NOVA

Most people sense a change in the weather.

It's not your imagination.

Mega-storms, droughts, fires.

We're seeing one-in-a-thousand-year floods

with astonishing frequency.

How many times does that have to happen

before it's not a fluke, but it's a trend?

Is this trend the new normal?

Our planet did not come with a manual of how it all works.

To understand how it works,

"NOVA" explores one of the greatest scientific quests

of all time.

This is the essence of science.

A global investigation of our climate machine.

Looking good back there?

And how it determines our weather.

Yeah, super-clean data.

The technology is a huge leap forward.

It's game-changing.

It's just been like flipping on the lights.

It is a historic adventure...

The science goes back almost 200 years.

It was one of these things waiting to be discovered.

Probing deep into our natural world...

There's really nothing like it in science.

Looking for clues from Greenland's ice sheet...

The only way out of there is that helicopter.

You're certainly not walking out.

To the desert of Australia.

That gives us a really important window into the past.

Oh.

The stakes are high...

yet the outcome uncertain.

We're poking at the climate system

with a long, sharp, carbon-tipped spear.

And we cannot perfectly predict all of the consequences.

Can these discoveries show us where our planet is headed?

What gives me hope is that we understand this.

So we actually can do something about it.

It's a planetary crisis,

but we're clever enough to think our way out of this.

Right now on "NOVA"...

"Decoding the Weather Machine."

Major funding for "NOVA" is provided by the following...

At a weather studio in Minneapolis, Minnesota,

there is a storm brewing.

The models aren't sure where this thing is going.

And TV meteorologist Paul Douglas

is trying to predict its path.

There's the eye.

So it's moving more northwest.

Wow.

It's still a very strong tropical storm.

I don't think anybody in their right mind

sets out to be a meteorologist.

Meteorologist Paul Douglas with an update on Irma...

"I'm going to be wrong frequently,

and people will second-guess me, and I will get verbal abuse."

And, of course, the big story: Marco.

The damage, quite extensive.

Predicting the future... 140 miles an hour...

it's not for the faint of heart.

Because the weather these days

is not for the faint of heart either.

All the ingredients converging

to turn this into a true superstorm.

While Paul is reporting

on a Category 5 hurricane threatening the U.S...

Once again, smoke dominating...

His team is also reporting on wildfires in the West,

We've got a multitude of active large fires, not only...

And another mega-storm en route.

It could be making a very close call with the Bahamas.

We'll keep you up to date.

It's an atmospheric free-for-all.

Now, the Twin Cities'

fastest-growing television news.

Over nearly four decades

of blizzards, hurricanes, and floods,

Paul has seen it all.

It may have been the most extreme outbreak

of heat and humidity on record...

In the grips of the worst blizzard of the century...

But over the years, storm by storm,

Paul began to develop an uneasy feeling.

He wondered, "Was something up with the weather?"

The rhythm of the atmosphere was off,

we were seeing more freakish weather,

storms were stronger and wetter.

It wasn't the old-fashioned

minus-20, minus-30 winters anymore.

It was raining in January.

How many times does that have to happen

before it's not a fluke, but it's a trend?

Douglas had heard about global warming,

but given all the crazy weather he'd experienced,

he was skeptical.

And he's not alone.

A third of Americans doubt humans are changing the climate.

We pray that you would awaken us...

Douglas understands where they're coming from.

Many in his community of Christian conservatives

are distrustful of big government.

A lot of the pushback

is because when people look at climate change,

they think, "Oh, my God!

"If this is true, the only possible solution

"is more government,

more regulation, EPA times a hundred."

But dealing with the weather

day in and day out forced Douglas

to confront a question we all ultimately face:

is the frequency of powerful storms and odd weather patterns

just normal weather variability...

Why has this gotten so big and so ferocious?

Or is it a new normal?

Shut down almost 30 roads...

Most people sense a change in the weather.

The weather's out of tune.

So how can we decode these changes?

Douglas is not the only one noticing changes.

Seven of the ten hottest years on record

have occurred within the last decade.

Wildfires are at an all-time high,

while Arctic sea ice is rapidly diminishing.

We are seeing one-in-a-thousand-year floods

with astonishing frequency.

When it rains really hard,

it's harder than ever.

We're seeing glaciers melting, sea level rising.

The length

and the intensity of heat waves has gone up dramatically.

Plants and trees are flowering earlier in the year.

Birds are moving pole-ward.

We're seeing more intense storms.

Changes like these have led an overwhelming majority

of climate scientists to an alarming conclusion:

it isn't just the weather that's changing,

it's what drives the weather:

earth's climate.

Climate change is happening now,

and the damage is happening now.

People notice extremes,

and climate change is increasing the risk or probability

of certain types of extreme weather events.

If we look all around us,

we see over 26,500 independent lines of evidence

that the planet is warming.

But while there may be evidence for a changing climate,

hasn't Earth's climate always been changing?

Glacier expert David Holland

says the evidence for that is as solid as rock.

Walking through Central Park in New York City,

he finds a huge boulder,

impossibly balanced on bedrock.

It's a different type of rock

than any rock that we can see in the neighborhood.

This rock was clearly transported here

by some mechanism.

And the mechanism powerful enough

to carry this huge boulder was a glacier...

A vast sheet of ice.

Unquestionably there was a very large glacier

over Manhattan almost 20,000 years ago.

20,000 years ago,

New York City looked very different from today.

It was a much colder place,

covered by ice that extended down from the North Pole.

And very carefully.

Open the pages of the book.

Oh yeah, look at that!

And there is evidence that millions of years before that,

the Arctic was completely different, too.

Fossils have been found of palm trees

in a place now famous for ice and snow...

Alaska.

Earth's history is full of dramatic swings

from hot to cold.

So isn't today's changing climate just natural?

The scientific evidence says no

and points to a very different cause:

us, primarily through our burning of fossil fuels.

That's a serious charge,

and addressing it will be enormously expensive.

So what is that evidence?

The quest to understand

what is behind our changing climate

began... surprisingly... More than 200 years ago.

At the end of the 18th century,

there's really this, this flowering

of fundamental exploration of science of all kinds.

Andrea Sella, a chemist at University College London,

says scientists at the time

were out exploring the natural world

and what factors control Earth's climate.

One of the things that's very interesting at the time

is this idea of what heat actually is.

People were beginning to realize

that there are these invisible radiations that can convey heat.

Today, we call it infrared radiation.