Nova (1974–…): Season 44, Episode 24 - Killer Hurricanes - full transcript
Our planet is capable of
unleashing extreme chaos.
Volcanoes, earthquakes,
hurricanes,
and floods can cause
untold devastation.
We may think we've seen
the worst Mother Nature
can throw at us,
but scientists struggling
to understand these disasters
are discovering evidence
that even more extreme events
have struck in the past.
So this is about 13 times
more powerful
than the Pompeii eruption.
They're uncovering clues
that the worst catastrophes
in history could strike again.
More than 200 years ago,
a disaster tore through
the Caribbean.
This is by far the deadliest
hurricane to ever impact
the entire Caribbean.
The Great Hurricane of 1780
was both huge and powerful.
But can we trace its impact
using today's tools
because it appears storms
are becoming more powerful.
We believe that there should be
more intense storms,
perhaps not as many of them are
happening, but when they do,
they'll be stronger.
The clues are here,
buried and hidden
beneath the waves
and beneath the ground.
There's this whole
history in here
about what's happened over time.
Now scientists and
historians come together,
to scour our volatile earth,
to find out if, in the future,
there will be more
"Killer Hurricanes."
Right now on NOVA
Hurricanes,
some of the most powerful
natural forces on earth.
Called typhoons or cyclones
in the Pacific,
these storms can build up over
warm waters and can reach
hundreds of miles across.
Storms like Harvey, Irma, Maria,
and Typhoon Haiyan
are synonymous
with death and destruction.
Hurricanes kill on average
10,000 people a year.
They can cause death.
They can actually destroy
infrastructures, entire cities.
It's just complete devastation,
it's unbelievable.
In 2017, a series of
catastrophic hurricanes...
Harvey, Irma, and Maria...
Impacted millions of people
in the U.S. and the Caribbean.
Entire islands and the city
of Houston were devastated.
Is this the worst that nature
can throw at us?
To find out,
scientists are hunting for clues
in the distant past.
The more we understand
about them,
the better we can predict them.
They're unearthing evidence
of the deadliest
hurricane in Atlantic history...
The Great Hurricane of 1780.
It destroyed every house
in Barbados.
And it devastated
this massive fort.
That storm was
truly exceptional.
And looking even further back
in time,
scientists are discovering that,
a thousand years ago,
major Atlantic hurricanes
may have struck more often.
And then you get this
really big layer here
that dates to
about a thousand years ago.
So were monster hurricanes
more frequent or more powerful
in the past?
And what does this bode
for the future?
Two record-breaking hurricanes
struck the Caribbean
in September 2017.
The first, Irma,
leaves a trail of destruction
across the islands of Barbuda,
St. Maarten, and St. John.
Its 185 mile an hour winds
blow for a record 37 hours.
Then, less than two weeks later,
comes Maria.
Its sustained winds blast the
entire island of Puerto Rico,
destroying the power grid, water
supply, roads, and cell towers.
For weeks, millions are stranded
in the dark without clean water,
food, gas, or phones.
The terrible toll
of these storms
puts them in the record books.
But there is growing evidence
that hurricanes just as powerful
could once have been
more common.
Wayne Neely, a meteorologist
and historian, has come
to the National Archives
on the island of Barbados,
the most easterly
of all the Caribbean islands.
He's here to investigate
the deadliest Atlantic
hurricanes since records began:
The Great Hurricane of 1780.
According to historical
documents,
this storm was so destructive
it killed
an estimated 22,000 people
across the Caribbean.
And on October 10, 1780,
the first place it strikes
is the island of Barbados,
then under British rule.
In the records from the time,
Wayne finds evidence
of the human cost.
Here, in these death records,
we have 4,500 names
of persons who died in
the Great Hurricane of 1780.
Elizabeth Finlay, Thomas Fisher,
Nehimah Fish, William Folks,
Richard Foster, Elizabeth Forte.
These are a few names of persons
who died in that storm
in Barbados.
And in the archives,
Wayne also finds
a harrowing eyewitness account
that describes the fate
that likely befell
many of these people.
It's a letter written
by the commander-in-chief
of the British Forces
in the Leeward Islands.
This is a letter written to the
king by Major General Warren.
"I do not believe that ten
houses are saved
"in the whole island.
"Whole families were buried in
ruins of the inhabitations.
"Many in attempting to escape
were maimed and disabled,
"the ground covered
with mangled bodies
of their friends and relations."
Almost all buildings, whether
stone or wood, were torn apart.
Well, it must have been
a really great storm to destroy
all the buildings on the island,
so you can imagine the horror
and the misery that the
residents of Barbados felt
during the peak of the storm;
it was horrifying and horrific.
You have no home to go to;
you have no food.
The fresh water supply
is now destroyed.
In 1780, the people of Barbados
are far from the only victims.
In the following days, the storm
kills thousands more on islands
to the north and west.
The whole region was devastated.
Islands such as Martinique,
St. Lucia, St. Vincent,
and Grenada all reported
death tolls from the storms.
The wind is going to destroy
your plantations.
It's going to destroy
everything.
You'll lose all your supplies.
In 1780, it's estimated that
22,000 people
are killed immediately.
Most of the victims are slaves,
brought over from Africa
to work on the sugar
plantations.
Then, thousands more die
in the aftermath
from starvation and disease.
It's always the lowest end
of the economic chain
that feels the effects
of these things first.
The slaves are going
to die off first.
And most of them did.
Certainly the 1780 hurricane
was the deadliest hurricane
we know about
in the western hemisphere.
The records also reveal,
just as in 2017,
this storm was one of
three devastating hurricanes
that struck in quick succession.
1780 was a terrible year
for hurricanes.
There were three
incredibly destructive ones.
Only a week earlier, another
hurricane had struck the region.
And then,
just over a week later,
another struck,
also with catastrophic effect.
But the death toll from
the Great Hurricane
overshadows them all.
Even today, storms like
Hurricane Katrina that struck
the Gulf Coast in 2005;
and Hurricane Mitch,
the deadliest Atlantic hurricane
in living memory, which hit
Central America in 1998,
can leave thousands dead
in their wake.
So what makes these
killer storms so unusual?
And will they become
more frequent?
Modern hurricanes, like Harvey,
Irma, and Maria,
are tracked by aircraft
and weather satellites.
What we've learned about them
gives scientists an idea
of how the 1780 storm
likely formed and developed.
On August 27, 2017,
nine days before it makes
landfall in the Caribbean,
Irma begins as a storm off
the west coast of Africa.
As it travels west across
the Atlantic Ocean,
it quickly gathers strength.
Heat rising from
the warm ocean waters
feeds energy
into the storm system.
Hurricanes are like
heat engines.
They actually convert the energy
from the ocean
into motion in the hurricane.
Warm, moist air cools as it
rises, and then condenses.
That releases that energy that
was carried away from the ocean
and that powers the storm.
And one of the reasons
hurricanes are so intense is
the ocean is very warm and the
air at the top of the hurricane
is very cold.
These winds can then spin
into a powerful cyclone,
partly a product
of Earth's rotation,
with rain bands stretching
hundreds of miles across.
August 30... as wind speeds
reach 50 miles an hour,
Irma becomes a named hurricane.
Over the next six days,
it intensifies rapidly.
By the time it slams into
tiny exposed Barbuda
on September 6,
with sustained wind speeds
of a 185 miles an hour,
Irma is a Category 5 hurricane.
It's likely the Great Hurricane
of 1780 formed in a similar way
to this recent superstorm.
But how strong did it get?
Historians are able to piece
together some details
of the storm's strength,
thanks in large part
to ships' records
kept by competing naval powers.
In 1780, the Caribbean
is a battleground
during the
American Revolutionary War.
Four years earlier,
the Americans had announced
their independence,
and the British decided,
"No, you don't.
"We're going to send a bunch
of our troops
over there to stop this."
In October, the area is full of
British and European warships.
There was a lot of European
ships in the area.
You had the French; you had
the Dutch and the Spanish
fighting against
British warships
for control of the Caribbean
and the region.
Like the communities
on the islands,
these ships were vulnerable
to violent hurricanes,
as the British Naval Records
in Barbados reveal.
Looking in the naval records,
you can see the loss
of so many ships...
HMS Laurel, HMS Andromeda,
and HMS Deal Castle,
all lost
in the Great Hurricane of 1780.
The fate of HMS Deal Castle is
depicted in paintings
from the period.
And historical documents reveal
that thousands of sailors
from all sides perished at sea.
So given its devastating scale,
was the Great Hurricane of 1780
more powerful than
more recent killer storms?
Well, we just don't know whether
it was a uniquely powerful
hurricane,
or whether it was just an
ordinarily powerful hurricane
that took a very
destructive path.
Given the lack
of scientific data,
how can experts today track
this megastorm from the past?
Climate historian Mike Chenoweth
has taken up the challenge.
He's scouring old ships' logs
hunting for hidden clues.
And he's uncovered an entry
from October 9,
the day before the hurricane
strikes Barbados.
One thing I found in doing
the research was
the first detection
of the hurricane
by the Spanish frigate Diana.
This is the earliest account
we have of a ship
encountering
the Great Hurricane.
And so they were about 300 miles
east of the island of Trinidad,
off to the southeast
of Barbados,
at 10 degrees of latitude.
"There bore down upon us
a violent hurricane
"which lasted 48 hours
without intermission.
"The wind ran the entire compass
with violent gusts
and the frigate moved heavily
in the swells."
So in several days ahead
of reaching Barbados,
it had already
become a hurricane.
But to quantify the strength
of the hurricane,
Mike faces a major problem.
In 1780, there were no
instruments for measuring
the actual speed of the wind.
The only clues are time of day,
wind direction, and estimates
of wind intensity.
Mike continues with logs
dated to October 10.
So, this is at 6:00
in the morning...
The hurricane has just finished
devastating
the island of Barbados.
Everything is
a complete wreck now.
This ship plot here is for
HMS Albemarle
off the west coast
of the island of Barbados.
They have a hurricane blowing
from the south on this map.
That's the approximate center
of the hurricane at this point
in time, and then we have
other ships off the coast
of St. Lucia reporting
northeast winds,
and another ship
approaching Martinique
with an east-northeast wind.
Mike draws together records
from all the ships
and plots the position of the
storm in six-hour intervals.
In this way, he tracks the storm
as it moves
across the Caribbean.
So from the 11th to the 15th,
this storm is out
in the eastern Caribbean
stirring up the water
with this huge wind field
that just continues to batter
the islands all in the region.
For nine days, the Great
Hurricane ravages the Caribbean
before passing
into the North Atlantic.
And Mike spots two features that
made this storm so destructive.
First, with hurricane force
winds that he estimates
extended up to 75 miles out
from the hurricane's eye,
the storm was vast.
75 miles is about triple
what we usually see
for strong hurricanes
in that area,
the gale force winds extending
out 220 miles to the north.
That means its strongest winds
may have blasted
an even greater area
than Irma's.
The storm was moving forwards
unusually slowly,
ravaging Barbados
for eight hours.
Because the storm is moving
slower than average,
it just had
more opportunity to keep
knocking more buildings down.
You've got thousands
of people dead.
From the ships' logs,
Mike is building up
a more accurate picture
of the path and size
of the 1780 megastorm.
But the logs can't answer
the most pressing question:
how powerful was this storm
by comparison
with hurricanes today?
To answer this question,
scientists are trying
to understand how
different conditions contribute
to creating monster hurricanes.
You have a complex
web of conditions that have
to come together
perfectly to produce this
intensifying storm,
and that's really a challenge.
Scientists agree there
are three key ingredients
for the perfect storm.
First, for a hurricane to grow
in strength and power,
there needs to be a layer of
warm ocean water reaching down
to at least 200 feet.
The hurricanes churn up
cold water
from beneath the warm water
on the surface,
so they cool the surface.
It's like throwing cold water
on a fire.
Second, crosswinds near the top
of the hurricane,
called wind shear,
can't be too strong
or they disrupt
the formation of the storm.
That tends to blow dry air into
the core of a hurricane.
That also is like throwing
cold water on the fire.
And, third,
hurricanes need moisture
throughout the atmosphere.
If all these conditions
come together,
wind speeds within the eyewall
of the hurricane
can rapidly rise.
They become the most powerful
storms on the planet.
On a scale of one to five,
a major hurricane is
a Category 3 storm or above,
with wind speeds
of 111 miles an hour or greater.
You could probably go outside
and walk around
in 75 mile an hour winds...
I wouldn't recommend it.
There's going to be things
flying through the air.
If it was
a Cat 3 or 4 hurricane,
you're not even going
to be able to walk or stand.
Generally, if over half
the buildings
are knocked down, that's usually
a good sign you've got at least
a Category 3 storm.
The deadliest storm ever to hit
the United States
was a Category 4 in Galveston,
Texas, in 1900
with estimates up to
12,000 dead.
Category 5 storms are the most
powerful hurricanes of all,
with wind speeds over
156 miles an hour.
There are very few structures...
Boats, buildings, cars...
That can withstand the force
of a Category 5 hurricane.
As wind speeds increase,
their destructive power grows
even faster.
It's not a sort of linear
change.
It's actually exponential,
so the wind is able to do
a lot more work.
If you double the wind speed,
you increase the destruction
by at least a factor of eight.
So a Category 5 hurricane
is at least
eight times more destructive
than a Category 1.
And recent history reveals
the extreme destructiveness
of these Category 5 storms.
In 2017, Hurricane Maria wrecked
power and water systems
across most of Puerto Rico.
Estimates put the damage
at over $90 billion.
In 1969,
Camille blasted Mississippi,
flattening hundreds
of miles of coastline.
And in 1935 one of the most
intense hurricanes
ever to hit the United States,
the Great Labor Day Hurricane,
ripped through the Florida Keys,
killing over 400 people.
But according to climatologist
Mike Chenoweth,
that the Great Hurricane of 1780
devastated a wider area
and left thousands
more people dead
than any of these modern
Category 5 storms.
And he's found detailed
eyewitness accounts
that reveal another reason why
this unusually large
and slow-moving storm
was so destructive.
Its power didn't come
from the wind alone.
Another devastating force in
a tropical storm is the water,
an intense surge from the sea...
...known as storm surge.
This is what killed most people
when Typhoon Haiyan
slammed into
the Philippines in 2013.
In the Philippines,
more than 60 percent
of the population lives
within a mile of the water.
One of the most powerful storms
ever to strike land,
Haiyan's wind speeds reached
a 195 miles per hour
as it moved slowly
across the islands.
You have the wind driving
this water towards the coast.
As the storm is approaching
landfall,
it's going from deeper water
to more shallow water.
Many people lost their lives in
that storm because of the surge.
Along any coastline, tsunami-
like waves pushed onshore
by hurricane winds can threaten
lives and property.
What you see is a wall of water
that just wipes out
the neighboring houses and trees
and everything before it.
And in some cases, this storm
surge can be ten to 20 feet high
and anything
within several feet to
up to a mile or so
of the coastline
can essentially be wiped out.
Anybody that's told to evacuate
because of the danger
of a storm surge,
they should not think twice
about it; just go.
Every year, millions of people
in the U.S., Central America,
and the Caribbean face the
threat of hurricane storm surge.
And it's storm surge that likely
caused much of the destruction
in Barbados in 1780.
Suddenly, these massive
storm surges came
which carry this
incredible force with them
and devastated the city.
Along the shore on Barbados,
Wayne Neely
is hunting for physical evidence
of the storm surge in 1780.
This is Fort Charles,
just outside the capital,
Bridge Town.
It was entirely rebuilt
after the 1780 hurricane
completely destroyed
the original.
In 1780, before the hurricane,
the fort itself was
a massive structure.
The walls were much higher and
were three to four feet thick.
The size was immense.
For the walls to be destroyed
from that hurricane,
it had to be
a catastrophic storm.
The records describe
an unusually high storm surge,
over 25 feet.
Eyewitness accounts tell us the
hurricane swept heavy cannons
140 yards inland.
Nothing stood in place;
it devastated this fort.
It destroyed every house
in Barbados,
and it devastated the Caribbean.
We had entire fortresses
and batteries of war,
you know, just totally
swept away.
The scale of destruction
reveals the extreme impact
of the 1780 hurricane.
And now, drawing together
all the clues,
it's possible to recreate
what happened.
On the night of October 9, 1780,
the Great Hurricane approaches
Barbados from the southeast.
The storm is
over 300 miles across.
On October 10, winds and rains
lashed the island.
Finally, as the eyewall
approaches land,
the huge winds push up a storm
surge 25 feet high.
It slams into the coast...
and inundates the land.
Ravaging the island
for over eight hours,
it leaves more than 4,000
dead...
And goes on to claim a total
of 22,000 lives
across the Caribbean.
The Great Hurricane of 1780
shows how devastating
a hurricane can be in an exposed
low-lying landscape.
Mike Chenoweth believes
its destructiveness
was unparalleled.
We haven't had a storm like
that since,
so we're talking about something
that's happened only once
in 400 years.
But what are the chances
of it happening again?
We don't know how far back
something similar
might've happened,
and we certainly don't know what
that possibility in future is.
Major hurricanes of Category 3
and above are not common events.
On average, one makes landfall
in the United States
every two years,
and Category 4 and 5 hurricanes
are even less frequent.
Category 5 hurricanes
are very rare.
There are far, far more
Category 1s than Category 5s.
But now, with the buildup
of greenhouse gases
in our atmosphere from
burning fossil fuels,
our climate is changing.
So many scientists like
Kerry Emanuel are predicting
that intense hurricanes
will become more frequent.
But it's a challenging problem.
Today, scientists rely on
complex weather data
from satellites and aircraft
to create computer simulations
that can help them
make predictions.
But this kind of precise data
only goes back a few decades.
We have reasonably accurate data
going back only to about 1970.
And if you go back in time,
we don't have satellites.
And then if you go back before
the 1940s,
we don't have aircraft.
There just isn't enough modern
data to discern patterns
in hurricane behavior.
Better data about hurricanes
in the past would be valuable.
If we have understanding of
the activity, the intensity,
the frequency of storms
a thousand, 2,000 years ago,
then that gives us better
confidence
in our ability to assess
what hurricanes are doing now
and in the future.
But extracting clues about
what hurricanes were doing
thousands of years ago...
Well before detailed
historic records...
Requires some
very clever detective work,
and some of it needs
to be done at sea.
Oceanographer Jeff Donnelly
is looking for evidence
of ancient hurricanes
on the sea floor.
His search has brought him over
1,200 miles west of Barbados,
to Jamaica.
This is Discovery Bay,
on the northern coast.
Jeff and his team want to expand
our understanding of hurricanes
by exploring the deep past.
We're looking into
the sediments to sort of
find these long-term records
to extend our knowledge
back thousands of years.
Jeff focuses on
one part of the bay,
next to a reef too shallow for
the research vessel Atlantis.
The only way to get there is
by building a raft...
and towing it out to position.
A blue hole...
A natural sinkhole created
in the limestone rock.
Jeff is interested
in the sediments trapped
at the bottom of this hole.
The blue hole is really
a good recorder of hurricanes,
so it's sort of
a nice time capsule.
The sediment can go in,
but it never can come back out.
On calm days,
fine grain silt and sand
drift into the hole
and accumulate over time.
But the violent force
of a major hurricane
propels a different kind
of debris into the hole.
When a hurricane will hit,
you'll get really strong winds,
big waves, storm surge.
That all sort of comes up
over the reef here,
and there are really strong
currents associated with that
that will tear up pieces
of coral that transport sand
into the blue hole.
The more intense the hurricane,
the larger the pieces of coral
and sand the waves transport.
And over thousands of years,
this sediment
builds up as layers
inside the blue hole.
The deeper the layers are,
the further back in time
they were laid down.
The team lowers a hollow tube,
vibrates it into the sediments,
and retrieves the sample
trapped inside.
Back on board Atlantis,
Donnelly cuts into the core.
So, we basically can
start at the top,
you know, this might be
what's depositing today,
and then you go back further
in time as you go down the core.
It's mostly fine, silty sand,
but Jeff spots one sediment
layer that's different.
When you get down to the bottom,
this interval here...
and there's really big bits of
shell and coral fragments
in there.
Washing and sieving the sample
reveals larger pieces of coral
mixed up in the sand.
It's quite coarse,
compared to the rest
of the core, but this was all
that material that was ripped up
and washed into this basin.
To Jeff, the coarseness of
the sediments
is clear evidence
of powerful waves,
most likely driven
by a major hurricane,
striking here
sometime in the past.
You'd have to have a quite
a high energy event
to be moving this kind of
sediment from the barrier reef
into that blue hole.
15-foot waves.
It's something like
an intense hurricane strike.
By retrieving organic materials
washed in with the storm,
like twigs and leaves
that contain carbon,
Jeff is able to radiocarbon
date these coarser layers.
It'll take months to know for
sure when this hurricane struck,
but he's dated layers
from cores taken from sites
all across the Caribbean.
So, this is a piece
of a sediment core that we took
in the Bahamas.
This particular section dates
to the 18th century.
See these light bands
here, here, and here
are these hurricane event beds.
They're much coarser than
the sediment around them.
You can really feel the grit
between your fingers.
And he's finding that the most
recent layers exactly match up
with the dates
of modern hurricanes.
We started coming into it, you
know, with a healthy level
of skepticism,
but all the storms you expect
to find end up being there.
That gives him confidence
that his technique is valid.
And now he's finding evidence of
hurricanes long before
historic records began.
At present, we've been able
to go back about 2,000 years
at most sites.
Every time we find a layer that
dates to before 1600, 1700 AD,
we're finding an event
that we never knew occurred.
By plotting the dates
of major hurricanes
back 1,400 years into the past,
Jeff sees a pattern emerge.
For the first 700 years,
during the height
of Mayan civilization,
and as the Vikings
were colonizing Greenland,
it appears powerful hurricanes
were more frequent than today.
Not necessarily any more intense
than the ones we've
experienced today,
they just occurred
much more frequently.
Then, over the next 700 years,
during the Renaissance
in Europe,
and as European settlers
were arriving in the Americas,
the record shows
a marked decrease.
And then, suddenly,
it shuts down.
The Great Hurricane of 1780
falls in the period
where there appears to have been
far fewer major hurricanes,
making it even more unusual.
So, what caused this decline
in hurricane activity
beginning about 700 years ago?
Jeff suspects it might be
partly due
to trends in
sea-surface temperature.
And it turns out
there's a way to recover
ocean temperature data
from the remains
of tiny animals.
We can find out about sea
surface temperatures in the past
by looking at these
fossil corals.
Corals build up giant colonies
that can last
for thousands of years.
Cores drilled out from deep
inside their structures
reveal layers of growth.
These corals grow almost like
trees, so each year,
it puts on a new band of growth,
and you can actually
count back in time.
While forming their skeletons,
corals absorb oxygen
from the seawater.
Oxygen comes in two forms...
Oxygen 16 has eight protons and
eight neutrons in its nucleus.
But oxygen 18
has two extra neutrons
and is more abundant
in the ocean
when temperatures are colder.
By measuring the ratio
of these two forms of oxygen
in the layers
of a coral skeleton,
scientists can calculate
relative ocean temperatures
over many thousands of years.
Using corals to reconstruct
sea surface temperatures
is really precise.
We're able to reconstruct
it right down to the year.
Plotting sea surface temperature
for the Caribbean
over the last 1,400 years
also reveals a trend.
The first 700 years
look generally warmer
than the next 700 years.
The results match
known historical
and scientific records that
chart a changing climate,
from an era known today as
the Medieval Warm Period
to a cooler period
known as the Little Ice Age.
And when Jeff compares
sea-surface temperatures
to his graph of hurricane
activity,
it appears that, in the past,
whenever the sea surface
was warmer, there were more
major hurricanes.
There are a whole variety
of factors that can influence
tropical cyclone activity
or hurricane activity,
but it's clear that there
is this interaction
between sea surface
temperatures and hurricanes.
The pattern seems to fit what is
known about hurricane formation.
The more energy available to
power a storm, it makes sense
that the storms are going
to potentially get stronger.
But these findings
present a puzzle.
1780, the year of
the Great Hurricane,
falls in the generally colder
period of the Little Ice Age.
It appears at first blush
to be quite an anomaly
that this 1780 season
and, actually, that
a couple of decades around it
are actually one of
the most active intervals.
But as Jeff looks more closely
at the sea surface temperatures,
he was able to detect a brief
but noticeable spike
in the decades around 1780.
And cool temperatures
in the atmosphere above
with warm ocean water below
is a known ingredient
for hurricane formation.
And whenever you have two bodies
of very different temperature,
you can create a lot
of energy that way.
So that might explain why in the
middle of the Little Ice Age,
we see, you know, an increase
in hurricane activity.
Jeff's work linking hurricane
events to ocean temperatures
could provide an explanation
for the intensity
of the 1780 hurricane.
And this research could sound
a warning for our future...
...because modern data reveals
that the sea surface temperature
of the Atlantic is now higher
than it was
a thousand years ago,
and is still rising.
We're actually warmer than any
point of the last millennium,
just a fraction of a degree
at this stage,
but the projections are that
that's going to continue.
But not only is it warmer
but it's increasing faster,
at a faster rate than we've seen
over the entire record.
As a result,
will we see major hurricanes
becoming more frequent?
We're likely to go back
into one of those
sort of intervals
where we're getting lots more
intense hurricane strikes.
The temperature
of our oceans is warming.
Greenhouse gases like
carbon dioxide,
generated by burning
fossil fuels,
are building up
in our atmosphere.
These insulate our planet,
holding in more
of the sun's heat,
causing the oceans
to warm more quickly
than we've detected in the past.
The problem right now
is that the rate at which
we're pushing the climate system
is very fast compared to
anything that's happened
in a very, very long time.
Whether this warming climate
means there will be
more Atlantic hurricanes
is still an open question,
but there is a growing agreement
that the hurricanes that do hit
will be stronger.
There is a pretty strong
consensus that,
as the planet continues to warm,
we're going to see
a greater incidence of
the high category hurricanes
in most places.
We believe that there should be
more intense storms.
Perhaps not as many of them
are happening,
but when they do,
they'll be stronger.
So, can scientists predict
where these strong hurricanes
will strike?
Amy Frappier, who studies
ancient climates,
has found an ingenious way to
look into the past for answers.
Compared to the last
four centuries,
she's finding that Atlantic
hurricanes are on the move,
likely heading towards
the big coastal cities
of the eastern United States.
The evidence comes
not from beneath the waves,
but from caves under the ground.
Locked inside stalagmites like
these are the chemical traces
of hurricanes from thousands
of years ago.
So here's a stalagmite
that we collected from Belize,
where we know hurricanes have
been part of the weather.
Rainwater that seeps through
the ground above a cave
dissolves minerals
from the surrounding rock.
Then, as it falls drop by drop
from the ceiling, it leaves
a little bit of this mineral
behind and a chemical signature
of the rainwater itself.
This forms stalagmites
that over the years grow upwards
from the cave floor.
Back in her lab,
Amy slices stalagmites open
and polishes the surfaces.
This reveals a series
of distinct layers.
You can see that there's
this whole history
in here about what's
happened over time.
In this one, it's got
lots of different changes
in color and texture
as we go from the older part
to the younger part at the top.
Hunting for the chemical traces
of a hurricane
in these layers is possible
because rain from hurricanes
is chemically different
from rain
during ordinary storms.
Again, a result thanks
to the difference between
oxygen 16 and oxygen 18,
which has two extra
neutrons in its nucleus.
In an ordinary storm, raindrops
evaporate slightly as they fall.
The lighter oxygen 16
evaporates more readily,
changing the proportions in rain
hitting the ground.
But in a hurricane,
the air is so humid
that there is very little
evaporation.
This means that in hurricane
rain, there's more oxygen 16
than in weaker, short-lived
rainstorms.
Whenever we see that
light oxygen signature,
we know that that
is a fingerprint
for a past hurricane.
To find this chemical signature,
Amy isolates individual layers
in the polished stalagmite,
then drills out
a minute sample as dust.
A mass spectrometer can read out
the chemical traces
locked inside the dust,
and it reveals which layers
are richer in light oxygen,
the signature of hurricane rain.
The results are so accurate
they allow Amy to tell
if a hurricane has hit
in any given year
thousands of years in the past.
The level of detail
is just unprecedented.
We can see
the difference between
years with a storm strike
in Belize
and years without
a storm strike in Belize.
With data from caves
across the Caribbean,
the evidence suggests that the
paths of Atlantic hurricanes
appear to be changing over time.
We're starting to be able
to have enough data
that we can see
not only overall patterns
of storm activity,
but also changes
in storm tracks.
Over a 450-year period,
the average track of hurricanes
has been moving ever closer to
the continental United States.
400 years ago,
the storm strikes were clustered
in the western Caribbean,
around Central America,
and now the storm strikes seem
to be happening
much more frequently
around the U.S. east coast.
It's a trend that Amy
is still exploring.
But based on satellite data,
Kerry Emanuel has come
to a similar conclusion.
We've discovered that
over the last 35 years,
the latitude at which
tropical cyclones
reach their peak intensity
has been shifting away
from the equator at a rate
of about 35 miles per decade.
Kerry thinks that climate change
is driving the recent shift.
What we see when we look
at global warming is that
the fastest warming
is occurring in the Arctic.
Hurricanes like warm waters
and so they're shifting
toward the poles.
In just 30 years, that's over
100 miles closer
to densely populated areas
of the United States
along the Eastern Seaboard.
The last major storm to hit
the northeast coast was
Megastorm Sandy in October 2012.
After leaving a trail of
destruction in the Caribbean,
Sandy approaches the New York-
New Jersey coastline.
Though most of the Atlantic
gets colder as you move north,
Sandy feeds off a ribbon of warm
water that keeps it alive:
the Gulf Stream.
This is a circulating current
that pumps warm water
from the Gulf of Mexico up
and across the Atlantic.
By the time Sandy strikes
on October 29,
it's been downgraded from
a Category 2 hurricane
to a Category 1 storm.
But as Sandy combines
with another North Atlantic
storm system,
it hits with
catastrophic impact.
A 14-foot storm surge
races into New York City,
flooding streets,
tunnels, and subways,
and shorting out
electrical transmission lines.
Across New York and New Jersey,
the storm leaves 60 people dead,
damages 650,000 homes and causes
over $70 billion in damage.
It's just complete devastation,
and, you know, my parents have
lived here for 40 years,
and it's unbelievable.
Superstorm Sandy
was massively large,
and hit
a densely populated area.
Its powerful storm surge
did most of the damage,
but its winds were
not especially strong.
I think many people would be
surprised to know that
Hurricane Sandy, at the time
it was impacting
New York and New Jersey, was not
considered a major hurricane.
Imagine if it had been
a Category 3 or higher.
It has happened before.
The strongest recorded hurricane
to strike this coast
hit nearly 200 years ago.
It's known
in historical records as
the 1821 Norfolk, Long Island,
Hurricane, and is now thought
to have come ashore as
a Category 4 storm,
far more intense and extensive
than Sandy.
Experts estimate that
if this storm struck today,
it would cause over
$100 billion in damage.
Imagine a Category 4 storm
impacting New York...
The flooding, the storm surge,
the winds associated with that.
Cities such as New York
need to be prepared
for this type of threat.
Many factors can affect
hurricane formation,
but as the climate warms,
the threat of major hurricanes
heading up from the Caribbean,
impacting the southern states
and striking
the northeast coast,
is one that climate scientists
are taking seriously.
And they're highlighting
a less well-known danger
of global warming,
one that will make hurricanes
even more destructive.
Warmer oceans cause
water volume to expand.
At the same time,
glaciers are melting.
Sea level
around the world is rising.
If you look at some of
the more recent data,
not only is it rising,
in more recent decades,
it's rising at a faster rate.
At the best guess now is that,
if we don't curb emissions,
we'll be up a meter or three
feet by the end of the century.
The rising sea level
increases the risk
of damaging storm surge.
When that storm surge rides up
on top of higher sea levels,
then it causes
a lot more destruction.
Today, millions of people in
coastal and island communities
are at risk.
With all of this infrastructure
very close to sea level,
we're much more vulnerable
to much smaller changes.
To better understand our future,
scientists are looking
into the past, and what they're
finding leads some to predict
that a hurricane as deadly as
the Great Storm of 1780,
with its huge storm surges,
will likely strike again.
We're going to see another
hurricane like
the Great Hurricane of 1780
again on our shores,
and it's going to hit land
at full intensity.
It's happened once before,
so there's no reason
to not expect it
to happen again.
While there is no way to predict
what lies ahead with certainty,
the evidence suggests we need
to be prepared to face more
killer storms in the future.
This NOVA program
is available on DVD.
NOVA is also available
for download on iTunes.
unleashing extreme chaos.
Volcanoes, earthquakes,
hurricanes,
and floods can cause
untold devastation.
We may think we've seen
the worst Mother Nature
can throw at us,
but scientists struggling
to understand these disasters
are discovering evidence
that even more extreme events
have struck in the past.
So this is about 13 times
more powerful
than the Pompeii eruption.
They're uncovering clues
that the worst catastrophes
in history could strike again.
More than 200 years ago,
a disaster tore through
the Caribbean.
This is by far the deadliest
hurricane to ever impact
the entire Caribbean.
The Great Hurricane of 1780
was both huge and powerful.
But can we trace its impact
using today's tools
because it appears storms
are becoming more powerful.
We believe that there should be
more intense storms,
perhaps not as many of them are
happening, but when they do,
they'll be stronger.
The clues are here,
buried and hidden
beneath the waves
and beneath the ground.
There's this whole
history in here
about what's happened over time.
Now scientists and
historians come together,
to scour our volatile earth,
to find out if, in the future,
there will be more
"Killer Hurricanes."
Right now on NOVA
Hurricanes,
some of the most powerful
natural forces on earth.
Called typhoons or cyclones
in the Pacific,
these storms can build up over
warm waters and can reach
hundreds of miles across.
Storms like Harvey, Irma, Maria,
and Typhoon Haiyan
are synonymous
with death and destruction.
Hurricanes kill on average
10,000 people a year.
They can cause death.
They can actually destroy
infrastructures, entire cities.
It's just complete devastation,
it's unbelievable.
In 2017, a series of
catastrophic hurricanes...
Harvey, Irma, and Maria...
Impacted millions of people
in the U.S. and the Caribbean.
Entire islands and the city
of Houston were devastated.
Is this the worst that nature
can throw at us?
To find out,
scientists are hunting for clues
in the distant past.
The more we understand
about them,
the better we can predict them.
They're unearthing evidence
of the deadliest
hurricane in Atlantic history...
The Great Hurricane of 1780.
It destroyed every house
in Barbados.
And it devastated
this massive fort.
That storm was
truly exceptional.
And looking even further back
in time,
scientists are discovering that,
a thousand years ago,
major Atlantic hurricanes
may have struck more often.
And then you get this
really big layer here
that dates to
about a thousand years ago.
So were monster hurricanes
more frequent or more powerful
in the past?
And what does this bode
for the future?
Two record-breaking hurricanes
struck the Caribbean
in September 2017.
The first, Irma,
leaves a trail of destruction
across the islands of Barbuda,
St. Maarten, and St. John.
Its 185 mile an hour winds
blow for a record 37 hours.
Then, less than two weeks later,
comes Maria.
Its sustained winds blast the
entire island of Puerto Rico,
destroying the power grid, water
supply, roads, and cell towers.
For weeks, millions are stranded
in the dark without clean water,
food, gas, or phones.
The terrible toll
of these storms
puts them in the record books.
But there is growing evidence
that hurricanes just as powerful
could once have been
more common.
Wayne Neely, a meteorologist
and historian, has come
to the National Archives
on the island of Barbados,
the most easterly
of all the Caribbean islands.
He's here to investigate
the deadliest Atlantic
hurricanes since records began:
The Great Hurricane of 1780.
According to historical
documents,
this storm was so destructive
it killed
an estimated 22,000 people
across the Caribbean.
And on October 10, 1780,
the first place it strikes
is the island of Barbados,
then under British rule.
In the records from the time,
Wayne finds evidence
of the human cost.
Here, in these death records,
we have 4,500 names
of persons who died in
the Great Hurricane of 1780.
Elizabeth Finlay, Thomas Fisher,
Nehimah Fish, William Folks,
Richard Foster, Elizabeth Forte.
These are a few names of persons
who died in that storm
in Barbados.
And in the archives,
Wayne also finds
a harrowing eyewitness account
that describes the fate
that likely befell
many of these people.
It's a letter written
by the commander-in-chief
of the British Forces
in the Leeward Islands.
This is a letter written to the
king by Major General Warren.
"I do not believe that ten
houses are saved
"in the whole island.
"Whole families were buried in
ruins of the inhabitations.
"Many in attempting to escape
were maimed and disabled,
"the ground covered
with mangled bodies
of their friends and relations."
Almost all buildings, whether
stone or wood, were torn apart.
Well, it must have been
a really great storm to destroy
all the buildings on the island,
so you can imagine the horror
and the misery that the
residents of Barbados felt
during the peak of the storm;
it was horrifying and horrific.
You have no home to go to;
you have no food.
The fresh water supply
is now destroyed.
In 1780, the people of Barbados
are far from the only victims.
In the following days, the storm
kills thousands more on islands
to the north and west.
The whole region was devastated.
Islands such as Martinique,
St. Lucia, St. Vincent,
and Grenada all reported
death tolls from the storms.
The wind is going to destroy
your plantations.
It's going to destroy
everything.
You'll lose all your supplies.
In 1780, it's estimated that
22,000 people
are killed immediately.
Most of the victims are slaves,
brought over from Africa
to work on the sugar
plantations.
Then, thousands more die
in the aftermath
from starvation and disease.
It's always the lowest end
of the economic chain
that feels the effects
of these things first.
The slaves are going
to die off first.
And most of them did.
Certainly the 1780 hurricane
was the deadliest hurricane
we know about
in the western hemisphere.
The records also reveal,
just as in 2017,
this storm was one of
three devastating hurricanes
that struck in quick succession.
1780 was a terrible year
for hurricanes.
There were three
incredibly destructive ones.
Only a week earlier, another
hurricane had struck the region.
And then,
just over a week later,
another struck,
also with catastrophic effect.
But the death toll from
the Great Hurricane
overshadows them all.
Even today, storms like
Hurricane Katrina that struck
the Gulf Coast in 2005;
and Hurricane Mitch,
the deadliest Atlantic hurricane
in living memory, which hit
Central America in 1998,
can leave thousands dead
in their wake.
So what makes these
killer storms so unusual?
And will they become
more frequent?
Modern hurricanes, like Harvey,
Irma, and Maria,
are tracked by aircraft
and weather satellites.
What we've learned about them
gives scientists an idea
of how the 1780 storm
likely formed and developed.
On August 27, 2017,
nine days before it makes
landfall in the Caribbean,
Irma begins as a storm off
the west coast of Africa.
As it travels west across
the Atlantic Ocean,
it quickly gathers strength.
Heat rising from
the warm ocean waters
feeds energy
into the storm system.
Hurricanes are like
heat engines.
They actually convert the energy
from the ocean
into motion in the hurricane.
Warm, moist air cools as it
rises, and then condenses.
That releases that energy that
was carried away from the ocean
and that powers the storm.
And one of the reasons
hurricanes are so intense is
the ocean is very warm and the
air at the top of the hurricane
is very cold.
These winds can then spin
into a powerful cyclone,
partly a product
of Earth's rotation,
with rain bands stretching
hundreds of miles across.
August 30... as wind speeds
reach 50 miles an hour,
Irma becomes a named hurricane.
Over the next six days,
it intensifies rapidly.
By the time it slams into
tiny exposed Barbuda
on September 6,
with sustained wind speeds
of a 185 miles an hour,
Irma is a Category 5 hurricane.
It's likely the Great Hurricane
of 1780 formed in a similar way
to this recent superstorm.
But how strong did it get?
Historians are able to piece
together some details
of the storm's strength,
thanks in large part
to ships' records
kept by competing naval powers.
In 1780, the Caribbean
is a battleground
during the
American Revolutionary War.
Four years earlier,
the Americans had announced
their independence,
and the British decided,
"No, you don't.
"We're going to send a bunch
of our troops
over there to stop this."
In October, the area is full of
British and European warships.
There was a lot of European
ships in the area.
You had the French; you had
the Dutch and the Spanish
fighting against
British warships
for control of the Caribbean
and the region.
Like the communities
on the islands,
these ships were vulnerable
to violent hurricanes,
as the British Naval Records
in Barbados reveal.
Looking in the naval records,
you can see the loss
of so many ships...
HMS Laurel, HMS Andromeda,
and HMS Deal Castle,
all lost
in the Great Hurricane of 1780.
The fate of HMS Deal Castle is
depicted in paintings
from the period.
And historical documents reveal
that thousands of sailors
from all sides perished at sea.
So given its devastating scale,
was the Great Hurricane of 1780
more powerful than
more recent killer storms?
Well, we just don't know whether
it was a uniquely powerful
hurricane,
or whether it was just an
ordinarily powerful hurricane
that took a very
destructive path.
Given the lack
of scientific data,
how can experts today track
this megastorm from the past?
Climate historian Mike Chenoweth
has taken up the challenge.
He's scouring old ships' logs
hunting for hidden clues.
And he's uncovered an entry
from October 9,
the day before the hurricane
strikes Barbados.
One thing I found in doing
the research was
the first detection
of the hurricane
by the Spanish frigate Diana.
This is the earliest account
we have of a ship
encountering
the Great Hurricane.
And so they were about 300 miles
east of the island of Trinidad,
off to the southeast
of Barbados,
at 10 degrees of latitude.
"There bore down upon us
a violent hurricane
"which lasted 48 hours
without intermission.
"The wind ran the entire compass
with violent gusts
and the frigate moved heavily
in the swells."
So in several days ahead
of reaching Barbados,
it had already
become a hurricane.
But to quantify the strength
of the hurricane,
Mike faces a major problem.
In 1780, there were no
instruments for measuring
the actual speed of the wind.
The only clues are time of day,
wind direction, and estimates
of wind intensity.
Mike continues with logs
dated to October 10.
So, this is at 6:00
in the morning...
The hurricane has just finished
devastating
the island of Barbados.
Everything is
a complete wreck now.
This ship plot here is for
HMS Albemarle
off the west coast
of the island of Barbados.
They have a hurricane blowing
from the south on this map.
That's the approximate center
of the hurricane at this point
in time, and then we have
other ships off the coast
of St. Lucia reporting
northeast winds,
and another ship
approaching Martinique
with an east-northeast wind.
Mike draws together records
from all the ships
and plots the position of the
storm in six-hour intervals.
In this way, he tracks the storm
as it moves
across the Caribbean.
So from the 11th to the 15th,
this storm is out
in the eastern Caribbean
stirring up the water
with this huge wind field
that just continues to batter
the islands all in the region.
For nine days, the Great
Hurricane ravages the Caribbean
before passing
into the North Atlantic.
And Mike spots two features that
made this storm so destructive.
First, with hurricane force
winds that he estimates
extended up to 75 miles out
from the hurricane's eye,
the storm was vast.
75 miles is about triple
what we usually see
for strong hurricanes
in that area,
the gale force winds extending
out 220 miles to the north.
That means its strongest winds
may have blasted
an even greater area
than Irma's.
The storm was moving forwards
unusually slowly,
ravaging Barbados
for eight hours.
Because the storm is moving
slower than average,
it just had
more opportunity to keep
knocking more buildings down.
You've got thousands
of people dead.
From the ships' logs,
Mike is building up
a more accurate picture
of the path and size
of the 1780 megastorm.
But the logs can't answer
the most pressing question:
how powerful was this storm
by comparison
with hurricanes today?
To answer this question,
scientists are trying
to understand how
different conditions contribute
to creating monster hurricanes.
You have a complex
web of conditions that have
to come together
perfectly to produce this
intensifying storm,
and that's really a challenge.
Scientists agree there
are three key ingredients
for the perfect storm.
First, for a hurricane to grow
in strength and power,
there needs to be a layer of
warm ocean water reaching down
to at least 200 feet.
The hurricanes churn up
cold water
from beneath the warm water
on the surface,
so they cool the surface.
It's like throwing cold water
on a fire.
Second, crosswinds near the top
of the hurricane,
called wind shear,
can't be too strong
or they disrupt
the formation of the storm.
That tends to blow dry air into
the core of a hurricane.
That also is like throwing
cold water on the fire.
And, third,
hurricanes need moisture
throughout the atmosphere.
If all these conditions
come together,
wind speeds within the eyewall
of the hurricane
can rapidly rise.
They become the most powerful
storms on the planet.
On a scale of one to five,
a major hurricane is
a Category 3 storm or above,
with wind speeds
of 111 miles an hour or greater.
You could probably go outside
and walk around
in 75 mile an hour winds...
I wouldn't recommend it.
There's going to be things
flying through the air.
If it was
a Cat 3 or 4 hurricane,
you're not even going
to be able to walk or stand.
Generally, if over half
the buildings
are knocked down, that's usually
a good sign you've got at least
a Category 3 storm.
The deadliest storm ever to hit
the United States
was a Category 4 in Galveston,
Texas, in 1900
with estimates up to
12,000 dead.
Category 5 storms are the most
powerful hurricanes of all,
with wind speeds over
156 miles an hour.
There are very few structures...
Boats, buildings, cars...
That can withstand the force
of a Category 5 hurricane.
As wind speeds increase,
their destructive power grows
even faster.
It's not a sort of linear
change.
It's actually exponential,
so the wind is able to do
a lot more work.
If you double the wind speed,
you increase the destruction
by at least a factor of eight.
So a Category 5 hurricane
is at least
eight times more destructive
than a Category 1.
And recent history reveals
the extreme destructiveness
of these Category 5 storms.
In 2017, Hurricane Maria wrecked
power and water systems
across most of Puerto Rico.
Estimates put the damage
at over $90 billion.
In 1969,
Camille blasted Mississippi,
flattening hundreds
of miles of coastline.
And in 1935 one of the most
intense hurricanes
ever to hit the United States,
the Great Labor Day Hurricane,
ripped through the Florida Keys,
killing over 400 people.
But according to climatologist
Mike Chenoweth,
that the Great Hurricane of 1780
devastated a wider area
and left thousands
more people dead
than any of these modern
Category 5 storms.
And he's found detailed
eyewitness accounts
that reveal another reason why
this unusually large
and slow-moving storm
was so destructive.
Its power didn't come
from the wind alone.
Another devastating force in
a tropical storm is the water,
an intense surge from the sea...
...known as storm surge.
This is what killed most people
when Typhoon Haiyan
slammed into
the Philippines in 2013.
In the Philippines,
more than 60 percent
of the population lives
within a mile of the water.
One of the most powerful storms
ever to strike land,
Haiyan's wind speeds reached
a 195 miles per hour
as it moved slowly
across the islands.
You have the wind driving
this water towards the coast.
As the storm is approaching
landfall,
it's going from deeper water
to more shallow water.
Many people lost their lives in
that storm because of the surge.
Along any coastline, tsunami-
like waves pushed onshore
by hurricane winds can threaten
lives and property.
What you see is a wall of water
that just wipes out
the neighboring houses and trees
and everything before it.
And in some cases, this storm
surge can be ten to 20 feet high
and anything
within several feet to
up to a mile or so
of the coastline
can essentially be wiped out.
Anybody that's told to evacuate
because of the danger
of a storm surge,
they should not think twice
about it; just go.
Every year, millions of people
in the U.S., Central America,
and the Caribbean face the
threat of hurricane storm surge.
And it's storm surge that likely
caused much of the destruction
in Barbados in 1780.
Suddenly, these massive
storm surges came
which carry this
incredible force with them
and devastated the city.
Along the shore on Barbados,
Wayne Neely
is hunting for physical evidence
of the storm surge in 1780.
This is Fort Charles,
just outside the capital,
Bridge Town.
It was entirely rebuilt
after the 1780 hurricane
completely destroyed
the original.
In 1780, before the hurricane,
the fort itself was
a massive structure.
The walls were much higher and
were three to four feet thick.
The size was immense.
For the walls to be destroyed
from that hurricane,
it had to be
a catastrophic storm.
The records describe
an unusually high storm surge,
over 25 feet.
Eyewitness accounts tell us the
hurricane swept heavy cannons
140 yards inland.
Nothing stood in place;
it devastated this fort.
It destroyed every house
in Barbados,
and it devastated the Caribbean.
We had entire fortresses
and batteries of war,
you know, just totally
swept away.
The scale of destruction
reveals the extreme impact
of the 1780 hurricane.
And now, drawing together
all the clues,
it's possible to recreate
what happened.
On the night of October 9, 1780,
the Great Hurricane approaches
Barbados from the southeast.
The storm is
over 300 miles across.
On October 10, winds and rains
lashed the island.
Finally, as the eyewall
approaches land,
the huge winds push up a storm
surge 25 feet high.
It slams into the coast...
and inundates the land.
Ravaging the island
for over eight hours,
it leaves more than 4,000
dead...
And goes on to claim a total
of 22,000 lives
across the Caribbean.
The Great Hurricane of 1780
shows how devastating
a hurricane can be in an exposed
low-lying landscape.
Mike Chenoweth believes
its destructiveness
was unparalleled.
We haven't had a storm like
that since,
so we're talking about something
that's happened only once
in 400 years.
But what are the chances
of it happening again?
We don't know how far back
something similar
might've happened,
and we certainly don't know what
that possibility in future is.
Major hurricanes of Category 3
and above are not common events.
On average, one makes landfall
in the United States
every two years,
and Category 4 and 5 hurricanes
are even less frequent.
Category 5 hurricanes
are very rare.
There are far, far more
Category 1s than Category 5s.
But now, with the buildup
of greenhouse gases
in our atmosphere from
burning fossil fuels,
our climate is changing.
So many scientists like
Kerry Emanuel are predicting
that intense hurricanes
will become more frequent.
But it's a challenging problem.
Today, scientists rely on
complex weather data
from satellites and aircraft
to create computer simulations
that can help them
make predictions.
But this kind of precise data
only goes back a few decades.
We have reasonably accurate data
going back only to about 1970.
And if you go back in time,
we don't have satellites.
And then if you go back before
the 1940s,
we don't have aircraft.
There just isn't enough modern
data to discern patterns
in hurricane behavior.
Better data about hurricanes
in the past would be valuable.
If we have understanding of
the activity, the intensity,
the frequency of storms
a thousand, 2,000 years ago,
then that gives us better
confidence
in our ability to assess
what hurricanes are doing now
and in the future.
But extracting clues about
what hurricanes were doing
thousands of years ago...
Well before detailed
historic records...
Requires some
very clever detective work,
and some of it needs
to be done at sea.
Oceanographer Jeff Donnelly
is looking for evidence
of ancient hurricanes
on the sea floor.
His search has brought him over
1,200 miles west of Barbados,
to Jamaica.
This is Discovery Bay,
on the northern coast.
Jeff and his team want to expand
our understanding of hurricanes
by exploring the deep past.
We're looking into
the sediments to sort of
find these long-term records
to extend our knowledge
back thousands of years.
Jeff focuses on
one part of the bay,
next to a reef too shallow for
the research vessel Atlantis.
The only way to get there is
by building a raft...
and towing it out to position.
A blue hole...
A natural sinkhole created
in the limestone rock.
Jeff is interested
in the sediments trapped
at the bottom of this hole.
The blue hole is really
a good recorder of hurricanes,
so it's sort of
a nice time capsule.
The sediment can go in,
but it never can come back out.
On calm days,
fine grain silt and sand
drift into the hole
and accumulate over time.
But the violent force
of a major hurricane
propels a different kind
of debris into the hole.
When a hurricane will hit,
you'll get really strong winds,
big waves, storm surge.
That all sort of comes up
over the reef here,
and there are really strong
currents associated with that
that will tear up pieces
of coral that transport sand
into the blue hole.
The more intense the hurricane,
the larger the pieces of coral
and sand the waves transport.
And over thousands of years,
this sediment
builds up as layers
inside the blue hole.
The deeper the layers are,
the further back in time
they were laid down.
The team lowers a hollow tube,
vibrates it into the sediments,
and retrieves the sample
trapped inside.
Back on board Atlantis,
Donnelly cuts into the core.
So, we basically can
start at the top,
you know, this might be
what's depositing today,
and then you go back further
in time as you go down the core.
It's mostly fine, silty sand,
but Jeff spots one sediment
layer that's different.
When you get down to the bottom,
this interval here...
and there's really big bits of
shell and coral fragments
in there.
Washing and sieving the sample
reveals larger pieces of coral
mixed up in the sand.
It's quite coarse,
compared to the rest
of the core, but this was all
that material that was ripped up
and washed into this basin.
To Jeff, the coarseness of
the sediments
is clear evidence
of powerful waves,
most likely driven
by a major hurricane,
striking here
sometime in the past.
You'd have to have a quite
a high energy event
to be moving this kind of
sediment from the barrier reef
into that blue hole.
15-foot waves.
It's something like
an intense hurricane strike.
By retrieving organic materials
washed in with the storm,
like twigs and leaves
that contain carbon,
Jeff is able to radiocarbon
date these coarser layers.
It'll take months to know for
sure when this hurricane struck,
but he's dated layers
from cores taken from sites
all across the Caribbean.
So, this is a piece
of a sediment core that we took
in the Bahamas.
This particular section dates
to the 18th century.
See these light bands
here, here, and here
are these hurricane event beds.
They're much coarser than
the sediment around them.
You can really feel the grit
between your fingers.
And he's finding that the most
recent layers exactly match up
with the dates
of modern hurricanes.
We started coming into it, you
know, with a healthy level
of skepticism,
but all the storms you expect
to find end up being there.
That gives him confidence
that his technique is valid.
And now he's finding evidence of
hurricanes long before
historic records began.
At present, we've been able
to go back about 2,000 years
at most sites.
Every time we find a layer that
dates to before 1600, 1700 AD,
we're finding an event
that we never knew occurred.
By plotting the dates
of major hurricanes
back 1,400 years into the past,
Jeff sees a pattern emerge.
For the first 700 years,
during the height
of Mayan civilization,
and as the Vikings
were colonizing Greenland,
it appears powerful hurricanes
were more frequent than today.
Not necessarily any more intense
than the ones we've
experienced today,
they just occurred
much more frequently.
Then, over the next 700 years,
during the Renaissance
in Europe,
and as European settlers
were arriving in the Americas,
the record shows
a marked decrease.
And then, suddenly,
it shuts down.
The Great Hurricane of 1780
falls in the period
where there appears to have been
far fewer major hurricanes,
making it even more unusual.
So, what caused this decline
in hurricane activity
beginning about 700 years ago?
Jeff suspects it might be
partly due
to trends in
sea-surface temperature.
And it turns out
there's a way to recover
ocean temperature data
from the remains
of tiny animals.
We can find out about sea
surface temperatures in the past
by looking at these
fossil corals.
Corals build up giant colonies
that can last
for thousands of years.
Cores drilled out from deep
inside their structures
reveal layers of growth.
These corals grow almost like
trees, so each year,
it puts on a new band of growth,
and you can actually
count back in time.
While forming their skeletons,
corals absorb oxygen
from the seawater.
Oxygen comes in two forms...
Oxygen 16 has eight protons and
eight neutrons in its nucleus.
But oxygen 18
has two extra neutrons
and is more abundant
in the ocean
when temperatures are colder.
By measuring the ratio
of these two forms of oxygen
in the layers
of a coral skeleton,
scientists can calculate
relative ocean temperatures
over many thousands of years.
Using corals to reconstruct
sea surface temperatures
is really precise.
We're able to reconstruct
it right down to the year.
Plotting sea surface temperature
for the Caribbean
over the last 1,400 years
also reveals a trend.
The first 700 years
look generally warmer
than the next 700 years.
The results match
known historical
and scientific records that
chart a changing climate,
from an era known today as
the Medieval Warm Period
to a cooler period
known as the Little Ice Age.
And when Jeff compares
sea-surface temperatures
to his graph of hurricane
activity,
it appears that, in the past,
whenever the sea surface
was warmer, there were more
major hurricanes.
There are a whole variety
of factors that can influence
tropical cyclone activity
or hurricane activity,
but it's clear that there
is this interaction
between sea surface
temperatures and hurricanes.
The pattern seems to fit what is
known about hurricane formation.
The more energy available to
power a storm, it makes sense
that the storms are going
to potentially get stronger.
But these findings
present a puzzle.
1780, the year of
the Great Hurricane,
falls in the generally colder
period of the Little Ice Age.
It appears at first blush
to be quite an anomaly
that this 1780 season
and, actually, that
a couple of decades around it
are actually one of
the most active intervals.
But as Jeff looks more closely
at the sea surface temperatures,
he was able to detect a brief
but noticeable spike
in the decades around 1780.
And cool temperatures
in the atmosphere above
with warm ocean water below
is a known ingredient
for hurricane formation.
And whenever you have two bodies
of very different temperature,
you can create a lot
of energy that way.
So that might explain why in the
middle of the Little Ice Age,
we see, you know, an increase
in hurricane activity.
Jeff's work linking hurricane
events to ocean temperatures
could provide an explanation
for the intensity
of the 1780 hurricane.
And this research could sound
a warning for our future...
...because modern data reveals
that the sea surface temperature
of the Atlantic is now higher
than it was
a thousand years ago,
and is still rising.
We're actually warmer than any
point of the last millennium,
just a fraction of a degree
at this stage,
but the projections are that
that's going to continue.
But not only is it warmer
but it's increasing faster,
at a faster rate than we've seen
over the entire record.
As a result,
will we see major hurricanes
becoming more frequent?
We're likely to go back
into one of those
sort of intervals
where we're getting lots more
intense hurricane strikes.
The temperature
of our oceans is warming.
Greenhouse gases like
carbon dioxide,
generated by burning
fossil fuels,
are building up
in our atmosphere.
These insulate our planet,
holding in more
of the sun's heat,
causing the oceans
to warm more quickly
than we've detected in the past.
The problem right now
is that the rate at which
we're pushing the climate system
is very fast compared to
anything that's happened
in a very, very long time.
Whether this warming climate
means there will be
more Atlantic hurricanes
is still an open question,
but there is a growing agreement
that the hurricanes that do hit
will be stronger.
There is a pretty strong
consensus that,
as the planet continues to warm,
we're going to see
a greater incidence of
the high category hurricanes
in most places.
We believe that there should be
more intense storms.
Perhaps not as many of them
are happening,
but when they do,
they'll be stronger.
So, can scientists predict
where these strong hurricanes
will strike?
Amy Frappier, who studies
ancient climates,
has found an ingenious way to
look into the past for answers.
Compared to the last
four centuries,
she's finding that Atlantic
hurricanes are on the move,
likely heading towards
the big coastal cities
of the eastern United States.
The evidence comes
not from beneath the waves,
but from caves under the ground.
Locked inside stalagmites like
these are the chemical traces
of hurricanes from thousands
of years ago.
So here's a stalagmite
that we collected from Belize,
where we know hurricanes have
been part of the weather.
Rainwater that seeps through
the ground above a cave
dissolves minerals
from the surrounding rock.
Then, as it falls drop by drop
from the ceiling, it leaves
a little bit of this mineral
behind and a chemical signature
of the rainwater itself.
This forms stalagmites
that over the years grow upwards
from the cave floor.
Back in her lab,
Amy slices stalagmites open
and polishes the surfaces.
This reveals a series
of distinct layers.
You can see that there's
this whole history
in here about what's
happened over time.
In this one, it's got
lots of different changes
in color and texture
as we go from the older part
to the younger part at the top.
Hunting for the chemical traces
of a hurricane
in these layers is possible
because rain from hurricanes
is chemically different
from rain
during ordinary storms.
Again, a result thanks
to the difference between
oxygen 16 and oxygen 18,
which has two extra
neutrons in its nucleus.
In an ordinary storm, raindrops
evaporate slightly as they fall.
The lighter oxygen 16
evaporates more readily,
changing the proportions in rain
hitting the ground.
But in a hurricane,
the air is so humid
that there is very little
evaporation.
This means that in hurricane
rain, there's more oxygen 16
than in weaker, short-lived
rainstorms.
Whenever we see that
light oxygen signature,
we know that that
is a fingerprint
for a past hurricane.
To find this chemical signature,
Amy isolates individual layers
in the polished stalagmite,
then drills out
a minute sample as dust.
A mass spectrometer can read out
the chemical traces
locked inside the dust,
and it reveals which layers
are richer in light oxygen,
the signature of hurricane rain.
The results are so accurate
they allow Amy to tell
if a hurricane has hit
in any given year
thousands of years in the past.
The level of detail
is just unprecedented.
We can see
the difference between
years with a storm strike
in Belize
and years without
a storm strike in Belize.
With data from caves
across the Caribbean,
the evidence suggests that the
paths of Atlantic hurricanes
appear to be changing over time.
We're starting to be able
to have enough data
that we can see
not only overall patterns
of storm activity,
but also changes
in storm tracks.
Over a 450-year period,
the average track of hurricanes
has been moving ever closer to
the continental United States.
400 years ago,
the storm strikes were clustered
in the western Caribbean,
around Central America,
and now the storm strikes seem
to be happening
much more frequently
around the U.S. east coast.
It's a trend that Amy
is still exploring.
But based on satellite data,
Kerry Emanuel has come
to a similar conclusion.
We've discovered that
over the last 35 years,
the latitude at which
tropical cyclones
reach their peak intensity
has been shifting away
from the equator at a rate
of about 35 miles per decade.
Kerry thinks that climate change
is driving the recent shift.
What we see when we look
at global warming is that
the fastest warming
is occurring in the Arctic.
Hurricanes like warm waters
and so they're shifting
toward the poles.
In just 30 years, that's over
100 miles closer
to densely populated areas
of the United States
along the Eastern Seaboard.
The last major storm to hit
the northeast coast was
Megastorm Sandy in October 2012.
After leaving a trail of
destruction in the Caribbean,
Sandy approaches the New York-
New Jersey coastline.
Though most of the Atlantic
gets colder as you move north,
Sandy feeds off a ribbon of warm
water that keeps it alive:
the Gulf Stream.
This is a circulating current
that pumps warm water
from the Gulf of Mexico up
and across the Atlantic.
By the time Sandy strikes
on October 29,
it's been downgraded from
a Category 2 hurricane
to a Category 1 storm.
But as Sandy combines
with another North Atlantic
storm system,
it hits with
catastrophic impact.
A 14-foot storm surge
races into New York City,
flooding streets,
tunnels, and subways,
and shorting out
electrical transmission lines.
Across New York and New Jersey,
the storm leaves 60 people dead,
damages 650,000 homes and causes
over $70 billion in damage.
It's just complete devastation,
and, you know, my parents have
lived here for 40 years,
and it's unbelievable.
Superstorm Sandy
was massively large,
and hit
a densely populated area.
Its powerful storm surge
did most of the damage,
but its winds were
not especially strong.
I think many people would be
surprised to know that
Hurricane Sandy, at the time
it was impacting
New York and New Jersey, was not
considered a major hurricane.
Imagine if it had been
a Category 3 or higher.
It has happened before.
The strongest recorded hurricane
to strike this coast
hit nearly 200 years ago.
It's known
in historical records as
the 1821 Norfolk, Long Island,
Hurricane, and is now thought
to have come ashore as
a Category 4 storm,
far more intense and extensive
than Sandy.
Experts estimate that
if this storm struck today,
it would cause over
$100 billion in damage.
Imagine a Category 4 storm
impacting New York...
The flooding, the storm surge,
the winds associated with that.
Cities such as New York
need to be prepared
for this type of threat.
Many factors can affect
hurricane formation,
but as the climate warms,
the threat of major hurricanes
heading up from the Caribbean,
impacting the southern states
and striking
the northeast coast,
is one that climate scientists
are taking seriously.
And they're highlighting
a less well-known danger
of global warming,
one that will make hurricanes
even more destructive.
Warmer oceans cause
water volume to expand.
At the same time,
glaciers are melting.
Sea level
around the world is rising.
If you look at some of
the more recent data,
not only is it rising,
in more recent decades,
it's rising at a faster rate.
At the best guess now is that,
if we don't curb emissions,
we'll be up a meter or three
feet by the end of the century.
The rising sea level
increases the risk
of damaging storm surge.
When that storm surge rides up
on top of higher sea levels,
then it causes
a lot more destruction.
Today, millions of people in
coastal and island communities
are at risk.
With all of this infrastructure
very close to sea level,
we're much more vulnerable
to much smaller changes.
To better understand our future,
scientists are looking
into the past, and what they're
finding leads some to predict
that a hurricane as deadly as
the Great Storm of 1780,
with its huge storm surges,
will likely strike again.
We're going to see another
hurricane like
the Great Hurricane of 1780
again on our shores,
and it's going to hit land
at full intensity.
It's happened once before,
so there's no reason
to not expect it
to happen again.
While there is no way to predict
what lies ahead with certainty,
the evidence suggests we need
to be prepared to face more
killer storms in the future.
This NOVA program
is available on DVD.
NOVA is also available
for download on iTunes.