0:00:10 > 0:00:13All of us, every day of our lives, are on the move.
0:00:13 > 0:00:16And we don't mean the morning commute
0:00:16 > 0:00:18or taking the kids to school.
0:00:18 > 0:00:21But a journey of epic proportions.
0:00:21 > 0:00:24Even now, as you are watching this,
0:00:24 > 0:00:28you're hurtling through space at 100,000 kilometres an hour.
0:00:30 > 0:00:33Every year, our planet, the Earth, travels around the sun
0:00:33 > 0:00:35and we go with it.
0:00:38 > 0:00:40'I'm Kate Humble.'
0:00:40 > 0:00:43This is it. The sun is directly overhead.
0:00:43 > 0:00:47My shadow is directly below me.
0:00:47 > 0:00:51In this series, we are going to follow
0:00:51 > 0:00:54the Earth's voyage through space for one whole year
0:00:54 > 0:00:58to witness the astonishing consequences
0:00:58 > 0:01:00this journey has for us all.
0:01:02 > 0:01:06'I'm Dr Helen Czerski and I study the physics of the natural world.'
0:01:06 > 0:01:07Wow, look at that!
0:01:09 > 0:01:13I'll be investigating how our orbit powers the most spectacular weather
0:01:13 > 0:01:16and how it's also shaped and reshaped our planet.
0:01:19 > 0:01:23We'll experience first hand the planet's most powerful forces.
0:01:23 > 0:01:27This is the moment we've been waiting for all day.
0:01:27 > 0:01:30And it's really raining hard now!
0:01:31 > 0:01:35We're going to dive to the deepest depths.
0:01:38 > 0:01:41And we'll reach for the greatest heights...
0:01:43 > 0:01:48..all to bring you the story of our planet's voyage around the sun.
0:02:05 > 0:02:08The Earth takes just over 365 days
0:02:08 > 0:02:11to make one complete orbit around the sun.
0:02:13 > 0:02:17In that time, it travels 940 million kilometres.
0:02:19 > 0:02:22For one year, we've been following that epic journey,
0:02:22 > 0:02:24every step of the way.
0:02:31 > 0:02:34We're going to begin on the island of Andoya,
0:02:34 > 0:02:37just off the northwest coast of Norway.
0:02:40 > 0:02:42It's July the 24th,
0:02:42 > 0:02:46and I'm here to enjoy a landmark in our journey around the sun.
0:02:48 > 0:02:53Back in late May, the sun rose here and since then it's never set.
0:02:53 > 0:02:56This is known as the midnight sun.
0:02:56 > 0:03:00It's risen and fallen in an arc above the horizon
0:03:00 > 0:03:03for the last nine weeks, but it's never dipped below it.
0:03:06 > 0:03:09Today, all that is about to change.
0:03:09 > 0:03:13The sun is going to set below the horizon completely,
0:03:13 > 0:03:16for the first time in 64 days.
0:03:22 > 0:03:24The midnight sun exists
0:03:24 > 0:03:27because of a special feature of Earth's orbit.
0:03:27 > 0:03:32As Earth travels around the sun, it doesn't spin upright.
0:03:32 > 0:03:38It spins round an axis that's tilted by just over 23 degrees.
0:03:38 > 0:03:40That means that in June,
0:03:40 > 0:03:45the northern hemisphere is facing the sun to its fullest extent.
0:03:45 > 0:03:47So, despite the Earth's rotation,
0:03:47 > 0:03:50all the land north of the Arctic Circle
0:03:50 > 0:03:55is bathed in sunlight all day and all night.
0:03:57 > 0:03:58But, as the year progresses,
0:03:58 > 0:04:02the northern hemisphere begins to point away from the sun
0:04:02 > 0:04:07and periods of darkness gradually return to the Arctic.
0:04:11 > 0:04:16The hour of sunset has come. It is now night-time, I think,
0:04:16 > 0:04:20although it's slightly odd, actually. It hasn't gone dark,
0:04:20 > 0:04:23but all the light has sort of leached out of the sky
0:04:23 > 0:04:25and this is the very first time
0:04:25 > 0:04:28that the sun has actually dipped below the horizon,
0:04:28 > 0:04:32in this part of Norway, in over two months.
0:04:34 > 0:04:37This first night is very short,
0:04:37 > 0:04:40but from now on, they will get longer and longer.
0:04:40 > 0:04:42By the time of the end of December,
0:04:42 > 0:04:46Andoya will be dark around the clock.
0:04:48 > 0:04:52Ten minutes ago, the sun set, and although we can't see it
0:04:52 > 0:04:55because of the bank of cloud right on the horizon,
0:04:55 > 0:04:58it's obviously beginning to rise again,
0:04:58 > 0:05:01because the light is coming back into the sky.
0:05:04 > 0:05:07This is because the northern hemisphere
0:05:07 > 0:05:11is no longer pointing so directly at the sun,
0:05:11 > 0:05:15The area experiencing 24 hours of sunlight has shrunk.
0:05:15 > 0:05:19Andoya is now just on the wrong side of the line.
0:05:25 > 0:05:28The coming of night to the Arctic
0:05:28 > 0:05:30is an evocative symbol of the seasonal change
0:05:30 > 0:05:35that we'll follow for the next five months, from July to December.
0:05:38 > 0:05:43The cycle of sunset and sunrise is also a reminder
0:05:43 > 0:05:46that the Earth isn't just moving around the sun.
0:05:46 > 0:05:50It's also spinning on its axis.
0:05:50 > 0:05:54Every 24 hours, the Earth makes one complete rotation.
0:05:56 > 0:05:59As it does, day gives way to night...
0:06:00 > 0:06:02...and back again...
0:06:03 > 0:06:06...365 a year.
0:06:08 > 0:06:11But the Earth's spin controls far more
0:06:11 > 0:06:13than the cycle of day and night.
0:06:13 > 0:06:16As we'll see over the next five months,
0:06:16 > 0:06:19it plays a central role in creating
0:06:19 > 0:06:22some of the most dramatic natural phenomena on Earth.
0:06:35 > 0:06:40To understand how the Earth's spin can have so much influence,
0:06:40 > 0:06:43we need to explore the place where it has its greatest impact...
0:06:45 > 0:06:47...the atmosphere.
0:06:48 > 0:06:52The spin of the Earth has a crucial influence on our atmosphere.
0:06:53 > 0:06:57To find out why spin is so important,
0:06:57 > 0:07:02we're going on a 25,000-metre journey up into the sky.
0:07:07 > 0:07:10'To get there, I'm going to need the help of a team of people
0:07:10 > 0:07:13'who know how to get to the edge of our atmosphere.'
0:07:14 > 0:07:16OK, it's on. It's in mode five.
0:07:16 > 0:07:21'This isn't exactly NASA, but, even so, we are about to visit a place
0:07:21 > 0:07:25'that normally only astronauts can go to.'
0:07:25 > 0:07:27Our vehicle is a balloon.
0:07:27 > 0:07:31we're doing now is putting helium gas into it
0:07:31 > 0:07:35and helium gas is lighter than the air around us here.
0:07:35 > 0:07:38So, once it's full, this balloon
0:07:38 > 0:07:42will just float upwards all the way through the atmosphere.
0:07:49 > 0:07:52'The balloon's journey will show us why the Earth's spin
0:07:52 > 0:07:55'has such a strong influence on the atmosphere.
0:07:57 > 0:08:01'We've attached a GPS transmitter to track its journey
0:08:01 > 0:08:04'and four cameras will record everything the balloon sees.'
0:08:04 > 0:08:06We've finished setting up now
0:08:06 > 0:08:09and hopefully this is the last this camera
0:08:09 > 0:08:13will see of ground for about three hours. See you when we get back.
0:08:42 > 0:08:44So it's gone.
0:08:44 > 0:08:48I can still see it, just that tiny speck in the sky now.
0:08:50 > 0:08:54To begin with, the balloon goes pretty much straight up.
0:08:56 > 0:08:57This is what you'd expect,
0:08:57 > 0:09:00because the atmosphere spins with the planet.
0:09:04 > 0:09:08But then the balloon starts to move sideways.
0:09:08 > 0:09:10We're going to follow it.
0:09:20 > 0:09:25The balloon is being carried away from us.
0:09:26 > 0:09:30This reveals a crucial fact about the atmosphere.
0:09:31 > 0:09:33Although it spins with the Earth,
0:09:33 > 0:09:37the atmosphere isn't completely locked to the surface.
0:09:38 > 0:09:41It's actually a fluid, so it can move in different directions,
0:09:41 > 0:09:43at different speeds.
0:09:48 > 0:09:51Today, the balloon is being pushed east.
0:09:53 > 0:09:55'We're driving at 50 miles an hour,
0:09:55 > 0:09:59'yet it's still racing ahead of us, as it continues to climb.'
0:09:59 > 0:10:02It's like a children's party game on an enormous scale, isn't it?
0:10:02 > 0:10:03Yeah!
0:10:03 > 0:10:06The balloon is now at 20,000 metres,
0:10:06 > 0:10:10twice the height at which airliners fly.
0:10:13 > 0:10:17It's nearly midday, but the sky is black.
0:10:21 > 0:10:25We think the balloon right now is up near the top of its trajectory,
0:10:25 > 0:10:27and up where it is, there's very little,
0:10:27 > 0:10:29very, very low air pressure,
0:10:29 > 0:10:32so about 95% of the atmosphere is below where this balloon is.
0:10:32 > 0:10:35And because the pressure's so low, the balloon will have expanded
0:10:35 > 0:10:38to about three times its initial diameter,
0:10:38 > 0:10:40but that is about as much as it can take.
0:10:46 > 0:10:48EXPLOSION
0:11:07 > 0:11:10As it falls back through the atmosphere,
0:11:10 > 0:11:13the burst balloon reaches speeds of over 100 mph.
0:11:35 > 0:11:39That's just shredded balloon! That's amazing! Look at that.
0:11:45 > 0:11:47That's just a fantastic picture.
0:11:47 > 0:11:51We can see the Earth and we can see
0:11:51 > 0:11:53black outer space outside it,
0:11:53 > 0:11:58and in between the two, there's this fuzzy, blue line,
0:11:58 > 0:12:00which is the atmosphere.
0:12:00 > 0:12:02It's fantastic.
0:12:03 > 0:12:07The atmosphere is a thin layer of air that spins with the Earth.
0:12:09 > 0:12:14But it's also full of moving currents that help create the weather.
0:12:15 > 0:12:19It's tempting to think of these currents as random and chaotic,
0:12:19 > 0:12:23but they're not. They're organised into distinct patterns.
0:12:25 > 0:12:28And the way these patterns are organised is controlled
0:12:28 > 0:12:29by the spin of the Earth.
0:12:35 > 0:12:38To see how spin can play such a powerful role,
0:12:38 > 0:12:43I've travelled to Ecuador in South America for a very special drive.
0:12:44 > 0:12:46Today, I'm going to get into a car
0:12:46 > 0:12:50and drive faster than I've ever driven before.
0:12:53 > 0:12:56Here's the car in question. Very ordinary.
0:12:56 > 0:12:58Absolutely nothing special about it.
0:12:58 > 0:13:01It doesn't have a huge engine. It doesn't run on rocket fuel.
0:13:03 > 0:13:05What is special, though, is not the car,
0:13:05 > 0:13:07but the road I'm going to be driving on.
0:13:13 > 0:13:17It may look like a perfectly normal road,
0:13:17 > 0:13:19but it's got two particular features.
0:13:19 > 0:13:22Its location and the direction it's heading.
0:13:28 > 0:13:33This road is right on the equator, and it's heading due east.
0:13:37 > 0:13:39The speedometer of this car
0:13:39 > 0:13:41is reading about 96 kilometres an hour,
0:13:41 > 0:13:46which is roughly 60 miles an hour, but that's not strictly true
0:13:46 > 0:13:50because I'm actually travelling a lot, lot faster than that.
0:13:54 > 0:13:56As we travel around the sun,
0:13:56 > 0:14:00the Earth's surface is spinning through space.
0:14:00 > 0:14:04And the place where it moves fastest is the equator.
0:14:12 > 0:14:17This road is spinning at over 1,000 miles an hour.
0:14:20 > 0:14:22And because I'm heading due east,
0:14:22 > 0:14:25in exactly the same direction as the Earth's rotation,
0:14:25 > 0:14:29I'm not travelling at a mere 60 miles an hour, oh no.
0:14:29 > 0:14:33I am also travelling at well over 1,000 miles an hour.
0:14:33 > 0:14:36And given that I am the only car
0:14:36 > 0:14:38on this piece of road, at this precise moment...
0:14:40 > 0:14:44..I could be the fastest driver in the world!
0:14:52 > 0:14:55The Earth moves fastest at the equator
0:14:55 > 0:14:58because this is where its circumference is greatest,
0:14:58 > 0:15:02so it has the longest distance to travel in a single day.
0:15:03 > 0:15:07But this also means that the further away from the equator you go,
0:15:07 > 0:15:10the slower you turn,
0:15:10 > 0:15:14until, if you stood at the poles, you'd barely be moving at all,
0:15:14 > 0:15:19just rotating gently on the spot in a 24-hour pirouette.
0:15:23 > 0:15:26These different speeds create an atmospheric force
0:15:26 > 0:15:29that has global significance.
0:15:29 > 0:15:33You can see it in action at one very particular time of the year,
0:15:33 > 0:15:36when it helps create the most destructive weather event
0:15:36 > 0:15:38on the planet.
0:15:49 > 0:15:52It's now early September.
0:15:52 > 0:15:54Although the summer is almost at an end,
0:15:54 > 0:15:57in the northern hemisphere, it has a sting in its tail.
0:15:58 > 0:16:01Because this is hurricane season.
0:16:04 > 0:16:07The development of a hurricane is a wonderful example
0:16:07 > 0:16:10of how the Earth's spin controls the weather.
0:16:12 > 0:16:14I'm hoping to see one in action.
0:16:15 > 0:16:19So, we've been following these storms for the past few weeks
0:16:19 > 0:16:21and all of them have their own stories.
0:16:21 > 0:16:23So, here, I can see that Tropical Storm Maria
0:16:23 > 0:16:26came all the way across the Atlantic and then fizzled out.
0:16:26 > 0:16:31Katia came around and swerved around the coast of the US,
0:16:31 > 0:16:33but didn't hit land at all, so we can't visit that one.
0:16:33 > 0:16:37Tropical Storm Nate. Now, that one looks like it's got potential.
0:16:37 > 0:16:40It's trapped in the Gulf, due to grow into a hurricane by tomorrow
0:16:40 > 0:16:44and it looks as though it's almost certain to get to the Mexican coast.
0:16:50 > 0:16:5324 hours later, I'm in eastern Mexico,
0:16:53 > 0:16:56heading towards the Gulf of Mexico and the oncoming storm.
0:16:57 > 0:17:01We're driving northwards up the coast.
0:17:01 > 0:17:04Our storm is about 100 miles that way, coming across here.
0:17:04 > 0:17:06So we're driving north so that tomorrow
0:17:06 > 0:17:09we can be at the place where it crosses the coastline.
0:17:11 > 0:17:14Next morning, and the first signs
0:17:14 > 0:17:16of Hurricane Nate are reaching the coast.
0:17:16 > 0:17:18The winds are building up
0:17:18 > 0:17:21and the normal sunny skies
0:17:21 > 0:17:24are replaced with cloud and rain.
0:17:25 > 0:17:27At this time of year,
0:17:27 > 0:17:31the Gulf of Mexico has the perfect ingredients to make a hurricane.
0:17:32 > 0:17:35The sea is relatively shallow and close to the equator,
0:17:35 > 0:17:39so the water gets particularly hot.
0:17:39 > 0:17:41This water is warm, really warm
0:17:41 > 0:17:44and the reason for that is that the ocean out there
0:17:44 > 0:17:46has been absorbing the sun's energy, storing it up.
0:17:46 > 0:17:50And now, it's that energy which can build tropical storms.
0:17:56 > 0:17:59The way the storm is built is that the warm ocean
0:17:59 > 0:18:01heats the air above it.
0:18:01 > 0:18:04And once the air is warm, it expands and rises.
0:18:07 > 0:18:09THUNDER RUMBLING
0:18:09 > 0:18:12As the warm air rises, the pressure drops,
0:18:12 > 0:18:16sucking in even more moist air, creating powerful winds.
0:18:21 > 0:18:26But there's one final ingredient needed to create a hurricane.
0:18:27 > 0:18:29It needs to start turning.
0:18:29 > 0:18:33And that rotation comes from the spin of the Earth.
0:18:38 > 0:18:41Out at sea, Nate has the characteristic rotating,
0:18:41 > 0:18:44swirling clouds of a hurricane.
0:18:46 > 0:18:49But, frustratingly, Nate begins to lose power.
0:18:51 > 0:18:54Before it can make landfall, the winds die away.
0:19:02 > 0:19:04Instead, the 2011 hurricane season
0:19:04 > 0:19:07became famous for a different storm.
0:19:09 > 0:19:10Hurricane Irene.
0:19:12 > 0:19:14Unusually for a hurricane,
0:19:14 > 0:19:17it travelled far enough up the east coast of the USA
0:19:17 > 0:19:19to flood parts of New York City.
0:19:24 > 0:19:28The powerful circulation of winds within a hurricane
0:19:28 > 0:19:30is generated by the Earth's spin,
0:19:30 > 0:19:33through a phenomenon known as the Coriolis effect.
0:19:36 > 0:19:40Now, the Coriolis effect can be a little bit counterintuitive,
0:19:40 > 0:19:42but there's a great way of seeing how it works
0:19:42 > 0:19:46with a ball and a children's roundabout.
0:19:46 > 0:19:49Now, let's say this is our planet, the northern hemisphere
0:19:49 > 0:19:51and that's the North Pole.
0:19:51 > 0:19:53Now, this planet isn't spinning,
0:19:53 > 0:19:58so when I throw a ball in a straight line...it travels in a straight line.
0:20:02 > 0:20:04But we live on a rotating world.
0:20:05 > 0:20:09So, let's take our planet and make it spin,
0:20:09 > 0:20:12round anticlockwise, like in the northern hemisphere.
0:20:17 > 0:20:21So, now I'm on a spinning planet, things look quite different.
0:20:21 > 0:20:24When I try and throw a ball in a straight line,
0:20:24 > 0:20:26it bends around to the right.
0:20:32 > 0:20:36From my point of view, this ball is always curving to the right,
0:20:36 > 0:20:40even though I'm trying really hard to throw it in a straight line.
0:20:42 > 0:20:45Now, the reason that this matters
0:20:45 > 0:20:49is that this ball represents winds on Earth
0:20:49 > 0:20:52and when the wind blows in the northern hemisphere,
0:20:52 > 0:20:54the wind is also moved to the right.
0:20:55 > 0:20:58In the southern hemisphere, the effect is reversed
0:20:58 > 0:21:01and the winds bend to the left.
0:21:02 > 0:21:05And that is all the Coriolis effect is.
0:21:16 > 0:21:20A hurricane shows the Coriolis effect in action.
0:21:22 > 0:21:25Winds are drawn inwards towards the low pressure
0:21:25 > 0:21:27at the centre of the hurricane.
0:21:29 > 0:21:31But as they head towards the centre,
0:21:31 > 0:21:34the Coriolis effect makes them turn to the right.
0:21:38 > 0:21:41This creates the hurricane's characteristic
0:21:41 > 0:21:43circular swirl of wind.
0:21:44 > 0:21:48It also means that the wind never reaches the centre of the storm.
0:21:50 > 0:21:53So the eye of the hurricane remains calm.
0:21:56 > 0:22:00The Coriolis effect is a direct consequence of our planet's rotation.
0:22:01 > 0:22:04But it does more than just make hurricanes spin.
0:22:04 > 0:22:08It's responsible for our climate patterns on a global scale.
0:22:12 > 0:22:14When you look at the Earth,
0:22:14 > 0:22:17you can see some fairly obvious bands.
0:22:18 > 0:22:20White snow at the poles,
0:22:20 > 0:22:25yellow deserts and then green vegetation in the tropics.
0:22:26 > 0:22:30Each band reflects a dramatically different climate zone,
0:22:30 > 0:22:32with its own distinctive weather.
0:22:33 > 0:22:38These major climate zones are caused by the spin of the Earth
0:22:38 > 0:22:40and the Coriolis effect.
0:22:46 > 0:22:51To see how the Coriolis effect creates these global climate bands,
0:22:51 > 0:22:53I've stayed on the equator
0:22:53 > 0:22:56and travelled into the highlands of Ecuador.
0:22:56 > 0:23:00It's late September and I'm here on a particularly significant day.
0:23:02 > 0:23:03For thousands of years,
0:23:03 > 0:23:09human beings have tracked and celebrated the progress of the sun.
0:23:09 > 0:23:14This spectacular plateau was once the sacred place
0:23:14 > 0:23:18of an ancient culture called the Quitos, who came from this region.
0:23:18 > 0:23:20And you can see why they chose it.
0:23:20 > 0:23:25It has uninterrupted, 360 degree views of the sky,
0:23:25 > 0:23:28so they would have been able to watch the sun rise and the sun set.
0:23:30 > 0:23:34Today is especially significant in understanding
0:23:34 > 0:23:38why the equator plays such an important role
0:23:38 > 0:23:41in the Earth's climate system.
0:23:41 > 0:23:46It's noon on September the 23rd, the autumn equinox.
0:23:50 > 0:23:54This is it. The sun is directly overhead.
0:23:54 > 0:23:58My shadow is directly below me.
0:24:01 > 0:24:04And for all those people living in the southern hemisphere,
0:24:04 > 0:24:07they can think, "Yay!", cos summer is on the way for them.
0:24:07 > 0:24:11But for us, who live in the northern hemisphere,
0:24:11 > 0:24:13well, sadly, winter is on its way.
0:24:15 > 0:24:19The midday sun is overhead on the equator on the equinox
0:24:19 > 0:24:22because of the Earth's tilt.
0:24:22 > 0:24:24After this September equinox,
0:24:24 > 0:24:28the path of the midday Sun travels south until December,
0:24:28 > 0:24:33before tracking back to the equator for the next equinox
0:24:33 > 0:24:37and then into the northern hemisphere to bring us summer.
0:24:37 > 0:24:41Which means that throughout the year, the equatorial regions
0:24:41 > 0:24:45receive more of the sun's heat than anywhere else.
0:24:45 > 0:24:50This has a profound effect on the Earth's climate.
0:24:53 > 0:24:56The heat of the equatorial region
0:24:56 > 0:24:59is the engine room for the world's climate.
0:24:59 > 0:25:02A system of wind starts here
0:25:02 > 0:25:06that dictates the climate across the whole of our planet
0:25:06 > 0:25:10and that is all controlled by the spin of the Earth.
0:25:10 > 0:25:15To find out how it works, I need to leave these beautiful highlands
0:25:15 > 0:25:17and head down into the rainforest.
0:25:30 > 0:25:32I'm travelling into the Amazon basin,
0:25:32 > 0:25:375.5 million square kilometres of rainforest
0:25:37 > 0:25:40stretching across Ecuador and into Brazil.
0:25:41 > 0:25:45This is the heart of the first climate zone,
0:25:45 > 0:25:47the green band that's centred on the equator.
0:25:59 > 0:26:02With all that heat concentrated at the equator,
0:26:02 > 0:26:06you wouldn't necessarily expect it to be so wet and lush,
0:26:06 > 0:26:09yet the majority of the world's rainforests
0:26:09 > 0:26:11are found in the equatorial region.
0:26:13 > 0:26:16There's about 2,000 species of tree here
0:26:16 > 0:26:19and it's dark, in amongst the trees,
0:26:19 > 0:26:23and that's because the very intense equatorial sunlight
0:26:23 > 0:26:28doesn't really penetrate through that thick canopy of leaves.
0:26:29 > 0:26:33The reason the heat of the equator creates this dense forest
0:26:33 > 0:26:35also explains why this region
0:26:35 > 0:26:38is the engine of the global climate system.
0:26:38 > 0:26:43To see how it works, I need to get above the canopy.
0:26:47 > 0:26:50The morning mists are a breathtaking sight,
0:26:50 > 0:26:52but the movement of air also shows
0:26:52 > 0:26:55an important atmospheric process in action.
0:26:57 > 0:27:00If you remember from your physics lessons, hot air rises,
0:27:00 > 0:27:03as we can see it doing beautifully over the trees here.
0:27:03 > 0:27:07And as it rises, it cools and some of it then condenses
0:27:07 > 0:27:09and falls back as rain.
0:27:13 > 0:27:16But some of the air keeps on rising.
0:27:16 > 0:27:18It's the start of an epic journey
0:27:18 > 0:27:22that will see it come under the influence of the Coriolis effect
0:27:22 > 0:27:27and then move on to create another huge climate band.
0:27:30 > 0:27:36The air rises high into the atmosphere to around 15,000 metres.
0:27:36 > 0:27:41This warm, rising air mass is then drawn towards the poles
0:27:41 > 0:27:44as it tries to equalise the temperature gradient
0:27:44 > 0:27:48between the heat of the equator and the cold of the poles.
0:27:48 > 0:27:51But the air doesn't reach the poles.
0:27:51 > 0:27:54Instead, it's bent to the right by the Coriolis effect.
0:27:54 > 0:27:58By the time it reaches about 30 degrees north of the equator,
0:27:58 > 0:28:03it's moving almost parallel to the equator.
0:28:03 > 0:28:05But it doesn't stay here for ever.
0:28:08 > 0:28:10The next leg of its journey
0:28:10 > 0:28:14will see it create a second great climate band that circles the planet.
0:28:15 > 0:28:18I'm going to join that air and travel with it
0:28:18 > 0:28:21as it changes direction once again.
0:28:21 > 0:28:23In the northern hemisphere,
0:28:23 > 0:28:26the Coriolis effect is bending those winds to the right,
0:28:26 > 0:28:28so they're not going northwards any more.
0:28:28 > 0:28:32And after a while, they cool down and get more dense
0:28:32 > 0:28:34and that wind starts to sink.
0:28:34 > 0:28:36And that's happening right here.
0:28:40 > 0:28:43This is a great place to join that air
0:28:43 > 0:28:47and I'm going to do it by going out of this door.
0:28:58 > 0:29:01OK, here we go!
0:29:12 > 0:29:16The ground is 3,000 metres below me...
0:29:17 > 0:29:20..but getting closer.
0:29:25 > 0:29:28As I fall, I'm travelling with the air that left the equator,
0:29:28 > 0:29:31because it too is now falling towards the ground.
0:29:44 > 0:29:48So we're falling now together along with all that air,
0:29:48 > 0:29:51this waterfall in the sky.
0:29:51 > 0:29:54I've got a fabulous view of where all that air is going.
0:30:26 > 0:30:28I'm glad to be back on the ground.
0:30:28 > 0:30:31It's so different from the rainforest that this air came from.
0:30:31 > 0:30:33Definitely, I've landed in a desert.
0:30:39 > 0:30:43This is the Sonoran Desert in the American state of Arizona.
0:30:44 > 0:30:46It's about 30 degrees north of the equator.
0:30:50 > 0:30:54Out here in the summer, it can reach 50 degrees centigrade,
0:30:54 > 0:30:56just horribly hot,
0:30:56 > 0:31:01but, now, the summer's long gone and it's actually quite cool here today.
0:31:01 > 0:31:05And what that tells us is that it's not heat that defines a desert.
0:31:08 > 0:31:10It's lack of water.
0:31:10 > 0:31:14Yearly rainfall can be as low as eight centimetres.
0:31:17 > 0:31:18The reason it doesn't rain much
0:31:18 > 0:31:21is that the air here has left much of its moisture
0:31:21 > 0:31:23behind at the equator.
0:31:31 > 0:31:34The Sonoran Desert is only here
0:31:34 > 0:31:39because the Coriolis effect deflects the winds that began at the equator.
0:31:43 > 0:31:46But it's not just the Sonoran Desert where this happens.
0:31:46 > 0:31:49The same effect helps create deserts
0:31:49 > 0:31:52at this latitude all around the world.
0:31:57 > 0:32:00There's the Thar Desert in India,
0:32:00 > 0:32:03the Arabian Desert
0:32:03 > 0:32:05and, of course, the Sahara.
0:32:07 > 0:32:09They're all created by falling dry air
0:32:09 > 0:32:12that originated close to the equator.
0:32:23 > 0:32:27Here we can really see the influence of the Earth's spin.
0:32:27 > 0:32:32This pattern of wet rainforest at the equator and dry deserts here
0:32:32 > 0:32:35is created by a giant system of winds.
0:32:38 > 0:32:41Even this is not the end of the cycle.
0:32:41 > 0:32:44The air that reaches the ground in the desert belt
0:32:44 > 0:32:46now heads back to the equator,
0:32:46 > 0:32:51drawn by the low pressure zone at the hottest part of the planet.
0:32:52 > 0:32:54And as it travels back to the equator,
0:32:54 > 0:32:57it's subject to the Coriolis effect,
0:32:57 > 0:32:59so, once again, it bends to the right.
0:33:04 > 0:33:08This creates very regular and reliable surface winds
0:33:08 > 0:33:12that blow from the northeast to the southwest - the trade winds.
0:33:15 > 0:33:18And that was used by the early human explorers
0:33:18 > 0:33:20and by traders for centuries,
0:33:20 > 0:33:23because it's much easier to travel if you're moving with the wind.
0:33:25 > 0:33:29From the 15th century onwards,
0:33:29 > 0:33:32European sailors increasingly exploited the trade winds.
0:33:35 > 0:33:40They played a central role in the colonisation of the Americas
0:33:40 > 0:33:43and the establishment of empires around the world.
0:33:48 > 0:33:51And so the history of human exploration of our planet
0:33:51 > 0:33:54would have been very different if our planet wasn't spinning.
0:33:59 > 0:34:03When the trade winds arrive back at the equator, it closes the circle.
0:34:07 > 0:34:11The resulting pattern of wind is called a circulation cell.
0:34:12 > 0:34:16But this circulation cell at the equator isn't the only one.
0:34:18 > 0:34:20The pattern repeats, so that, in total,
0:34:20 > 0:34:25there are three circulation cells in each hemisphere, making six.
0:34:30 > 0:34:35In each cell, air rises and is then bent by the Coriolis effect
0:34:35 > 0:34:39until it cools, sinks and returns to the surface.
0:34:49 > 0:34:51So far on our journey,
0:34:51 > 0:34:54we've experienced the way the Earth's rotation
0:34:54 > 0:34:56organises the atmosphere,
0:34:56 > 0:34:59creating spectacular weather
0:34:59 > 0:35:03and huge climate systems.
0:35:08 > 0:35:10But that's not the end of the way
0:35:10 > 0:35:13the Coriolis effect influences our planet.
0:35:13 > 0:35:17It also affects the oceans.
0:35:22 > 0:35:26I've come to Chile, to the world's biggest ocean, the Pacific,
0:35:26 > 0:35:30to see a dramatic example of how the Coriolis effect
0:35:30 > 0:35:34has transformed the ocean and the life that depends on it.
0:35:41 > 0:35:43This is such a treat for me.
0:35:43 > 0:35:46There's this fantastic colony of birds perched up on this rock.
0:35:46 > 0:35:50Pelicans, just taking off and flying over here.
0:35:50 > 0:35:52There are cormorants but, most excitingly,
0:35:52 > 0:35:56just on the back there are Humboldt penguins.
0:35:56 > 0:35:59Now, they are a species of penguin that live in temperate climates.
0:35:59 > 0:36:02They're endangered, so it's a real treat to see them,
0:36:02 > 0:36:07and all these birds are here for just one thing.
0:36:10 > 0:36:12Fish.
0:36:12 > 0:36:14Millions of them.
0:36:15 > 0:36:18This is one of the richest fishing grounds in the world.
0:36:19 > 0:36:22Less than 1% of the planet's ocean
0:36:22 > 0:36:26provides up to 20% of the total fish catch.
0:36:26 > 0:36:32And they're all here as a direct result of the spin of our planet.
0:36:33 > 0:36:35There are plenty of fish here
0:36:35 > 0:36:37because of a nutrient-rich current of water
0:36:37 > 0:36:40that flows right along the west coast of South America.
0:36:40 > 0:36:42It shares its name with the penguins.
0:36:42 > 0:36:44It's called the Humboldt Current.
0:36:46 > 0:36:49Just as the Coriolis effect deflects the winds,
0:36:49 > 0:36:52it also deflects surface currents in the ocean.
0:36:52 > 0:36:56It turns them to the right in the northern hemisphere,
0:36:56 > 0:37:01creating a clockwise spiral, and here, in the southern hemisphere,
0:37:01 > 0:37:05it turns the currents to the left, forming a counter-clockwise spiral.
0:37:07 > 0:37:10These spirals are called gyres.
0:37:12 > 0:37:15Despite the fact that we're so close to the tropics,
0:37:15 > 0:37:18the water is freezing. It's about 15 degrees.
0:37:18 > 0:37:22Well, that's because the current originates in Antarctica
0:37:22 > 0:37:23and travels all the way up here.
0:37:27 > 0:37:32That cold Antarctic water is driven up along the coast
0:37:32 > 0:37:34by the South Pacific Gyre.
0:37:37 > 0:37:41The current pulls nutrients up from the depths,
0:37:41 > 0:37:44and these sustain the largest fishery on Earth.
0:37:48 > 0:37:50And, in turn, quite a lot of sea birds.
0:37:56 > 0:37:59This circular flow of water is a phenomenon
0:37:59 > 0:38:01repeated around the world.
0:38:03 > 0:38:07There are similar ocean currents in the North and South Atlantic,
0:38:07 > 0:38:08and in the Indian Ocean.
0:38:13 > 0:38:17The Earth's spin creates large-scale circulation patterns
0:38:17 > 0:38:20in both the oceans and the atmosphere.
0:38:20 > 0:38:23These patterns define the weather
0:38:23 > 0:38:28and control the ocean circulation across the planet.
0:38:35 > 0:38:40But the Earth's spin has another influence on the oceans.
0:38:40 > 0:38:44And it reaches a peak at this time of year, in early autumn.
0:38:44 > 0:38:46The tides.
0:38:50 > 0:38:54The tides are what make our shoreline endlessly fascinating.
0:38:54 > 0:38:56WATER RUSHING
0:38:58 > 0:39:00I love the noise. It's brilliant.
0:39:05 > 0:39:11The scene here is always changing as they go in and out twice a day.
0:39:11 > 0:39:13And you're probably familiar with the idea
0:39:13 > 0:39:17that the main factor driving all this is the moon.
0:39:22 > 0:39:25Our cycle of tides happens because
0:39:25 > 0:39:28the moon's gravity tugs at the ocean...
0:39:31 > 0:39:33..creating a bulge of water
0:39:33 > 0:39:36that's pulled away from the Earth towards the moon.
0:39:40 > 0:39:42But that's not the whole story.
0:39:44 > 0:39:46It's the spin of the Earth
0:39:46 > 0:39:50that's responsible for this daily cycle of the tides.
0:39:50 > 0:39:53As the Earth rotates underneath the moon,
0:39:53 > 0:39:56it also rotates underneath this tidal bulge.
0:39:59 > 0:40:03And when that water hits land, it creates our tides.
0:40:12 > 0:40:16Here in Britain, we have some pretty big tides.
0:40:16 > 0:40:21But to see the largest tides of all, you need to cross the Atlantic.
0:40:24 > 0:40:28It's now September the 29th.
0:40:28 > 0:40:31We've come to the eastern coast of Canada,
0:40:31 > 0:40:34the best place - and today is the best day -
0:40:34 > 0:40:37to witness one of nature's great events.
0:40:38 > 0:40:40This is the Bay of Fundy,
0:40:40 > 0:40:43a massive stretch of water, at high tide.
0:40:45 > 0:40:48But at low tide, all the water has gone,
0:40:48 > 0:40:52leaving me just enough time to reach those islands before it returns.
0:40:54 > 0:40:57Now, the Bay of Fundy is famous
0:40:57 > 0:41:01for having the greatest tidal range anywhere in the world
0:41:01 > 0:41:06and today, it's due to be the biggest tide of 2011.
0:41:11 > 0:41:15It's a three-mile walk from the high-tide mark.
0:41:20 > 0:41:23We've come from right back there on the shoreline.
0:41:23 > 0:41:25A certain amount of wading -
0:41:25 > 0:41:27low tide doesn't mean it's completely without water -
0:41:27 > 0:41:31but, we have now reached
0:41:31 > 0:41:35the sea, precisely on low tide.
0:41:38 > 0:41:41So, we're looking at pretty much slack water now,
0:41:41 > 0:41:43but when the tide turns, a vast volume of water
0:41:43 > 0:41:47is going to be dragged back down this channel,
0:41:47 > 0:41:50filling this entire bay.
0:41:58 > 0:42:02At its peak, the water advances at around 10 metres a minute.
0:42:05 > 0:42:10I can't believe how fast the water's coming in now.
0:42:11 > 0:42:16You can see it rippling in over all these dips and troughs,
0:42:16 > 0:42:21filling them and then moving them on in a constant wave of water.
0:42:26 > 0:42:30Look, all that land that was behind me has totally disappeared.
0:42:39 > 0:42:45As the tide comes in, 115 billion tonnes of water flow in to the bay.
0:42:54 > 0:42:57The Bay of Fundy has the highest tides in the world
0:42:57 > 0:42:59because of its shape.
0:42:59 > 0:43:03The water is funnelled up a channel that gradually narrows.
0:43:11 > 0:43:14It seems extraordinary that just this morning,
0:43:14 > 0:43:17we were walking past this island
0:43:17 > 0:43:22and the path that we were walking on is now 30 or 40 feet under water.
0:43:30 > 0:43:34But the reason why the tides are at their biggest at this time of year
0:43:34 > 0:43:37is down to the interaction between the Earth's spin
0:43:37 > 0:43:40and a very particular orbital alignment.
0:43:45 > 0:43:48The highest tides happen when the gravity of the moon
0:43:48 > 0:43:50and the sun work together.
0:43:51 > 0:43:55But around the equinoxes, something special happens.
0:43:57 > 0:43:59At this time of year, both the sun
0:43:59 > 0:44:02and the moon are tracking along the equator.
0:44:02 > 0:44:05And as they pass over the centre of our planet,
0:44:05 > 0:44:10we spin right through the middle of a mammoth tidal bulge,
0:44:10 > 0:44:13giving us the biggest tides of the year.
0:44:17 > 0:44:21Geographical peculiarities create different tidal phenomena
0:44:21 > 0:44:24in different parts of the world at this time of year.
0:44:26 > 0:44:29Where big tides pour up river valleys,
0:44:29 > 0:44:32they often result in a tidal bore.
0:44:34 > 0:44:37In Britain, the Severn Bore is one example.
0:44:39 > 0:44:43Even bigger is the Amazon tidal bore.
0:44:50 > 0:44:54But the biggest of all is in southeast China...
0:44:58 > 0:45:02..where crowds gather, often at great personal risk,
0:45:02 > 0:45:03to see the bore arrive.
0:45:17 > 0:45:19Today's tides are pretty impressive,
0:45:19 > 0:45:23but they were actually much, much bigger in the past.
0:45:23 > 0:45:27The evidence for that is just off the coast of Bermuda.
0:45:27 > 0:45:29Understanding how the tides
0:45:29 > 0:45:32have changed gives us a surprising insight
0:45:32 > 0:45:35into the history of the Earth's spin.
0:45:42 > 0:45:45I'm looking for a particular sort of sea creature.
0:45:45 > 0:45:47It's lived on Earth for millions of years
0:45:47 > 0:45:50and it can tell us extraordinary things about our past.
0:46:06 > 0:46:09It's coral.
0:46:09 > 0:46:12Encoded in coral reefs all over the world
0:46:12 > 0:46:16is a daily record of a very significant feature
0:46:16 > 0:46:18of our planet's history.
0:46:19 > 0:46:23Because, as it builds an external skeleton - the coral reef -
0:46:23 > 0:46:27it lays down a very thin layer of limestone each day,
0:46:27 > 0:46:32a bit like the rings on a tree but daily, rather than annually.
0:46:33 > 0:46:38Effectively, corals record how many days there are in a year.
0:46:49 > 0:46:54On a piece of modern coral, these orange bands are annual rings
0:46:54 > 0:46:57and, in between them, virtually invisible,
0:46:57 > 0:47:01are 365 daily growth rings.
0:47:03 > 0:47:06But, if you look at a much older piece of coral,
0:47:06 > 0:47:09it tells a very different story.
0:47:09 > 0:47:14This, amazingly, is about 400 million years old.
0:47:14 > 0:47:16It is a piece of coral.
0:47:16 > 0:47:19I know it looks like an insignificant bit of rock,
0:47:19 > 0:47:22but, to the expert eye, this is as good as a history book.
0:47:25 > 0:47:29And it gives a really faithful record
0:47:29 > 0:47:32of what life on Earth was like, way back then.
0:47:34 > 0:47:38There are rings, just like the modern coral.
0:47:38 > 0:47:40What's really surprising, though,
0:47:40 > 0:47:44is that if you count those daily growth rings,
0:47:44 > 0:47:46you'll get a total of 410.
0:47:52 > 0:48:00400 million years ago, a year lasted not 365 days but 410.
0:48:02 > 0:48:06So, the explanation for ancient corals like this piece
0:48:06 > 0:48:09to have 410 daily growth rings
0:48:09 > 0:48:16is that when this was alive, a day wouldn't have lasted 24 hours but only 21.
0:48:16 > 0:48:20And for that to happen, the Earth had to be spinning faster.
0:48:23 > 0:48:24To find out why,
0:48:24 > 0:48:28you have to go back to the earliest days of the Earth's history.
0:48:35 > 0:48:404.5 billion years ago, the Earth was hit by another planet.
0:48:43 > 0:48:45EXPLOSION
0:48:58 > 0:49:01Debris from the impact created the moon,
0:49:01 > 0:49:04which would have been much closer to the Earth than it is today.
0:49:06 > 0:49:09It also set the Earth spinning much faster.
0:49:12 > 0:49:14When the first oceans formed,
0:49:14 > 0:49:16that combination would have meant
0:49:16 > 0:49:19the tides would have been simply huge.
0:49:22 > 0:49:26Just imagine, instead of these small tides
0:49:26 > 0:49:29of a few metres that we have today,
0:49:29 > 0:49:32there would be enormous tides, hundreds of metres high,
0:49:32 > 0:49:35crashing into the coastlines all around the world.
0:49:38 > 0:49:42But as the moon's gravity pulled on these huge tides,
0:49:42 > 0:49:44it acted as a kind of brake.
0:49:45 > 0:49:48Gradually, this slowed the Earth down.
0:49:49 > 0:49:54And the same process meant that the moon drifted gradually further away.
0:49:58 > 0:50:00SHE LAUGHS
0:50:02 > 0:50:05As the moon got further away,
0:50:05 > 0:50:09its gravitational pull on the tides decreased,
0:50:09 > 0:50:11so the tides got lower.
0:50:11 > 0:50:16But, even today, the rotation of the Earth is slowing down
0:50:16 > 0:50:19and our days are still getting longer
0:50:19 > 0:50:24but only by about 2.3 milliseconds every century.
0:50:33 > 0:50:36We're now heading into winter.
0:50:36 > 0:50:38Because of the Earth's angle of tilt,
0:50:38 > 0:50:40the northern hemisphere is leaning
0:50:40 > 0:50:43further and further away from the sun
0:50:46 > 0:50:50So temperatures are falling and the days are getting shorter.
0:50:54 > 0:50:57The natural world responds by starting to shut down.
0:51:00 > 0:51:02Trees detect the shortening day length
0:51:02 > 0:51:06and stop producing green chlorophyll in their leaves.
0:51:06 > 0:51:09The golden colours of autumn take over.
0:51:13 > 0:51:15The snow begins to fall.
0:51:16 > 0:51:18In Yellowstone Park, black bears
0:51:18 > 0:51:21head for their dens and winter hibernation,
0:51:21 > 0:51:23100 days without eating.
0:51:26 > 0:51:28Birds like snow geese,
0:51:28 > 0:51:31that spent the summer in the Arctic, now head south,
0:51:31 > 0:51:35often in huge numbers, to spend the winter in more temperate climes.
0:51:40 > 0:51:42By the end of November,
0:51:42 > 0:51:47most of the Arctic is experiencing 24 hours of darkness.
0:51:47 > 0:51:49The polar night.
0:51:56 > 0:51:58It's now early December
0:51:58 > 0:52:01and we are coming towards the end of our journey.
0:52:04 > 0:52:08Our final destination is a place where the Earth's rotation
0:52:08 > 0:52:10has a particularly powerful impact on the weather.
0:52:10 > 0:52:12Britain.
0:52:17 > 0:52:20You can't imagine a day that's more typical
0:52:20 > 0:52:23of what we think of British weather.
0:52:23 > 0:52:26We arrived this morning and it was raining
0:52:26 > 0:52:29and then the sun came out and then there was a squall,
0:52:29 > 0:52:32and now the sun's come out again
0:52:32 > 0:52:35and we've got this really strong wind.
0:52:37 > 0:52:41The British winter is notoriously unpredictable.
0:52:41 > 0:52:45Sometimes cold and dry, sometimes mild and wet.
0:52:50 > 0:52:53This unpredictability is a consequence of the Earth's rotation.
0:52:57 > 0:53:01The key factor is Britain's location.
0:53:01 > 0:53:04We sit underneath the boundary
0:53:04 > 0:53:07between two of the Earth's climate cells.
0:53:07 > 0:53:09This means that, above our heads,
0:53:09 > 0:53:13there's a battle going on between two different types of air.
0:53:15 > 0:53:18I'm going to draw a map to show you.
0:53:19 > 0:53:21This is the south coast
0:53:21 > 0:53:23and Scotland's up here.
0:53:26 > 0:53:29And we're down here, in Cornwall.
0:53:30 > 0:53:32And Ireland is out here.
0:53:34 > 0:53:38Up here, to the north of us, there's cold, polar air,
0:53:38 > 0:53:41and down on this side, to the south,
0:53:41 > 0:53:44is warm air that's come from the tropics.
0:53:44 > 0:53:46And the boundary between the two
0:53:46 > 0:53:49can lie right over the British Isles.
0:53:49 > 0:53:51And what's going on above our heads
0:53:51 > 0:53:54is a clash of the cold air and the warm air
0:53:54 > 0:53:58and it's where they're pushing against each other and mixing it up
0:53:58 > 0:54:02that we get this changeable, messy weather
0:54:02 > 0:54:05that we love to complain about in this country.
0:54:10 > 0:54:16In December 2011, we saw this battle in action.
0:54:16 > 0:54:19A succession of storms battered the country
0:54:19 > 0:54:24as warm and cold air struggled for supremacy above our heads.
0:54:28 > 0:54:30But there's a further factor
0:54:30 > 0:54:34that influences the outcome of this battle between warm and cold air.
0:54:36 > 0:54:39The boundary between the cells can move.
0:54:41 > 0:54:44This movement can be affected by a phenomenon that's generated
0:54:44 > 0:54:48right at the boundary between the cells.
0:54:50 > 0:54:52And it's a product of the Earth's spin.
0:54:53 > 0:54:56Right at the boundary, high up in the sky,
0:54:56 > 0:54:59a wind blows about 10 kilometres up.
0:55:00 > 0:55:03It's really, really fast.
0:55:03 > 0:55:08It can travel at speeds of up to 450 kilometres per hour.
0:55:08 > 0:55:13It coils all the way around the planet, at about our latitude,
0:55:13 > 0:55:15and we call it the jet stream.
0:55:22 > 0:55:24The jet stream is crucial
0:55:24 > 0:55:27because it influences the boundary between the cells,
0:55:27 > 0:55:30and therefore between cold air to the north
0:55:30 > 0:55:31and warm air to the south.
0:55:37 > 0:55:39You can see the significance of this
0:55:39 > 0:55:44by looking at the weather 12 months earlier, in December 2010.
0:55:48 > 0:55:53The whole country shivered under a blanket of snow and ice.
0:55:53 > 0:55:57It was one of the coldest winters since records began.
0:55:57 > 0:56:02The reason was that the jet stream had developed a kink.
0:56:02 > 0:56:07Over the Atlantic, it sat much further north, near the Arctic.
0:56:07 > 0:56:10Then it swung down, over Britain.
0:56:10 > 0:56:13This temporarily shifted the boundary between the cells
0:56:13 > 0:56:17and brought cold, polar air across the whole country.
0:56:20 > 0:56:22Unfortunately for our weather forecasters,
0:56:22 > 0:56:25it's particularly difficult to predict
0:56:25 > 0:56:28the meanderings of the jet stream.
0:56:30 > 0:56:33The spin of the Earth makes the weather
0:56:33 > 0:56:35here in the UK unusually changeable,
0:56:35 > 0:56:39and particularly hard to predict.
0:56:39 > 0:56:41The fact that you wake up every morning
0:56:41 > 0:56:43and the atmosphere surprises you
0:56:43 > 0:56:46and it just adds to the spice of life.
0:56:51 > 0:56:53We've travelled five months
0:56:53 > 0:56:56and it's now December the 22nd, the winter solstice.
0:56:57 > 0:57:00This is the day when the northern hemisphere
0:57:00 > 0:57:03receives the least amount of sunshine in the year.
0:57:04 > 0:57:07And it marks the end of our journey, for now.
0:57:08 > 0:57:10Over the last five months,
0:57:10 > 0:57:13we've seen how the Earth's spin plays a critical role
0:57:13 > 0:57:15in defining the weather across the planet.
0:57:17 > 0:57:19Spin moves oceans...
0:57:19 > 0:57:21SHE SQUEALS
0:57:21 > 0:57:24..and it gives us a global pattern
0:57:24 > 0:57:27of climate zones that can be seen from space.
0:57:31 > 0:57:37Next time, we journey from the winter solstice to the spring equinox.
0:57:37 > 0:57:43It's the most astonishing landscape that I've ever seen.
0:57:43 > 0:57:47It's a time of paradoxes and extremes.
0:57:49 > 0:57:52And I just drop into the abyss.
0:58:12 > 0:58:15Subtitles by Red Bee Media Ltd