Comm: "The Science of Climate Change has been fraught with uncertainty, claim and counter claim.

In this programme we take a look at the history of the evolving and sometimes conflicting theories of Climate Change.

Over millions of years forests have absorbed carbon dioxide from the atmosphere, locking it into the earth as oil and coal.

With the start of the industrial revolution less than two centuries ago the widespread burning of fossil fuel and the forests began to release this CO² back into atmosphere.

For just as long climatologists have been preoccupied with its effect.

As long ago as 1827 French scientist Jean-Baptiste Fourier first suggested the existence of an atmospheric effect that would make the earth warmer than it would otherwise be. He was the first to use the analogy of a greenhouse trapping the warmth of the sun to help explain why the earth was not as cold as Mars.

In 1863 Irish Scientist John Tyndall using instruments he designed such as the ratio spectrophotometer first showed how gasses such as water vapour, carbon dioxide and hydrocarbons are greenhouse gasses, absorbing and reflecting heat.

Building on this work Swedish professor Svente Arrehuis in 1896 published an article putting forward the idea that the amount of carbon dioxide in the atmosphere has a direct relationship to temperature. He predicted that if CO² levels doubled, the temperature of the atmosphere would rise by 5 degrees."

Stephen H Schneider: "What made him different was he did a calculation and he also said humans through the use of their fossil fuels might affect things. So, in essence he deserves the title of being the founding father of the global warming debate because global warming is not about the natural greenhouse effect it's about the augmentation of natural gases with human produced kind when we use the atmosphere as a sewer and dump it and he calculated that we might make a difference. So, what he saw was pretty far away."

Comm: "Arrenhuis realised that burning fossil fuels could lead to global warming, what he did not know, was that it had already started.

Between 1890 and 1940 the average surface air temperature increased by a quarter of a degree centigrade. It doesn't sound much but some scientists see the American dust bowl of the 1930s as an early sign of the greenhouse effect at work. To place it in context just 4 degrees of surface air temperature separates this century from the last ice age."

Archive sounds: "The motorisation of our economy, so new, so powerful, so revolutionary is this force that we have hardly been able to appraise its influence."

Comm: "In March 1958, a young scientist in San Diego began the search for the first scientific proof that carbon dioxide levels are rising dangerously. Everyone else he said, had been underestimating the problem."

Charles D Keeling: "All these measurements were misleading, and I mean all of them. When I first made this pronouncement I was twenty-seven years old, just past my schooling and I was telling these people that the whole field was pretty badly screwed up."

Comm: "Scientists had been measuring CO² in the atmosphere for decades, but Keeling insisted that their readings had failed to give accurate results. He was convinced he could set the record straight."

Charles D Keeling: "My data were sufficiently compelling and I got to a couple of people you see like the Director of Weather Service and the Director of Scripp (Institute of Oceanography) and persuaded them that these measurements were probably right and the others were wrong and they gave me a chance.

Comm: "To record his measurements he went to a new more reliable place, Mauna Loa observatory in Hawaii."

Charles D Keeling: "This location sits out in the middle of a huge ocean away from contamination, sources of carbon dioxide which would have interfered with trying to determine what's going on in the world's atmosphere. If you had to pick a spot anywhere which would have given representation of the whole world with one single site Mauna Loa observatory probably is about the best choice."

Comm: "Into this ideal environment Keeling introduced the technology that would give him his breakthrough. Readings were taken every ten seconds for the next 40 years. The results provided dramatic new evidence for global warming. His readings gathered together into the so-called `Keeling Curve' showed that CO² levels had risen alarmingly since 1958."

Charles D Keeling: "The increase in carbon dioxide since I started my measurements is twice the total amount of CO² that was added to the air prior to that so the forty year record now is captured enough that we can be pretty sure that we know how to represent the effect of carbon dioxide on the greenhouse effect."

Archive sounds: "Unless we learn otherwise it will be prudent to suppose that the next ice age could begin to bite at anytime."

Comm: "However, the mounting evidence that climate change fuelled by CO² emissions would lead to a hotter world was soon to be challenged by a new theory.

In 1974, after a series of unusually cold winters, scientists claimed the earth was not warming but cooling and that we were on the verge of entering a new ice age."

George Kukla: "The warm periods are much shorter than we believed originally. They are something around ten thousand years long and I am sorry to say that the one we are living in now has just passed its ten thousand years birthday. The ice age is due now any time."

Comm: "The cooling theory identified a new culprit, not carbon dioxide but dust and smoke in the atmosphere."

Reid Bryson: "A man made dust bowl is spreading over the earth. The use of the soil in a dry country produces dust which the wind blows into the air. This dust all added together spreads around the world blots out the sun and causes cooling on a world wide scale."

Stephen H Schneider: "Early calculations under a set of specified assumptions, which we admitted were not certain, nonetheless showed that if the dust were around the world it would win and that it would cool the earth down by several more degrees if the trends for population growth and affluence growth continued into the twenty-first century. Several degrees is sufficient according to other theories at the time to trigger an ice age. In fact, I agree, several degrees would trigger an ice age. And since the world was temporarily, at least the northern hemisphere, on a cooling trend in the nineteen sixties here this theoretical calculation came along and said potential ice age possible from human dust and I got that label pinned on me even though I was just doing the calculations."

Comm: "Then in the 1980s came a string of hot summers, and all talk of a new ice age melted away. It had all been a big mistake."

Stephen H Schneider: "What happened the next few years is we studied and found that the dust is not globally distributed that it's largely concentrated in industrial areas or in agricultural areas. So therefore not the entire earth is covered by it so that the cooling effect is only regional whereas the greenhouse gas effect was global. The second thing is the early calculation that we did neglected the stratosphere, the high part of the atmosphere where the ozone is, we didn't think that would have much to do with CO² but like all things in science you keep checking your assumptions, so I re-did the calculations of the stratosphere and said whoops we underestimated by more than 50% how much warming there would be."

Archive sound (Former UK Prime Minister, Margaret Thatcher): "Every new bit of information which comes along confirms that the ozone layer is being damaged by CFCs and other chemicals and that if we don't soon succeed in slowing down and then reversing that process our health and our whole way of life will suffer."

Comm: "To those who doubted that human activitiy could alter the atmosphere, the year 1985 came as a big shock - for the first time we had first indisputable proof that humans could influence what was happening at the very border of our atmosphere with outer space. The link here is not clear - ozone depletion has nothing to do with climate, it's about Ultraviolet radiation. In the late 1990s, scientists found that, perversely, global warming made ozone depletion worse, as it causes lower temperature in the stratosphere. Another link is that CFCs (but also their substitutes) are potent global warming gases. It was the discovery of a hole in the ozone layer almost the size of the United States by Jo Farman a scientist with the British Antarctic Survey in Cambridge."

Joe Farman: "16th of May 1985 is I suppose now notorious because that is when our results were first published and showing that there had been a 30% reduction of ozone over Antarctica in September and October and this was the first evidence ever put forward that there had been substantial change in the ozone layer since it had been studied in 1925."

Comm: "Ozone is a gas in the earths atmosphere, it protects us from the harmful effects of the suns ultra violet rays which in too great a quantity leads to eye damage and skin cancer. Without the ozone layer in the upper atmosphere life on earth would be virtually impossible. The evidence pointed to man-made causes of the depletion of the protective ozone shield."

Joe Farman: "Really there was no other explanation but it had to be chemistry and the only possible chemistry in this situation really had to be chlorine because that was the only new thing in the atmosphere."

Comm: "Chloro fluoro carbons or CFC's used in aerosols, packaging and as a cleaner in the electronics industry were entering the atmosphere and releasing the chlorine that was destroying the protective ozone layer. The main areas of depletion were over the poles, measurements in Antarctica showed a dramatic loss of ozone coverage, while in Australia, Chile and Argentina there were rising cases of skin cancer. But Farman was having trouble being heard, NASA questioned whether his rather elderly equipment was giving accurate readings."

Joe Farman: "The instrument which we use is the Dobson spectometrometor invented in 1927, still going strong, it's a very, very precise instrument for measuring the ratio of the intensity of two wavelengths and if you do this twice and take the differences you end up with a signal which depends, almost entirely on ozone and not on the other conditions in the atmosphere."

Comm: "Nasa still doubted the British Scientist, as their sophisticated computer read outs showed nothing unusual."

Joe Farman: "It turned out that they had put up a little barrier to finding the ozone hole, that is to say they quite reasonably decided to ignore very high values and very low values and to look at these later. They just wanted to get the main facts straight away but they had, in fact, stopped themselves from finding it."

Comm: "In 1985 NASA came back with its re-worked data, finally the ozone hole was official.

Washington, the hottest day of 1998, the US Senate Energy Committee was to hear startling new evidence from leading climate scientist James Hanson. What he said was to set alarm bells ringing around the world."

James Hansen: "That day in 1988 June 23rd, I do remember was an extremely hot day it was approximately 100 degrees in both New York and Washington. My testimony was in the afternoon, in the morning I was at a scientific meeting. I remember the chairman of the meeting said it may be getting warmer but no respectable scientist would say that there is a connection between the greenhouse effect and the observed warming. And at that time I was still writing down my summary for my testimony that afternoon and I said I don't know if he is respectable but I know someone who is going to make that connection."

Archive sound (Hansen testimony to US Congress): "In 1988 so far, is so much warmer than 1987 that barring a remarkable and improbable cooling 1988 will be the warmest year on the record."

James Hansen: "Altogether this evidence presents a very strong case, in my opinion, that the greenhouse effect has been detected and it is changing our climate now."

Comm: "This was dramatic testimony, for the first time governments were confronted by hard evidence that the world was getting warmer. Sophisticated computer modelling showed that recent higher temperatures were part of a consistent and rising trend. Hansons warning had all the more impact as it coincided with an enormous drought across the US. The dangers of a changing climate burst onto the front pages. Within months the United Nations set up a new global body to investigate global warming, the intergovernmental panel on climate change or IPCC. One man's evidence had started an intense debate on how we should protect our planet in peril.

Then in 1991 there was a massive volcanic eruption at Mt Pinatubo in the Philippines throwing debris into the stratosphere shielding the earth from the suns solar rays. It interrupted the warming trend, average temperatures dropped for two years. The event provided further evidence of how susceptible the climate is to change.

As with the ozone hole, the effects of the eruption called into doubt the traditional view that big climatic changes take place over thousands of years. Long term weather records taken from sea bed soil samples and rock formations show how over the last million years huge ice sheets have slowly spread across the continents and then gradually shrunk back. Ten times the ice has advanced and retreated, the climate seemed to be marching to a slow and steady beat. This was the prevailing view when scientist Richard Alley started out and it was all down to the sun. Small changes in the earths orbit seemed to account for the climates leisurely ebb and flow."

Richard Alley: "The prevailing view of climate change has been that the ice comes and the ice goes slowly. It happens because the earth's orbit around the sun has interesting little features in it, little wobbles and changes in shape that change where and when we get sunshine on earth. We still get the same amount of sunshine but do we have long, hot summers in Europe or do we have short, cool summers in Europe and those change over tens of thousand of years and a cold time would bring the ice and then eventually it would warm and then it would cool a hundred thousand years later."

Comm: "What was needed was a more accurate record of past weather patterns. The answer was falling from the sky."

Richard Alley: "Snow is one of the great materials for solving climate riddles. It's sampling the atmosphere as it comes down. The snow flakes go around dust particles and they pick up pollen particles as they fall down through the air and the types of those tell us something about how cold or how warm it was, how windy it was, where the dust was coming. Other characteristics of the snow really, tell us what the temperature was when it fell."

Comm: "Snow is like a historical thermometer, find the snow from a thousand years ago and it will tell you the temperature, there was one problem. Snow melts. So Richard had to go to a place where the snow never melts (1989). The Greenland ice cap has snow compacted in glaciers from the last ice age. By drilling ice cores out of the snow he was able to reconstruct past temperature records in unparraled accuracy. What he found stunned the scientific community."

Richard Alley: "When one looks at a piece of ice like this the first thing we look for is the layering. And it is moderately clear when one looks at this ice that it's layered and each of this layers is representing the snowfall for a year. What the huge surprise that came from this ice core is that we had expected the climate change to go wah wah wah over tens of thousands of years and in fact climate does have a little of slow change in it but mostly what we see is that climate goes boing boing boing with the changes happening in years rather than tens of thousands of years."

Comm: "Similar work carried out by a Norwegian team had shown that these sudden changes in climate could in part be linked to volcanic eruptions where vast amounts of sulphuric gasses cooled the planet to a significant degree.

There was to be another explanation, but in Madrid in November 1992 the IPCC Intergovernmental Panel on Climate Change comprising over 150 of the worlds top climate scientists released a dramatic report, in charge was Ben Santer."

Ben Santer: "In the first assessment report in 1990 scientists had felt that we did not know enough in order to definitively say that human activity had contributed to climate change. On the 29th November 1995 we made a different statement - that after full examination of the scientific evidence we felt that a majority of that evidence pointed towards a human affect on climate. That is what was historic about Madrid."

Comm: "There was finally a consensus that human influence was changing the climate, the report stated that `the balance of evidence suggests a human influence on global climate', agreeing those words had not been easy."

Sir John Houghton: "The whole meeting struggled for three or four hours with a single sentence as to how we were going to express whether we had seen human influence on climate, how certain were we about it, what was the nature of the evidence, was it strong evidence, was it significant evidence. We ended up with a balance of evidence, did the balance of evidence demonstrate that we had seen it, did it indicate that we had seen it or did it suggest that we had seen it. We settled for suggest."

Ben Santer: "These were issues, subtleties of language that we hadn't even considered. Now we had to consider them."

Sir John Houghton: "When that word discernible came - this discernible influence on climate - everybody cheered actually. We had been struggling for so long to find the right, just the right word to use."

Comm: "In the late 1990's scientist Wally Broker came up with an explanation for the sudden climate changes that had been found in the Greenland ice cores. The 25 years he had spent studying the ocean made him realise it had the potential power required to switch the climate so quickly. He knew the oceans have a huge influence on the earth's climate. The Atlantic for instance soaks up heat in the tropics creating a warm current that heads north and crosses the Atlantic. This is why Northern Europe is so much warmer than Labrador, even though it's on the same latitude. Wallys inspired new thought was that this warm current might be connected to a deep water current like an underwater conveyor belt. He called this system the Atlantic Conveyor."

Wally Broeker: "The Atlantic Conveyor transports an enormous amount of water. It's equal to all the rainfall in the world. If you had two pipes one transporting conveyor water and one transporting gutter pipe taking all the rain in the world they would have about equal amounts of water coming out. It means that the Conveyor is equal to something like seventy to eighty Amazon Rivers."

Comm: "Wally worked out that this mighty flow of water contributed about 30% of the entire heat received by Europe. It's equivalent to the heat from a million power stations. So if the conveyors circuit was to go wrong the temperature in Northern Europe would suddenly plunge."

Wally Broeker: "This is an important point in my career because I had spent 30 years up until that time studying, on one hand ocean circulation and on the other hand paleo climate and the two didn't really overlap very much and all of a sudden they came together because I realised that these two states could be the conveyor mode of circulation in the ocean on and the conveyor mode of circulation in the ocean off. And that hit me like a flash."

Comm: "But what would switch the conveyor on and off. This demonstration shows how the conveyor works. When the warm salty water from the tropics, here coloured dark blue, is cooled by the arctic winds in the north it gets denser and sinks. This sinking process is called convection. It's the mechanism that drives the conveyor. But if fresh water here coloured light blue floods the surface of the sea then it dilutes the salt water so it's no longer dense enough to sink, convection fails and the conveyor switches off. The search was then on to find out what source of fresh water could have regularly switched the conveyor on and off.

The culprit was melting ice. A warming atmosphere causes an armada of ice bergs to break away from the poles and melt diluting the salt water and forcing the conveyor to shut down. Only when the fresh water has sufficiently diluted over thousands of years can the ocean achieve the salinity required to restart the conveyor and warm the northern regions."

Richard Alley: "We are fortunate that a beautiful hypothesis was out there and that is Wally Broker's global conveyor shut-down. And it's very clear, to me, that what a global conveyor shut-down predicts is what we see in the ice core."

Comm: "The scenario of a big freeze in Northern Europe returns, but this time backed with strong scientific evidence and political acceptance. At a meeting of the world's ministers in Kyoto, Japan in 1997 there seemed finally to be a real understanding the something had to be done."

Ben Santer: "If the science is credible then people will do something about it if it is not credible then people will not do something about it. It was encouraging to me that what happened at Kyoto, I think, was a recognition - yes the science is credible."

Comm: "Next week we examine how governments are responding to the threat of climate change, and what impact the big climate conferences such as Kyoto and the Rio Earth summit have had in controlling greenhouse gas emissions.

What is increasingly certain is that global warming, fuelled by man is changing the climate. Whether it will get hotter or colder, wetter or dryer depends on the region of the world and the time of year. But all will share far greater extremes of weather than have been seen for hundreds, perhaps thousands of years."

Michael Meacher: "We are increasingly seeing that once in a century phenomena are now happening every year. And most people and the scientists certainly believe that this has a great deal to do with global warming. We have got to act for the future of mankind."