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00:00the earth is our home our natural environment results from complex
00:11relations between the Sun the oceans and the atmosphere the polar ice and the
00:19tropical heat represent the extremes of our planet's climate in reality this is
00:27a very narrow temperature band completely different from any other planet we've
00:31observed the stability of the earth's environment has allowed life to emerge
00:38and life has changed the planet as far as we know the earth is the only planet in
00:47the universe to have given rise to life
00:57the
01:20the Orion Nebula is a vast cloud of gas and dust in the Orion constellation it's a
01:25place where new stars are being created
01:30as part of the nebula condenses it separates into clumps as each clump contracts under
01:37its own gravitation it begins to swirl flattening into a disk
01:44they're called protoplanetary disks or propelids in the center of a propelid as
01:51the molecules are squeezed together a fusion reaction begins and a star ignites
01:56some propelids occurring close to an established star shine brightly under the
02:02influence of their neighbor while this makes them easier to observe the glowing
02:06gas and dust is being stripped away by the stellar winds from the adjacent star
02:13dark propelids only observable as silhouettes maintain their surrounding ring
02:19of gas and dust as the system matures this stellar debris will form a planetary system
02:25the Hubble Space Telescope has recorded numerous examples of this process enough for astronomers
02:32to understand that the formation of planets is commonplace
02:37this is how our own Sun started its life 4.6 billion years ago
02:44this is how our own Sun started its life 4.6 billion years ago
02:51but the planets would take longer to emerge small grains within the disk began accreting forming planetesimals
03:01the larger a clump became the stronger its gravitational attraction in turn leading to more rapid growth
03:07an early version of Jupiter would have been the first to coalesce completely clearing its orbit
03:16around a core of heavy metal and rock Jupiter's atmosphere mainly of hydrogen was compressed by its strong gravitation
03:28any solid surface lay beneath thousands of kilometers of liquid gas
03:33our observations of exoplanets have revealed Jupiter sized gas giants orbiting close to their stars
03:41astronomers believed the young Jupiter would have begun a track toward the Sun dragging asteroids and comets in with it
03:49but Jupiter's inward path reversed as it was pushed into an orbital resonance with the emerging Saturn
03:58not all of the objects forming in the early solar system stayed orbiting the Sun
04:05smaller objects passing a planet would be deflected by the stronger gravitation or even captured becoming a moon
04:13it 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
04:27at this time collisions in the developing planetary system were common
04:32and evidence from the Apollo moon rocks suggest an impact between the early Earth
04:36and an ancestor of our moon was important in our planet's evolution
04:48the Earth has a larger than expected iron core and gravitational analysis of the moon suggests its core is lighter than expected
04:56a collision between the bodies would explain the moon's loss of much of its heavy material to the more massive Earth
05:03the impact was a glancing blow that set the Earth rapidly spinning with a five-hour day
05:11the moon that we know coalesced from the molten debris
05:15although our moon is not the largest in the solar system it is closer in mass to its parent planet than any other moon
05:20the stabilizing effect that the moon has upon the Earth's rotation is significant
05:27over long periods the Earth's axis will vary by as much as one degree
05:32without the moon's influence this variation could be as much as 85 degrees with drastic implications for the climate's stability
05:39the debris in the early solar system was cleared by the planets in a period called the heavy bombardment
05:46the emerging Earth was peppered with asteroids and comets delivering water necessary for life
05:54while tectonic forces erase the bombardment scars from Earth the moon, which endured the same travails is still covered with craters
06:15When chaos in the developing solar system settled down,
06:19the young Earth was in a unique position.
06:22The Earth's distance from the Sun was just right
06:25for the abundance of water on the planet to exist in liquid form.
06:29As the Moon had drifted away, the planet's rapid rotation had slowed,
06:34and the Sun's heat was evenly shared across the surface.
06:39The Earth's large metallic core, combined with the planet's rotation,
06:44meant that a magnetic field stretched out around the planet,
06:48deflecting the charged solar wind
06:51and protecting the surface from extremes of solar radiation.
06:56In a hostile universe, the Earth was a uniquely benign environment.
07:05The geological record shows that around 2.7 billion years ago,
07:09oxygen began occurring in the atmosphere.
07:13The vast iron ore regions of Western Australia were formed
07:17as iron in the oceans reacted with a new abundance of oxygen to form iron oxide.
07:25Simple plant life was using the sunlight and carbon dioxide to live,
07:29and it produced highly reactive oxygen as a waste product.
07:33This enabled more complex life to emerge,
07:36building an intricate web of interrelated plants and animals,
07:40completely transforming the planet.
07:46The change in the atmosphere had other dramatic consequences.
07:49Oxygen stripped much of the highly insulating gases from the air,
07:54drastically cooling the Earth.
07:56A sequence of ice ages began.
07:58Though there is an abundance of evidence showing planetary glaciation punctuated by warm periods,
08:04the factors triggering these cycles are complex.
08:08Fault lines are clues to the movement of continents leading to diversions of ocean currents.
08:16The effect of volcanic activity on the atmosphere.
08:28And changes in the direction of the Earth's axis with regard to our planet's elliptical orbit around the Sun,
08:34all contributors to long-term fluctuations in the Earth's climate.
08:41Analysis of ice cores deposited in the Antarctic or Greenland
08:44is an accurate way to see how the composition of the atmosphere has changed over the previous 800,000 years.
08:56Bubbles of air caught between snowflakes before being rigidly trapped as the snow becomes ice,
09:01can be accurately sampled.
09:05One thing is clear.
09:07Carbon dioxide reaches a peak of around 270 parts per million during the warm periods
09:13and drops to approximately 170 parts per million when glaciation is at its greatest.
09:20But from this data, it's hard to know if extra CO2 causes the warming
09:24or the warming leads to extra CO2.
09:27In 1958, Dave Keeling, working for the Scripps Institute,
09:34began recording accurate levels of atmospheric CO2
09:38at the Mauna Loa Observatory in Hawaii.
09:41It was the beginning of a unique record known as the Keeling Curves.
09:50Keeling's graph revealed a seasonal variation corresponding to spring and summer
09:54in the northern hemisphere where land mass and plant cover is greater.
09:59During the northern spring and into the summer,
10:02CO2 levels dropped because of the increase in photosynthesis.
10:07By the 1970s, a disturbing trend had emerged.
10:11CO2 levels were in a steady rise.
10:13At first there was uncertainty about the implications.
10:19Extra CO2 could trap more heat leading to a warming effect,
10:24known as the greenhouse effect.
10:26But some scientists were worried that aerosol pollution could attenuate levels of sunlight reaching the planet,
10:32resulting in a cooling environment.
10:34As the decades passed, different pieces of evidence were collected.
10:41Drill cores from the ocean floor revealed that ice ages had been triggered by Milankovic cycles,
10:47the variations between Earth's tilt and its elliptical orbit.
10:50Though these effects were minor, the correlation was obvious.
10:56If such a small nudge could alter the climate,
11:00perhaps changes in CO2 could as well.
11:03Scientists were realizing just how poorly they understood planet Earth.
11:08At the beginning of the space age, scientists were keen to make weather observations from orbit.
11:27Launched in 1960, Tyros-1 was the first weather satellite.
11:33It was equipped with two TV cameras,
11:35regularly transmitting images of global cloud patterns.
11:42It provided meteorologists with a unique view,
11:45and it was followed by improved versions.
11:48Because these early satellites were in highly inclined low Earth orbits,
11:52the data gathered covered the whole planet and it was shared across the world.
11:59Since 1873, nations have been cooperating on weather prediction
12:03via the International Meteorological Organization,
12:07which in 1951 became the World Meteorological Organization,
12:11an arm of the United Nations headquartered in Geneva.
12:19With a UN resolution calling for international cooperation in the peaceful uses of outer space,
12:25weather satellites of different nations were soon being coordinated for the benefit of all mankind.
12:30In 1964, the Nimbus program began.
12:34The series of seven satellites included a more sophisticated set of sensors.
12:41Nimbus was a test bed for new technologies,
12:47and it gathered data about different areas.
12:49along with cloud patterns was information about the atmosphere and sea ice.
12:54This was the pre-digital age, and all electronic image data was burnt to and stored on 70mm film.
13:09Little thought was given to establishing an archive for future reference.
13:14The Nimbus program was an early example of Earth observation rather than just a group of weather satellites.
13:20And meteorologists started seeing the planet as a complex and interconnected system.
13:27Today, a fleet of satellites is in operation monitoring the atmosphere, the oceans, the ice, the land and the biosphere.
13:39It is now understood that ice, particularly sea ice, plays an important role in the Earth's climate system.
13:50Polar 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.
14:05These currents also move nutrition, which is important for the survival of life.
14:14Global winds also circulate water via clouds, keeping the land moist and able to support vegetation.
14:21Plant life in both the oceans and the atmosphere removes CO2 from the air and replenishes the atmospheric oxygen.
14:28Both the ice, known as the cryosphere, and the clouds reflect a proportion of the sun's energy back out into space.
14:39The extent of the ice and cloud cover are important factors in the Earth's energy budget.
14:44As ice melts, it exposes ocean or rock which absorbs more solar energy.
14:51Similarly, cloud cover, or the absence of it, will have an effect upon the land or sea beneath.
15:01Vegetation is also an important climate factor as land plants pump huge amounts of water vapour into the atmosphere.
15:08But things are changing. Humanity, simply through weight of numbers, is influencing key elements of the planet's climate system.
15:19In 50 years, the Earth's human population has risen from just over 3.5 billion to 7.7 billion today.
15:27More people need more resources.
15:35And while there have been revolutions in agriculture and in technology, the Earth's reserves are not limitless.
15:42In 1979, Europe began launching spacecraft.
15:47And while the new Earth observation satellites were revealing changes, scientists were reluctant to reach conclusions about long-term trends.
16:00They understood that there was a certain amount of variability in the planet's climate cycle.
16:04And 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.
16:21Since 1913, spectroscopy had revealed that a layer of ozone in the stratosphere blocked harmful UV sunlight from reaching the ground.
16:33In 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.
16:49In the 1980s, meteorologists working in Antarctica found the evidence.
16:57The polar vortex above the southern continent concentrates the CFCs in the stratosphere.
17:05Mother-of-pearl clouds in the polar skies contain ice crystals which, in combination with ultraviolet, split chlorine from the CFC molecule.
17:14Each chlorine atom can break down over 100,000 ozone molecules.
17:21A large area centred over Antarctica showed almost no ozone.
17:26It became known as the hole in the ozone layer.
17:29The United Nations began talks aimed at limiting the production of CFCs, and in 1989 an international treaty known as the Montreal Protocol capped the production of CFCs and ultimately resulted in a ten year phase out of CFC production.
17:48All countries signed the agreement, and the Montreal Protocol is seen as a model of international cooperation.
17:56In 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.
18:09Most of our planet's freshwater is locked in the polar ice caps. 61% of this ice covers the Antarctic continent.
18:21In the north, Greenland is also covered by an ice sheet.
18:25There 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.
18:37Ice 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.
18:53These 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.
19:12The two 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.
19:27This data is accurately measured, allowing researchers to record changes due to variations in groundwater or in ice thickness.
19:35During the life of the first GRACE mission, Greenland lost 285 gigatons of ice per year. On average, Antarctica lost 137 gigatons per year.
19:51From 2005 to 2016, sea levels rose by 3.7 centimetres due to melting ice sheets and to expansion of seawater.
20:01Sea levels have been monitored from space since 1992, initially with the Topex Poseidon satellite, and more recently with the Jason series of satellites.
20:16Jason-3 uses a precision radar altimeter to measure regional and global variation in sea levels.
20:23In the 20 years to 2014, the average rise was 6 centimetres, but the increase is not uniform.
20:31The red areas show the greatest rise, with white representing no change, and blue signifying a decrease.
20:38The 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.
20:51All these factors must be accounted for to arrive at a baseline against which to measure changes.
20:56These blue areas in the Atlantic show a shift in the Gulf Stream.
21:09The Comargue region of southern France is a low-lying area at the delta of the Rhône River.
21:14In the 1980s, a sea wall was built to prevent the encroaching Mediterranean.
21:20Over the last 30 years, the coastline here has been pushed back by several hundred metres.
21:27Scientists are convinced that a warming global climate is responsible,
21:31and that our reliance on the burning of fossil fuels has led to an excess of carbon dioxide in the atmosphere, which traps heat.
21:4393% of this heat has been taken up by the oceans.
21:47Data from the Argo network of ocean buoys shows an average warming of 0.9 degrees Celsius since the 1950s.
21:55While this may not sound like much, meteorologists understand how sea surface temperatures drive hurricanes and cyclones,
22:07and early predictions of storms of greater magnitude are being realised.
22:12Long-standing weather records are being broken, and broken again.
22:16In 2017, NASA, NOAA, and the UK Met Office all agreed that 2016 had been the hottest year on record.
22:26Globally, 16 of the 17 hottest years have all occurred since the year 2000.
22:34Both NASA and ESA have been monitoring the distribution and concentrations of CO2 in the atmosphere since 1992.
22:40This visualisation from data collected in 2006 shows the yearly fluctuations of carbon dioxide and carbon monoxide.
22:51While most CO2 emanates from the populous northern hemisphere,
22:56seasonal fires in Africa, Australia and South America generate much of the carbon monoxide.
23:02prolonged droughts and more severe forest fires are another aspect accompanying increased levels of atmospheric CO2 that are currently unfolding.
23:14Such events inject a huge pulse of greenhouse gases into the atmosphere, magnifying the problem.
23:21The European Space Agency's Copernicus Programme, with its sentinel Earth observation satellites,
23:30has committed to making information about the changing climate freely available to policy makers, businesses and research institutions.
23:37Joseph Aschbacher is ESA's Director of Earth Observation Programmes.
23:47What you see here on this graph is the CO2 concentrations of the atmosphere over the last 800,000 years.
23:55And you see that these values are going up and down in different phases.
23:59You see on 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.
24:10But you also see that over the last 800,000 years, the value was always below 300 parts per million,
24:16and suddenly, since the last century, it goes up very steep towards 400 parts per million or even beyond.
24:22The recent climate summit, COP25, held in Madrid, made little progress toward an international agreement to cut greenhouse gas emissions.
24:34While some businesses and economies will have to adjust, that task only gets more difficult as time passes,
24:42and far greater adjustments will be forced upon everyone.
24:45The Earth is the only place we know that harbors life, but the stability that has enabled this web of life is fragile.
24:58Plants and animals interact for mutual benefit.
25:01Our benign environment results from the complex and varied creatures with which we share the planet.
25:09It's important that we look after our home.
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