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00:00The Sun. Seemingly unchanging, it is in fact a gigantic nuclear reactor.
00:08Its surface is in a constant state of flux.
00:12It sends out violent solar storms and streams of radiation hurtling toward Earth.
00:19Sunspots break through its fiery surface and its giant magnetic field ripples throughout the solar system.
00:29We are only just beginning to understand the Sun's impact on Earth.
00:34It brings havoc, but as global temperatures rise, could it also be our savior?
00:41Music.
00:56The Sun. A raging nuclear ball of superheated gas so large more than a million Earths could fit inside.
01:06And it makes all life on Earth possible.
01:10It powers the growth of plants and forests, providing a continuous stream of energy day in, day out.
01:17It has fueled our planet for four and a half billion long years.
01:22To mankind, the Sun's energy seems constant.
01:28Since the last major ice age 10,000 years ago, moderate temperatures on Earth have helped man to flourish and build technologically advanced societies.
01:38But this may not last forever.
01:42We are now beginning to understand that our planet's relationship with the Sun is complex and turbulent.
01:50On a regular basis, solar storms rage.
01:54Gigantic clouds of plasma fly out from the Sun's surface and strike the Earth's outer atmosphere, sometimes disrupting satellites and power grids.
02:05Every minute there's a battle going on between the Sun's magnetic field and the Earth's magnetic field.
02:10These Sun surges emanate from deep within the Sun, rising to the surface to create visible dark patches called sunspots.
02:19The activity of the magnetic fields waxes and wanes over an 11-year cycle.
02:25Solar maximum sees the greatest number of sunspots and solar minimum the fewest.
02:32But what does this mean for us on Earth, 93 million miles away?
02:37Scientists are just beginning to understand that these magnetic fields may be much more influential than was once thought,
02:45and could have been responsible for historical climate change events.
02:50From the historical record, changes in solar activity does have a measurable impact on Earth's climate globally.
02:59A race is now on to understand this connection between the Sun and the Earth, so mankind can prepare for all possible outcomes.
03:13Space-based observatories provide us with a unique view of solar activity.
03:20In 2006, NASA launched twin state-of-the-art satellites to study at close hand solar storms and sunspots,
03:29visible signs of deep magnetic activity that affects the whole solar system.
03:37The scientists borrow a trick from 1950s B-movies to create a 3-D image of the Sun.
03:44They deploy two satellites orbiting in tandem, one in front of the other, so they can build a three-dimensional image back on Earth.
03:53This 3-D image will provide crucial new data on massive explosions of electrified plasma called solar storms.
04:01Billions of tons of superheated gas fly into space and buffet the Earth's atmosphere, creating the most dramatic northern and southern lights.
04:10Michael Kaiser of the Solar Terrestrial Relations Observatory, or STEREO.
04:15We want to monitor these storms so that we can better predict them.
04:18These storms are basically electrical storms and they can affect spacecraft, ground power systems, GPS can be upset.
04:26Solar storms are caused by lines of magnetic force ripping through the Sun's gaseous surface and snapping,
04:33spewing out hot gases and a fierce stream of charged particles.
04:37The most powerful type of what's called solar wind.
04:40Some storms take two days to strike the Earth, while very large ejections arrive in only 12 hours.
04:47STEREO could give us time to put satellites and electric power grids into safe mode and move astronauts into protected sections of the space station.
04:57The ones we're interested in, the ones coming right at us, are particularly difficult to estimate the speed and velocity.
05:05A simple demo shows how two satellites allow scientists to calculate the speed of this solar wind.
05:13Michael Kaiser ejects a jet of liquid at a plate of glass.
05:18From the front, it's difficult to measure the speed.
05:21This is the way older satellites used to view solar storms.
05:27But from the side, you can measure two points along the projectile and calculate the speed more easily.
05:35Studying solar storms not just from the front, but the side as well, doesn't just reveal their speed.
05:43It also shows where they come from.
05:46The answer turns out to be the area around sunspots.
05:50These dark spots on the Sun's surface were shrouded in mystery until the 20th century,
05:56when scientists realized that they were connected with the way the Sun generates heat at its core.
06:03Once scientists understood that the Sun got its energy from nuclear reactions, the answer became clear.
06:09Nuclear fusion within the Sun creates the conditions for powerful magnetic effects.
06:15The currents of superheated gas generate intense magnetic fields.
06:20As the Sun's interior churns, vast loops of magnetic force appear, merge and disappear, creating sunspots.
06:29Luckily, there's a way to visualize it right here on Earth, in the comfort of your own kitchen.
06:36NASA astronomer Sten Odenwald compares magnetic field lines to spaghetti.
06:43The surface of the Sun is very hot gases that are turning over in a boiling motion.
06:48What you're seeing in the pot of water is the convecting water coming up to the surface and releasing its heat
06:56and then sinking back down into the pot to get reheated.
07:00The rolling strands of spaghetti are like the magnetic field lines churning beneath the Sun's surface.
07:07And these fields come to the surface, get concentrated into sunspots and flares and things like that.
07:14The turbulence that causes sunspots doesn't just come from heat, it also comes from the Sun's rotation.
07:22On solid planets like the Earth, every part of the planet rotates uniformly.
07:28But the Sun is a ball of gas, and the same rules don't apply.
07:32The equator rotates in 25 days, but the poles take 35 days.
07:39The magnetic loops get stretched and distorted as it turns.
07:43And where they break the surface, sunspots emerge.
07:48Sunspots are immense.
07:50A spot can be anything from the size of the African continent to 30 times as wide as the whole Earth.
07:57It's thought that the bigger the spot, the bigger the magnetic instability that lies beneath,
08:03leading to more severe storms and powerful invisible radiation, like X-rays and gamma rays.
08:10And what's weird is that they are not dark at all.
08:14They just appear dark because of the brightness around them.
08:18In fact, a sunspot is 10 times brighter than the full Moon.
08:23Solar physicist and expert on sunspot prediction, Leif Svalgaard,
08:28can demonstrate how the eye is tricked by this illusion of light, using a small light bulb and an overhead projector.
08:36A sunspot is very hot, around 8,000 degrees.
08:40It's represented by the glowing filament of this light bulb.
08:43This appears bright until Svalgaard turns on the overhead projector, which represents the Sun.
08:51And if you now switch on the rest of the Sun, at 10,000 degrees, you will see that the sunspot now appears dark.
08:59So it's only by this contrast that it looks dark.
09:05Sunspots are in effect a window on the Sun's hidden magnetic activity.
09:10But they may also be an indicator of another more profound effect that science is only now beginning to understand.
09:18Unknown to medieval astronomers, a dramatic decrease in the number of sunspots may have been linked to a period of significant climate change,
09:26now known as the Little Ice Age, a harrowing time when numerous crops failed and some lands became uninhabitable.
09:36Sunspots are as familiar to astronomers as the planets and our Moon.
09:44Up until the middle of the 19th century, they were just an astronomical curiosity.
09:50But now, some scientists think that sunspots are visible signs of a mysterious mechanism that spawned significant climate change in Earth's past.
10:00Their theories are based on the frequent correlation between sunspot numbers, as recorded by astronomers down the centuries, and climate records.
10:10Scientists are now discovering that solar variation affects our climate in complex and subtle ways.
10:18The number of sunspots on the surface, the number of solar flares, the amount of ultraviolet light, does have a measurable impact on Earth's climate.
10:27The first record of sunspots dates back to 800 B.C.
10:33Galileo was the first astronomer to study sunspots scientifically, famously drawing the position of the spots in his notebook.
10:42Astronomers' records show that between 1645 and 1714, the numbers were so low as to be almost absent.
10:52At the same time, Europe and North America was suffering a period of cooling known as the Little Ice Age, which lasted for around 500 years.
11:02But during the Little Ice Age, there was a shorter period of brutal cold, lasting for just over 70 years, known as the Maunder Minimum.
11:12One winter during the Little Ice Age, it was possible to walk all the way from Manhattan to Staten Island over the ice.
11:19And in London, the Thames froze over for months on end. Londoners even held ice fairs out on the river.
11:27The fact that part of this period of severe cold was matched by low sunspot numbers has intrigued scientists ever since.
11:35A leading expert on how solar radiance influences our climate, Judith Lean.
11:41There's a lot of anecdotal evidence that connects the sun's variability and climate change through indirect indicators of the sun's brightness and also of the surface temperature.
11:54And it's a very controversial topic because to understand it properly, we really need long-term records of the brightness changes itself and of the climate change.
12:05Scientists needed more data, and that was a challenge.
12:10Galileo's records are the earliest that give us a clear idea of how much activity was going on.
12:16But now scientists have records of sunspots going back over thousands of years.
12:22They learned the key was not to look at sunspots themselves, but rather at an astronomical phenomenon which at first glance appears unrelated, cosmic rays.
12:33Scientists believe that cosmic rays originate from sources all over the universe, such as massive exploding stars.
12:41Charged particles fly out at close to the speed of light.
12:45Space is full of cosmic rays.
12:48They bombard the Earth continually, and we can measure the intensity of this bombardment over time.
12:54Cosmic rays collide with molecules in the atmosphere to produce isotopes, such as carbon-14 in tree rings and beryllium-10 in ice deposits.
13:06Thousands of years later, scientists can unearth the hidden records of this bombardment by measuring levels of these isotopes.
13:14We can use carbon-14 to trace the sun's activity cycle going back literally thousands of years.
13:20And that's really amazing.
13:23Levels of carbon-14 and beryllium-10 are affected by the sun's magnetic field in space.
13:31The sun's magnetic field is vast.
13:34Normally it extends 8 billion miles into space.
13:38But when the sun is more magnetically active, it stretches to 10 billion miles.
13:42Because cosmic rays are charged particles, magnetic fields deflect them.
13:47The more magnetically active the sun is, the more cosmic rays are deflected, leaving fewer markers in ancient trees and ice cores.
13:56Magnetism has long been used to deflect charged particles on Earth, too.
14:01Cathode ray tubes in TV sets do so to create a picture.
14:04Oxfordshire, England.
14:06At the Rutherford Appleton Advanced Physics Laboratory,
14:10British professor Mike Lockwood demonstrates how easily magnetic fields deflect cosmic rays.
14:16A simple beam of electrons created in a laboratory behaves in the same way as cosmic rays upon hitting the sun's magnetic field.
14:25This glass case is called a cathode ray tube.
14:28It behaves in the same way as cosmic rays upon hitting the sun's magnetic field.
14:33This glass case contains a green beam of electrons that are physically similar to cosmic rays.
14:40Lockwood will simulate the sun's magnetic field with two metal coils.
14:47When I pass electric current through a coil, I generate a magnetic field.
14:51So if I turn the current up, I increase the magnetic field inside the bulb and I start to deflect the beam.
14:58And the more I turn the current up, the larger the magnetic field and the more the deflection.
15:03Just like the experiment when the sun is at its solar maximum every 11 years,
15:09the sun deflects more cosmic rays away from Earth.
15:13So the number of sunspots appears to be directly related to the amount of cosmic ray deflection.
15:19This all ties together with events during the Maunder Minimum.
15:23The Carbon-14 data from trees reveals that the cosmic ray flux increased during this period,
15:30which suggests the sun's magnetic field became less active and the spots almost vanished from the surface.
15:36We had the Maunder Minimum where there were a few sunspots that were higher than normal flux cosmic rays.
15:43We can find other examples like that and we can find periods like recent times
15:48when the sun's solar activity has been unprecedentedly high and the cosmic rays have been low as a result.
15:57Every 100,000 years or so, the Earth goes through a major ice age,
16:03due to a change in the shape of its orbit around the sun.
16:07Our orbit isn't a perfect circle and fluctuates over time,
16:11putting the Earth either closer or further away from the sun.
16:14At its most elliptical, there is a 23% difference in solar radiation between the two most extreme points in the orbit.
16:22Right now it's only 7%, providing us with a temperate climate since the last major ice age.
16:31But what about other influences of the sun, apart from these periodic changes in orbit and tilt?
16:38Are changes in solar radiance enough to affect our climate and weather patterns?
16:45The answer is, it depends how long the changes last.
16:54Sunspots change over an 11-year cycle.
16:58But that's not enough time for the small differences in energy output to make a difference.
17:02Our planet just can't heat and cool that fast.
17:06This is because the oceans absorb lots of energy and take decades, even centuries, to reflect the changes.
17:14There's no doubt that if the solar output decreased by enough on those timescales,
17:21then the Earth would cool in response.
17:24The 11-year cycle has little impact.
17:27But that's not the end of the sunspot cycle.
17:29Other trends are also found in the records.
17:32The Maunder Minimum may have been a result of a longer cycle.
17:38And that could be long enough to make a real difference.
17:43Exactly how much difference?
17:46But the problem is, although you can trace the activity of the sun,
17:50it's very hard to trace how the climate of the Earth has changed in step with that.
17:56Accurate climate records going back thousands of years
18:00will be the only way to understand if the sun periodically has bigger cycles
18:05and potentially a larger impact on global climate.
18:10And that's what two American scientists think they have discovered, deep in the caves of New Mexico.
18:20Paleoclimate is not a science.
18:23Paleoclimatologist Yemani Asmaram and his colleague Victor Polyak of the University of New Mexico
18:31have found an ingenious way to accurately calculate the weather from our Earth's past,
18:37using stalagmites in ancient caves.
18:42When you look at the climate record over 10,000 years based on stalagmites,
18:48the match is surprising and also fairly robust.
18:55The deep caves of New Mexico in the southwest United States
19:00have preserved a perfect record of changes in climate.
19:05Through them, these scientists have established a climate record for the American Southwest
19:11over a 3,000 year period during the late Holocene.
19:15This covers the most recent period of Earth's climate history, from when the last ice age receded.
19:22One of the important attributes of stalagmite is that it can obtain absolute ages precisely
19:30and they also contain annual laminations just like tree rings
19:34and they contain evidence of climate change at a fine scale.
19:39But to retrieve the data, the samples need careful preparation.
19:44The stalagmites go through a three-stage process.
19:49This stalagmite grew from 3,000 years ago to present and it exhibits annual bandings.
19:58First, a drill grinds out some sample powder.
20:01This is more than enough powder to establish an accurate age for that particular layer.
20:10Next, Polyak mixes the sample with chemicals.
20:15This separates the sample into uranium and thorium isotopes.
20:21Lastly, the elements go into a mass spectrometer.
20:25This process measures the amount of uranium in the sample.
20:29This process measures the amount of uranium that has decayed over time
20:34and the amount of thorium isotopes produced.
20:37Because they know how long decay or production of these isotopes takes,
20:42they can work out exactly how old the sample is.
20:45They can also work out from its chemical and mineral composition
20:49how dry the climate was during that particular year.
20:53Amazingly, the periods of drought shown by these records
20:57accurately match sunspot activity as measured by carbon-14 data.
21:03Stalagmites provide accurate records going back hundreds of thousands of years.
21:10The scientists' unique methods may explain the mysterious disappearance
21:16of an ancient Native American civilization
21:18330 miles north of the caverns in Chaco Canyon.
21:25The Chacoan people settled here in northwest New Mexico in 850 A.D.
21:31The Chaco complex is considered one of the regional centers for ancestral Americans.
21:38At its time, this was a center of activity very complex,
21:42comparable to other communities the world over.
21:44Then suddenly, 400 years later, experts believe the climate dried up dramatically.
21:50The Native Americans left the canyon for good.
21:54Unfortunately, in spite of their sophistication,
21:57they didn't have the adaptive capability to survive such a dramatic climate change.
22:02The stalagmites recorded these changes with incredible accuracy
22:07and revealed that around the year 1250, it was indeed a severe drought.
22:12But did the sun force the climate to change?
22:16Did it simply produce more heat than normal during this dry period?
22:20The statistical link between climate and sunspot numbers
22:25doesn't tell us how the climate and weather might be changed by the sun's activity.
22:30What evidence is there that a more magnetically active sun
22:34produces more heat as we feel it on Earth?
22:37To help solve this mystery, scientists have been trying to understand
22:41how the sun generates its seemingly endless stream of heat and light.
22:46The sun's energy is generated by immense pressures at its core.
22:51Surprisingly, the energy that we feel every day
22:55was not generated eight and a half minutes previously,
22:59the time it takes light to travel from the sun,
23:02but produced in the core of the sun.
23:04Change in the sun's energy production at its core
23:08would only be felt by us eons in the future.
23:14Photons of light bounce around inside the sun,
23:18exchanging heat and energy for thousands of years
23:22before they escape and travel toward Earth.
23:28It's a puzzle.
23:30How can we measure the sun's energy production
23:34if the energy we receive is itself so ancient?
23:38Austrian-born US physicist Wolfgang Pauli
23:42proposed that the sun also expels billions of neutral particles from its core
23:47that strike the Earth virtually uninterrupted
23:51but were invisible to scientific instruments.
23:55Pauli suggested that they had to have almost no magnetic field
23:58and suggested that they had to have almost no mass
24:02and have the ability to pass through any object, the Earth included.
24:09They're known as neutrinos.
24:12Neutrinos are unique messengers
24:15because they can go through the outer part of the sun
24:18with virtually no interference.
24:21Scientists theorized that one of these particles
24:24could penetrate a block of lead a light-year in length.
24:26In one second about 100 billion neutrinos will pass through my thumb
24:31but these will not be absorbed
24:34and virtually all of them go through without any interaction.
24:39Solar models predicted that the neutrino rate should be constant
24:43explaining why the sun's energy output varies little.
24:47But first, science had to prove they even existed.
24:52So in 1990, scientists built a facility almost 7,000 feet underground
24:59in a working mine near Sudbury, Canada.
25:03The idea was to create an area free of another common particle in the solar system
25:09cosmic rays.
25:11Eight years and tens of millions of dollars later, it was complete.
25:16It's perhaps one of the largest physics experiments ever conceived.
25:21One of the physicists involved in the immense project is Professor Doug Hallman.
25:27The reason we're underground is because these signals are very small
25:32and we have to avoid backgrounds or the normal signals
25:38that would interfere with our measurements from cosmic rays
25:42and so going deep underground allows us to avoid those interferences.
25:46They can only detect all types of neutrino by creating a special medium
25:51a tank with a thousand tons of neutron-enriched water
25:55provided by the nuclear power industry.
25:58They ship heavy water from commercial nuclear reactors in tankers.
26:02Neutrinos react with this heavy water to produce tiny flashes of light.
26:07Thousands of light sensors placed over the large tank detect these flashes or photons.
26:13Of the billions that pass through, around 20 a day produce a signal.
26:18We can think of them as very tiny
26:21so that they really aren't affected by the individual atoms of ordinary materials.
26:27Previous smaller detectors built in Japan and the U.S. found less than predicted.
26:33This new facility has been able to prove that neutrinos change form
26:38evading early attempts to find them.
26:41The neutrino mystery was actually cleared up
26:43when they discovered that neutrinos can actually change their identity from one type to another.
26:48The Sudbury detector has confirmed what astrophysicists thought all along.
26:53The sun's core generates a steady rate of energy.
26:57So these missing neutrinos were found in our experiment
27:01and we could determine that the sun's rate of production of neutrinos
27:05really in fact was what the models were predicting.
27:09What impact does this steady rate of energy production have on the Earth?
27:13A simple way to measure the sun's output
27:16is to look at how much a small area of Earth is heated during the 11-year solar cycle.
27:21On a sunny day, every square yard of this planet's surface
27:25receives 1,000 joules of energy per second from the sun.
27:29This solar energy, or radiance, is partly absorbed and partly reflected back to space.
27:35Over the 11-year solar cycle, this varies by a surprisingly tiny amount.
27:40A simple way to demonstrate this change in output is with this basic electric heater,
27:45which produces an equivalent amount of power as the sun does per square yard.
27:51Solar physicist Joanna Haig shows us how little the difference in heat output really is.
27:57So we can see the intensity that's arriving from the sun.
28:00Now, how much of that is varying over the 11-year solar cycle?
28:04It's only about a tenth of a percent and we can see what that means
28:06by looking at the radiation coming out of a light coming out of this little torch here.
28:12Incredibly, this small flashlight generates the same amount of extra energy
28:17as the sun does at solar maximum compared to solar minimum.
28:24You can see it's a very small amount and it's very difficult to understand
28:28how this very small change in solar radiance could account for any significant impact on climate.
28:33So, if as Haig contends, one-tenth of one percent is too small
28:38to cause the climate change we've seen in the past,
28:42then what mechanism is driving those changes in climate, as confirmed by records?
28:47Haig has a theory. It might not be the sun's brightness that causes the change.
28:52It might be another aspect of the sun's energy altogether, one we can't see.
28:57Perhaps increases in ultraviolet radiation lead to significant changes in weather and climate.
29:07Scientists have discovered a possible link between the dark solar spots of the sun
29:12and historical periods of dramatic climate change.
29:16But the sun's natural heat output varies very little over an 11-year cycle.
29:21People often refer to the sun as a solar constant,
29:24as expert Barbara Thompson of NASA testifies.
29:28The solar constant is not really a constant.
29:31It's fairly steady, so you'll get throughout the solar cycle
29:36variations in how much solar output the sun is putting out.
29:40It's not a huge change.
29:43You actually need some pretty sophisticated instruments just to measure the change.
29:47So why is there a statistical link between solar activity and historical periods of dramatic climate change?
29:54Why are there historical changes in climate and weather?
29:57The answer may lie in the fact that the sun doesn't just generate heat.
30:01The sun also generates radiation, with wavelengths in the invisible end of the spectrum.
30:07One such type is best known to sunbathers as ultraviolet radiation.
30:12We don't see UV rays, or microwaves, or X-rays for that matter.
30:17But the sun generates them along with heat and visible light.
30:22Scientists discovered that emissions of these invisible waves
30:26also fluctuate over the 11-year solar cycle.
30:30UV rays can increase up to 100% from solar minimum to solar maximum
30:36when the sun's magnetism is at its strongest.
30:41Significantly, recent satellite observations of the sun
30:45show it emits more UV when there are more sunspots.
30:48So sunspots mean increased UV radiation striking the Earth's atmosphere.
30:55This image of the sun, taken from NASA's SOHO satellite,
31:00shows the UV rays emitted during a solar storm.
31:05And this is the amount of UV radiation emitted during a quiet period of solar minimum.
31:11And by the time you get to the X-ray region, it's varying by 100%,
31:15so it's doubling from solar max to solar min over the 11-year cycle.
31:20What other effects could increased amounts of UV have on our climate?
31:25UV reacts with oxygen, the chemical element in the atmosphere
31:29that gives us life and forms ozone.
31:32A layer of ozone surrounds the Earth, providing a blanket of protection.
31:37So on my hand here I've written a secret code which you can't read,
31:41and you can't read it even if I shine the torch on it.
31:43There doesn't seem to be anything on there.
31:46If, however, I shine the ultraviolet light, you can see the secret code.
31:53And what's happening here is that the chemicals that are in that ink that's on my hand
31:58are responding specifically to ultraviolet light,
32:02in rather the way that ozone in the stratosphere is going to absorb ultraviolet light and not normal radiation.
32:08The ozone layer is located around 12 to 30 miles above the Earth's surface.
32:13It protects us from the worst effects of UV,
32:17but it also has another important atmospheric role to play as a greenhouse gas.
32:22So it traps heat radiation that comes from below,
32:26and it acts like a blanket and is warming the climate.
32:29When electromagnetic radiation peaks at solar max,
32:32ozone levels in the stratosphere rise by about 3%
32:36due to the increase in UV rays reacting with the oxygen molecules.
32:39The theory is that this increase in the ozone, along with the extra UV,
32:44creates a warm layer which traps air in the lower atmosphere.
32:48So if we change the properties of the stratosphere, if we change its temperature or its height,
32:53that affects the circulations of the atmosphere below.
32:57The movement of the hot air in the tropics pushes storm tracks toward the northern Atlantic and Pacific Oceans,
33:05which would explain why the Little Ice Age was localized to those areas.
33:11For now, scientists can't prove that UV has a large enough influence
33:16to cause some of the more dramatic swings in our climate.
33:19Variations in solar activity can definitely affect the climate.
33:23The problem we have is in understanding how large these variations are.
33:27So UV radiation is a possible cause of localized climate change.
33:32But one lone British scientist thinks there's something else about the sun that affects our planet.
33:38Atmospheric physicist Dr. Neil Arnold believes that the solar wind itself might alter climate.
33:45The solar wind is made up of a stream of charged particles,
33:49high-energy electrons and protons, expelled by the sun constantly,
33:54and especially strong during periods of high magnetic activity.
33:58Arnold believes that the solar wind collides with Earth's upper atmosphere, called the thermosphere,
34:04which in turn stirs up the climate miles below, causing global warming effects.
34:09The solar wind interacts with the Earth's upper atmosphere quite freely, creating big changes there.
34:20This idea flies in the face of conventional thinking about solar wind.
34:25Most scientists would conceive no possibility of it being able to make a significant change to the weather and the climate.
34:35To understand the theory, we have to understand how our climate is kept in balance by Earth's rotation and gravity.
34:43These create an effect called the Coriolis force.
34:47Our planet's atmosphere has a fine equilibrium.
34:50Without the Coriolis force, hot air from the equator would rush to the cooler poles, destabilizing our climate.
34:58Instead, atmospheric circulation travels from east to west around the globe, kept in balance by the Earth's rotation.
35:07We can demonstrate the Coriolis force by showing how a ball reacts to being rolled in a straight line on a children's merry-go-round.
35:16This reveals that the ball rolls in a curved trajectory rather than running straight off the surface of the merry-go-round.
35:26So the Coriolis force prevents the circulation of atmosphere from heading toward the cooler poles, driving the system east to west.
35:37But Arnold believes that when the solar wind emitted from clouds of plasma strikes the thermosphere, it disrupts this carefully balanced Coriolis force.
35:50The hot air moves from warm regions toward the cold polar regions and vice versa.
35:58The whole atmosphere is disrupted by the hot air now circulating toward the colder poles.
36:07According to Arnold, this overall stirring up prevents some heat from being radiated back into space, raising global temperatures.
36:17It's a controversial theory, as solar storms can hit the Earth on a daily basis.
36:25People are skeptical that things happening in the upper atmosphere around a few hundred kilometers, where for example low Earth orbiting spacecraft are, actually has an impact on the surface.
36:39If solar storms and UV rays aren't the cause of historical climate change, then what other mechanism could be responsible?
36:48As we have seen, paleoclimatologists have well-established records of Sun activity over centuries by using isotope analysis and radiocarbon dating.
36:59When solar activity is high, the Sun's magnetic field balloons, deflecting galactic cosmic rays.
37:07When the solar activity is low, more cosmic rays buffet the Earth.
37:11Could cosmic rays themselves be the missing link between solar activity and global climate change?
37:21The Sun is the most powerful object in the solar system.
37:26Scientists are just beginning to understand its effects on our planet.
37:30It appears that historical changes in climate are linked to the strength of the Sun's magnetic fields.
37:37Records from the last 1200 years have shown an emerging pattern of solar influence.
37:44Around 800 AD, there was a period of unusually warm weather that lasted for around 400 years.
37:51Then the climate seesawed back to cooler conditions.
37:55By around 1250, the Viking colonies on Greenland had turned from fertile farmlands into barren wastelands.
38:03In the 17th century, London saw the Thames freeze over.
38:08Up until the 20th century, the cause of the swings of temperatures was a mystery.
38:14The Sun seems to be a catalyst, but exactly how it has driven past climate change events is still unknown.
38:25One possible explanation involves UV rays and solar storms disrupting our weather systems.
38:31But there could be a more subtle and surprising cause.
38:35One that begins its life outside our solar system, deep in space.
38:40The amount of interstellar cosmic rays hitting the Earth is regulated by the strength of the Sun's magnetic field at that particular time.
38:49Isotope analysis on ice and tree rings gives us an extraordinary record of this.
38:54But what if the cosmic rays themselves affect our climate and weather systems more directly?
39:02Could these energetic particles emanating from exploding stars be the actual mechanism behind some climate change?
39:10The first clue may be linked to an everyday meteorological phenomenon.
39:15Clouds.
39:18Low-level cloud coverage generally exerts a cooling effect on the Earth's surface.
39:24As cloud coverage increases, heat from the Sun is reflected back into space.
39:30This allows the Earth's surface and oceans to cool down.
39:34It's thought by some that a 2% increase in low cloud cover would reduce temperatures back to pre-industrial times.
39:42The link between cloud coverage and climate change intrigues Danish physicist Henrik Svensmark.
39:482% doesn't sound like very much, but it's actually quite important for our climate.
39:55Clouds form when rising air from the heated surface of the Earth cools to a point where some of the water vapor molecules clump together faster than they can be pulled apart by their own energy.
40:08The water vapor then condenses to form cloud droplets.
40:13With this simple device here, where I have a bottle with a little bit of water in, I can try to demonstrate how clouds form.
40:21First, the water saturates the air inside the bottle.
40:26The conditions are now right for forming a cloud.
40:29All that's needed is the addition of some tiny particles to act as seeds for the water molecules to clump around.
40:37Svensmark will use smoke.
40:40And then I try to do a super saturation by just pressuring this.
40:47And then I release, and you'll see that it starts getting white when I release.
40:54And that's because there's a super saturation of vapor and it sticks to these small particles.
41:01The experiment shows that the introduction of a few small particles in the atmosphere could encourage clouds to form.
41:09Seeding of clouds happens naturally in our atmosphere.
41:12But what if the seeding was supplemented from outside our atmosphere?
41:17Svensmark believes that an old theory that cosmic rays can seed clouds might explain climactic periods like the Maunder Minimum, a time when the volume of the cosmic rays hitting the Earth was very high.
41:31So you will actually have more clouds on the Earth, and that will give you a cooling of the temperatures.
41:39For the cosmic rays theory to be credible, the team first had to look for a statistical link between cloud coverage and a variation in cosmic rays flux.
41:50They analyzed weather satellite records from 1979 to 1992.
41:55This period was long enough for the Sun to have completed the well-established 11-year cycle of activity.
42:03Svensmark claims to have found that the Earth was 3% cloudier at solar minimum.
42:09A statement some scientists dispute.
42:13Cosmic rays are invisible to us.
42:16But they can be seen indirectly in this special laboratory chamber.
42:21Inside we have a very high super saturation of, it's actually alcohol.
42:27And when a charged particle goes through like a cosmic ray, it creates like a contrail of small droplets in its wake.
42:37They are everywhere, maybe 140 particles hits me every second and going straight through my body.
42:46Like any theory, Svensmark needed evidence to back it up.
42:51He needed to prove how a cosmic ray could act as a seed in saturated air in the laboratory.
42:58In 2005 his team of Danish scientists designed an experiment to see if cosmic rays could seed clouds.
43:07The larger chamber was built for testing at sea level, while a smaller one is designed to be taken underground to screen out the rays.
43:16The idea is that scientists inject air and trace gases like sulfur dioxide into the tank to imitate the air above the ocean.
43:26Instead of the Sun, they use a UV lamp attached to one end.
43:31The last element doesn't need any assistance.
43:34Cosmic rays penetrate the steel outer casing naturally.
43:39As cosmic rays naturally strip electrons from the artificial air, clumps of molecules form around these tiny charged particles.
43:48These cloud condensation nuclei are recorded by a special counter.
43:54The Danes have shown perhaps the very first stage of the formation of cloud condensation nuclei.
44:01But they need evidence that the particles could grow bigger before forming water droplets.
44:08And that requires more research in more controlled conditions.
44:13Such research is planned for 2010 and will take place at CERN in Switzerland, in the world's largest particle accelerator, sunk deep underground.
44:24A beam of accelerated particles simulating cosmic rays will be fired into saturated air.
44:30Only then could we discover if the Danes' small particles really can grow to the size where clouds begin to form.
44:38This will be a very interesting experiment because this whole area is something we know very little about.
44:44It could confirm the theory that they could grow into something big enough to help clouds form.
44:49Scientists are only just discovering the extent to which our Sun influences Earth's climate and weather patterns.
44:55Thirty years ago, few thought that solar variation had any influence on climate variation.
45:02But a small growing band of scientists believe that it certainly does.
45:06If the solar cycles are really helping to drive our climate, then the activity of the Sun will be crucial to the Earth over the next century.
45:15We're beginning to understand there are these subtle links between the solar wind and aspects of our atmosphere.
45:23Man-made greenhouse gases are warming our planet.
45:28But could big changes in the Sun's magnetic activity also be an important factor in the future?
45:34If there is a crash, then global warming may be slower than expected, potentially saving parts of the globe from flood and famine.
45:43Despite this possibility, many believe that carbon emissions would still need to be cut.
45:48We need to still continue with that because when the Sun finishes going through its hundred year period of low activity,
45:56we're going to be right back to where we started before with a vengeance.
46:01We know we have the power to change our planet's climate.
46:05It's a power we need to use responsibly.
46:08But ours is not the only power at work.
46:11Variations in the Sun have happened over eons and changes in the energy coming out of the Sun will affect climate on Earth
46:19because the energy is the main driving force for climate.
46:22The Sun has been influencing the long-term climate here on Earth for as long as we've measured.
46:28It could be that the less magnetically active it is, the cooler we become.
46:33We don't fully understand how it happens.
46:36We don't fully understand how it happens, be it UV rays, solar wind or even cosmic rays.
46:42But one thing is certain.
46:44Our well-being and the well-being of planet Earth is dependent on the Sun in ways we're only now beginning to understand.
47:05NASA Jet Propulsion Laboratory, California Institute of Technology