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A Perfect Planet.
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We live in a world
with a violent atmosphere.
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Rain clouds form, and powerful winds
carry their fresh water around the globe.
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00:01:08,819 --> 00:01:13,574
Without this, our perfect planet
simply couldn't function...
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00:01:14,784 --> 00:01:19,121
...for all life on land
depends on the weather.
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We all know that the weather
can change on a daily, even hourly, basis.
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00:01:40,393 --> 00:01:45,022
But annual weather patterns
have been stable for millennia...
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...and it's this reliability
on which life depends.
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Every year in October, the weather
brings a dramatic transformation
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to this tiny patch of forest in Zambia.
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Storm clouds begin to build.
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00:02:21,851 --> 00:02:24,562
And right on cue,
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straw-coloured fruit bats start to appear.
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00:02:34,697 --> 00:02:39,785
They've travelled hundreds,
if not thousands, of miles to be here.
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00:02:47,543 --> 00:02:51,756
And they always arrive
at exactly the same time.
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They know that these rains
will transform this forest,
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allowing countless fruit trees to ripen.
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00:03:07,229 --> 00:03:11,859
And the bats gorge
on the new-found abundance.
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For just 12 weeks every year,
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this forest becomes home
to ten million fruit bats.
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One of the greatest gatherings
of mammals on Earth,
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all crowding into an area no bigger
than a dozen football pitches.
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From this hub, the bats fan out,
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consuming more than
300,000 tonnes of fruit,
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spreading the seeds
and regenerating the forests.
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Africa's largest wildlife migration -
entirely dependent on the rain
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that comes to this small corner of Zambia
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at the same time each year.
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Every second,
over 13 million tonnes of water
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evaporate from our oceans,
forming clouds.
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The spin of the Earth
and the prevailing winds
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determine where these clouds blow.
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As a consequence,
some places get less rain...
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...and others much more.
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The Amazon rainforest...
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...one of the wettest places on Earth.
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It gets three metres of rain a year...
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...s0 life has learned to deal
with the near-daily downpours.
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00:06:06,867 --> 00:06:11,247
Every year, for thousands of years,
the persistent rains
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00:06:11,372 --> 00:06:15,084
have flooded vast tracts of the Amazon...
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00:06:17,127 --> 00:06:21,799
...turning the jungle
into a seasonal wetland.
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Anything living here
must either climb or swim.
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But there's one extraordinary animal
that has turned this deluge
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from a disaster into an opportunity.
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This fire ant has reached the edge
of her known world.
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Her way forward has now become
blocked by the rising waters.
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She's one of many, and in a few minutes
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their underground home will be submerged.
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Forced to evacuate, workers and soldiers
try to save the larval young.
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As their nest floods,
the colony seems to be doomed.
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But from chaos comes order.
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The fire ants band together,
each locking legs with its neighbours.
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They're building a living raft.
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Each ant is covered in fine hairs
that trap air against its body.
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As the raft forms, this air creates
a cushion for them all to float on.
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This is the power of the colony.
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By working together,
they've become unsinkable.
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And no-one gets left behind.
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Pulled from the shallows, the colony
is now at the mercy of the flood.
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00:09:01,542 --> 00:09:03,585
Holding tight to the larvae
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and keeping their queen hidden
at the centre of the raft,
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the colony drifts into deeper water...
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...where they're vulnerable to fish
that now swim through the flooded forest.
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Those that lose their grip
must get back to the safety of the raft.
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00:09:46,170 --> 00:09:50,174
With jaws that join to become
a surgical needle,
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this pond skater could suck an ant dry.
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00:10:05,814 --> 00:10:12,237
But together, the colony is strong,
and it's time to repel boarders.
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00:10:24,166 --> 00:10:27,753
The ants can travel like this for weeks.
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They've even come to depend
on the flood to carry them
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to new feeding grounds.
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00:10:50,400 --> 00:10:54,530
At last,
the ants can make their raft secure.
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00:11:00,619 --> 00:11:03,956
Surging forward,
they claim their new home...
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...evicting current tenants
without hesitation.
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One of the first to safety
is their larval queen,
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carried from the heart of the raft.
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This palm will be their home
for the next three months,
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until the floodwaters recede
and they can head back underground.
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The average temperature of our planet
hasn't varied
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by more than a single degree Celsius
in 10,000 years.
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This has made our climate stable,
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allowing animals
to fine-tune their behaviour
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around predictable weather patterns.
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October in the Amazon.
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The heaviest rains have come to an end,
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and the falling river level exposes
a new landscape.
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00:12:26,330 --> 00:12:31,877
Three weeks ago,
these mile-wide sandbars didn't exist.
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00:12:34,338 --> 00:12:38,759
In another three months,
they'll be back under water.
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00:12:41,345 --> 00:12:47,768
But now they provide a crucial opportunity
for giant river turtles.
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They've been coming here at precisely
this time of year for generations.
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50,000 of them -
a quarter of the world's population.
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00:13:10,582 --> 00:13:12,542
They're all here for one reason.
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But their window of opportunity is short,
so timing is everything.
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Scaling the three-metre-high banks
will take this female higher and drier
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than she's been for months.
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She's come here to lay her eggs.
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00:13:41,321 --> 00:13:43,365
But others have beaten her to it.
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00:13:54,418 --> 00:14:00,382
The early arrivals have already claimed
nearly every inch of the beach...
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00:14:01,633 --> 00:14:04,177
...and there are still many more turtles
to come.
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Wherever she turns, the space is taken.
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00:14:23,572 --> 00:14:27,576
But being fashionably late
does have an advantage.
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Had she arrived earlier,
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her eggs might have been dug up
by those searching for somewhere to lay.
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She's found her spot.
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Settling down, she lays nearly 100 eggs.
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Burying them keeps them safe
from predators,
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and the warm sand incubates the clutch.
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They must hatch before the river rises
again and floods the sandbar.
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Any turtles that lay after her
may have left it too late.
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Hopefully, she has got her timing right.
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Two months on,
and the hatchlings emerge into the world.
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They were laid at the perfect time.
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Hundreds scramble for the river
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just as the water starts to rise.
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Those still to hatch aren't so lucky.
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This year,
the heavy rains have returned early.
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The nesting beach is beginning to flood.
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Most hatchlings can escape in time.
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Those still below ground...
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...will drown in their nests.
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00:17:33,553 --> 00:17:38,475
For thousands of years, giant
river turtles have timed their breeding
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around the Amazon's
reliable cycles of rain.
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But today, our weather is changing.
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Disastrous early floods like this
used to happen once every 20 years.
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00:18:01,373 --> 00:18:06,795
Now the turtles have to deal with them
every four.
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00:18:21,977 --> 00:18:25,981
Winds may carry huge amounts
of rain to the Amazon,
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00:18:26,106 --> 00:18:31,236
but they don't provide this service
to every corner of the planet.
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00:18:32,988 --> 00:18:39,494
A third of the land receives
less than 25 centimetres of rain a year.
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Deserts are scarred by desiccating winds
and baked by the sun.
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00:18:53,049 --> 00:18:58,555
But even weather as challenging as this
can be perfect for the locals.
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As darkness falls
in the coastal deserts of South Africa,
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the dunes come alive...
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...with the call
of a surprising desert dweller.
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A rain frog - not what you'd expect
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in a place that gets
just seven centimetres of rain a year.
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00:19:52,776 --> 00:19:56,780
To survive here, she has to avoid
the heat of the day
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00:19:56,905 --> 00:19:58,907
buried in the sand.
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00:20:01,618 --> 00:20:07,332
But each night, she heads out
on her hunt for moisture.
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00:20:11,294 --> 00:20:15,799
Short stumpy legs and a plump body
are ideal for digging...
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...but not so good for getting around.
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00:20:25,975 --> 00:20:32,565
She can't hop,
so she waddles across the dunes.
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00:20:40,323 --> 00:20:44,744
The world's slowest steeplechaser.
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Obstacles are tackled
with dogged perseverance.
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She can travel
a whopping 38 metres a night,
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00:21:05,557 --> 00:21:10,979
no mean feat when you're the same size
and shape as a marshmallow.
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Termites.
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00:21:18,945 --> 00:21:22,490
They are 75% water...
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...a meal and a drink in one.
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But she's not the most agile predator.
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00:21:37,130 --> 00:21:41,217
Maybe if they just came a little closer...
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00:21:45,847 --> 00:21:47,307
Oh, dear.
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00:21:49,893 --> 00:21:52,770
Perhaps if they stop moving...
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At last!
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00:22:17,712 --> 00:22:21,591
But now she has another challenge.
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To swallow her food, she must squash in
her eyeballs to push it down her throat.
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Termites may be juicy,
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but they don't provide her
with quite enough water to survive.
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It rarely rains here,
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00:22:49,911 --> 00:22:55,500
but coastal deserts do get
another reliable source of moisture.
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00:23:07,220 --> 00:23:08,221
At night,
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cool moist air is blown in from the ocean,
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forming fog banks that shroud
the desert in mist.
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It condenses on vegetation,
wetting the sand beneath.
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00:23:33,413 --> 00:23:38,960
So it's here that she waits,
absorbing moisture through her skin.
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Rain frogs are so dependent on this water
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that they can only survive in places
with at least 100 days of fog a year.
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00:23:59,897 --> 00:24:05,069
And on the foggiest nights, when
other frogs have emerged onto the dunes,
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00:24:05,194 --> 00:24:09,198
she takes her opportunity to find love.
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00:24:16,914 --> 00:24:20,877
Male rain frogs are smaller
than the females,
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and his stubby legs
make it hard to hold on,
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so he glues himself onto her back.
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Still locked in their embrace,
the pair head back beneath the sand,
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where they'll lay their eggs,
safe from the heat of the desert sun.
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00:25:01,501 --> 00:25:05,213
But there's one desert that gets so cold
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that liquid water simply can't exist.
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00:25:12,470 --> 00:25:16,474
Winter in Mongolia's Gobi Desert...
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...40 degrees below freezing.
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One of the driest and most extreme
environments in the world.
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00:25:35,660 --> 00:25:39,497
Most animals can't survive
weather like this...
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00:25:42,125 --> 00:25:48,047
...but there's one unique mammal
that manages to eke out a living here.
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00:25:50,842 --> 00:25:52,844
The Gobi is home
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to the last 1,000 wild Bactrian camels
on Earth...
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00:26:00,101 --> 00:26:03,020
...surviving at the very edge
of what's possible.
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00:26:06,816 --> 00:26:12,905
Even camels need moisture,
but any water here is now frozen solid.
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00:26:16,993 --> 00:26:20,163
It's down to the bull to find a solution.
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00:26:27,378 --> 00:26:33,426
Setting off with his herd, his search
could cover thousands of square miles.
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00:26:39,766 --> 00:26:44,645
Driving them forward,
he can keep going for days on end.
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00:26:55,865 --> 00:26:59,243
Herds come together
from across their vast range...
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00:27:00,995 --> 00:27:03,289
...all looking for the same thing.
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00:27:12,215 --> 00:27:18,095
These long-distance specialists
can smell moisture from 30 miles away...
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00:27:19,180 --> 00:27:21,140
...and they've picked up a scent.
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00:27:26,479 --> 00:27:30,525
Even in the Gobi,
one of the driest places on Earth,
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00:27:30,650 --> 00:27:35,154
wind can provide
a rare source of moisture.
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00:27:37,406 --> 00:27:41,661
Snow is blown to this desert from Siberia.
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00:27:43,704 --> 00:27:49,001
Where it settles is impossible to predict,
and it may not last long.
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00:27:56,509 --> 00:28:01,848
But for now, at least, this bull has found
what he's been searching for.
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00:28:12,567 --> 00:28:14,527
In the cold, dry air,
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00:28:14,652 --> 00:28:16,737
snow doesn't melt...
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00:28:18,865 --> 00:28:21,158
...s0 it must be eaten.
199
00:28:30,710 --> 00:28:35,047
The Gobi's windblown snow is a lifeline
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00:28:35,172 --> 00:28:38,426
that will sustain his herd
throughout the winter.
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00:28:46,767 --> 00:28:50,021
Even in this most hostile of places,
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00:28:50,146 --> 00:28:54,609
weather still provides just enough
for survival.
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00:29:06,954 --> 00:29:11,250
The largest, most unpredictable weather
on the planet
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starts far out at sea.
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00:29:19,926 --> 00:29:24,472
Hurricanes, typhoons and tropical cyclones
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00:29:24,597 --> 00:29:28,434
are violent, short-lived megastorms.
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00:29:30,102 --> 00:29:33,189
But there's a far more reliable
weather system
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00:29:33,314 --> 00:29:35,524
that originates over the ocean...
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00:29:36,734 --> 00:29:41,238
...one that is eagerly anticipated
by all in its path.
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00:29:44,408 --> 00:29:51,165
Monsoons are seasonal winds that blow
at the same time each year...
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00:29:53,751 --> 00:29:58,714
...and they carry colossal amounts
of water from the ocean to the land.
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00:30:06,597 --> 00:30:08,182
Christmas Island.
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00:30:09,767 --> 00:30:13,187
A remote speck of rock
in the Indian Ocean.
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00:30:18,109 --> 00:30:24,448
For the last four months, its forest
interior has remained dry and dusty.
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00:30:27,618 --> 00:30:31,664
Life here is waiting for change.
216
00:30:35,042 --> 00:30:40,047
In November, the first storms
of the monsoon reach the island.
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00:30:58,441 --> 00:31:02,945
They're a welcome relief for those
that have suffered through the dry.
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00:31:07,783 --> 00:31:12,955
And they are vital for the island's
most numerous residents.
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00:31:27,470 --> 00:31:31,140
The red crabs of Christmas Island.
220
00:31:34,727 --> 00:31:39,273
They've spent the dry season
sheltering in damp burrows
221
00:31:39,398 --> 00:31:40,900
beneath the leaf litter.
222
00:31:44,445 --> 00:31:48,491
Crabs breathe through gills
that must be kept moist.
223
00:31:53,537 --> 00:31:56,832
So it's only with the return
of the annual monsoon
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00:31:56,957 --> 00:32:01,253
that these land crabs can finally emerge.
225
00:32:08,928 --> 00:32:15,226
With the humidity now high enough,
they can begin an epic trek to the coast.
226
00:32:28,114 --> 00:32:33,327
Every red crab comes together
from across the island,
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00:32:33,452 --> 00:32:36,205
and they do so in their millions.
228
00:32:37,665 --> 00:32:41,210
50 million, to be precise.
229
00:32:55,891 --> 00:33:01,897
They've come to release their eggs
that can only develop in the ocean.
230
00:33:03,357 --> 00:33:06,318
There's just one small problem.
231
00:33:07,403 --> 00:33:08,946
They may be crabs...
232
00:33:10,281 --> 00:33:12,449
...but they can't swim.
233
00:33:16,412 --> 00:33:18,831
They're scared of the sea.
234
00:33:33,345 --> 00:33:35,389
But they don't have a choice.
235
00:33:37,057 --> 00:33:41,353
They must release their eggs
on the highest tide.
236
00:33:48,027 --> 00:33:51,947
Each carries around 100,000 eggs,
237
00:33:52,072 --> 00:33:54,783
so over just two or three nights,
238
00:33:54,909 --> 00:33:58,162
trillions are released into the ocean...
239
00:34:00,706 --> 00:34:04,460
...though some are more successful
than others.
240
00:34:30,527 --> 00:34:35,449
Once their work is done,
the crabs will return to the forest.
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00:34:52,967 --> 00:34:55,886
Then, four weeks later,
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00:34:56,011 --> 00:34:58,722
on the next highest tide...
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00:35:03,978 --> 00:35:06,272
...having hatched out to sea,
244
00:35:06,397 --> 00:35:11,860
a new generation of red crabs
returns to the same beach.
245
00:35:13,404 --> 00:35:15,823
In good years like this one,
246
00:35:15,948 --> 00:35:20,119
countless millions arrive
back on the shores of Christmas Island,
247
00:35:20,244 --> 00:35:22,788
turning the beaches red.
248
00:35:40,723 --> 00:35:45,561
Like their parents, they also need
moisture in the air to breathe...
249
00:35:48,230 --> 00:35:50,482
...50 before the rains move on,
250
00:35:50,607 --> 00:35:56,739
the young crabs must undertake
their own epic journey into the forest,
251
00:35:56,864 --> 00:36:00,367
where they'll wait out
the next few months of dry.
252
00:36:21,555 --> 00:36:23,349
The Christmas Island crab -
253
00:36:23,474 --> 00:36:28,562
entirely reliant on the return
of the monsoon.
254
00:36:39,865 --> 00:36:45,996
The annual rhythms of the weather
shape life across our planet.
255
00:36:48,540 --> 00:36:50,793
In some parts of the world,
256
00:36:50,918 --> 00:36:53,545
seasonal cycles of wet and dry
257
00:36:53,670 --> 00:36:55,589
can bring dramatic change.
258
00:36:58,425 --> 00:37:03,347
And there are few places where this is
more apparent than Southern Africa.
259
00:37:10,854 --> 00:37:12,856
The Zambezi River.
260
00:37:14,775 --> 00:37:21,281
It flows across six countries
and drains half a million square miles.
261
00:37:35,754 --> 00:37:38,841
At the peak of the wet season,
262
00:37:38,966 --> 00:37:42,052
5,000 tonnes of water cascade
263
00:37:42,177 --> 00:37:45,389
over Victoria Falls every second.
264
00:37:48,350 --> 00:37:52,187
And yet, each year when the rains stop,
265
00:37:52,312 --> 00:37:55,399
these falls run dry.
266
00:38:03,574 --> 00:38:07,244
It's almost as if someone
turns off the tap.
267
00:38:12,833 --> 00:38:14,084
May.
268
00:38:17,796 --> 00:38:19,506
December.
269
00:38:22,968 --> 00:38:24,470
Wet season.
270
00:38:28,557 --> 00:38:30,392
Dry season.
271
00:38:32,436 --> 00:38:37,149
It's happened like this
for thousands of years.
272
00:38:42,905 --> 00:38:47,868
But there are signs
that the weather here is changing.
273
00:38:48,994 --> 00:38:50,245
In recent years,
274
00:38:50,370 --> 00:38:56,168
the volume of water flowing over
Victoria Falls has dropped by half...
275
00:39:01,006 --> 00:39:04,343
...a concern for animals
that have come to rely on
276
00:39:04,468 --> 00:39:08,180
the natural rhythms of wet and dry.
277
00:39:21,693 --> 00:39:27,950
Zambia's Luangwa River
is @ major tributary of the Zambezi.
278
00:39:29,785 --> 00:39:32,913
Every year, as the dry season takes hold,
279
00:39:33,038 --> 00:39:36,583
it dwindles into pools.
280
00:39:39,628 --> 00:39:43,423
Accommodation starts to get tight
for the locals.
281
00:39:47,469 --> 00:39:52,432
With no other water around,
the river becomes a magnet for visitors.
282
00:39:58,855 --> 00:40:03,360
Millions of red-billed quelea
flock to the water's edge.
283
00:40:08,365 --> 00:40:12,327
These seed-eaters
need to drink every day...
284
00:40:32,222 --> 00:40:34,933
...and Nile crocodiles know it.
285
00:40:36,602 --> 00:40:38,979
They may not have eaten for six months.
286
00:40:40,397 --> 00:40:45,277
For them, the dry season
is the start of the good times.
287
00:40:55,412 --> 00:41:00,083
And they are not the only ones
to depend on this time of year.
288
00:41:05,797 --> 00:41:09,801
Carmine bee-eaters have flown
hundreds of miles
289
00:41:09,926 --> 00:41:12,763
from the rainforests of the Congo...
290
00:41:14,014 --> 00:41:17,017
...arriving at the peak of the dry season,
291
00:41:17,142 --> 00:41:22,481
when steep sandbanks
are exposed by the falling water.
292
00:41:28,654 --> 00:41:34,368
They're a perfect place to nest,
out of reach of predators from above.
293
00:41:44,711 --> 00:41:50,133
Bee-eater burrows can extend
for two metres into the soft river sand.
294
00:41:51,385 --> 00:41:54,513
Already home to 6,000 nests,
295
00:41:54,638 --> 00:41:59,643
real estate at Bee-eater Towers
is in high demand.
296
00:42:03,814 --> 00:42:07,567
But it pays not to build too close
to the neighbours.
297
00:42:18,912 --> 00:42:23,709
As more birds arrive, competition
for the best nesting sites heats up.
298
00:42:35,679 --> 00:42:37,514
It's thirsty work.
299
00:42:48,650 --> 00:42:52,946
In the sudden commotion,
they're vulnerable from below...
300
00:42:55,157 --> 00:42:56,366
...and above.
301
00:43:00,954 --> 00:43:03,373
African fish eagles.
302
00:43:12,048 --> 00:43:14,926
They are permanent residents here.
303
00:43:15,051 --> 00:43:20,098
But at this time of the year,
they don't just eat fish.
304
00:43:24,644 --> 00:43:28,231
The safest place to be is inside a burrow.
305
00:43:30,192 --> 00:43:36,072
But an eagle fly-by sends shockwaves
of panic through the colony.
306
00:43:48,543 --> 00:43:54,591
The eagle's strategy is to pin
their prey against the river bank.
307
00:43:59,095 --> 00:44:04,017
With the colony in disarray,
the predators have the advantage.
308
00:44:46,393 --> 00:44:50,397
These fish eagles also choose
to breed in the dry season
309
00:44:50,522 --> 00:44:54,776
because they need the bee-eaters
as food for their chicks.
310
00:45:02,659 --> 00:45:07,747
But this year's dry season
shows no sign of letting up.
311
00:45:15,797 --> 00:45:18,842
Parts of the river are now bone dry,
312
00:45:18,967 --> 00:45:22,971
forcing huge male hippos from their home.
313
00:45:34,190 --> 00:45:35,984
With nowhere left to turn,
314
00:45:36,109 --> 00:45:40,113
they must converge
on the few remaining patches of water.
315
00:45:41,865 --> 00:45:44,951
But these are already occupied.
316
00:45:57,422 --> 00:45:59,966
The resident bull here
317
00:46:00,091 --> 00:46:04,596
can't tolerate another big male
in his shrinking pool.
318
00:46:36,211 --> 00:46:38,964
The newcomer is banished.
319
00:46:51,309 --> 00:46:54,187
Still, the sun bakes the land...
320
00:46:57,148 --> 00:47:01,069
...with devastating consequences.
321
00:47:34,019 --> 00:47:37,147
Hundreds of nests are wiped out.
322
00:47:45,572 --> 00:47:49,659
Southern Africa has experienced
dry seasons
323
00:47:49,784 --> 00:47:52,787
for thousands of years.
324
00:47:53,955 --> 00:47:56,708
But this is something different.
325
00:48:01,546 --> 00:48:07,969
Record high temperatures
and the lowest rainfall in nearly 40 years
326
00:48:08,094 --> 00:48:14,142
have thrown parts of Africa into
one of the worst droughts in a century.
327
00:48:29,449 --> 00:48:35,288
Across the planet,
our once stable climate is changing.
328
00:48:40,835 --> 00:48:43,004
Weather is less reliable...
329
00:48:45,799 --> 00:48:48,927
...and is getting more extreme.
330
00:48:52,931 --> 00:48:55,600
Wildfires are becoming more frequent.
331
00:49:12,617 --> 00:49:15,036
Droughts are more intense.
332
00:49:26,506 --> 00:49:30,969
And storms are more ferocious.
333
00:49:34,848 --> 00:49:40,311
All this from a recent rise
in global temperatures
334
00:49:40,436 --> 00:49:43,439
of just a single degree Celsius.
335
00:49:45,066 --> 00:49:48,778
Yet if climate change continues unchecked,
336
00:49:48,903 --> 00:49:54,993
we may see a rise of almost five degrees
by the end of the century.
337
00:49:57,036 --> 00:50:01,541
We can only imagine what this will do
to our weather.
28663
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