03 > 0:40:08For a start, rather than relying on one or two intensive crops,
0:40:08 > 0:40:13they instead diversified into a wide range of wild food sources.
0:40:13 > 0:40:17And also, instead of living in permanent, settled communities,
0:40:17 > 0:40:20they lived instead in small, mobile groups,
0:40:20 > 0:40:24always able to move in search of food.
0:40:28 > 0:40:31The differing fate of Australia and China
0:40:31 > 0:40:35is down to large-scale wind patterns over continents
0:40:35 > 0:40:38that are stable over thousands of years.
0:40:41 > 0:40:46But the wind has had some of its most dramatic effects on human history
0:40:46 > 0:40:49when it interacts with the energy of the oceans.
0:40:52 > 0:40:57It's an interaction that can have major long-term consequences,
0:40:57 > 0:41:01but it can also bring short-term disaster.
0:41:01 > 0:41:05The sea acts as an immense store of the sun's heat.
0:41:05 > 0:41:09There's more energy in the top three metres of the ocean
0:41:09 > 0:41:13than the whole of the atmosphere - enough to power America for 50 years.
0:41:18 > 0:41:21By pumping this energy into the air,
0:41:21 > 0:41:24the ocean is constantly influencing the wind...
0:41:26 > 0:41:31..a principle that is graphically demonstrated each year.
0:41:43 > 0:41:46Hurricanes are the most extreme storms on Earth,
0:41:46 > 0:41:49the ultimate example of the violent partnership
0:41:49 > 0:41:52between the atmosphere and the ocean.
0:41:52 > 0:41:56The hotter the ocean, the faster the air above rises,
0:41:56 > 0:41:59drawing the wind inwards in a vicious spiral.
0:41:59 > 0:42:02Each one degree rise in sea temperature
0:42:02 > 0:42:07increases wind speeds by more than 20 kilometres per hour.
0:42:07 > 0:42:10Around the eye of the hurricane,
0:42:10 > 0:42:13the clouds build up like the inside of a stadium,
0:42:13 > 0:42:18leaving a calm centre around which the winds rotate.
0:42:26 > 0:42:31It's the spin of the Earth that gives a hurricane its distinctive spiral shape.
0:42:37 > 0:42:40And as they move across the surface of the globe,
0:42:40 > 0:42:43hurricanes are caught up in the same atmospheric circulation
0:42:43 > 0:42:46that drives the trade winds and westerlies.
0:42:46 > 0:42:49Their tracks cluster in bands of destruction
0:42:49 > 0:42:52on either side of the equator.
0:42:57 > 0:42:59Devastating as hurricanes are,
0:42:59 > 0:43:04on a planetary scale, their effects are relatively minor and short-lived.
0:43:07 > 0:43:10But it turns out that the ocean affects winds
0:43:10 > 0:43:13over much larger areas and longer timescales,
0:43:13 > 0:43:16and that discovery has answered a great puzzle
0:43:16 > 0:43:20in the story of the human conquest of the globe.
0:43:24 > 0:43:28The Pacific is the largest ocean on Earth.
0:43:28 > 0:43:31The only land is a scattering of tiny islands,
0:43:31 > 0:43:34some of the most inaccessible places on the planet.
0:43:39 > 0:43:43Ever since modern humans left Africa several tens of thousands of years ago,
0:43:43 > 0:43:47our distant ancestors have spread across the continents.
0:43:49 > 0:43:55But there's always been a bit of a gap - the Pacific Ocean.
0:43:57 > 0:44:01Long after the rest of the planet was colonised by humans,
0:44:01 > 0:44:04the Pacific lay empty.
0:44:06 > 0:44:09With its scattering of tiny islands,
0:44:09 > 0:44:13it's little wonder that the Pacific remained unexplored for so long.
0:44:13 > 0:44:17If you were a would-be explorer heading out into the unknown,
0:44:17 > 0:44:20the chances are you'd run out of food or water
0:44:20 > 0:44:24long before you reached the next tropical paradise.
0:44:32 > 0:44:37Then, just over 3,000 years ago, sailors set off from Asia
0:44:37 > 0:44:41and began to spread to nearly every island in this vast ocean,
0:44:41 > 0:44:44ending up in the distant, far-flung islands
0:44:44 > 0:44:48of Hawaii, New Zealand and Easter Island.
0:44:48 > 0:44:52It was a journey that took them a quarter of the way around the world.
0:44:58 > 0:45:03You know, it's not just the distances that people travelled that amazes me,
0:45:03 > 0:45:04it's also the direction.
0:45:04 > 0:45:07This is my crummy map of the Pacific.
0:45:07 > 0:45:09Here's Asia over here, with Japan.
0:45:09 > 0:45:13This is supposed to be the Americas here. Australia down here.
0:45:13 > 0:45:17It's thought that this whole area was peopled by going from west to east,
0:45:17 > 0:45:20but the thing is, in this region, the winds blow in the opposite direction -
0:45:20 > 0:45:22from east to west.
0:45:22 > 0:45:25Trying to sail into the wind from such long distances
0:45:25 > 0:45:28would have taken a lifetime.
0:45:28 > 0:45:31So quite how they did this has always been a big mystery.
0:45:34 > 0:45:40The answer lies in that turbulent link between the atmosphere and the ocean,
0:45:40 > 0:45:44and the best place to see it in action is in the middle of the Pacific.
0:45:48 > 0:45:50An island like Yap.
0:45:51 > 0:45:54A tiny dot of dense rainforest
0:45:54 > 0:45:57over 1,000 kilometres from the nearest continent.
0:46:00 > 0:46:06The question is, how did people get to islands like Yap
0:46:06 > 0:46:09and then move on to the other islands of the Pacific
0:46:09 > 0:46:12when they were heading into the prevailing winds
0:46:12 > 0:46:17and all they had were these - wooden outrigger canoes?
0:46:19 > 0:46:21TRUMPETS
0:46:40 > 0:46:43These boats have barely changed
0:46:43 > 0:46:47since the first sailors set off across the Pacific.
0:46:52 > 0:46:57So how did they sail across the entire ocean against the wind?
0:47:00 > 0:47:04Normally, sailing into the wind would involve taking a zigzag route
0:47:04 > 0:47:06called tacking.
0:47:09 > 0:47:12The problem with sailing into the wind is this -
0:47:12 > 0:47:14you keep needing to tack all the time,
0:47:14 > 0:47:16which means you need to move the sail from the front to the back
0:47:16 > 0:47:19by swinging the mast and the boom round,
0:47:19 > 0:47:22so that the front of the boat becomes the back.
0:47:22 > 0:47:26And then... It's actually quite tricky and quite dangerous.
0:47:31 > 0:47:35By moving this sail from the front of the boat to the back,
0:47:35 > 0:47:41these canoes can indeed tack back and forth across the wind,
0:47:41 > 0:47:43gradually moving forward.
0:47:44 > 0:47:47But it's a slow and difficult process.
0:47:49 > 0:47:52It's good? Yeah?
0:47:52 > 0:47:53I always get slightly nervous.
0:47:53 > 0:47:57For you, thousands of times. For me, this looks dangerous.
0:47:57 > 0:48:01Ali Haleyalur is the chief navigator.
0:48:03 > 0:48:08So in the past, when your predecessors made lots of long journeys,
0:48:08 > 0:48:10how did they do that against the wind?
0:48:11 > 0:48:13If it's really far, it's not safe to go east,
0:48:13 > 0:48:19because within that four or five days that you tack in it,
0:48:19 > 0:48:21you still cannot arrive,
0:48:21 > 0:48:23and then another storm hits you there.
0:48:23 > 0:48:27So it's better you have to wait when the westerly wind comes.
0:48:29 > 0:48:32There are always short periods when the wind blows from the west
0:48:32 > 0:48:34due to seasonal changes,
0:48:34 > 0:48:38but not long enough to undertake long voyages.
0:48:38 > 0:48:41But the ancient navigators realised
0:48:41 > 0:48:44that there are certain times when the winds change direction
0:48:44 > 0:48:48and blow consistently for long periods from west to east.
0:48:50 > 0:48:53The secret of this change lies in the relationship
0:48:53 > 0:48:55between the Pacific Ocean and the winds.
0:49:00 > 0:49:04Every few years, warm water from the west Pacific
0:49:04 > 0:49:07surges into the cooler waters of the east.
0:49:07 > 0:49:11This warm water heats the air above, changing air pressure
0:49:11 > 0:49:15and making the trade winds weaken or swap directions completely.
0:49:19 > 0:49:24Today we know this phenomenon as El Nino.
0:49:25 > 0:49:30These changes over the Pacific have a huge impact on the weather...
0:49:32 > 0:49:37..causing flash floods on the American continent.
0:49:39 > 0:49:44Meanwhile, in places as far apart as Australia and Africa,
0:49:44 > 0:49:48temperatures soar, causing wildfires.
0:49:55 > 0:50:00But for the ancient Pacific colonisers, it would have transformed their options.
0:50:00 > 0:50:04With the wind blowing consistently from west to east,
0:50:04 > 0:50:07the exploration of the Pacific would have been much easier.
0:50:08 > 0:50:11So what happens to the winds during El Nino years?
0:50:11 > 0:50:16I realised that during the El Nino years,
0:50:16 > 0:50:20the wind is extended very long and very strong.
0:50:20 > 0:50:26It remains coming from the west. That's what I see during that time.
0:50:26 > 0:50:29So the westerlies stay for longer.
0:50:29 > 0:50:31- Yeah, kind of stay for a longer time. - Right.
0:50:35 > 0:50:40And this may be the key to the mystery of how the Pacific was colonised.
0:50:40 > 0:50:44El Ninos tend to come in phases.
0:50:44 > 0:50:46It now seems that in the past,
0:50:46 > 0:50:51each El Nino phase coincided with a wave of colonisation across the Pacific.
0:50:54 > 0:50:58And so the most epic journeys in history,
0:50:58 > 0:51:02journeys that took people to the most far-flung corners of the world,
0:51:02 > 0:51:06were at least partly the result of how the ocean affects the winds.
0:51:11 > 0:51:14It would be nice to think that the ocean and winds
0:51:14 > 0:51:20always had positive effects on history. But the reality is more complex,
0:51:20 > 0:51:25because El Nino is just one phase in a larger climatic system
0:51:25 > 0:51:27called the Southern Oscillation.
0:51:28 > 0:51:32This oscillation in the Pacific is so powerful
0:51:32 > 0:51:38that it's had profound effects on civilisations across much of the planet.
0:51:43 > 0:51:48Chaco Canyon in the south-west corner of the USA,
0:51:48 > 0:51:52once home to a people who built a sophisticated civilisation.
0:51:59 > 0:52:01Oh, wow! Look at that.
0:52:01 > 0:52:03She's beautiful.
0:52:03 > 0:52:05That is so big!
0:52:05 > 0:52:07I mean, that's what really strikes you - this is a big landscape,
0:52:07 > 0:52:09and still this jumps out at you.
0:52:09 > 0:52:14You can just tell that this place was built to last.
0:52:14 > 0:52:19It looks like the people here figured they'd be here for a very long time.
0:52:22 > 0:52:24At the heart of the canyon are the remains of a structure
0:52:24 > 0:52:26called a "great house".
0:52:28 > 0:52:30Pueblo Bonito.
0:52:38 > 0:52:43It was built by the Anasazi over 1,000 years ago.
0:52:50 > 0:52:52Ooh!
0:52:52 > 0:52:55Must have been a wee bit smaller than me!
0:52:55 > 0:52:59Pueblo Bonito was the centre of the Anasazi civilisation.
0:52:59 > 0:53:05Thousands of people lived nearby in the surrounding farms and villages.
0:53:10 > 0:53:12You know, there's a good reason why the people at Chaco Canyon
0:53:12 > 0:53:15built their settlements at the base of these massive cliffs,
0:53:15 > 0:53:18and that's because the water is from up there.
0:53:18 > 0:53:21There's hardly any rainfall around here,
0:53:21 > 0:53:25but the rain that does fall lands on the mesa behind here, runs off into ravines
0:53:25 > 0:53:29and then comes cascading down into the valley.
0:53:42 > 0:53:44Rather than let it drain off into the river,
0:53:44 > 0:53:48the Anasazi would build dams and channels to pool the water
0:53:48 > 0:53:50or to divert it off to where it was needed.
0:53:57 > 0:54:02But by 1300, this whole region had become effectively deserted,
0:54:02 > 0:54:05and the big question was why.
0:54:12 > 0:54:16The answer lay thousands of kilometres away.
0:54:16 > 0:54:20Unknown to them, they were at the mercy of the Southern Oscillation
0:54:20 > 0:54:22in the distant Pacific Ocean.
0:54:29 > 0:54:33When unusually warm water moves to the west of the Pacific,
0:54:33 > 0:54:34it changes the winds,
0:54:34 > 0:54:38taking rain and storms away from the Americas
0:54:38 > 0:54:41and leaving communities inland parched.
0:54:54 > 0:54:58Normally, this isn't enough to have a lasting impact,
0:54:58 > 0:55:03but around 1300 AD, the climate got stuck in this phase,
0:55:03 > 0:55:07leading to a series of mega droughts lasting decades.
0:55:12 > 0:55:16It wasn't just the Anasazi civilisation that was affected.
0:55:16 > 0:55:19Each time the Southern Oscillation got stuck in this position,
0:55:19 > 0:55:23the result was a similarly devastating mega drought.
0:55:27 > 0:55:31The Fremont, Mogollon and Hohokam cultures
0:55:31 > 0:55:35all declined at the same time as the Anasazi.
0:55:36 > 0:55:41In South America, the Tiwanaku and the Sican,
0:55:41 > 0:55:44and in Central America, the Toltecs and the Zapotecs
0:55:44 > 0:55:46were all weakened or collapsed
0:55:46 > 0:55:49because of changes in the Southern Oscillation.
0:55:50 > 0:55:52And droughts caused by the Southern Oscillation
0:55:52 > 0:55:58also brought to a close the first era of the mighty Mayan empire.
0:56:02 > 0:56:05Severe droughts weren't the only factor
0:56:05 > 0:56:07behind the collapse of these civilisations.
0:56:10 > 0:56:16At Chaco Canyon, the people were living close to the limits of their resources,
0:56:16 > 0:56:20so they were highly vulnerable to climatic changes.
0:56:24 > 0:56:28For me, that's a message that still resonates today.
0:56:36 > 0:56:41The impact of the winds on human history has been subtle and often unseen,
0:56:41 > 0:56:44but extraordinarily powerful.
0:56:45 > 0:56:49They define climate zones that, for thousands of years,
0:56:49 > 0:56:54set the limits for human development over much of the world.
0:57:01 > 0:57:07Then, paradoxically, the winds set us free from these limits.
0:57:09 > 0:57:13Now, as our climate is changing,
0:57:13 > 0:57:17we can expect significant changes in wind patterns,
0:57:17 > 0:57:22altering the distribution of heat and moisture around the world.
0:57:23 > 0:57:28How we cope will depend on how close we are to our own limits.
0:57:34 > 0:57:36Whether it's on land or at sea,
0:57:36 > 0:57:41we've gained so much by exploiting and adapting to the rhythms of the wind.
0:57:41 > 0:57:44But we've never really mastered it.
0:57:44 > 0:57:46We can only ever be one step behind.
0:57:46 > 0:57:48I mean, even today,
0:57:48 > 0:57:52when we can virtually track every twist and turn of the air above our head,
0:57:52 > 0:57:55the atmosphere is still mysterious, still erratic
0:57:55 > 0:57:59and ultimately still shapes our future.
0:58:01 > 0:58:03Next time - fire.
0:58:03 > 0:58:04Oh!
0:58:04 > 0:58:09It's deadly and yet it's also the power behind human progress.
0:58:09 > 0:58:14Our dependence on fire means that events deep in the Earth's past
0:58:14 > 0:58:17have changed the course of human history.
0:58:17 > 0:58:19Ah...
0:58:45 > 0:58:48E-mail: subtitling@bbc.co.uk