Heat Wild Weather

Heat drives our weather.

From the rage of a tropical storm,

the blinding heat of the desert,

to the violence of a summer sky.

I'm Donal MacIntyre and I'm about to take a journey with heat...

..from the equator to the Poles

to see for myself the awesome power it can unleash around the world.

From its birth in the tropics, through the perfect summer,

into a hotter world, one which could turn the weather of the future into a nightmare.

This is Wild Weather.

Have you ever wondered what's the power behind the weather, what makes it tick?

In just a few moments' time, we're going to see the true source of all weather.

And this is it - the sun, the fuse that lights the weather.

It's over a 100 times bigger than the earth.

Every second, it releases enough energy to power the USA for 9 million years.

It also takes one million years for the heat at its core to reach the surface.

Once it does, it makes its journey here in just 8½ minutes.

A journey that ends in a blaze of glory every single day.

All that blinding heat and light is blasted out through space towards us.

As it homes in on our little planet,

it's at its most intense heading for the steaming jungles of the tropics.

The sun's rays hit the equator.

It's the start of heat's epic journey around the planet.

But to find out what it does to the weather down here,

I'm heading to where the sun's energy is most intense.

Trapped beneath the jungle canopy, all that heat creates one of the most extreme environments there is.

So to find out what all that heat does to the weather,

I'm going to spend 24 hours in the jungles of Belize.

If you're in the jungle, and you don't know what you're doing, like me,

you're already this close to death.

This is Sergeant Bob McCloud,

an expert in jungle survival, and a very handy man to know.

-Hello. Morning.

-You're looking after me.

-I sure am.

-That's a heavy responsibility.

-I mean, one second it's torrential rain, the next second it's a sauna.

-Yeah, you're constantly wet.

And it'll go from one extreme to another in such a short time.

-Hypothermia and dehydration in one day?

-Yeah.

-That's crazy.

-Follow me, I'll show you.

For most of the year, the sun lies directly overhead,

so there are no conventional seasons here, just hot and wet, then a little less wet.

Even the daily weather is delightfully predictable.

There are clear skies in the morning, showers in the afternoon, clear skies again in the evening.

It's a weatherman's dream.

The one wild card in all this predictability

is the vast amount of energy constantly being built up in all this heat and humidity.

It's all that energy that makes this place as cloudy as it is.

The heat warms the land,

rainwater evaporates from the vast amount of vegetation and rises.

The water vapour condenses into tiny droplets that create huge clouds.

The droplets collide, growing larger until gravity pulls them down again.

The weather here is in a continuous cycle fuelled by heat.

And whether you're in the water or on the river bank, it doesn't make a whole lot of difference

because everything is permanently soaked.

-Everything's wet, wet, wet.

-That's the big problem in the jungle.

It doesn't matter whether it's hot or actually raining like it is here, everything ends up wet.

The only way round it is having a dry set of kit and a wet set of kit,

and tonight, make sure you get into your dry kit, so you have 12 hours where your body can recuperate.

-In the morning, you've got to get into your wet gear?

-Yes. If you don't, then things will start to rot.

Your boots and your clothing will go and your skin will start to rot away.

You can end up with crotch rot and foot rot.

Bob has spent the last five years training the British Army how to deal with life in this kind of heat.

God, I'm knackered.

As I struggle through the jungle, my body produces yet more heat.

My blood carries that heat away from the muscles and is cooled when it finally reaches the skin.

Out here that's never enough, so we sweat.

One drop of sweat can cool a litre of blood as it evaporates off the skin's surface.

Keep going. Get up there.

It's the process of evaporation that cools you down, but it's not working here.

The hotter I get, the faster my heart beats and the tireder I feel.

Go on, keep moving. Get up there.

I'm soaked in sweat, but the air is so damp that it can't evaporate.

Stop moaning and keep going.

I'm a dangerous man with a weapon like this.

You're being a bit of a cowboy there.

-Am I?

-Even using your machete, there's a technique to it.

-Yeah?

This is crazy terrain.

But it is what every kid trained for, aged six and seven, hacking through the jungle.

I'm just doing it a little late in life.

As the day wears on, it gets hotter and hotter.

More and more moisture fills the air until it becomes saturated with water.

Finally, it reaches a point where your sweat literally can't evaporate into the air any more.

I'm pouring sweat, but it's not doing me any good.

You can't see heat or humidity,

but to appreciate it, all you've got to do is imagine closing your bathroom door,

knocking the central heating up to full blast, turning the hot taps on

and leaving it on for a couple of hours.

That gives you a sense of it.

-Give us a break, Bob.

-Breaks are for losers. Come on, keep moving.

Fortunately, this kind of weather is rare outside the jungle.

But occasionally it reaches out beyond the tropics and, when it does, the results can be lethal.

In 1995, tropical weather descended on Chicago.

Even in a modern city like this, it brought chaos and death.

July, and the temperatures were already soaring

when heavy rains drenched the great plains outside the city.

The air mass above these fields became hot and steamy.

Days later, things took a turn for the worse.

A mass of warm, moisture-laden air from the Gulf of Mexico forced its way north.

The 2.8 million inhabitants of Chicago were about to experience the extremes of tropical weather.

That's when it really hit you, and you sat back and said, my gosh!

700 people died because of this event.

Weathermen stationed in the Midwest

realised something was wrong.

We're taking a look at temperatures well over 100 degrees,

widespread, not just one or two places.

High pressure produced hours of uninterrupted sunshine

and as the moist air from Mexico arrived in the area, levels of humidity shot up to 90%.

This mass of sweltering tropical air was then blown over Chicago by south-westerly winds.

It sat over the city like a steaming wet blanket.

Day two - heat wave. The city is an oven. All over Chicago, an invisible enemy takes hold.

It was like, you know,

hitting a brick wall.

It just totally surrounded you, like walking into a blanket.

You could put your bathing suit on and be in the water, and it would still be hot.

It affected the sound, too, when you walked out.

For Gabby Kuhn, this freak tropical weather made life difficult,

but for Mabel, her elderly neighbour, it was deadly.

It was about the second day of the heat wave, Mabel had done fine,

we had set up fans in the house.

She sat in this seat and we put a fan that would blow on her face.

The next day - normally she called me around two in the afternoon when she got up - and she didn't call.

Day three, the story's the same all over the city.

The emergency services are going into free fall.

And she's not alert or oriented?

The city's emergency warnings have failed to reach those most at risk.

As the heat increases, the emergency centre is swamped with thousands of calls for help.

Back in the suburbs, Gabby still hadn't heard from Mabel.

I said to my daughter, I think I need to go and check on Mabel.

She usually calls between two and three in the afternoon. I called her and she didn't answer.

I tried a couple of times, so I thought I should come over.

I came in and when I walked into the house I found her, and she was laying right here,

in between the dining room and the bathroom.

Apparently she tried to get into the washroom and didn't make it, and collapsed here on the floor.

The ironic thing is that this is my house right here, and it's probably three feet or a metre away.

And I didn't see her. I often think about that.

Is the patient conscious and breathing?

By Saturday, 165 people lay dying all over Chicago.

Many would not be discovered for days. By then it would be too late.

Help is on the way over there. You watch for the ambulance, right.

When it really hit us, we started watching television ourselves,

and seeing that they were starting to have pictures of the morgues and the bodies were starting to pile up.

It was a shock.

Mabel was one of the first 20 to die in the city of heat-related...

..and then there were more.

Day four. Hospitals all over the city are at breaking point.

It started on a Thursday and it continued to build Friday.

By Saturday, we started having such a huge influx of patients

that where we used to have one cubicle, we'd now have 3A, 3B, 3C, 4A, 4B, 4C.

The death toll rose dramatically. Most victims were the elderly or impoverished,

whose bodies found it more difficult to cope with the extreme temperature conditions.

Firstly, the body's temperature rises to dangerous levels,

bringing about a state of confusion.

In this state of mind, we're less likely to seek shelter or the aid of a cooling fan.

As the body dehydrates, we slip into coma.

In these super-heated conditions, our internal structure changes.

Our blood loses its ability to clot, leading to a cruel and bizarre fate.

Blood oozes... from almost any orifice,

out of your nose, and your mouth and your rect...your bottom, from your stomach,

anywhere in your body, and people just die from that.

Day five. By the time all the victims had been discovered

the heat wave had already left Chicago.

It's just unbelievable

that so many people can die so quickly, just from the weather.

It was an awful week.

In the end, the tropical heat wave had claimed 525 victims in under a week.

The city and its people were simply not prepared for the intense jungle weather that invaded their lives.

With only 12 hours left in the jungle, I'm about to experience night-time weather in the tropics.

As the heat of the day subsides,

all the moisture hanging in the air means nightfall can bring heavy rain or worse.

Bob and I are making sure we're ready for anything.

Have you bought the duvets?

I'm afraid not, not out here. We do have sleeping bags.

Where's my little Coke? And a little kind of mini-bar and a phone here for room service.

-The creature comforts, eh?

-Plenty of creatures, no comforts here. Ah!

You're looking at a good 12 hours of darkness,

and we wouldn't move during the night because of how thick the jungle is.

From stopping, you'll probably get a good 12 hours' kip.

Any Maltesers, chocolates, Pringles?

I've got some noodles.

Yeah.

I can't remember where I left my machete.

As night falls, a stormier kind of weather takes hold.

After 12 hours of sunshine, when hot, humid air releases massive amounts of energy,

this is the result.

THUNDER CRASHES

A big storm can dump several inches of rain in a night,

equal in power to an atomic bomb.

They can also reduce the jungle to matchwood.

RAIN BATTERS DOWN

I know there aren't supposed to be seasons in the jungle, but this certainly feels like winter to me.

It's about 7 o'clock in the morning,

it's raining outside, it's cold,

I've had an awful sleep.

And I'd just like to say

that communing with nature in the jungle

isn't all...

it's set up to be.

(Oh, God!)

Sorry.

-Disaster, Bob.

-I did warn you.

At least the spiders that were in them have now gone, or drowned.

DONAL LAUGHS The main thing is to learn something.

I thought the tropics, where the sun's energy is at its most intense, would be the hottest place on earth.

But I'm wrong. I'm about to get out of the frying pan and get into the fire.

I'm heading to the hottest place on earth.

From the heart of the tropics, all that warm air rises, dumping its rain as it goes.

At around nine miles high, at the edge of the troposphere, it can rise no further,

so it begins to head both north and south of the equator.

About 1500 miles later, at about 20 degrees latitude, the air begins to sink back down to earth,

warming as it drops.

Where it falls, it creates two strips of arid land that circle the globe.

That's where you'll find the great deserts of the world.

And the greatest of them all is the Sahara.

Having left all that wet heat in the jungle, I am about to find out what dry heat does to the weather.

The air above me is so warm that water cannot condense into rain,

so it hangs there, trapped, above the very places that need it most.

Just look around me at the results. Theoretically, there's more moisture in the sky above me now

than over the skies of Britain and yet it's completely clear.

This desert only gets three inches of rain every year.

Even when it does rain, the sun's rays are so intense

that it evaporates 200 times the amount that falls.

So, this is what we're left with.

The sun cooks the desert rocks,

causing the minerals to expand so much that the rocks eventually shatter.

Over thousands of years, powerful desert winds grind them all to sand.

The Sahara covers an area of over 3 million square miles, almost as big as the USA.

It's also record-breakingly hot.

In 1922, the highest air temperature ever recorded was taken here,

a staggering 58 degrees Celsius, 136.4 degrees Fahrenheit.

Just one of these dunes is made up of thousands of tons of sand.

All those tiny grains go to make up our most romantic and enduring image of the world's deserts...

..endlessly driven by the winds, like some half-frozen ocean.

This is an amazing place.

The vast stillness is completely overwhelming.

It's timeless. There's a real sense that nothing here has ever changed.

But that's an illusion.

Beneath this ocean of sand lies an incredible secret.

In 1981, 140 miles above my head,

the space shuttle Columbia looked down upon this desert and took a hi-tech snapshot.

What they saw took them completely by surprise.

Instead of a flat and barren expanse of sand,

the infrared revealed mountains and river valleys underneath.

That picture revealed a hidden world only a few metres beneath my feet.

As they saw through the layers of sand,

they where amazed to discover that, 35 million years ago, the Sahara was once a great fertile savannah

with rivers and lush meadows.

Over time, small changes in the global climate meant that life simply withered and died.

We like to think of the desert as timeless, but in fact it is constantly changing.

Here in the dry heat of the desert my journey continues,

this time to see if I can survive the highest temperatures on the planet.

Instead of the sunbathing and camel treks I'd hoped for,

I have to face a tougher test, so I'm practising for the most gruelling marathon on earth.

I've come here to run in the toughest race in the world, the infamous Marathon Of The Sands.

Seven days through some of the hottest and most hostile environments on the planet.

If you really want to experience the very worst the desert weather can throw at you,

this is the one event that promises to hit you with everything.

Cutting desert winds, killer dehydration, blinding dust and the unbearable searing heat.

Earlier on, it seemed like a very good idea.

STARTER COUNTS DOWN

Unlike in the jungle, all this hot, dry air literally sucks the water out of you,

so I've been told to carry and drink at least nine litres per day.

And when it really heats up, I'll be losing a litre an hour.

This is the really tough part. I can hardly move.

I haven't been running for too long, but already I can feel myself sweating all over.

You can't really see it, because the sun's evaporating it straight from my skin, but if you do this,

you can taste the salt and the sweat.

And the more I sweat, the more salt I lose. In a full day, I can lose about three teaspoonfuls.

That could be really dangerous. It could give me severe muscle cramps.

And because salt's essential for brain function, it can leave me disorientated and confused.

No change there, then.

The desert heat can play tricks on you at the best of times. Without water, these tricks can be lethal.

The temperature on the ground here can get close to boiling point.

It's only about 9am, but already the heat is vicious.

I can feel my head throbbing and tightening as the sun takes its toll.

But if I do this, that's when the heat really hits you. Down here it's 50% hotter than at eye level.

The temperature difference creates strange, sometimes deadly effects.

We've all heard the stories.

You're lost, you've used your last drop of water.

And just as it looks like it's all over, you see a lake shimmering on the horizon.

In the distance you see the water you've been so desperately searching for,

but however fast you run towards it, it never gets any closer.

Desert mirages occur because of the temperature differences between here...

and here. It cools by nearly 20 degrees in less than two metres.

That incredibly hot layer near the ground can behave just like a lens.

Like the lens in your spectacles, it can refract, actually bend the light.

When I look out there towards the horizon, I can't see a cool lake of water.

What I'm actually seeing is the sky refracted, so it appears to be lying on the ground.

A cruel trick indeed.

Oh, what monster designed that race?

Every time you sink in the sand and it's blistering with the sun.

And there's dust in your ears and your eyes, burning your throat, and it's like, oh... It's a killer.

But at the end of the day, the desert has another trick of the light up its sleeve.

There's one kind of mirage you can see out here just about every day.

The sun I'm looking at has actually already set. It's exactly the same effect as the lake mirage.

This optical illusion gives us two minutes of extra light at the end of the day.

Out here, you can drive for days without seeing any signs of life whatsoever.

And if that's not worrying enough, the desert also has some special weather treats in store

for those foolish enough to venture into its dusty heart.

Here in the desert, there is a menace as old as the wind that turns day to night in an instant.

The heat rising from the desert floor mixes with the powerful easterly winds,

creating a vicious turbulence that whips the sand up and blasts it into the air.

It's called a haboob.

When the wind really gets going and you're in its way, it can be very nasty indeed.

Sometimes it can look like the whole desert is on the move.

The sight can be truly apocalyptic.

It happened in Melbourne, Australia, in February 1983,

when a massive cold front gathered to the north of the city.

As it flowed south, a thunderstorm grew along its leading edge

causing a downdraught that kicked up the dust beneath it and drove it forward like a vast, red wave.

As it swept into town,

this huge wall of dust blotted out the sun in an instant and it brought the city to a standstill.

The cloud was 320 metres thick

and dumped over 1,000 tons of sand in an hour.

From miles above the Sahara,

we can see clouds of incredibly fine sand that dwarf even Melbourne's experience.

When the wind and the sun get going,

the clouds they create can be truly global.

Some of them can be the size of Europe.

Caught up in the winds that blow west across the Atlantic,

these fine sands are carried as far as the Caribbean, where they help top up the perfect beach.

From the mountains of Morocco to the palm trees of the Caribbean,

these enormous dust clouds travel 4,500 miles,

bringing about 90 million tons of the Sahara here to the Caribbean every single year.

That's an awful lot of beach.

My journey has finally arrived in the kind of heat we all love.

A friendly sun, a cooling dip - it all makes for a holiday mood.

The sun's rays boost our levels of serotonin, a brain chemical that makes us feel good.

But this sense of wellbeing can be deceptive.

It's easy to forget, as we cover ourselves in sun cream,

the price we pay to soak up those precious rays.

This feels great. Lying here is deeply relaxing.

I'm getting a good dose of vitamin D from the sun's rays.

But, as the hours tick by, it's a very different story.

Sunburn!

Beneath the surface of my skin, only half that vicious ultraviolet light from the sun is getting through.

But even so, it's destroying the skin cells nearest the surface.

My skin reddens as blood flow increases, carrying nutrients and oxygen to repair the damage.

The longer I spend in the sun, the more permanent the damage becomes.

Like me, the planet also has a protective skin.

The atmosphere above us stops half of the sun's lethal rays,

which are absorbed or reflected back into space

by clouds, particles in the air and atmospheric gases.

Without the atmosphere, life wouldn't be possible.

But the skies that shield us from these harmful rays also contain their own deadly energy.

It's one of summer's biggest killers - lightning.

Viewed from space,

NASA cameras captured these amazing images of our electric skies.

Right at this very moment,

there are almost 1,800 thunderstorms taking place around the planet.

On average, lighting strikes the earth about a hundred times a second.

When the lightning hit me, it was like nothing I could have imagined.

I felt like someone had thrown a hand grenade in my face.

To get as close as I could to being struck by lightning,

I went to see Mike Alexander at the Theatre of Electricity in Boston.

-Well, Mike, this is your very own lightning machine.

-That's right.

It's a Van de Graaff generator. It was invented here in Boston.

It works in a very simple way. It stores a lot of extra negative charge on the top of those two spheres,

-till there's enough charge up there to make about 1.5 million volts.

-That can do a lot of damage.

Well, everyone's safe out here, but inside this cage, it can get a little bit dangerous.

Your hair stands on end, you get a bluish glow off your nose, you feel a shock whenever you touch anything.

The scientists tell me

that if you were hit by one of those lightning bolts, you would probably live. But I haven't tried that yet.

They say that you will feel your hair stand up on your arms or your skin tingle. I didn't.

I felt this enormous blast.

This enormous, white light blinded me

and I felt the electricity going through my body. That's the last thing I felt,

because, at that point, it picked me up and threw me at the concrete and knocked me out.

Would you like to come in?

While the machine is working, this is the safest place to be - surrounded by metal.

It seems that all this metal is the most unsafe it could possibly be.

Yeah, it goes against your common sense, but if you're completely surrounded by metal, you're safe.

-The lightning can't get in to where you are.

-If you're in a thunderstorm and in a car,

-does that mean that's a safe place to be?

-It is, surprisingly enough. It has nothing to do with the tyres.

The metal surrounding you protects you. But it has to be a METAL car. A fibreglass car is no protection.

-What about rubber soles, Wellington boots, lightning all around you?

-It would probably keep your feet dry,

-but it won't stop a lightning bolt from hitting you.

-You've just buried another old wives' tale. Terrible!

You feel a bit like it's God's booth up here, lightning at command.

Yeah, it's great, isn't it? You feel like the guy in the Wizard Of Oz behind the curtain.

And they say lightning never strikes twice.

Not so for Linda Cooper.

I answered the telephone. It was my daughter. She wanted her dad.

About the time she said, "Is Dad...?" lightning struck the telephone.

I had the receiver up to my face.

I could feel the electricity going into my face. I dropped the phone and screamed.

And I said, "It got me again." I cannot believe that it got me again.

The pain was nothing like the first time.

The first time was like being hit by a truck, the second time like a moped. But the fear!

I had just come back from years of studying, years of trying to get my health back, my strength back.

And here it got me again. I thought it was going to steal all that away from me.

To the naked eye, lightning always looks like it comes from the sky.

But that's only half the story.

What you can't see is that the big flash is shooting up from the ground

into the clouds in one ten-thousandth of a second.

At 30,000 degrees Celsius, the bolt superheats the air around it,

making it literally explode...

-LOUD CRASH

-That's the sound of thunder.

Some day something's going to go wrong here, somebody's going to be zapped. Let's hope it's not today!

-It's pretty safe, though?

-Yes, it's very safe. You don't have to worry.

As long as you stay inside this metal cage, the lightning can strike just half an inch away from you

and you're still absolutely safe. Put your finger out, you'll get a bad zap.

I've done it a couple of times by mistake, and it hurts.

-What's it like getting 1.5 million volts in your little finger?

-It feels like being hit by a hammer.

-Your muscles tense all of a sudden. It's not pleasant.

-OK.

You look a bit like a mad professor.

It feels that way sometimes.

Three, two, one...

A bolt of lightning can be up to 30 miles long, and it's just the width of my thumb.

It's also six times hotter than the sun, so I'm going to be very careful.

In the real world though, the chances of being hit by lightning are pretty minimal.

Even so, about a 1,000 people are killed and struck by lightning every year.

There's about 1.5 million volts hitting my finger right now.

Oh, my God. Thank God for that!

The third time I was struck was totally different than the first two.

I thought the storm was gone, so I got up and made jello.

I went to wash out the cup after I'd finished making the jello.

I put it in to the sink and turned on the water faucets.

I didn't realise that the cold water faucet was a ground to your house.

Lightning struck, came through the cold water faucet,

ran up both of my arms and across my chest. I felt like I was on fire.

This was totally different than the other two times.

This time I felt like somebody had taken a torch and lit both of my arms. I put them inside the freezer.

I leaned into my freezer and stayed there for I don't know how long.

Lightning is nature's electricity.

It's in the air, and it's going to hurt you if it hits you.

It could kill you, but if you live, you will never be the same,

you will never feel the same, you will never think the same.

And I wouldn't wish that on anyone.

In the future, the violence of our summer skies may be about to get worse.

So the next time you're caught in a storm, consider this -

it could be all your own fault.

It's Friday and time to go home.

The weather's been lovely all week and everyone's looking forward to a weekend in the sun.

But have you ever noticed how the weather goes and messes it all up?

You may think rain at the weekend is just bad luck,

but scientist Randy Savini has stumbled on something really strange - WE may be the cause of it.

My research into weekend rainfall began as a fortunate accident.

I had been studying hurricanes

and inadvertently ran a computer programme that classified hurricane observations by day of the week.

When I plotted out those hurricane observations, I found a very bizarre, interesting pattern.

He found that the strength of hurricanes seemed to differ depending on the day of the week.

What Randy's computer told him about hurricanes

led him to realise that the way we live and work may be directly changing the weather around us.

It all comes down to the seven-day week.

Given that the seven-day cycle is something that doesn't occur in nature,

that it is only the result of man, if we see changes in weather that are occurring on a seven-day cycle,

the assumption is that it's something that we're doing.

To prove we are influencing the weather on a weekly basis, Randy needed more evidence.

We went back to the archives and grabbed 20 years of data and looked at rainfall.

Rainfall is something that's easily measured, that is measured in a lot of different locations

and is very important to people. And for location after location,

we found that rainfall showed the same exact cycles as we were seeing with hurricanes.

It was a lot wetter on the weekends than it was during the week.

Randy found that, as pollution levels built up over the course of the working week,

from car exhausts and factories, the warm air carries these particles of pollution upwards.

They rise high above the city and begin to seed the clouds.

Moisture attaches to the particles, which eventually turn into water droplets.

By the end of the week, it has all drifted out into the suburbs, bringing thunderstorms and showers.

So the ironic twist is that we work all through the week

to be able to enjoy a weekend barbecue,

and our midweek activities are going to rain out our barbecue.

But it's not just our cities we are affecting.

It seems that the whole planet is warming up. The next stage of my journey is to Hawaii,

and if this can tell us anything, it will be that a big change is just around the corner.

I'm on my way to find the cleanest air on the planet,

and when I get there, I'm going to show you something that changed the world.

When it comes to the fate of the weather,

it's the most important scientific device of the last 100 years.

And it's just over there.

Just a second.

It's over here.

Hang on a minute.

I'll just try and find the lights.

Yes, this is it. You guessed it.

You're looking at the Ultramat III, the machine that changed the world.

The reason the Ultramat III is so important

is because up here at 14,200 feet in the middle of the Pacific is the purest air on earth,

so it's the best place to detect any changes in the global atmosphere.

The Ultramat III sniffed out a big change.

The recent burning of fossil fuels has put more carbon dioxide gas into the air

than at any other time in the last 20 million years.

The gas acts like a greenhouse, letting the sun's energy into the atmosphere

but preventing it leaking back into space.

So it heats up - 0.6 degrees Celsius in the last 150 years.

A tiny amount, but we are already seeing the effects.

One of the biggest concerns is how these changes will affect the oceans.

This small rise in global temperature is warming the sea, causing the water to expand.

Even a fraction of a degree could mean that the sea level will rise by as much as a metre.

Research by NASA's Goddard Space Institute

has already produced a glimpse of the future for New York's 20 million inhabitants.

In the next 100 years,

there could be as much as 42 inches of higher seas surrounding Manhattan and New York.

In the most catastrophic case, Manhattan turns into two islands.

Combined with higher sea levels,

even an ordinary storm will have drastic consequences for cities by the sea.

'This just in. City Hall has issued an urgent flood warning.

'A major storm surge is expected to swamp areas from the Battery to the Midtown area.

'The Mayor's office is advising the immediate evacuation of basements...'

The subterranean basements of New York flood about once every 100 years.

But the research suggests that in the future this could happen once every TEN years.

But it's not just New York.

Every city by the sea faces the same future.

As the world heats up and the oceans expand, the sea level will rise.

Around the world other low coastlines,

like those around Bangladesh or Mozambique, face an even more uncertain future.

In London, the Thames will rise.

And already we can see the effects on our coastline.

Further inland, the future will bring more rain and more floods.

It's wet, it's flooded and it's cold.

It's also the future.

This is Britain tomorrow - wetter, stormier and altogether under water.

Back in the clear, clean mountain air of Hawaii,

where we first realised that big change was on the way,

the Ultramat III is still quietly counting the cost of our effect on the weather.

Which is why this little machine is so important.

There are many theories about what the weather will be like over the next 50, 100 or 200 years' time.

One thing's for sure, a warmer climate means wilder weather.

The question we all have to ask is what kind of world do we want?

Because to a certain extent, each of us holds that in our own hands.

Every time you flick a switch, you affect the future.

We've already seen the changes around us.

All we can do is learn to cope, whatever those changes bring.

My journey is at an end.

I've been blasted, roasted and soaked by the invisible forces that drive our weather.

It's been a wild ride, and in the future it may be about to get even wilder.

Subtitles by Dorothy Moore and Audrey Flynn BBC Broadcast 2002

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