20080914_CW

People:

• Professor Tim Ball: Retired professor of Geography, University of Winnipeg
• Joseph L Bast: President, The Heartland Institute
• David Bellamy: Environmental campaigner and botanist
• Boutros Boutros-Ghali: Sixth Secretary-General of the United Nations
• George Bush, Snr: President of the United States, 1989 - 1993
• George W Bush: President of the United States, 2001 - 2009
• Nigel Calder: Science writer and former editor of New Scientist
• Piers Corbyn: Astrophysicist and weather forecaster
• Dr James Hansen: Head of the NASA Goddard Institute for Space Studies
• Senator Michael Jungbauer: Republican Member of the Minnesota Senate, United States
• Frank Luntz: American political consultant and pollster
• Professor Michael Mann: Climatologist, director of the Earth System Science Center, Pennsylvania State University
• Lord Robert May: Former President of the Royal Society
• Professor Pat Michaels: Climatologist and distinguished senior fellow at George Mason University
• Marc Morano: Climate sceptic, executive editor of Climate Depot website
• Lord Christopher Monckton: 3rd Viscount Monckton of Brenchley
• Professor Fred Singer: Emeritus professor of Environmental Science at University of Virginia
• Tim Slagle: American stand-up comedian and pundit
• Dr Roy Spencer: Climatologist and a Principal Research Scientist for the University of Alabama in Huntsville
• Professor Iain Stewart: Geologist and Professor of Geoscience Communication at the University of Plymouth
• James M Taylor: Conference coordinator and senior fellow, The Heartland Institute

Iain Stewart: Global warming - the defining challenge of the 21st century. According to some, it's the greatest threat now facing the human race.

James Hansen: By the middle of the next century, the warming will be on a level which the earth has not experienced since the age of the dinosaurs.

Iain Stewart: But for more than 20 years, a group of scientists have passionately argued that there is no climate crisis.

Fred Singer: There is no scientific evidence that greenhouse warming is occurring, or if it is, that it would lead to disaster.

Iain Stewart: They are the climate change sceptics, and they've turned global warming into the most hotly-debated issue that science has ever seen. It was a debate in which hard science was mixed with vitriol and personal abuse on both sides.

[Footage from separate conversations at 2008 International Conference on Climate Change.]

Lord Monckton: This was deliberately bent.

Joseph L. Bast: It's a scandal.

Tim Ball: If it's fraud, they should be in jail.

[End of footage.]

Iain Stewart: Because the sceptics challenged everything about global warming, that it was manmade, that carbon dioxide was causing it, even that it was happening at all. Everything that we thought of as solid fact was called into question. I'm lain Stewart, a geologist at the University of Plymouth, and I'm going to look at how the arguments over global warming were fought over the last two decades... who won, who lost. This is a debate that matters to all of us. Our future depends on it. This was science's great battle for the truth.

In the early '90s it seemed so clear - scientists had revealed that the planet faced a new threat. They said the earth was heating up.

James Hansen [addressing Congress] :This evidence represents very strong case that the greenhouse effect has been detected and it is changing our climate now.

Iain Stewart: The culprit was emissions of carbon dioxide and other greenhouse gases - the result of human activity. Without drastic action to curb these gases, they said, the planet would face a climate crisis.

Unidentified scientist: If measures are not undertaken soon to limit the warming, humans face an increasingly difficult future.

Iain Stewart: The challenge was great, but at least the world was united. In 1992 almost every head of state and an entire army of reporters descended on Rio for the Earth Summit.

[TV Footage from 1992.]

Boutros Boutros-Ghali: The spirit of Rio that is the spirit of planet Earth will spread throughout the world.

Newsreader: All the countries are expected to sign the climate change convention.

George Bush, Snr: We come to press on with deliberate purpose and forceful action, and such action will demonstrate our continuing commitment to leadership and to international cooperation on the environment.

[End of footage.]

Iain Stewart: I remember the Rio summit cos I remember my geography colleagues getting all excited about the world becoming united in its concern for the environment. And global warming was centre stage. Everyone was talking about what it would mean, how to prevent it, even some people that you wouldn't actually think of as being arch environmentalists. But then the consensus started to break up. Politicians, businessmen and even a few scientists began to queue up to say there was no climate crisis, after all. A few of them are still saying that.

[Footage from the Heartland Institute's 2008 International Conference on Climate Change.]

Iain Stewart [alone, speaking to camera]: 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.

Tim Slagle [addressing conference]: Thank you. Thank you, all. I think it's ironic that we even have to have this conference in the middle of the coldest winter in 40 years... I mean, couldn't global warming be a good thing? You know, I think New York might be pretty with a palm tree or two.

Iain Stewart [to Tim Slagle]: What's it like being a climate change comedian?

Tim Slagle: Lonely!

Iain Stewart [alone, speaking to camera]: But this conference has a serious purpose, to question the idea that we're facing a climate crisis.

[Fragments of separate conversations at the 2008 International Conference on Climate Change.]

Joseph L. Bast: Global warming is not a crisis. This conference proved there's no consensus.

Senator Michael Jungbauer: CO2 is in no way connected to global warming. And it never has driven temperature. It never will.

Marc Morano: Schoolchildren are being scared to death based on speculative, unproven computer models, and a lot of people, including the media, should be ashamed of themselves.

Iain Stewart [alone, speaking to camera]: Some of the scientists here have spent years questioning 'catastrophic global warming, like climatologist Pat Michaels.

Iain Stewart [to Pat Michaels]: You seem to really thrive on the energy of the debate of this.

Pat Michaels: Well, sure. I picked up this was going to happen somewhere around 1972. I date myself... Woody Allen... [?]

Iain Stewart: Have you lost friends over this, for example, or does it get to that level?

Pat Michaels: No, I don't think anybody should go into science to make friends.

[Fragments of separate conversations at the Heartland 2008 conference.]

Fred Singer: The carbon dioxide is not a pollutant.

Piers Corbyn: Are you saying we're now at a climate optimum?

Unidentified man: I do not know of a single scientist who accepts the fact that there's been any increase in global warming.

Iain Stewart [alone, speaking to camera]: Some see these people as heroes, as modern-day Galileos, speaking out against oppressive orthodoxy. Others compare them to Holocaust deniers. I mean, that is one hell of a difference of opinion. This has been happening since the world began. They're controversial because, for two decades, the sceptics have been questioning every piece of the global warming theory. They've laid down challenge after challenge to the proponents of climate change.

[End of footage from 2008 International Conference on Climate Change.]

Fred Singer: According to these global warming enthusiasts, the main villain is the burning of fossil fuels, but they've left science and scientists far behind.

Pat Michaels: There always seems to be an apocalypse around the corner. And it seemed to me that global warming was just another in a long series...

David Bellamy: The world is not going to die because of carbon dioxide being put into the atmosphere, and there's plenty of proof.

Iain Stewart: They questioned the causes of global warming.

Unidentified man: It's kind of a natural phenomenon.

Iain Stewart: They questioned whether it was anything unusual.

Nigel Calder: England was just as warm as it is now.

Iain Stewart: And their first line of attack was to question the most basic claim of all. They said the world wasn't actually getting warmer. It seems like such a simple question: is the world getting hotter or not? Surely science can answer that without too much trouble? And yet, how do you measure the temperature of a planet? I mean, where do you stick the thermometer? The answer is: everywhere. All over the world, from Morocco to Montana, from New Zealand to Norway, on mountains, in deserts, even in people's back gardens, you'll find little wooden boxes. These unassuming things are what all the fuss is about. You find a lot of them in schools.

And here at Stonyhurst, a Catholic college in Lancashire, they've got a really special one. And here it is. Look at that! I mean, on the face of it, there's nothing special about it - the box keeps out the sun and slats let the air through. And inside are simple mercury thermometers. These two are the important ones. This one measures the maximum daily temperature, which is about 16 degrees Celsius. And this one measures the minimum, which is about one degree Celsius. Now, if you take a point exactly halfway between the two, you get today's average temperature. What makes this special is that it's part of the oldest temperature record in the world. They've been measuring temperature here since 1846. Now, back then, this place was run by Jesuit priests - just the kind of methodical, dedicated people that you needed for a job like this. For over a century, they would come out every day. Nowadays it's all computerised, but they're still taking measurements daily, which means you can make a direct comparison between temperatures here today and temperatures in the past. For over a century, people all around the world have been collecting this data. This is real science. Painstaking work by thousands of forgotten volunteers. They probably never imagined just how important their work would be, because when all the temperature data was put together, it told a striking story.

Starting in 1910, according to the thermometers, the global temperature started to rise. Records were broken. And broken again. This warming phase lasted until the 1940s. Then the warming paused. Only to start again in the '70s. This was the second warming phase of the 20th century, and, according to the instruments, it was even more dramatic than the first.

Newsreader [Michael Buerk]: England has been basking in the heat wave again. In many parts of the country it's been hotter than Hong Kong or Honolulu.

Iain Stewart: Throughout the '80s and '90s, almost every year broke records.

Newsreader [Martyn Lewis]: The Met Office says the last 12 months have been the warmest since their records began in the 17th century.

Newsreader [Michael Buerk?]: Last year the earth recorded its highest average temperature since climate records began.

Iain Stewart: In total, the global temperature has increased by almost one degree Celsius in the last century. That may not sound like much, but to climatologists this is a big deal. The headlines were hard to ignore. Something was happening to our planet. It was almost as if we'd turned up the gas, and the earth was beginning to cook. But even with thousands of weather stations round the globe, there were still huge areas of the world with hardly any temperature data. For the sceptics, this made the thermometer records deeply suspect.

Fortunately, a new technology had arrived on the scene - satellites. These precision instruments were the space-age way to measure the true global temperature. They're really extraordinary pieces of technology. I use data from satellites all the time. I even teach a little bit about satellites. But I've never seen one. I've never been close to one. Right. This is NASA's latest Earth observation satellite, due to be launched into space in 2010. Here's the baby. Look at it - she's beautiful! All right. There's a few things you have to know about this. First of all, this is pretty much how it goes up. Actually, some of the bits are coated over for protection, so they strip that off and they strip off some of the wire and it's just testing, but it pretty much goes up. There's no shields or anything like that. The other thing that's odd is it's actually upside down. That is space and the roof is where the Earth would be. Now, in terms of your instruments, up here, behind this very fetching orange, is a visible camera, in the sense that it records the images just like the human eye does. And this one here you've got infra red.

Now, this, this, this is the important one. This is what gives us temperature. This is a microwave sounding unit, which kind of acts like a microwave oven, but in reverse. Instead of emitting microwaves, it receives and records microwaves. And, depending on the amount of microwave radiation it receives, that gives us an idea about temperature. With global coverage and high-tech instruments, satellites seemed like a much better way of measuring global temperatures than thermometers. And in the early '90s, scientists put together the satellite data. What they found rocked the entire global warming community. The satellites showed that the earth wasn't warming - in fact, it was slightly cooling. One of the scientists who performed the calculations was Dr Roy Spencer.

Roy Spencer: When we first did the satellite monitoring and got 10 years of data worth, it did show a slight cooling, which was a surprise to us.

Iain Stewart: This result was in stark contrast to what other scientists had been saying.

James Hansen [addressing Congress]: The rate of warming in the past 25 years is the highest on the record.

Roy Spencer: It was about this time that Jim Hansen was talking about catastrophic global warming or potentially catastrophic global warming, and here we had the satellites telling us it's been cooling for 10 years.

Iain Stewart: It was a huge victory for the sceptics. And it soon became a key piece of evidence against global warming, as this documentary from 1990 shows.

[Footage from 'The Greenhouse Conspiracy', produced by Hilary Lawson, Channel 4, 1990.]

Narrator: New data from space has made the land record more doubtful. Until recently, we've had no alternative but to rely on thermometers and weather balloons, but now, for the first time, satellites are giving us another source of information.

Roy Spencer: We've found we can monitor globally averaged atmospheric temperatures with a high level of precision, even on a monthly basis.

Narrator: Over the last 10 years the thermometer record has shown an underlying upward trend. But according to the satellite information the earth was rather warmer in the first half of the '80s and rather cooler in the second half.

[End of footage.]

Iain Stewart: Wow! Well, that's a pretty striking difference. I mean, you could see why the climate sceptics were delighted when they got hold of this satellite data because you've got the red lines showing the thermometer data, and it's clearly going up. And then you've got the blue line showing the satellite data with no sign of warming at all. The question is, which one of those is right? It is the humble thermometer or is it the high-tech satellite? It's a classic scientific problem. You've got two different sets of data which are saying conflicting things. And the one thing that science tells us is that there's going to be a showdown. And only one set of data is going to be left standing. First on the attack were the sceptics. They said there was one very obvious flaw in the data from the thermometers - they had ignored human progress.

Welcome to Las Vegas. Las Vegas. Like it or not, it's one of the 20th century's greatest achievements. They don't do that in Glasgow. [Watches young woman dancing in bikini and rollerskates.] And this is where Britney got married - for 55 hours. This is the perfect place to test out a phenomenon which became central to the sceptic's case against the thermometer record. The thing is I'm not really here to have fun. I'm actually here to measure temperature, which, according to this thermometer, even though it's late at night, is 22 degrees Celsius, which is pretty warm.

Man in suit: It's Vegas, baby!

Iain Stewart: So it's hot?

Man in suit: It's hot all the time!

Iain Stewart: But the significant thing is, drive out of the city and into the desert proper, and the temperature drops. Well, now we're... um... I don't know where we are actually, in the middle of nowhere, but outside the city limits, and I've got my thermometer, and it's reading... Well, it's reading about 18 degrees C, so, much cooler than it was in there. And the reason's simple; all that concrete, all those roads and cars, all the stuff you get in modern cities, absorb the heat of the day and then they release it at night. And those tall buildings, they trap the warm air that would otherwise blow away. It's the same story all over the world - cities are heat traps. It's called the Urban Heat Island Effect. And that effect, said the sceptics, had created the false impression of a warming planet.

Take what happened to the Las Vegas weather station. It was built in 1942 out in the desert, next to the local airstrip. But then Las Vegas grew. It's America's fastest growing city. Its population has tripled in just 30 years. The weather station's still at the airport, you can see it just over here, behind this fence. Las Vegas airport has been gradually swallowed up by the city. Over the back there, you can see the famous Las Vegas strip. So we are in the middle of the city, and that means we're in the middle of the urban heat island. And that means it's much hotter here than it would be naturally. Sure enough, this weather station has shown a four-degree warming over the past 50 years, whereas a nearby desert station shows a warming of less than one degree. So the sceptics said, "Yes, sure. "All around the world the weather stations "are recording ever-increasing temperatures. "But that's because of the growth of cities. The planet? "That's not getting warmer at all. " If they were right, the thermometer record was indeed faulty, and global warming was a false alarm.

But there was a counter argument - it wasn't only cities that were heating up. All across the globe, there was evidence that the world was warming. In the countryside, spring was coming earlier. In the mountains, glaciers were retreating further than they had for centuries. So much so that all sorts of things were melting out of the ice, including a human body frozen 5,000 years before. Oetzi the iceman. Even the oceans were warming - not a lot of urban development there. All these things seemed to back up the thermometer record, not the satellites. It was deadlock - one side had to be wrong, but it wasn't clear which one.

Finally, after almost 10 years of poring over the data, someone did find a fault. And it was with the data from the satellites. The problem turned out to be friction. Even at 800km, the satellites were still affected by the earth's atmosphere. That made them slow down. So every year they fell about 1km closer to the earth. To work out the temperature they needed to take into account the height, so having the wrong height meant the temperature was wrong, too. To make matters worse, the drag also affected the satellite's timing. Take a satellite which started off measuring the temperature at 2:00 in the afternoon. After a few years, it was measuring at 6:00 in the evening. So it looked like the temperature had cooled, when it hadn't. Once this was pointed out, even the scientists behind the original calculations admitted they were wrong.

Roy Spencer: I think it is a bit embarrassing for scientists when someone shows they're wrong on something. So yes, it is a little embarrassing when somebody finds an error in your data.

Iain Stewart: Oh, I mean, you've got to feel for him. I mean, I would be absolutely mortified if I had to admit a high profile mistake like that. For me, the important thing is that Spencer admitted he'd made a mistake. When the error was pointed out to him he redid his calculations and right enough he came up with a rather different answer.

Roy Spencer: I think when we made that correction, if I'm remembering correctly, I think we went from a cooling trend to a slight warming trend. And then, ever since then, it's been a warming trend, actually by sort of ever-increasing amounts.

Iain Stewart: Now, even die-hard sceptics had to accept that there had been warming in the second half of the 20th century.

[Footage from separate conversations at 2008 International Conference on Climate Change.]

Pat Michaels: Yeah, when somebody says there's no such thing as warming, I squirm, yes. Yeah. It's hard to look at all those records and entertain that.

Fred Singer: How can you argue with thermometers? Yeah. I don't argue with thermometers.

[End of footage.]

Iain Stewart: The rising temperature was now a fact, with thermometers and satellites confirming it. The sceptics' challenge had actually made the case stronger. But the battle was far from over. The sceptics hit back with a crucial question: was the warming man-made or natural? If it was natural, there was no reason to think it would continue, and nothing we could do about it, in any case. And the sceptics said they had evidence that it was just natural variation, because they said it had happened before. And the proof could be found in history.

In 1,000 AD, the Viking Erik the Red was banished from his native land for murder. He landed on this coast and made it his home. And he gave it a surprising name. Quite how this rather bleak landscape came to be known as Greenland is still debated. Some say it was a masterful piece of spin by Erik, designed to entice settlers to his new home. Others said that it may have been more truthful than it seems. They argue that, back then, Greenland was warmer and more hospitable than it is today, a genuinely green and fertile land. What's certain is that he was able to survive here. On this now barren land, the Vikings grew crops and farmed cattle. This, said the sceptics, was proof that Greenland was warmer 1,000 years ago.

And this warmth was also felt closer to home. According to English historical records, the centuries around 1,000 AD were warm and favourable. Harvests were good, the population grew and culture flourished. This was when Westminster Abbey and Salisbury Cathedral were built. And, just like today, it was warm enough to grow grapes in England. Scientists gave this period a name - the Medieval Warm Period. To the sceptics, the Medieval Warm Period showed that today's temperatures are not unusual.

Nigel Calder: It just doesn't make sense, if you know anything about climate history and how much warmer it was in Viking times, for example.

Fred Singer: All the evidence shows that medieval warming was a great deal warmer than it is today. So there's nothing unusual about the current warming.

Iain Stewart: If the Medieval Warm Period really was hotter than today, as the sceptics said, it would support the idea that global warming is just part of the climate's natural cycle. The historical evidence seemed to back up the claim. But what scientists needed was hard data. They needed to know what the temperature really was 1,000 years ago in the Medieval Warm Period. In the 1990s, a scientist called Michael Mann took on the task. But he faced a major challenge.

Michael Mann: It's not easy. We have instrumental records on a widespread global basis, really for only, at most, the past century. Then, maybe back into the mid-19th century, enough instrumental data to say something, for example, about the average temperature of the Northern Hemisphere. But by the time you go farther back, there are very few instrumental records.

Iain Stewart: With no thermometer records, Michael Mann needed something that could act like a natural thermometer - going back centuries. And this is where he found it.

I'm in the White Mountains in California and this area is a real mecca for scientists studying past climate. That's because this is no ordinary forest. It's home to the oldest living things on the planet. These trees live for thousands of years. They're called bristle cone pines and they're found only in a few small areas of the western USA. This is strangely wonderful. It feels as if it's oozing out everywhere. Mind you, it's a bit of a surprise, considering how old it is. You'd think it was much bigger. I guess it shows its age in other ways. I mean, look at this weather-beaten and gnarled texture. I'm told that this one is about 2,000 years old. But some of the trees are about 4,000 years old. When they were saplings, my ancestors were living in straw huts. Stonehenge was modern architecture. It really stretches your mind. These were just what Michael Mann was looking for, because inside, they contain a record of past temperatures. Like any tree, these pines lay down rings - one for each year of their life. These rings are the key to past climate. This is a slice from one of the trees. Take a look. You can barely see the tree rings. They're in there, all right - they're just really tightly packed. And the reason that each ring is so fine is because the tree grows a tiny amount every year. That is 100 years. And it's these rings that tell us about past temperatures, because they tell us how much the tree grew in that year. In a warm year, the snows will melt earlier and the trees will grow more and leave a fatter ring. In a cold year, they'll hardly grow at all.

It's called a climate proxy. You can't read temperatures directly like reading it from a thermometer, but you can use the evidence to estimate what the temperature was. But, of course, this only tells you about the conditions in this one place. So Michael Mann and his team needed to find other temperature proxies from all round the world - places that could tell them what the temperature really was as far back as the Medieval Warm Period. They searched the world getting data from other proxies, like corals from the Red Sea and ancient layers of snow from the mountains of Peru. And then they had to add in the recent thermometer records. Combining the different numbers to reconstruct global temperatures is a fiendishly difficult task. It needs the kind of statistical analysis that makes my head hurt. Michael Mann put all the numbers together and used it to create a very special graph.

And here it is. It's basically a graph of temperature over the last 1,000 years [Hockey Stick Graph is displayed on a huge mobile billboard!] And the first thing that hits you is there's virtually no sign of the Medieval Warm Period. I mean, the sceptics would have a big bump in temperature just here when the world got warmer. Instead, it looks like for at least 900 years, give or take a few ups and downs, it's incredibly flat. It's not until you get to the 20th century and BANG! Temperatures shoot up in a way unlike anything we've seen for at least a millennium. Now, this graph tells a very different story from the sceptics. They say present temperatures are nothing special. This graph says the opposite. The simplicity of this graph makes it a really powerful image. And it's even been given its own name - the Hockey Stick. It became one of the most famous and controversial graphs in science. It was so dramatic that it became an icon - an instantly recognisable symbol of man-made climate change. Al Gore even used it in his Oscar-winning movie.

Not surprisingly, sceptics hated it. They said the Hockey Stick was a fiction because there was virtually no trace of the Medieval Warm Period. They accused Mann of using faulty data and dodgy statistics to rewrite history. The Hockey Stick still provokes strong reactions today.

[Footage from separate conversations at 2008 International Conference on Climate Change.]

Iain Stewart: What was your reaction when you see that? It's probably the most famous graph in the world, isn't it?

Joseph L Bast: I think: what a shame. What a shame that a scientific scandal like this would be perpetrated on the American public and on the United Nations.

Iain Stewart: A scandal?

Joseph L Bast: It's a scandal. This is absolutely outrageous!

Marc Morano: This has even been discredited by the National Academy of Sciences. They said it was unsupportable.

Iain Stewart: When you see this, what goes through your mind?

Fred Singer: The first thing is that I have great disbelief.

Iain Stewart [alone, speaking to camera]: Scientists are always bitching about each other. I've been at a conference where someone has said, "You know nothing about this subject." But the kind of enmity that's been directed at Michael Mann is something else. Some even accused him of the ultimate scientific crime - fraud.

Tim Ball: If it's fraud, they should be in jail. If it was incompetence, they should be fired.

Michael Mann [separate footage, not at conference]: I never expected the sort of attacks we were subject to when I began this work.

Lord Monckton: This was clearly - and I'm going to say it bluntly - deliberately bent.

Michael Mann [separate footage, not at conference]: If you can't win your argument based on science, you try to win based on defamation, of slander, of rhetoric that sounds convincing, but has no basis in fact.

Senator Michael Jungbauer: I would say it's as close to scientific fraud as you can get.

[End of footage.]

Iain Stewart: Michael Mann was attacked in print, and even more viciously on the web. Entire websites were set up to pick holes in the Hockey Stick. But whilst the sceptics were busy attacking Mann, other researchers were doing their own science, hunting for more proxies and using different methods to work out past temperatures. Soon, Michael Mann's graph was joined by many others, all reconstructing the past 1,000 years of temperature. The question was would they back up Michael Mann, or would they prove him wrong? It might look confusing, but this graph has a really clear message - the red line is Michael Mann's original Hockey Stick graph. It's very flat, with hardly any Medieval Warm Period. The other lines are the reconstructions that have been done since.

Now, there's a big spread. In other words, scientists disagree about a lot of the temperatures here. That's not really surprising, because working out the temperatures for the past few hundred years is a really difficult task. It largely depends on what indications you use. But the crucial part is over here. This is 1000 AD. Now, some of the reconstructions show temperatures a little warmer than Mann's curve, and some of them also show going into much colder conditions at the end of the Medieval Warm Period. What that probably means is that Michael Mann underestimated some of the variation in the past 1,000 years. In other words, the Hockey Stick is a little bit too straight, but it depends on the reconstruction you use. What these lines all agree on, though, is one thing - there's no evidence of any period in the past 1,000 years that's as warm as the second half of the 20th century. In other words, the end of the 20th century really is unprecedented. Once again, the sceptical attacks have made the science stronger. We now have a whole hockey team's worth of graphs. They make a very convincing case that the global warming detected by the thermometers and satellites really is unusual.

But the sceptics said that still doesn't prove that humans are to blame. They had one more line of scientific attack. They said global warming has nothing to do with carbon dioxide, so leave those smokestacks and gas guzzlers alone. It was all the fault of the Sun. Of course, the Sun influences climate - the sun is the source of all weather. Every storm, every shower, every breath of wind, is ultimately driven by the Sun. The sceptics argued that since the Earth's climate is so dependent on the Sun, it would only take small changes in the Sun's behaviour to have a big effect on the climate. The key was sunspots. These dark patches are magnetic storms on the surface of the Sun. They're constantly changing, which is why the sceptics believed they could reveal the true cause of climate change.

This observatory has been measuring sunspots since 1881. And this is how they do it - the dome moves around until it gets to the direction of the sun, the roof opens, and then the sun comes down this telescope here and projects onto this sheet of paper. Now, I'm not putting my eye up here, because, if I did, this is what would happen. The Sun, just like a big magnifying glass, just sets fire to the leaf. But anyway, listen. So what you do is rather than put your eye there, you put a bit of paper there. Now, you have to adjust it, because the Sun has to be sitting right in the middle. Focus a little. You then draw on the position of the sunspots. And we've got two today. OK. These spots may look tiny, but each one is half the size of the Earth. And this is a relatively quiet Sun. At other times, it has more spots - sometimes dozens of them. This is what scientists call an "active Sun" and at these times, the Sun sends out huge waves of charged particles called the solar wind. For centuries, astronomers all around the world have been counting the number of sunspots. This record's from the mid-1830s and you can just see the detail is incredible. Each of these plots is a different day. Apparently some scientists even went blind from all that staring at the Sun. But what you really get from here is the dedication and devotion to record-keeping. And it's from records like this that we've learned something absolutely intriguing.

Back in the 17th century, there was a 50-year period in which there didn't seem to be any sunspots at all. And the fascinating thing is that this coincided with a particularly cold period of history - the so-called Little Ice Age. This was the time of frost fairs, when the river Thames froze over. It was also a time of bitter winters and famines. So people began to wonder if there was a connection between sunspots and the weather. For instance, William Herschel, the astronomer who discovered Uranus claimed to have found a link between the number of sunspots and the price of wheat. The more sunspots, he argued, the better the weather, and the better the harvest. Mind you, he also thought that the sun was inhabited by intelligent life-forms. The real problem for the theory was that no-one could work out how sunspot activity could be linked to the climate. The actual amount of heat given off by the Sun hardly changes at all, regardless of how many sunspots there are. So the theory was largely forgotten.

But in the 1990s, sunspots made a comeback, because some people argued that it was the Sun - and not carbon dioxide - that was the cause of global warming. And they had a trump card. They believed that they'd solved the mystery of how the sun changes the climate. According to the new theory, it wasn't that the sunspot activity made the sun hotter or colder - it was much more complicated than that. It all starts far out in space, where exploding stars, called supernovas, send out powerful cosmic rays. The theory goes that when these cosmic rays get to the Earth, they interact with the atmosphere to create clouds. But when the sun is active and has lots of spots, it sends out a powerful solar wind which blows the cosmic rays away. So an active sun means fewer clouds and a warmer world. This theory wasn't by any means proven, but it was possible. And that led some sceptics to argue that today's global warming might be caused by the natural fluctuations of the sun, and not carbon dioxide. That was the message of a recent high-profile television documentary [The Great Global Warming Swindle.]

[Footage from 'The Great Global Warming Swindle' (2007). Director: Martin Durkin. Producer: Eliya Arman.]

Narrator: And as evidence, they showed how solar activity and temperature seem to match up. Solar activity, they found, rose sharply to around 1940, fell back until the 1970s and then started to rise again.

[End of footage.]

Iain Stewart: Well, you have to say it's a pretty convincing connection. But there is one wee problem - the graph ends in 1980. Now, when the documentary was made a couple of years ago, they had data from the 1980s and the 1990s, but they didn't show it. If we extend that graph to show that data, what you see is that the blue temperature curve should rise up. Look - there it goes. It just soars off the graph, and the red solar activity just levels off. In fact, since the 1990s, solar activity looks as if it's been on the decline, which should mean the planet has been getting cooler. Instead, we've reached record temperatures. So it's hard to escape the thought that although the sun may have played a significant role in the past, it just can't explain the present warming. The only convincing explanation is that it's down to us - human activity.

There are only a tiny number of scientists who still question a human influence on climate, and yet climate scepticism hasn't gone away. You'll still see websites claiming that the Earth isn't warming up - that it's all down to the urban heat island, but that's not true. You'll still hear claims that there's proof that the Earth was hotter during the Medieval Warm Period, but that's not true. And you'll still hear people claiming that the sun somehow disproves global warming. But that's not true, either. So why is this stuff still around?

The problem is there are a lot of people who don't want global warming to be true. The fact is, I'm one of them - I wish there were no such thing as global warming, because taking action to prevent climate change is going to affect all our lives, and mean giving up some of our freedom. The freedom to go anywhere, do anything, to consume whatever you want, when you want. The freedom to have an open road and a car full of cheap petrol.

It's not only my freedom that's threatened - cutting back on greenhouse gases threatens the freedom of companies to go about their business. Not surprisingly, they wanted to fight their case. A new alliance was formed. It was a who's who of household names - Exxon, BP, General Motors, Shell, Ford and many others. They called themselves the Global Climate Coalition. Throughout the '90s, the Global Climate Coalition embarked on a marketing campaign to convince the public there was no need to take action.

[Global Climate Coalition TV commercial.]

Woman's voice: What do you know about the United Nations' proposed climate treaty?

Customer in gas station forecourt: Isn't that about global warming?

Woman's voice: It would force the US to cut energy use by over 20%. Gasoline prices could go up for over 50 cents a gallon. Heating and electricity prices could soar, and higher energy costs will raise the price of almost everything we buy.

[End of clip.]

Iain Stewart: Industry was fighting back. A key part of their strategy was to highlights doubts about the science. They used the media and the internet to promote the views of the minority of scientists who were sceptical. And the campaign received a huge boost with the election of Republican President George W. Bush.

[Footage of George W Bush.]

Reporter at press conference: I've got a question about global warming. I want to know, what is your plan?

George W Bush: Good. We, uh... first of all, I... there is... uh, the, uh... the globe is warming. The fundamental debate - is it man-made or natural?

[End of footage.]

Iain Stewart: Bush's views on climate change were no secret, but what was a secret was the strategy the Republicans used to get the American public on their side. That is, until a revealing document came to light in 2003. Frank Luntz was a pollster and political advisor with an impressive reputation.

Frank Luntz [addressing group of people]: My name is Frank Luntz, and you've been invited to participate in a people meter session.

Iain Stewart: He'd been hired to help Bush get re-elected. When an internal campaign memo he wrote in 2002 was leaked, it revealed that it was the issue of the environment on which Republicans felt most vulnerable. Well, this is it - this is the memo. It's basically a policy document on how Republican politicians should address questions about the environment, about global warming, and there's a few really interesting points on this. It says, "The scientific debate "is closing against us, but not yet closed. "There is still a window of opportunity "to challenge the science. " To me this says, "Look, we know we are on the losing side now, we know the science is starting to close in on us, "but there's still a window of opportunity "to get our point across," not to say, "All right, guys. We accept there's a good chance "that global warming is happening. "We're going to change our mind. "We're going to change our approach. " No. I mean, look at that raw cynicism. Now, this is interesting. "The scientific debate remains open. " "Should the public come to believe that the scientific issues "*are* settled, the views about global warming should change accordingly. "Therefore," - this is in bold - "you need to continue to make "the lack of scientific certainty a primary issue in the debate. "

That's saying you need to keep stirring it. Whenever there's uncertainty or discord among science, you just bring that out. It's not about trying to resolve the science to make the science better - it's just trying to sow the seeds of discontent. There's another one here that kind of reveals the strategy. "Act only with all the facts in hand. " In other words, if you create that element of scientific uncertainty, and you say, "We can only act with all the facts in hand," that is a recipe for inaction 'cos science has never got all the facts in hand. It's always looking for more information. This really has got nothing to do with science - this is about how to skirt around the issues.

It's very clever - I have to give it that - there's bits where you just go, "Of course. "That's a very clever way to do it. " But it's just depressing. We should be trying to find out the truth. It's pretty obvious that the aim of all this is to avoid taking action on climate change. As long as the public believe that scientists disagree on the issue, they won't demand action. 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.

Lord May: The science that said the world is warming, and the world is warming as a result of human activities, is beyond any reasonable doubt.

Iain Stewart: The Global Climate Coalition has now disbanded, with many of the companies involved accepting the reality of climate change. 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.

[Footage from the Heartland Institute's 2008 International Conference on Climate Change.]

Lord Monckton: When you get the National Climate Data Centre withholding the locations of its temperature stations - and at 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. It's quite simple. If you can see serial, deliberate falsifications of data, withholding of data, manipulation of data - these are simple matters to track. The thing about all fraud - however complex they look to the outsider, once you understand them, they're always simple.

Iain Stewart: "Fraud" is a big word to use in science, and you've said it's littered with it. Equally, scientists have made a genuine attempt to do analysis and then someone comes along and says, "You missed out this."

Lord Monckton: No, that's known as falsification. That's a perfectly proper process. If, on the other hand, you find all those departures from the line of accuracy are in one direction and one direction only, then you know that somebody is fiddling it. It's absolutely clear - it works every time.

Iain Stewart: Such a demoralising view of science. I just don't see it.

Lord Monckton: No, it's not a demoralising view of science - it's a view of those scientists who are trying to bend the results.

Iain Stewart [voice over]: To me, such attacks are a sure sign that the scientific battle is over. And, sure enough, perhaps the most surprising thing at the sceptics' conference is what I heard at the keynote speech.

James M Taylor: Ladies and gentlemen, it is my distinct pleasure to introduce Dr Patrick Michaels.

Pat Michaels: Thank you. Thank you. Thank you very much. I'd like to talk to you about some convenient facts on global warming, if I could.

Iain Stewart [voice over]: For years, climatologist Pat Michaels has been one of the most vocal sceptics. And yet today he's in surprising agreement with the advocates of global warming.

Pat Michaels: There are, in fact, two distinct warmings here - there's a warming of the early 20th century and there's a warming of the later 20th century, which has some very interesting characteristics, namely...

Iain Stewart [voice over]: He accepts the globe is warming, but the truly astonishing thing is he also accepts that we are partly to blame.

Pat Michaels: Fine. So global warming is real. In the second warming of the 20th century, people have something to do with it. All right? Now, get over it! OK, now you're all mad that I said that...

Iain Stewart [alone, speaking to camera]: You know, I've heard things here that's really surprised me. I've heard things I really didn't expect climate sceptics to say. They say global warming's happening, temperatures are going up, and that humans are somehow implicated in some degree. That's amazing. Those issues, it looks like, are behind us. But that doesn't mean to say the debate's over because there's a new debate in town, and that is - how bad is it going to be?

[End of footage.]

Iain Stewart: In the next episode, the science of climate change enters a new and even more controversial phase - predicting the future. Just what will global warming mean for our lives in the years ahead?