The Earth is our home.
Our natural environment results from complex relations
between the Sun, the oceans, and the atmosphere.
The polar ice and the tropical heat
represent the extremes of our planet's climate.
In reality, this is a very narrow temperature band,
completely different from any other planet we've observed.
The stability of the Earth's environment
has allowed life to emerge,
and life has changed the planet.
As far as we know,
the Earth is the only planet in the universe
to have given rise to life.
(bright inspiring music)
The Orion Nebula is a vast cloud of gas and dust
in the Orion constellation.
It's a place where new stars are being created.
As part of the nebula condenses, it separates into clumps.
As each clump contracts under its own gravitation,
it begins to swirl flattening into a disk.
They are called protoplanetary disks or proplets.
In the center of a proplet,
as the molecules are squeezed together,
a fusion reaction begins and a star ignites.
Some proplets, occurring close to an established star,
shine brightly under the influence of their neighbor.
While this makes them easier to observe,
the glowing gas and dust is being stripped away
by the stellar winds from the adjacent star.
Dark proplets, only observable as silhouettes,
maintain their surrounding ring of gas and dust.
As the system matures,
this stellar debris will form a planetary system.
The Hubble Space Telescope has recorded
numerous examples of this process
enough for astronomers to understand
that the formation of planets is commonplace.
This is how our own sun started its life
4.6 billion years ago.
But the planets would take longer to emerge.
Small grains within the disk began accreting,
forming planetesimals.
The larger a clump became,
the stronger its gravitational attraction,
in turn leading to more rapid growth.
An early version of Jupiter would have been
the first to coalesce completely clearing its orbit.
Around a core of heavy metal and rock,
Jupiter's atmosphere, mainly of hydrogen,
was compressed by its strong gravitation.
Any solid surface lay beneath thousands
of kilometers of liquid gas.
Our observations of exoplanets
have revealed Jupiter-sized gas giants
orbiting close to their stars.
Astronomers believe the young Jupiter
would have began a track toward the Sun
dragging asteroids and comets in with it.
But Jupiter's inward path reversed
as it was pushed into an orbital resonance
with the emerging Saturn.
Not all of the objects forming
in the early solar system stayed orbiting the Sun.
Smaller objects passing a planet
would be deflected by the stronger gravitation
or even captured becoming a moon.
It is thought that there were up to 20 smaller planets
orbiting in the inner solar system
from which the four remaining terrestrial planets
were formed.
At this time, collisions in the developing planetary system
were common, and evidence from the Apollo moon rocks
suggest an impact between an early earth
and an ancestor of our moon
was important in our planet's evolution.
(bang)
The Earth has a larger than expected iron core,
and gravitational analysis of the Moon
suggests its core is lighter than expected.
A collision between the bodies would explain
the Moon's loss of much of its heavy material
to the more massive Earth.
The impact was a glancing blow
that set the Earth rapidly spinning with a 5-hour day.
The Moon that we know coalesced from the molten debris.
Although our moon is not the largest in the solar system,
it is closer in mass to its parent planet
than any other moon.
The stabilizing effect that the Moon has
upon the Earth's rotation is significant.
Over long periods, the Earth's axis will vary
by as much as one degree.
Without the Moon's influence,
this variation could be as much as 85 degrees
with drastic implications for the climate stability.
The debris in the early solar system
was cleared by the planets
in a period called the heavy bombardment.
The emerging Earth was peppered with asteroids
and comets, delivering water necessary for life.
While tectonic forces erased
the bombardment scars from Earth,
the Moon, which injured the same travails
is still covered with craters.
When chaos in the developing solar system settled down,
the young Earth was in a unique position.
The Earth's distance from the Sun was just right
for the abundance of water on the planet
to exist in liquid form.
As the Moon had drifted away,
the planet's rapid rotation had slowed
and the Sun's heat was evenly shared across the surface.
The Earth's large metallic core,
combined with the planet's rotation,
meant that a magnetic field stretched out
around the planet, deflecting the charged solar wind
and protecting the surface from extremes
of solar radiation.
In a hostile universe,
the Earth was a uniquely benign environment.
The geological record shows
that around 2.7 billion years ago,
oxygen began occurring in the atmosphere.
The vast iron ore regions of Western Australia
were formed as iron in the oceans reacted
with the new abundance of oxygen to form iron oxide.
Simple plant life was using the sunlight
and carbon dioxide to live
and it produced highly reactive oxygen
as a waste product.
This enabled more complex life to emerge,
building an intricate web of interrelated plants
and animals completely transforming the planet.
The change in the atmosphere
had other dramatic consequences.
Oxygen stripped much of the highly insulating gases
from the air, drastically cooling the Earth.
A sequence of ice ages began.
Though there is an abundance of evidence
showing planetary glaciation punctuated by warm periods,
the factors triggering these cycles are complex.
Fault lines are clues to the movement of continents
leading to diversions of ocean currents.
The effect of volcanic activity on the atmosphere
and changes in the direction of the Earth's axis
with regard to our planet's elliptical orbit around the Sun,
all contributors to long-term fluctuations
in the Earth's climate.
Analysis of ice cores deposited in the Antarctic
or Greenland is an accurate way
to see how the composition of the atmosphere
has changed over the previous 800,000 years.
Bubbles of air caught between snowflakes
before being rigidly trapped as the snow becomes ice
can be accurately sampled.
One thing is clear.
Carbon dioxide reaches a peak
of around 270 parts per million
during the warm periods,
and drops to approximately 170 parts per million
when glaciation is at its greatest.
But from this data, it's hard to know
if extra CO2 causes the warming
or the warming leads to extra CO2.
In 1958, Dave Keeling working for the Scripps Institute
began recording accurate levels of atmospheric CO2
at the Mauna Loa Observatory in Hawaii.
It was the beginning of a unique record
known as the Keeling curves.
Keeling's graph revealed a seasonal variation
corresponding to spring and summer
in the Northern hemisphere,
where landmass and plant cover is greater.
During the Northern spring and into the summer,
CO2 levels dropped because of the increase
in photosynthesis.
By the 1970s, a disturbing trend had emerged.
CO2 levels were in a steady rise.
At first, there was uncertainty about the implications.
Extra CO2 could trap more heat
leading to a warming effect,
known as the greenhouse effect.
But some scientists were worried
that aerosol pollution could attenuate
levels of sunlight reaching the planet
resulting in a cooling environment.
As the decades passed,
different pieces of evidence were collected.
Drill cores from the ocean floor
revealed that ice ages had been triggered
by Milankovitch cycles,
the variations between Earth's tilt
and its elliptical orbit.
Though these effects were minor,
the correlation was obvious.
If such a small nudge could alter the climate,
perhaps changes in CO2 could as well.
Scientists were realizing just how poorly
they understood planet Earth.
(bright music)
A Thor-Delta rocket blasts aloft
from Cape Canaveral, carrying a robot weatherman
into orbit for America's--
At the beginning of the space age,
scientists were keen to make weather observations
from orbit.
Launched in 1960, Tiros-1
was the first weather satellite.
It was equipped with two TV cameras,
regularly transmitting images of global cloud patterns.
It provided meteorologists with a unique view
and it was followed by improved versions.
Because these early satellites
were in highly inclined, low earth orbits,
the data gathered covered the whole planet
and it was shared across the world.
Since 1873, nations have been cooperating
on weather prediction
via the International Meteorological Organization,
which in 1951, became the World Meteorological Organization,
an arm of the United Nations headquartered in Geneva.
With a UN resolution calling for international cooperation
and the peaceful uses of outer space,
weather satellites of different nations
were soon being coordinated
for the benefit of all mankind.
In 1964, the Nimbus program began.
The series of seven satellites
included a more sophisticated set of sensors.
Nimbus was a testbed for new technologies
and it gathered data about different areas.
Along with cloud patterns was information
about the atmosphere and sea ice.
This was the pre-digital age
and all electronic image data was burnt to
and stored on 70-millimeter film.
Little thought was given to establishing
an archive for future reference.
The Nimbus program was an early example
of Earth observation
rather than just a group of weather satellites,
and meteorologists started seeing the planet
as a complex and interconnected system.
Today, a fleet of satellites is in operation
monitoring the atmosphere, the oceans,
the ice, the land, and the biosphere.
It is now understood that ice,
particularly sea ice, plays an important role
in the Earth's climate system.
Polar ice slowly flows to the coasts
where it melts, providing a source of cold water
that drives the ocean currents
responsible for the transfer of heat
from the equatorial regions to the poles.
These currents also move nutrition,
which is important for the survival of life.
Global winds also circulate water via clouds,
keeping the land moist and able to support vegetation.
Plant life in both the oceans and the atmosphere
removes CO2 from the air
and replenishes the atmospheric oxygen.
Both the ice known as the cryosphere
and the clouds reflect a proportion
of the Sun's energy back out into space.
The extent of the ice and cloud cover
are important factors in the Earth's energy budget.
As ice melts, it exposes ocean or rock,
which absorbs more solar energy.
Similarly, cloud cover, or the absence of it,
will have an effect upon the land or sea beneath.
Vegetation is also an important climate factor
as land plants pump huge amounts of water vapor
into the atmosphere.
But things are changing.
Humanity, simply through weight of numbers,
is influencing key elements
of the planet's climate system.
In 50 years, the Earth's human population has risen
from just over 3.5 billion to 7.7 billion today.
More people need more resources.
And while there have been revolutions
in agriculture and in technology,
the Earth's reserves are not limitless.
In 1979, Europe began launching spacecraft.
And while the new Earth observation satellites
were revealing changes,
scientists were reluctant to reach conclusions
about long-term trends.
They understood that there was a certain amount
of variability in the planet's climate cycle.
And though climate science knew about the steady rise
in atmospheric CO2 revealed by the Keeling curve,
researchers were looking for additional, solid evidence
that change caused by human activity was happening.
Since 1913, spectroscopy had revealed
that a layer of ozone in the stratosphere
blocked harmful UV sunlight
from reaching the ground.
In 1974, Mario Molina,
a postdoctoral fellow working on hot atom chemistry,
published a paper suggesting that the family
of industrial chemicals known as chlorofluorocarbons,
or CFCs, could damage the ozone layer.
In the 1980s, meteorologists working in Antarctica
found the evidence.
The polar vortex above the Southern continent
concentrates the CFCs in the stratosphere.
Mother of pearl clouds in the polar skies
contain ice crystals, which,
in combination with ultraviolet,
split chlorine from the CFC molecule.
Each chlorine atom can break down
over 100,000 ozone molecules.
A large area centered over Antarctica
showed almost no ozone.
It became known as the hole in the ozone layer.
The United Nations began talks
aimed at limiting the production of CFCs.
And in 1989, an international treaty,
known as the Montreal protocol,
kept the production of CFCs
and ultimately resulted in a 10-year phaseout
of CFC production.
All countries signed the agreement
and the Montreal protocol is seen as a model
of international cooperation.
In the 1980s, an upward trend
in global temperature averages
was becoming clear,
and a scientific consensus emerged
that the burning of fossil fuels
was altering the balance of gases in the atmosphere.
Most of our planet's freshwater
is locked in the polar ice caps.
61% of this ice covers the Antarctic continent.
In the North, Greenland is also covered by an ice sheet.
There is no land mass at the North pole,
but a large area of sea ice grows
and shrinks with the seasons.
Seasonal sea ice also fringes Greenland and Antarctica.
Ice shelves are a third manifestation of polar ice.
These are thick layers of ice
that extend into the ocean from the mouths of glaciers.
Periodically icebergs will break away from these regions.
These areas are important to the circulation
of global winds and ocean currents.
And since 2002, NASA has tracked the prevalence of water
in general and ice in particular
via the Grace satellites,
which were recently replaced by a similar pair
of Grace Follow On satellites.
The two follow the same orbit
and minute changes in the Earth's gravitational field
will cause them to change speed
with a variation in the distance between them.
This data is accurately measured,
allowing researchers to record changes
due to variations in groundwater
or in ice thickness.
During the life of the first Grace mission,
Greenland lost 285 gigatons of ice per year.
On average, Antarctica lost 137 gigatons per year.
From 2005 to 2016,
sea levels rose by 3.7 centimeters
due to melting ice sheets
and to expansion of sea water.
Sea levels have been monitored from space since 1992,
initially with the Topex Poseidon satellite,
and more recently, with the Jason series of satellites.
Jason-3 uses a precision radar altimeter
to measure regional and global variation in sea levels.
In the 20 years to 2014,
the average rise was six centimeters,
but the increase is not uniform.
The red areas show the greatest rise
with white representing no change
and blue signifying a decrease.
The unevenness of the sea surface is due
to a complex interaction between ocean currents,
the Earth's spin, and the topography of the ocean floor.
All these factors must be accounted for to arrive
at a baseline against which to measure changes.
These blue areas in the Atlantic
show a shift in the Gulfstream.
The Camargue region of Southern France
is a low lying area at the delta of the Rhone river.
In the 1980s, a sea wall was built
to prevent the encroaching Mediterranean.
Over the last 30 years, the coastline here
has been pushed back by several hundred meters.
Scientists are convinced that a warming global climate
is responsible, and that our reliance
on the burning of fossil fuels has led
to an excess of carbon dioxide in the atmosphere,
which traps heat.
93% of this heat has been taken up by the oceans.
Data from the Argo network of ocean buoys
shows an average warming of 0.9 of a degree Celsius
since the 1950s.
While this may not sound like much,
meteorologists understand
how sea surface temperatures
drive hurricanes and cyclones
and early predictions of storms of greater magnitude
are being realized.
Longstanding weather records are being broken
and broken again.
In 2017, NASA, NOAA and the UK Met Office
all agreed that 2016 had been
the hottest year on record.
Globally, 16 of the 17 hottest years
have all occurred since the year 2000.
Both NASA and ESA have been monitoring
the distribution and concentrations of CO2
in the atmosphere since 1992.
This visualization from data collected in 2006
shows the yearly fluctuations
of carbon dioxide and carbon monoxide.
While most CO2 emanates
from the populous Northern hemisphere,
seasonal fires in Africa, Australia, and South America
generate much of the carbon monoxide.
Prolonged droughts and more severe forest fires
are another aspect accompanying increased levels
of atmospheric CO2 that are currently unfolding.
Such events inject a huge pulse
of greenhouse gases into the atmosphere,
magnifying the problem.
The European Space Agency's Copernicus program
with its Sentinel Earth observation satellites
has committed to making information
about the changing climate freely available
to policymakers, businesses, and research institutions.
Josef Aschibacher is ESA's Director
of Earth Observation Programs.
What you see here, on this graph,
is the CO2 concentrations of the atmosphere
of the last 800,000 years.
And you see that these values are going
up and down in different phases.
You see the blue lines here
are indicating ice ages,
and the orange lines here are indicating periods
between ice ages or periods where it's much warmer.
But you also see that over the last 800,000 years,
the value was always below 300 parts per million.
And suddenly, since the last century,
it goes up very steep
towards 400 parts per million or even beyond.
The recent climate summit COP25,
held in Madrid, made little progress
toward an international agreement
to cut greenhouse gas emissions.
While some businesses and economies
will have to adjust,
that task only gets more difficult as time passes
and far greater adjustments will be forced upon everyone.
The Earth is the only place we know that harbors life,
but the stability that has enabled
this web of life is fragile.
Plants and animals interact for mutual benefit.
Our benign environment results
from the complex and varied creatures
with which we share the planet.
It's important that we look after our home.
(inspiring music)