"Scattered amongst the craggy peaks of the Swiss Alps is a series of strange geological features." "For many years these features were a puzzle." "When geologists eventually learnt how to interpret the landscape they uncovered the first hints of a long chain of dramatic events that have transformed the planet throughout its history." "Stranded in the middle of the Swiss countryside is this enormous boulder." "It's been made a national monument." "Christian Schluchter, a local geologist, explains why it's so important." "What we see here is really a strange piece of rock." "It actually doesn't belong to this area where it is now." "Its composition is different from the bedrock here." "Bedrock is beautiful sandstone and this is a gneiss so it must come from somewhere else." "If you look around in the Swiss Alps then you find the places in the mountains of the canton of Valais where this comes from, so it has traveled let's say between 200 and 250 kilometers to come here." "It is what we call an erratic boulder." "People, of course, were thinking for many, many centuries how this actually came to rest here because it was obvious it had to be moved somehow, so the first idea was that it has been brought here" "by a huge big flood, by the waters of a big, big flood originating high up in the Alps." "Erratic boulders like this were found all over northern Europe and America." "To 19th-century geologists they seemed like good evidence that the earth had once been covered by enormous floods, just as the Bible described, but as they looked further up the valleys" "Swiss scientists could see that water was not the only thing that could move rocks." "All these boulders around here were carried down by the actively advancing glacier." "The advancing glacier from up the valley here carried and put them down here in the 1850s and piled up this beautiful dam we call a terminal marain." "This jumbled wall of boulders is now several hundred meters from the snout of the glacier." "Back in the last century glaciers all over the Alps stretched further own the mountains than they do today." "It was around this time that a Swiss naturalist," "Louis Agassiz, began to wonder how far these great rivers of ice had once reached." "The answer, as is so often the case, was in the rocks." "This here is one of the places gassiz was visiting when he did his studies on glaciers and it's a very special place." "It's one of the most beautifully polished bedrock surfaces." "Here it's a polished surface of the Grimsel granite." "Now how does such a beautiful polish actually happen." "It happens at the base of a moving glacier where enough rock flower is available to act as a polishing agent." "Tiny fragments of rock trapped in the ice rubbed at this slab like fine grade sandpaper." "The smooth surface stretching far up the side of the mountain shows that the ice here was once one kilometer thick." "But the ice carried more than just powdered rock." "These scratches on the bedrock surface here are typical for formerly glaciated areas." "They are proof of the moving boulders at the base of the glacier." "Following the scratches across the landscape," "Agassiz realised that it wasn't biblical floods that had left erratic boulders stranded, it was ice that once had filled this entire valley." "Geologists have now been all over the Alps looking for evidence of rock that had been shattered and pulverized by the glaciers." "They've plotted the location of terminal marains and erratic boulders to see the maximum extent of the ice and they've found that practically the entire country would have been covered." "18,000 years ago a sea of ice one kilometer thick would have covered the site of Geneva." "It soon became clear that the ice had spread beyond Switzerland." "Erratic boulders found in other countries, marked the outlines of vast ice sheets that had also covered much of Europe and Northern America." "The ice was up to four kilometers thick in places, transforming the landscape into bleak, featureless plateaux." "The discovery that the earth's climate had once been completely different had a profound impact." "Geologists started on a journey through time to trace the tangled history of climate change on our planet." "A crucial step in understanding the history of the massive ice sheets came from looking at a place, thousands of kilometers from the furthest reaches of ice cover:" "The tropical island of Barbados." "Maureen Raymo is a geochemist visiting Barbados to track the precise course of the Ice Age." "Strange as it may seem this far south, the ice has left its mark on the rocks that cover the island." "The island is made almost entirely of ancient coral reefs." "Unlike the other islands of the eastern Caribbean which are volcanic, this one is constructional having been made out of coral reefs." "Everything we're seeing here is an ancient fossilized coral reef." "It's beautiful, I mean you can even see the individual polyps on these corals still." "Here's a huge conch shell beautifully preserved." "This fossilized reef can only have been stranded by a massive drop in sea-level." "The cause of this drop was surprisingly obvious." "As the ice sheet grew it locked up millions of cubic kilometers of water." "At their maximum extent ice sheets caused world-wide sea-levels to drop by 120 meters." "This would have had a global effect changing the shape of the continents." "In Barbados the coral reef growing around the island would have emerged and become dry land." "But it's not just one coral terrace on Barbados, there are several stepping up the side of the island." "Repeated terraces must mean repeated changes in sea-level and repeated changes in sea-level mean not one but many ice sheets waxing and waning." "Barbados is the only island to have these multiple terraces and they exist because it's doing something rather strange." "Barbados is very unusual island because it's very slowly being uplifted out of the sea by tectonic forces." "So what we see on Barbados is a series of steps made up of coral reefs that go up in elevation and also go back in time because you can imagine the, the highest coral reef is the one that's been lifted out," "has been lifted out of the ocean the longest so they're all slowly being pushed up out of the ocean." "Because Barbados is being lifted up it's producing a unique record of changing sea-levels and climate." "Every time sea-levels rise and fall a new coral terrace emerges." "So here we are, we're on the ancient reef crest right now and we know it's the top of the reef because there's all these cervicornis or stag horn coral pieces and that's a type of coral that only grows" "within a few meters of sea-level, so we have very concrete evidence that, that what we're standing on used to be at sea-level." "It's been uplifted by the tectonic uplift of Barbados and we can very clearly see one more terrace below and just over that terrace just out of sight is a third terrace." "All three of these terraces are reflecting times when it was very warm, when the sea-level was very high." "Now by the late 60s/ early 70s we'd developed techniques that allowed us to date specimens such as this and so we now know that this reef system right here is 125,000 years old." "The one we can see right there is 105,000 years old, and the one that's just out of sight is 82,000 years, so what we have is a really nice record of warm climates going back in time." "On the other side of the world is direct evidence of the colder periods in time." "The finely crushed gravel in this Swiss quarry was left behind by the glaciers." "This particular quarry consists of distinct layers which piled up over half a million years." "This sediment up here with these quite large boulders in it, it's deposited by a glacial melt water stream right in front of the active ice, maybe a few tens to a few hundreds of meters at the most," "so this is a direct evidence of the presence of the ice at that place, and then if you look down here that's a sediment deposited in a small lake which was produced by a glacier." "So we have evidence of two glaciations within these three meters of a geologic section." "Sandwiched between the two layers showing when temperatures were cold is a third layer which tells a very different story." "You see these peculiar pieces of something sticking out." "If I grab one of these pieces we have a beautiful piece of fossil wood." "If we analyse all the fossil pieces of wood in here we can conclude that the temperature was even warmer than at present when the surrounding forests existed here by about 2-2.5 degrees Celsius, so this layer is an important document" "telling us that in-between two layers of very cold geologic environment we find this spread of actually warmer than present climate." "The change from cold to warm and back to cold happened in just 150,000 years." "In fact, the quarry shows that the climate flipped at least three times in the remarkably short period." "The evidence from places like Switzerland and Barbados has revealed a pattern in the Ice Age." "Over the last million years the ice sheets have waxed and waned 10 times, but they've never entirely disappeared." "Yet a million years is just a brief moment in earth's history." "To see whether this pattern continued back indefinitely meant looking in a surprising place." "This ship is pushing back the boundaries of climate history." "It's the only ship in the world that drills deep into the ocean sediment." "It drills 24 hours a day, seven days a week." "The running costs are $45 million a year, and all this to bring up kilometer after kilometer of mud." "The notion of glaciations and inter-glaciations, the waxing and waning of continental ice sheets, was exactly that, it was first recognised and studied on continents." "The trouble with continental records is that they're fragmented." "You're studying outcrops, erosion is there, you're missing part of the record." "That is not the case, nearly as much in the oceans." "The cores of mud are reduced to this dusting of microscopic shells." "The shells belong to animals called forams." "Imprinted in the shells is information about what the climate was like when the forams were alive." "When they died they sank to the sea floor and they were incorporated in layers." "Those layers stacked up over time and we core those layers continuously to get a continuous record of climate change." "And this particular place is a good place because we have a very fixed section so that we can tell that story in great detail." "This section of mud built up over 20,000 years." "At this site in the North Atlantic, there's 20 million years of mud stacked up on the ocean floor." "A constant supply of forams is produced by the drilling programme." "Different species thrive in different water temperatures." "Counting the various types of forams and analysing the chemistry of their shells gives an indication of the climate at the time the forams were alive." "The analysis is agonizingly slow work, but it has revealed the pattern of climate change since the age of the dinosaurs." "We've been able to reconstruct how global temperatures have changed over the last 70 million years." "Here is today, and this is 70 million years ago, the time of the dinosaurs, and this is warm hot climates and this is cold." "What we've seen is from about 70 to about 40 million years ago it was extremely hot, much warmer than today, about 15 degrees warmer than today, on average, and that, since that time temperatures have been gradually falling." "At 35 million years a very rapid cooling associated with the glaciation of the Antarctic." "In the last few million years we've been growing large ice sheets under North America and Scandinavia, so really seen a large-scale pattern of global cooling that's characterized the last 70 million years." "So the pattern of fluctuating ice sheets is a comparatively recent event and in geological terms we're still in the Ice Age." "There are still permanent ice sheets on Antarctica and Greenland and glaciers in the high mountains." "Thanks to the forams we now know that this hasn't always been the case." "During the time of the dinosaurs, and for millions of years after, it was too warm for ice to exist anywhere on Earth." "What about before the dinosaurs though?" "To find out whether the climate had always been warm you need to travel back in time." "Maarten de Wit is a geologist well used to travelling back in time," "back through hundreds of millions of years." "This mosaic of rock fragments is called tillite and when it was discovered here in South Africa it turned geologists' view of the African climate on its head." "Look at this extraordinary rock, this, it's a very strange rock and what makes it very strange is, is all these rock fragments - big ones and small ones, round ones." "This is the unusual thing, you don't usually get angular and round ones together and big ones and small ones together." "This is just chaotic." "It must have been extremely difficult to interpret this rock." "The first geologists to map this in detail spent some time in the northern hemisphere and the way they interpreted this was that these rock fragments must have been deposited by some sort of ice sheet." "The ice sheet would have moved over the bedrock, picked up a lot of rock, round it to a very fine powdery matrix, this grey-green material, plucked up a whole lot of rock fragments everywhere, moved over a water body" "and as it sat over that water body and melted it would have dropped all its material and that reasonable explanation, it seems to be the best explanation, to explain this sort of chaotic set of fragments in this rock flower." "Below and above it we have fossils and we know the age of these fossils and it turns out that this particular tillite is 300 million years old, so that's, that's an amazing thing to think," "300 million years ago that this area here in South Africa was covered by a very thick ice sheet." "Temperatures here in this climate must have been very different, an Ice Age, a huge ice sheet covering this, this countryside." "The ancient tillite found in this part of South Africa has also been found scattered in other continents like Antarctica, India and Australia." "It's all about the same age - 300 million years or so - but this widespread distribution does make perfect sense, as Maarten explains." "Well you, you've got to remember that 300 million years ago the world was very different." "All the continents in the southern hemisphere were together as one big super continent." "Over here, here's India and Madagascar, can see Australia over there and the centerpiece here stills makes this large land mass of Africa." "In this framework and bunched together the deposit makes sense in terms of a huge ice sheet that was covering part of, or the largest part of this super-continent called Gondwana and of course the centre of this ice sheet would have been over here," "so this part of it would have been sitting around the South Pole." "The tillites have revealed that the Earth has experienced an Ice Age before." "On that occasion ice gripped the super-continent for more than 60 million years." "This is not the only Ice Age we've had." "We know in the far distant past we've had more than one glaciation." "Even in southern Africa we have evidence, good evidence for a glaciation in the Ordovician" "430/440 million years ago and further a field in Africa, many parts of Africa we have examples of glaciation 700 million years ago and elsewhere in the world we can go back as far as almost 21/2 billion years ago," "a set of tillites in North America so it looks like that as far back as we can go in this record that the earth has been in and out of Ice Ages." "Looking at these tillites and combining them with the evidence from the ocean floor it's been possible t build up a picture of Earth's changing climate." "For most of its history it seems to have been warmer than today, but every now and then Earth has been plunged into vicious cold so that huge areas have been covered by ice for millions of years." "Then the ice is shaken off again and the obvious question is:" "Why?" "The first hint of the answer came from looking at the ice remaining from the current Ice Age." "This is one of the most isolated laboratories on the face of the planet." "Apart from the occasional wayward bird, the nearest sign of life is 500 kilometers away." "This is the North Grip campsite in the centre of Greenland." "For 3 months of the year it's the home to a team of 30 scientists." "Until about 12,000 years ago the whole of Scandinavia was covered by a large ice sheet," "This ice sheet also stretched into parts of Germany and Great Britain." "Iceland had a separate ice sheet covering it completely and then we had a huge ice sheet over all of Canada reaching into the present United States." "Then this dramatic change comes about in only a few thousand years." "All these big ice sheets they disappeared completely except for the Greenland ice sheets on which we are sitting right now." "It's very good that we have this ice sheet, this remnant of the Ice Age, because it really makes it possible for us to understand what was going on at the time really." "This is what we are aiming at with our work here." "The scientists here have one aim in mind:" "To produce one of the longest continuous cores of ice ever drilled." "So far they're about half way." "There's one and a half kilometers to go." "Each meter of ice brought to the surface is a step further back into the Ice Age." "We see structural difference between fine grained winter snow and coarse grained summer snow and these differences are preserved in the ice so we are able to count annual layers all the way down through just like tree rings." "If you measure the lead content in the ice cores down through time you can see that this increased during Roman Times because the Romans they had a lot of lead mines all over their Empire and then you see that this decreases" "after the decline of the Empire." "You see it increases in our century and when everybody stops using leaded gasoline then the curve is falling again you know." "There's much less lead in the atmosphere, so everything that has to do with the atmosphere, the history of it and the history of human beings is really preserved in those ice cores and it's really fantastic." "The ancient history of the atmosphere can also be found in the ice." "Tiny pockets of air become trapped as snow falls and compacts." "These bubbles of atmosphere are time-capsules." "When researchers began sampling them to test for carbon dioxide content, they found something that stopped them in their tracks." "During the last cold period, carbon dioxide levels were much lower than today." "This is very interesting and makes sense, because of the role that carbon dioxide plays in controlling earth's climate." "It's a greenhouse gas that's always present in our atmosphere and it acts as, as, as a thermal blanket keeping the earth's surface temperature warmer than it would otherwise be if there were no CO2," "if there were no greenhouse gases, so the fact that during the cold periods that these greenhouse carbon dioxide levels went down and the climate got colder, makes sense from, from our understanding of the physics and chemistry of the greenhouse effect." "In recent years we've heard a lot about the possible links between carbon dioxide levels today and global warming." "But could it be that carbon dioxide is behind the swings in temperature which have taken place over hundreds of millions of years?" "Bob Berner, a geo-chemist, believes it is." "Before humans were adding carbon dioxide to the atmosphere there were other natural processes that were adding and sub-tracting carbon dioxide from the atmosphere, and these are all part of what is known as the long-term carbon cycle which operated over many millions of years." "The whole process starts with the introduction of CO2 to the atmosphere by CO2 coming out of volcanoes." "Every time a volcano erupts carbon dioxide spews out into the atmosphere." "Left unchecked it would build up, but rain gradually washes it out and plants draw it into the soil." "This carbon dioxide in the soil reacts with the rainwater that's percolating into the soil to form an acid." "The acid eats away at the rock in a process called weathering which converts carbon dioxide into carbonate." "This dissolved carbonate eventually makes its way into rivers and eventually by flow of rivers to the sea." "The dissolved carbon is removed from sea water by coral and other organisms." "When those organisms die, their remains build up on the seabed eventually turning into limestone." "Now this limestone we have down here completes the cycle eventually because it becomes buried to such a depth that it's heated, broken down and the carbon dioxide comes off of the, is removed from the limestone and it finds its way back to the surface" "in the form of seepage out of the ground or eruption from volcanoes, and this is the long-term carbon cycle." "All things being equal, levels of carbon dioxide," "CO2, would stay constant as the gas is continuously pumped in and out of the atmosphere, but the planet is in a constant state of flux." "Continents drift across the face of the earth, volcanoes burst into life, and then become extinct, vegetation comes and goes." "All these factors can affect the carbon cycle, so using geologist knowledge of earth's history" "Bob Berner set out to estimate how much CO2 levels have actually changed over time." "Bob has now calculated CO2 levels over half a billion years." "As you can see most of the time carbon dioxide's been considerably higher than it is at present and you see high values in the earliest period dropping to lower values in intermediate times and to intermediately high values between that time and the present," "but the lowest levels you can see are the present in a time about 300 million years ago." "This drop here is caused by one particular factor in Bob's equations:" "Plants." "Plants help to remove CO2 from the atmosphere by speeding up the weathering of rocks." "So when plants first evolved and flourished" "CO2 levels began to fall." "Those levels reached an all-time low 300 million years ago, precisely the time when a massive Ice Age left its imprint in the rocks of South Africa." "This is very gratifying and indicates that this drop" "I believe is due to the rise of the plants and their acceleration of weathering." "This acceleration of weathering I believe caused the CO2 drop which lead to the glaciation at 300 million years ago and was I think the major cause of this glaciation." "It is amazing to think that plants could have triggered the Ice Age 300 million years ago." "But carbon dioxide levels also appear to have been falling over the last 65 million years, a decline that seems to have led to the Ice Age we're in today." "An explanation for this drop is also in the equations:" "Mountain building." "We know that CO2 gets into the atmosphere through volcanoes but it comes out through to rock weathering, and rock weathering goes on primarily in the mountainous regions of the world." "We know that for the last 40-50 million year have been unusually active with respect to mountain building." "There's the Himalayas, the Andes, the Rockies, and this tectonic activity has probably been in a large part responsible for the reduction in atmosphere of carbon dioxide levels." "Now that's very interesting, it's obviously been cooling over that time period so we probably are seeing this causal link between the earth's tectonic activity and the earth's climate." "Now we can begin to understand the pattern of climate change." "It's a pattern which changes to the rhythms of evolution and the movement of the Earth's tectonic plates." "The climate wanders from one Ice Age to another as the continents drift around the planet." "But the movements of the continents can't explain everything." "Over the last million years the ice sheets have been pulsating to a rhythm faster than continental drift." "Something else must be driving these cycles." "Ice will never accumulate if all the snow of winter melts the following summer, but if summers are cold snow will survive from one winter to the next." "Eventually the layers will build up and several decades of cold summers will result in a sizeable ice sheet." "If summers warmed up again the ice sheet would shrink back." "The idea that the pattern of fluctuating ice sheets was caused by fluctuating summer temperatures was taken up early this century by a Serbian scientist called Milankovich." "He believed that the cause of these slow repetitive changes was due to the way the Earth orbits the sun." "The Earth circles the sun with its axis tilted." "That tilt gives us our seasons." "When the North Pole points away from the sun, we experience our winter, the southern hemisphere its summer." "On the other side of the orbit, the situation is reversed." "This is the now the northern summer." "Over thousands of years the precise orbit and the tilt of the Earth varies slightly." "It wobbles and dips making our summers hotter or colder as the northern hemisphere moves toward or away from the sun." "Using this information Milankovich calculated when the summers would become cool enough to cause the ice to return." "Despite the logic of his idea it was impossible to prove at the time." "Nobody knew precisely when summers had warmed and cooled." "Then, 10 years after Milankovich died, the coral terraces of Barbados were dated for the first time." "This is a curve of how hot northern hemisphere summers had been over the past 250,000 years." "This curve was first calculated, predicted by Milankovich and what you can see is that there are times where northern hemisphere summers are quite warm and at other times, for instance down here, the summers are much cooler" "and that these cooler summers, these low periods would be glacial periods and these would be the warm periods with higher sea-levels and less ice volume." "Now if we compare this curve to the Barbados data what you see is that these coral terraces, including the one we're standing on right now, their ages line up almost perfectly with the time periods that Milankovich" "would have predicted would be warm, therefore less ice and higher sea-levels and indeed it was the dating of these coral reef terraces in the early 70s that proved seminal for most people accepting the Milankovich hypothesis that indeed this was what caused climate change." "This tidy fit between Milankovich's predictions and the coral dates appear to complete the picture." "With this complex pattern of climate change behind us what can history tell us about the future?" "Today the fear is that man-made global warming could bring about a sudden collapse of the ice sheets." "And the fact is that it looks like such breakdowns have happened several times in the past with dramatic and unexpected effects." "Once more the story's in the mud of the ocean floor." "In his lab near New York, geologist Gerard Bond was looking at a core from the North Atlantic when he spotted some subtle variations." "We noticed as you can see in this core of 150 centimeters, there are a number of changes in colour." "Here's a light layer here, a little darker layer here, an intermediate colour layer here, becomes light again down to about here, this one's a little lighter, this one's lighter yet, and then it goes back to a darker layer here," "and we knew from radiocarbon dating of this core that the top is about 9,000 years, this level is 14,000 years and about 20,000 years here." "These bands were coming very fast and what that meant was that these changes in colour were coming about every 1,000-2,000 years." "Having identified these strange bands of colour," "Gerard set to work to find out what caused them." "It was a grueling process." "Sample after sample of the cores were reduced to sand grains." "Each grain was counted, classified and re-counted." "After about a million grains of sand," "Gerard took stock of his curious findings." "We found six layers that had a marked increase in limestone and dolomite fragments." "The origin of these appears to have been eastern Canada." "In addition, when we look more carefully at the sediment, in-between these six events there were additional layers." "These showed increases in volcanic ash that came from Iceland and increases in grains mostly quartz and feltzspar that were stained with an iron oxide that's called hematite and you see some of that here and here and we believe that these particular grains" "are coming from the Gulf of St Lawrence." "There's only one way so many grains could have been lifted from the bedrock of Canada and Iceland and transported to the ocean - they must have hitched a ride." "During the last glaciation ice sheets scraped over the continents picking up rock fragments on their way to the sea." "From there, icebergs carried the grains across the Atlantic." "As the ice melted, the grains were released and drifted to the bottom of the ocean." "The sheer number of grains found in the layers of the sea floor suggest that enormous armadas of icebergs swept across the ocean every few thousand years." "What-ever caused this, work on the Greenland ice core suggests the invasion of the ocean by icebergs could have tipped the climate into turmoil." "Each of these slices of ice represents6 weeks of climate history." "When the researchers looked at the ice from the last glaciation in this kind of detail, they found a completely unexpected series of temperature jumps." "These jumps coincided with the surges of the icebergs." "By looking at the ice core in such detail the researchers in Greenland discovered the most astonishing thing." "Within the glacial period there are climate cycles that are even more rapid." "They last a few thousand years, so if I describe a single cycle, you can imagine along the slow cooling and then there's a very rapid warming" "10-12 degrees Celsius and that warming happens within the span of a single human lifetime." "It's quite astonishing how quickly the regional climate of the north Atlantic changed." "Ever since these frenetic changes in temperature came to light researchers have struggled to understand the cause." "One thing they do know is that climate in the North Atlantic is strongly influenced by the warm water flowing up from the tropics." "The oceans play a vital role in climate." "Much of the sun's energy is received here in the Tropics, but ocean currents carry that heat towards the Poles." "In particular the Gulf Stream system in the North Atlantic carries a vast amount of heat from the lower, the lower latitudes up to the higher latitudes." "In fact probably about 30% of, of the heat delivered to Europe, western Europe," "Great Britain is, is brought by the Gulf Stream system." "This warm water is drawn up from the tropics because of sinking cold water in the North Atlantic." "In the tropics, evaporation caused by the sun's heat creates surface waters that are particularly salty as well as warm." "As the Gulf Stream carries this warm water northwards it gives up its heat, becoming cold and dense." "Near Greenland it's dense enough to plummet to the ocean floor, drawing up more tropical waters behind." "It's the sinking of this cold, salty water which is the engine behind a conveyor belt that's bringing warmth to the northern latitudes." "Stop this water from sinking and you stop this heat supply to the north." "And that's exactly what scientists believe the armadas of icebergs may have done." "Now of course if you have the North Atlantic choke full of icebergs, all those icebergs are going to melt and deliver a huge amount of fresh water to the surface waters and this fresh water would have lowered the solidity of the surface water, lowered the density" "and shut down the conveyor belt." "By shutting down the conveyor belt the heat supply to the north would have been cut off and temperatures on land would have plummeted." "So perhaps here's the explanation of the rapid flips in climate during the last glaciation." "Enough icebergs surging out into the Atlantic would have switched off the conveyor." "After the ice had melted the conveyor would suddenly switch back on leading to rapid warming in the north." "These sudden swings happened at least 20 times in 60,000 years but eventually the icebergs stopped coming and the climate calmed down." "This is a time that agriculture's developed, cultures have flourished, but this is also a very unusual time for climate." "It's been very calm, very stable." "We know from the geologic record that in fact usually climate is much more dynamic." "We're going very quickly between colder periods and warmer periods." "Indeed some climate changes can happen in the course of a single human lifetime as we know from the end of the last glacial to the present warm period." "Perhaps human civilization only emerged because this rapid change came to an end." "Today we may be reaping the benefit of a few thousand years of stable temperatures but no-one knows how long this benign lull will last." "All the factors that influence climate in the past will continue to have an effect in the future." "Now there is the additional concern that mankind will prematurely tip the balance back into more turbulent times." "As they've traveled back in time, geologists have uncovered a history of climate change far more profound than anything the Swiss pioneers could have suspected." "Everything they've found shows that climate change is a natural result of the way the Earth works." "Climate has been changing one way or another throughout Earth's history and there's no reason to believe that it will ever stop changing." "Subtitles:" "Thor"