Horizon (1964) s00e88 Episode Script

Climate Change: A Horizon Guide

1 WAVES CRASH Today, climate change seems to be everywhere.
A chunk of ice the size of the Isle of Man has started to The last decade has been the warmest period since records began.
Firefighters are stretched to the limit .
Scientists say is further evidence of a warming climate.
Yet 40 years ago, climate change was virtually unheard of.
Since then, Horizon and the BBC have followed scientists as they've grappled with one of the most complex and challenging problems they've ever faced.
This unique archive has captured a constantly-surprising journey of discovery Whoa! .
seen scientists face a barrage of controversy and criticism .
One of the world's leading climate research units is to come under unprecedented scrutiny.
and tells the story of the transformation of a little-known theory into one of the greatest scientific undertakings in history.
On April 22nd, 1970, 20 million Americans celebrated the first Earth Day.
# There must be some kind of way out of here Said the joker to the thief For many, it marked the start of the environmental movement.
I can't get no relief It seemed as if the planet faced an ecocatastrophe.
Ploughmen dig my earth Pollution was poisoning the earth.
Deforestation was damaging ecosystems.
And acid rain was destroying forests and lakes.
It led some to predict that our very survival was at stake.
If you had to ask me now what the chances are of civilisation reaching the turn of the century, I'd have to say 1-2%, if we're lucky.
But from today's point of view, one very important topic was largely missing.
Climate change.
And when it finally did hit our screens, there was a twist.
The weather satellite depicts a planet that grieves for its lost harvests while the price of food keeps going up.
The climate was becoming an issue, but the central message was rather different to today.
Will a new ice age claim our lands and bury our northern cities? It's buried Manhattan Island before when glaciers half-a-mile thick filled the valley of New York's Hudson River.
Unless we learn otherwise, it will be prudent to suppose that the next ice age could begin to bite at any time.
Global warming, as the theory was called then, was also being studied by scientists and it was mentioned in the same programme.
But almost as an interesting aside.
And there is a lot of oil and there are vast amounts of coal left.
We seem to be burning it with an ever-increasing rate.
And if we go on doing this, in about 50 years' time, the climate may be a few degrees warmer than today.
We just don't know.
Let us therefore keep an eye on the amount of carbon dioxide in the air.
It would be global warming, not the threat of an ice age, that would go on to become the dominant scientific issue.
It's fascinating to look back to a time when global warming wasn't the main story.
Scientists were only just beginning to get to grips with the complexities of the climate system and how and when it might be changing.
And there just wasn't enough information around for them to be confident about what was happening.
But that was beginning to change.
In the late 1970s, the arguments for a new ice age began to melt away.
The theory was based on emissions of the gas, sulphur dioxide, then a major atmospheric pollutant.
This gas was known to have a cooling effect and some scientists calculated that this could push the planet into an ice age.
But it soon became clear that both the amount of sulphur dioxide pollution and the size of its cooling effect had been overestimated.
There would be no big freeze after all.
Even so, the case for future warming was far from certain.
Gases like carbon dioxide were known to trap heat within the atmosphere.
But would human emissions be enough to force up global temperatures? In 1979, the US government sought expert advice.
They turned to a trusted, highly-secretive group of scientists known as the JASONs.
A few hundred miles apart, fallout patterns can overlap.
Most of what they do today and have always done is to do with defence.
Tests on Nike Zeus continued in the past year as But in 1978, they were asked to investigate the growing evidence for global warming.
One JASON remarked that it made a bit of a change.
Instead of finding ways to destroy the world, now they were being asked to save it.
There was one potential problem - few of them knew anything about climate.
The JASONs decided to build their own computer model of the global climate system.
They called it the JASON Model of the World, and what came out of it was a report.
The JASONs were convinced we faced warming, but the report was secret.
As far as the public was concerned, global warming remained in the shadows.
And for those arguing against the theory, it had a major flaw.
It seemed impossible that anything humans did could be the dominant influence on something as vast and complex as the climate.
But then came a shocking discovery.
Scientists from the British Antarctic Survey have been manning yearly expeditions to the Polar South as part of a long-term programme of Antarctic research.
Then, in 1985, evidence suddenly appeared of alarming fluctuations in the polar atmosphere.
Well, we discovered that in the early spring, soon after the sun rose again after the long polar night, there was a very rapid decrease of ozone.
This has grown to the extent that now 50% of the ozone layer disappears in about 30 days.
And this was no natural phenomenon.
CFCs, man-made chemicals used in aerosols, packaging and fridge-freezers, were destroying the ozone layer, a crucial barrier blocking harmful UV radiation from the sun.
Clear proof that humanity could bring about profound change in the atmosphere.
With the ozone hole making headlines around the world, the plausibility of global warming increased.
At the same time, experimental data was giving scientists the clearest picture yet of what was happening to the atmosphere.
One of the most significant pieces of research only existed thanks to the determination of one man.
In 1958, Dave Keeling started to measure the amount of carbon dioxide in the atmosphere.
He doggedly stuck to his measurements, even as many who saw it as pointless attempted to cut his funding.
By the late 1980s, his dedication had paid off.
He had produced a continuous record going back nearly 30 years.
The resulting graph clearly showed that levels of carbon dioxide were creeping inexorably up from 315 parts per million when he started to 340 parts per million.
The last crucial piece of evidence was whether that increase in carbon dioxide had caused a detectable effect on the climate.
At East Anglia University, they have been looking for the effect of that CO2 rise on temperature, painstakingly going through past temperature records across the world.
And they have found that the world really is getting hotter.
The temperature has risen half a degree Celsius this century.
Though not a large increase, it's only the beginning.
In a little over a decade, any prospect of a new ice age had been buried under the ever-increasing weight of evidence for a warming world.
14 years on from The Weather Machine, Bert Bolin was back, summarising the journey scientists had been on.
20 years ago, when this matter was discussed among scientists, the response was one of dismissing it.
"This is fiction, we don't believe it.
" Today, many are concerned, and that is a major difference.
It has been an evolutionary process in people's minds as well as with regard to our knowledge about the phenomenon.
What is happening is that we as human beings are bringing about a climatic change.
We are emitting things into the atmosphere now with a rate that will change the climate more rapidly than it has changed naturally during the last hundred thousands of years.
It looked as if the major scientific question was settled - the Earth was warming and humans WERE responsible.
What's interesting now is how uncontroversial it seemed then.
It wasn't long before the media picked up on scientists' findings and politicians began to respond.
Global warming was about to complete its journey from the shadows to centre stage.
Britain's then Prime Minister, Margaret Thatcher, was one of the first to acknowledge the challenge.
Mrs Thatcher was a scientist as well as a politician, and she decided to take a lead on the issue.
APPLAUSE The evidence is there.
The damage is being done.
What do we, the international community, do about it? It's no good squabbling over who is responsible or who should pay.
We have to look forward, not backward.
And we shall only succeed in dealing with the problems through a vast international cooperative effort.
APPLAUSE It marked a decisive turning point.
Climate change was no longer simply a scientific issue .
but also a political one.
At the Rio Earth Summit in 1992, politicians began work on the first attempt to curb greenhouse gas emissions.
But, by then, opposition had already started to surface.
If you look at what it would take to make a radical reduction in greenhouse gas emissions, the 20% that some of the Europeans have called for, it would almost certainly cause a recession in advanced economies.
There's not substantial scientific evidence yet to cause anyone to be as concerned as the hype of the popular establishment news media, and the liberal politicians who love government hype this thing all the time.
The controversy would intensify over the coming years.
As the political arguments began to simmer, the scientists just ploughed on, because as far as they were concerned, the question of whether human-induced climate change was real had been settled.
What was left was the far harder question of how and when the climate would change and what the consequences would be.
And they were about to discover some worrying lessons about what might happen in the future from Earth's past.
A breakthrough came from a remarkable natural record of how the Earth's climate has changed over time.
One that only exists thanks to a very familiar element of the weather.
Snow is one of the great materials for solving climate riddles.
It's sampling the atmosphere as it comes down.
The snowflakes grow around dust particles and they pick up pollen particles as they fall through the air.
Other characteristics of the snow tell us, really, what the temperature was when it fell.
And in places like Greenland, the snow has been building up for tens of thousands of years, forming giant ice sheets in places up to 3km thick.
Within that ice is an incredible record of past climate waiting to be tapped.
And that's exactly what Richard Alley did.
It's moderately clear, if you look at the ice, that it is layered.
And each of these layers is representing the snowfall from a year.
The ice core layers were like frozen tree rings.
Richard's minute examination would reveal tiny changes in the ice from year to year, back over the centuries.
The biggest challenge was to convert those tiny changes in the composition of the snow into one long, unbroken record of climate.
It took three years and the results were stunning.
Well, the huge surprise that came out of this ice core was that we had expected that climate changed - "wah, wah, wah" - over tens of thousands of years, and, in fact, climate does have a little ofslow change in it, but mostly what we see is that climate goes "boing, boing, "boing, boing, boing, boing", with the changes happening in years rather than tens of thousands of years.
This is not your lifetime, this is not even a single human generation.
It's shorter than that.
The ice cores revealed that, in the past, the climate had changed suddenly and dramatically.
The question now became, could such a sudden climate shift happen as a result of global warming? To answer this, scientists needed to identify the mechanisms capable of causing such abrupt climate change.
One candidate was buried in a peat bog.
For 25 years, Dicky Clymo has been working on peat.
He has been trying to measure decomposition deep down in the bog.
It's not a fashionable branch of science and Dicky has had to spend much time inventing his own experimental equipment.
We suspect that gas, methane and carbon dioxide may be produced in measurable amounts deep down in the peat.
But the difficulty is to get a sample of the gas to analyse.
So we devised these collectors, which we're now going to put into the ground, and they will eventually become filled with gas from deep down in the peat and we can sample them through a tube which comes up to the surface.
We fill them with helium gas, and the collectors themselves are condoms attached to the end of a piece of plastic tube.
We just seal the aluminium around that and then put it on the end of this hollow steel the tube.
Dicky currently has about 25 little rubber gas collectors in the peat.
There's one.
I'm afraid it's not going to inflate.
Yes, it is, it inflated itself.
But I felt it and you won't have seen it.
Nevertheless, there's a nice sample.
The gas samples show the decay occurs throughout the bog, matching the growth of fresh peat.
The warmer climate could end that steady state.
Decay would increase, carbon dioxide and methane would be pumped into the air.
If the world's peat bogs released a fraction of their stores of carbon, then nature would wrest control of the greenhouse effect from the humanity that set it in motion.
Rising global temperatures could trigger the release of buried stores of greenhouse gases like methane.
This could result in a sudden, dramatic increase in warming.
Peat bogs are one such reservoir of methane, but there are also very large amounts lying trapped in permafrost, areas of permanently frozen ground found in places like Siberia.
There could be serious consequences if warming was to destabilise those stores.
Inside the permafrost is a very large volume of dead plants.
And what's happening is that the permafrost is melting and thawing and slumping into the bottoms of the lakes.
Those dead plants thaw out and they ferment in the bottom of the lake and methane is the by-product.
Methane comes out.
If Katey is right, then we should be able to find methane almost everywhere.
Ahh! This is the ice.
Got to the ice.
Look at that! That's beautiful.
Oh, there's bubbles! The ice is over a metre thick and it's obvious that it's full of bubbles trapped inside it.
The trouble is, it won't stay trapped in these bubbles for long.
When the ice thaws in spring, the gas will escape.
Methane is a greenhouse gas that's 23 times stronger than carbon dioxide.
So we're very interested in understanding how much methane is coming out of these lakes.
There's one sure way to check just how much methane is in these bubbles, because it's highly flammable.
Wow! My God! Whoo! I can't believe it's a fire coming out of ice.
Isn't it amazing? It's a bit surreal.
We're on a lake in Siberia and the lake is burning.
It's pretty amazing, huh? I still don't It never ceases to surprise me.
Alarmingly, these bubbles can be found all over the place, which means there must be enormous amounts of methane trapped here.
Whoa! You all right? You OK? Yeah.
You ready? Ooh.
That's nice, isn't it? This place is just full of these.
Whoo-hoo! 'Fire coming out of ice is one of the most bizarre things I've ever seen.
'But it has very serious implications.
' Global warming causes the permafrost to melt.
The more the permafrost melts, the more fermentation happens in the bottoms of the lakes, the more methane comes out, which enhances global warming.
And it feedbacks to itself.
It just goes on and on and on and on and on.
So, melting, methane, melting, methane.
It's almost like there's a time bomb waiting to go off.
Climate change was no longer a distant threat.
Increasingly, it looked like one that could strike at any moment.
But the sheer complexity of the climate system meant it wasn't enough to know just what was happening to the atmosphere.
Scientists were also trying to work out the effects of climate change on the natural world, and that was proving tricky because the natural world changes all the time and you need to separate out those normal changes from anything caused by warming.
You can do it, but you need data sets that have been recorded over a really long period of time, and those were in really short supply.
But when they started looking, scientists did find that information in some quite unorthodox places.
Tenacious, sometimes bizarre long-term research is emerging as science's most valuable instrument in the study of the greenhouse.
Arthur and Dorothy Willis are the classic example.
Number? 1D.
1D Professor Willis has visited Bibury in Gloucestershire every summer for 32 years just to measure the grass on the roadside verge.
Put together with local weather records, the control data form a near-perfect chronicle of how an English roadside responds to climate.
At the Rothamsted Insect Survey in Harpenden, they've been trapping aphids since 1964.
Fred Last has been writing down the time of flowering of every plant in his garden for 13 years.
Back yard obsessives, in the best tradition of British science.
These days, climate science is a huge international effort.
And it's hard to express the importance of those early pioneers.
But thanks to a small army of dedicated individuals, we do now have the records that are letting us pick out the effects of our warming world.
Researchers have been scouring the country and have actually found historical books and papers from dozens of private individuals and organisations that provide them with a truly long-term, geographically widespread account of what seasonal changes have taken place over centuries.
Their work suggests that spring, on average, is happening 11 days earlier than it was 30 years ago, and that the last 25 springs have been the earliest on record for the last 200 years.
So nature, our unbiased and honest commentator, has done what we humans with all of our charts, all of our graphs, have been trying to do.
It's shown us very clearly that climate change is happening right now.
There are now many long-term studies dedicated to identifying the effects of climate change.
Thank to these efforts, the impact of rising temperature has been documented across the planet.
And there are a few individuals who have been uniquely placed to see some of the changes first-hand.
I've been to South Georgia several times and seen how greatly the glaciers there have changed.
This photograph of a glacier reaching right down to the sea was taken just six years before I first visited in 1981.
Now that glacier has retreated by 400m away from the beach.
Temperatures in South Georgia have risen sharply, but the southern hemisphere's most dramatic warming has happened a little further south.
Here, on the Antarctic Peninsula, the changing wind patterns have driven temperatures up by nearly three degrees centigrade over the last 50 years, ten times the average rate of the rest of the planet.
17 years ago, when I was last in the Antarctic, there were large colonies of Adelie penguins all along the Antarctic Peninsula.
Now, warming temperatures have meant less sea ice and Adelie penguin numbers are in decline.
We've only started to see changes in the Arctic and Antarctic recently, so it's hard to predict exactly what impact these changes will have.
But we can see for ourselves that these places are changing, and on a scale that is hard to ignore.
Other less obvious effects of climate change have also been documented.
As carbon dioxide is pumped into the atmosphere, the oceans absorb more of the gas, and this has a significant effect on the chemistry of sea water.
When carbon dioxide goes into sea water, it reacts with water molecules to produce an acid.
Now it's not just the extra acidity of the sea water that's a problem, the fact we're blowing carbon dioxide into this solution also changes the concentration of a chemical species known as carbonate.
Now that carbonate is what corals need to build their skeletons.
Already at the concentration of CO2 we have in the atmosphere, we're already seeing very large responses from coral reefs.
We're seeing large-scale mortality events, and scientists are now recording the decline in the calcification that's going on in reefs.
And this is not seen in hundreds and hundreds of years of records.
So if we go forward in time, we may see reefs degrading such that over time we'll lose these great wonders of the ocean.
Scientists have now identified many impacts of climate change.
But as levels of carbon dioxide continue to increase, what will happen to the climate in the future? Possibly the biggest challenge facing climate scientists is prediction.
Just how is our planet going to respond to this ongoing emission of greenhouse gases? For our society to make plans or to take effective action, we need to have a good idea of what's going to happen next.
To try and answer these questions, scientists began to construct computer models of a climate.
If they could build a working simulation, researchers could then tweak various aspects, like levels of carbon dioxide, and see how the climate responded.
A very simply premise, but also incredibly ambitious.
Here at Princeton's geophysical fluid dynamics laboratory, they've been working since the early '70s on predicting the future climate in a CO2-rich world.
The fact is that the climate system is a horrendously complicated mess.
And the question comes down to, "How can you describe that?" The way we do that is to break up the entire atmosphere into what I will call bite-size boxes.
Suppose that these boxes are 400km on a side.
Then you essentially make a grid that, say, looks something like this.
And you can think of this grid as being much, much larger than this.
But these are boxes that are 400km on a side.
Suppose that this box is centred on London, for example.
Then we have to describe how the sun shines at the particular time of year, and how it's changing, the effect of clouds, the effect of the ground in absorbing the radiation, whether it's winter or summer, it's going to be different The effect of the heat coming in and how it evaporates water and how that water enters the atmosphere and how it turns to change its form by turning from water vapour into precipitation.
And that precipitation turns around and changes the way that the atmosphere is heated and that heating of the atmosphere changes the way the wind blows.
Breaking the world down into boxes gave scientists some method to deal with the complexity of the climate system.
But for the models to be accurate, you need to understand the processes at work well enough to be able to describe them mathematically.
That turned out to be incredibly tricky.
Every process was stubbornly complex.
Take the behaviour of clouds, for example.
The problem with clouds is that they can both warm and cool the Earth's atmosphere.
The low-level fluffy clouds that we often associate with rain, like some of these here, reflect the sun's short-wave radiation back out into space, so effectively, they actually make the Earth cooler.
But high above this layer is another layer.
The thin, icy wisps of cirrus.
Made up of many types of tiny ice particles, it's known that they can warm the Earth by trapping the long-wave radiation it gives off.
But quite how much they do that and how that will alter the greenhouse effect is little understood.
The only way to find out is to study it close up.
So a project has been set up called the International Cirrus Experiment, of which this plane is a major part.
It bristles with sensors for measuring the temperature and compositions of all types of clouds, including the icy cirrus.
But really crucial to understanding the secrets of the cirrus is the equipment in these two pods here where a laser beams across at a special camera to produce pictures at the heart of the problem, the ice crystals.
' 'OK, turning 280.
'Climb speed and safety altitude noted.
'Climbing to 31,000.
' What they're trying to establish is the type of ice crystals formed under different conditions.
And how they affect the reflection of heat by the cirrus.
With this device, we can actually count the number of ice crystals that are going past the sensors out there on that wing.
And these are the type of traces you get.
There we have a beautiful ice crystal, right there on the screen.
But these pictures are only in two dimensions.
So that's why the laser camera, which we talked about earlier, is on the other wing.
It's producing holographic pictures of the minute ice particles as they flash through the beam at 200mph.
Back on the ground, a laser reconstructs the images in three dimensions.
This is called a bullet rosette.
But how do these shapes relate to the greenhouse effect? Well, the crucial thing to find out is what type of crystals contribute to warming and which to cooling.
Almost certainly, in a warmer climate, there will be an increase in cloud cover.
Now this may act as a sort of brake to total global warming, or it may speed it up.
Only when projects like this reveal more about the elusive cirrus can that knowledge be included in the computer models and the true climactic effect of the clouds be known.
After 30 years of effort, much more is known about how clouds form and interact.
But the fundamental question - will they reduce or amplify warming? - still remains.
That creates a major source of uncertainty in the models.
It's not just the amount of warming that models are concerned with.
A vital function is also to predict how different parts of the planet will change as a result of rising temperatures.
One phenomenon of particular importance is how warming will affect sea levels.
A key element will be how the ice sheets that blanket Greenland and Antarctica respond to climate change.
That response is only simply represented in most models.
To improve that situation, we need more information.
In 2012, I joined an ambitious expedition that placed scientists on and in front of a calving glacier .
to try and work out what factors were controlling the break-up and flow of ice into the sea.
That is a major calving event.
Oh, look at the wave, look at the wave! Look at the wave! In order to accurately model this, we need to know much more about the balance between melting and calving at the front of the glacier and the build-up of snow further upstream.
A major influence is thought to be meltwater that gathers on top of the glaciers every spring, forming spectacular sapphire-blue lakes.
If those lakes drain to the bottom of the glacier, then that water could influence how fast the glacier flows by lubricating the base of the ice.
As the glaciers flow more quickly, it leads to more melting and calving, which would deliver more meltwater to the ocean, helping to raise sea levels.
But little is known about the actual processes at work in these lakes.
Do you want to pick it up? Are you happy with that? No-one has ever dived a blue lake.
If the lake unexpectedly drains, they could be sucked down into the glacier.
The safety team would then attempt to haul them back on lifelines.
Three, two, one, jump.
It's absolutely beautiful down here.
All these shades ofwhite and blue.
I'm going to .
try and place this sensor here.
The sensor will now record any change in depth.
Let's have a bit of an explore and see if we can find where this plughole is, eh? Andy is keen to try to track down the opening through which the lake could drain.
Oh! Dougthere's a big, big cave here, going straight down.
Just going to have a look.
This could be the lake's plughole.
For Andy, it's a challenge he can't resist.
It's pretty dark in here.
It's definitely getting narrower.
No way.
It's getting too tight.
It's getting way too tight.
Stillnowhere near the bottom.
40 minutes on the dive now.
41 now, so it's getting to be a long dive.
And the maximum dive length we agreed on wasn't much longer than this, so And it's cold and they'll be using air quickly so they'll be out very soon, whatever they're doing.
But something more urgent threatens Andy.
HE BREATHES HEAVILY I need to surface.
I think this air hose is freezing up.
The team calculates just this one lake now contains over five million cubic metres of water.
That's 2,000 Olympic swimming pools.
A staggering quantity.
Together with the other blue lakes and meltwater on Store, that's easily enough water to help the glacier slide towards to sea and create more icebergs.
Which, as the glacier reminded us, is a spectacular process.
Just phenomenal.
That iceberg is a kilometre across.
This research will ultimately feed into the models and help improve predictions of sea level rise.
Through this and many other research efforts, models are constantly updated and tweaked as we improve our understanding of the processes at work.
I find climate models incredibly impressive.
They bring together humanity's best understanding of so many aspects of our climate discovered over decades by thousands of scientists, and this huge collective effort now lets us mimic our planet in the virtual world better than ever before.
Models can never be perfect.
But they have become a very powerful tool for investigating and predicting the future path of climate change.
They've also been crucial in answering one of the most contentious issues at the heart of the debate - the extent to which we humans are responsible for the changing climate.
The key question, of course, is how can we distinguish between variations due to natural causes and those variations of the climate that are induced by human activity? And the key thing that convinced me, at any rate, was a graph like this one that we marked out on the floor, that had been prepared from climate scientists like Professor Peter Cox.
Now, explain to us the significance of this graph.
OK, what we're going to do is take a walk through time and the first thing to know as we walk through is this, that the climate is naturally variable.
It's a spiky beast.
Occasionally, there is a downward trend that is associated with a volcano going off, that cools the system down because of the dust it throws up, but generally, it just oscillates around.
And then we get to a period around about 1910, where you can start to see an upward trend, a warming of the climate - global warming, if you like.
And the issue is, what caused that? Was that humans, or was that natural? So what we do to try and work that one out is to take a climate model and to put in the various factors.
And what we can see with this green curve here is a climate model that includes just these natural factors.
So this is when volcanoes go off, and the output from the sun.
And you can see that the green curve can reproduce, reasonably well, this mid-century warming.
So up to this point, you could reasonably argue that climate variation can be explained by natural factors.
But as we move on, we can see that's no longer true as you get to the latter part of the 20th century.
From about 1970 onwards here, you can see the red curve, the observed temperatures and the green curve really beginning to diverge.
And the question again is, what caused this recent warming? So we ran the model again and we include human factors.
Particularly, we include the greenhouse effect from, um, mostly from carbon dioxide that comes from fossil fuel burning and then we get this yellow curve and we can see, as well as reproducing the mid-century warming, we get this recent, rather rapid warming reproduced.
And that tells us two things.
One is that the model looks realistic - it looks like the real world - and the second thing the model tells us is that this recent warming is due to human beings.
So, there you have it.
There seems little doubt that this recent rise, this steep rise in temperature is due to human activity.
The science points towards some unavoidable conclusions that the climate is changing, global temperatures are rising and that humans are the main cause.
Yet, there is a significant section of both the public and politicians who remain unconvinced.
That's partly down to the nature of climate change.
The effects can be subtle and complicated and they're difficult to spot on a day-to-day basis.
On top of that, the science itself can seem dauntingly complex and so the public is often left just feeling as though they have to take scientists' word for it, and not everyone has been prepared to do that.
GENERAL HUBBUB This is a gathering of the world's most vocal global warming sceptics.
At this conference, there are scientists, but also economists, philosophers, politicians and campaigners .
even a stand-up comedian.
APPLAUSE But this conference has a serious purpose So, the focus on .
to question the idea that we're facing a climate crisis.
Causes all of that structure Global warming is not a crisis.
I think this conference proves that there's no consensus.
CO2 is in no way connected to global warming Yeah.
it never has driven temperature, it never will.
Schoolchildren across the world are being scared to death based on speculative, unproven computer models and a lot of people, including the media, should be ashamed of themselves.
They've laid down challenge after challenge to the proponents of climate change.
But as the scientific evidence has accumulated in favour of global warming, it's become harder and harder to claim that there's any real scientific disagreement on the core issues.
But there are still sceptics who maintain that the science ISN'T settled.
And they explain away the mass of scientific opinion by claiming that the whole global warming theory is a fraud.
When you get the National Climate Data Center withholding the locations of its temperature stations the moment one or two of them were found to be in urban heat island areas, you find the "hockey stick" data suppressed, hidden, not released until two years of bullying eventually made the authors part with a sort of messy version of it, then one immediately smells a rat.
The vast majority of the points raised by the sceptics HAVE been countered by the developing science, but a group remain vehemently convinced that climate change is NOT an issue.
Some even say that it's one of the greatest scientific frauds ever committed.
And in 2009, it seemed some evidence of fraud had been discovered.
The work of one of the world's leading climate research units at the University of East Anglia is to come under unprecedented scrutiny.
"Climategate", as the controversy was inevitably labelled, involved the University of East Anglia's Climate Research Unit.
The centre specialises in constructing long-term temperature records.
They were one of the first research institutes to identify the warming trend in Earth's temperatures.
But a series of e-mails hacked from the university's servers seemed to suggest that the team, led by Professor Phil Jones, had used dubious methods to construct some of the records.
As Paul Nurse discovered when he looked into the controversy, it caused outrage.
Just look here Christopher Booker in the Sunday Telegraph - "This is the worst scientific scandal of our generation.
" Here, the Daily Express - "Now there are lies, dammed lies and global warming," implying that global warming is nothing but lies and a sham.
And this reaction wasn't limited to the UK.
The controversy reached as far as the United States Senate.
I certainly think that we should stop everything that we're doing now and investigate to see the authenticity of this science and the truth of these e-mails.
So, was this the systematic fraud that the sceptics had been looking for? PAUL NURSE: Tree rings have been shown to be a good way of measuring ancient temperatures and they've mostly matched instrumental measurements since the advent of thermometers.
However, after about 1960, some tree ring data stopped fitting real temperatures so well.
The cause of this isn't known.
When Dr Jones was asked by the World Meteorological Organisation to prepare a graph of how temperatures had changed over the last 1,000 years, he had to decide how to deal with this divergence between the data sets.
He decided to use the direct measurements of temperature change from thermometers and instruments rather than indirect data from the tree rings to cover the period from 1960.
It was this data splicing and his e-mail referring to it as a "trick" that formed the crux of Climategate.
The organisation wanted a relatively simple diagram for their particular audience.
What we started off doing was the three series with the instrumental temperatures on the end, clearly differentiated from the tree ring series Mm.
but they thought that was too complicated to explain to their audience.
So what we did was just to add them on and to bring them up to the present.
And, as I say, this was a World Meteorological Organization statement.
It had hardly any coverage in the media at the time and had virtually no coverage for the next ten years, until the release of the e-mails.
There were at least four independent reviews of the work of CRU.
The reports found there was no evidence of dishonesty.
They said splicing the temperature data wasn't misleading .
but this technique should have been made plain.
They said, generally, the unit should have been more open, but crucially, they found no evidence of deliberate scientific malpractice.
This seems to have been the greatest scientific scandal that never really took place.
I mean, it just doesn't make sense to me at all why it got blown out of proportion.
And through all this noise, people are left to try and make sense of it all.
Good morning, could I have a Times and an Independent, please? Yeah.
Starting with Climategate, the Daily Mail concludes in its headline - "Secretive and unhelpful, "but scientist in Climategate storm still gets his job back.
" A completely different tone about this news item in the Guardian - "Climategate scientist cleared "of manipulating data on global warming.
" It's difficult to imagine it's reporting the same thing.
It's not surprising that the public are confused reading all of this different stuff.
There's these lurid headlines and there's political opinions, I think, filtering through, which probably reflects editorial policy within the newspapers.
And we get an unholy mix of the media and the politics and it's distorting the proper reporting of science, and that's a real danger for us if science is to have its proper impact on society.
Over the last 40 years, the evidence for human-induced climate change HAS become overwhelming.
In the end, it may not be the slow, steady accumulation of scientific data that convinces anyone that's still unsure, often the most convincing evidence is the evidence of your own eyes and it may be that the basic physics of a warming world will provide that to everyone within the next few decades.
As temperatures rise, the Earth's atmosphere has more energy in it and as the air warms, it can hold more water, which could be driving a trend towards extreme weather.
THUNDER RUMBLES AND CRACKS No one single event can ever be pinned directly on climate change, but the frequency of those extreme events can be.
As the Earth struggles for climate stability, the weather begins to get extreme.
THUNDER CRACKS AND ROLLS Dice are a great way to picture what climate change is doing to our world.
We always have a chance of rolling that six, whether it's extreme heat or record-setting rainfall, or even the longest drought on record, that could always happen naturally.
What climate change is doing, though, is one by one, it's taking those sixes, those weather extremes, and adding a few more to the dice, so that now our chances of a record-breaking heat wave are twice what they used to be.
Our chances of record-setting rainfall events have increased relative to the last 50 years.
We'll never know for sure if that six that we roll, that extreme weather event, is the natural one, or the climate change one, but we do know that the chances of rolling those sixes are increasing.
More extreme weather appears to be the new normal.
SHIP'S HORN BLARES The record-breaking rains in Scotland last year .
and the worst spring drought ever in parts of eastern England .
could be a taste of things to come.
However we choose to deal with global weather extremes, one thing is clear .
the world has changed.
The past is no longer a guide to the future.
Our climate, the average conditions that we grew up with, is not the same now as it was 30 years ago.
Events that used to be very random and extreme are becoming much more frequent and more severe.
We are going to be living in a different world than the one we grew up in.
Patient work over many decades has turned a little-known theory into one of the most important bodies of scientific research of recent times.
It's an incredible example of science doing what science does best - constantly interrogating the evidence and questioning the conclusions drawn.
That is why the consensus on the core science of climate change is so formidable.
Over the last 50 years, a huge scientific effort has revolutionised our understanding of how our climate works.
We know why it's changing and how, and we've got some idea of the likely consequences if we continue to emit greenhouse gases.
Climate science is a fantastically powerful tool to have on our side and it's only getting better, but now the real question is, what do WE decide to do with all this new information?