About the history of climate change science. Sometimes it’s thought, sometimes it’s claimed, that climate change science is some new idea, some very strange bizarre idea. A few people, pretty outrageously, even say it’s a hoax but climate change science actually dates back almost two centuries. Now the basics have become very well understood, even though of course there are many uncertainties about this specifics of our extremely complicated planet.
The core notions of climate change science really date back to the 1820’s and rather than take us through a lot of equations and specific technical I thought I would introduce you to some of the greater thinkers who have been the pioneers, who helped us find our way to understand what this human-induced climate change is really all about. Now the first of these great scientists is Joseph Fourier, a great French scientist who, in the eighteen twenties, thought very deeply about a basic problem about the Earth’s temperature and the Earth’s place in the solar system. And he made a calculation and said you know given where the Earth is, 93 million miles away from at the sun, given the sun’s energy, the Earth really should be a colder planet, like the moon. The moon is a considerably colder than the Earth. And so Fourier asked the question, ‘what is it that is making Earth warmer than one would predict simply given the solar radiation and the physics of the Earth as a planet circulating the Sun?’
And he intuited something with startling brilliance and that is that the Earth’s atmosphere is a kind of blanket that warms the planet relative to what it otherwise would be. He realized even more deeply that perhaps because of the chemistry of the Earth’s atmosphere, which he could not know at that stage of Earth science, that the atmosphere would allow the solar radiation into the Earth, actually, to be absorbed by the planet and to warm the planet but that the atmosphere somehow would trap that heat that the Earth would otherwise re-radiate back to space. He said that the Earth would be in a kind of thermal equilibrium, or energy balance; that it would take in energy from the Sun; that would warm the Earth; as a warm body the Earth would radiate its own energy back into space; and the Earth would arrive at a balanced temperature, such that the energy outgoing from the Earth would balance the energy coming in from the Sun. And that would be the thermal equilibrium.
That would determine the Earth’s temperature. But Fourier said, ‘Hmm, suppose that the atmosphere traps some of that outgoing radiation, then the Earth would end up being warmer than otherwise and that is the famous greenhouse effect that Joseph Fourier first pioneered. It was a brilliant insight. In later decades, other great scientists, and I would mention John Tyndall in Britain, deepened this insight by understanding more deeply the atmospheric chemistry. Tyndall realized that even a small amount of carbon dioxide in the atmosphere could be part of that heat trapping blanket that surrounds the Earth in the atmosphere and that causes the greenhouse effect. And Tyndall also realized that as the greenhouse effect operates to warm the Earth, that the air being warmer would also thereby hold more water vapor, H2O, and that water itself would have a greenhouse effect, trapping some of the heat that otherwise would be radiated from Earth into space.
And so the carbon dioxide would trap heat warm the planet; with warmer air there would be more water vapor in the atmosphere; water itself in the atmosphere would be another greenhouse gas that would further amplify the warming; and it would be the combination of carbon dioxide and water, thought Tyndall, which would explain the overall greenhouse effect.
Now from Fourier’s work and Tyndall’s work came an absolutely magnificent and brilliant contribution a by another genius: Svante Arrhenius. Svante Arrhenius is a Nobel Laureate Swedish chemist who made many many great discoveries at the end of the 19th century in the early 20th century and at one point around 1896 Arrhenius being the genius that he was, decided with paper and pencil, of course not a computer to be available for dozens and dozens of years later and with no climate model, that he would calculate numerically what the effect of more carbon dioxide in the atmosphere would mean for the Earth’s temperature. And by paper and pencil and extraordinarily brilliant insight, understanding how carbon dioxide absorbs part of the radiation from Earth back into space, Arrhenius was able to calculate astoundingly that if the carbon dioxide were to increase significantly in the atmosphere and Arrhenius himself used the standard of carbon dioxide doubling compared to its baseline level and he also looked at what would happen if carbon dioxide halved compared to the baseline level that the temperature change that would result from that would be pretty significant.
In Arrhenius’ calculations that turned out to be four or five degrees Celsius, and he hit it almost on the mark. Of course that calculation has been refined since then and there are many many complexities and many debates about the specific sensitivity of temperature to carbon dioxide in the atmosphere. But I marvel at the fact that well over a century ago, without climate models, without computers available, Arrhenius was able to really hone in and make a brilliant calculation and come up with the basic relationship that every doubling of carbon dioxide would lead to a certain step increase of the temperature on the planet and almost nailed how much that increase would be. Now it turns out that the Earth is pretty complicated. It’s not just a solid sphere with a cover of atmosphere. We have a lot of complexity on the planet. We have oceans and atmosphere and very complicated water cycle and many factors that mean that the kinds of calculations that Tyndall and then Arrhenius made are subject to many deep questions. As the atmosphere warms what happens to the water vapor in the atmosphere? What is that feedback mechanism? As carbon dioxide builds in the atmosphere how much of the carbon dioxide gets absorbed in the ocean and thereby is taken out of the atmosphere?
These are not just complex details. They determine a lot about the climate sensitivity to carbon dioxide. Now, Arrhenius, being the genius that he was, realized that not only would carbon dioxide change the temperature on the planet, but that humanity would have a large-scale effect on the amount of carbon dioxide in the atmosphere because by the end of the 19th century, in the age of steam and soon to be the age of automobiles and oil, Arrhenius realized we’re burning a lot of the fossil fuels – the coal, oil, and in the 20th century and 21st century natural gas – that we use for our transport, in our heating and cooling, in our industrial processes to make iron and steel, and so many other vital parts of our economy.
And Arrhenius said as we continue to burn the fossil fuels we will then change the carbon dioxide measurably and thereby change the mean temperature on the planet according to his calculations. But he didn’t quite get it right because he did not anticipate the geometric growth of the world economy. He underestimated how fast the world economy would grow. He underestimated as all of us did how fast China would grow, for example, at the end of the 20th century and into the 21st century.
And so Arrhenius said it would take about seven hundred fifty years for the carbon dioxide to double from its pre-industrial concentration. Well that wasn’t as good as his climate calculations because it turns out that he was writing in 1896 and best guess for us now is that the carbon dioxide relative to its pre-industrial concentration could double by the year 2050. We’re on a path of a period in which it’s going to be 150 years from Arrhenius’ writing, not seven hundred fifty years, and that is what leads us to the drama our present-day. Now after Arrhenius made these calculations, there ensued decades of complicated debate but one thing has become clear.
Arrhenius was right that carbon dioxide would shoot up under human effect and that would warm the planet. This is a figure well-known in the scientific community which shows the ups and downs of carbon dioxide on natural cycles, starting from the left hand side of this graph, 800,000 years ago coming to the present. And what you can see is that from 800,000 years ago to 700,000 years ago and so forth, carbon dioxide fluctuated up and down between a range about 150 and 250 parts per million in the atmosphere, what are called ppm. What is that parts-per-million? It means that in our atmosphere, which is filled with nitrogen and oxygen and just a small amount of carbon dioxide, carbon dioxide molecules only account for right now around 400 molecules for every 1 million molecules in the atmosphere. In other words four hundred parts per million. Well before the Industrial Revolution, the carbon concentration, or carbon dioxide concentration, was roughly between 150 and 250 parts-per-million, up and down up and down. What was causing these fluctuations? These were fluctuations that were caused by natural changes of the Earth’s orbital characteristics around the Sun. But look what happens suddenly just at the very right-hand margin of this grab. Up and down for 800,000 years within a band and then suddenly the graph shoots straight up, just takes of like a rocket.
That is humanity putting carbon dioxide into the atmosphere every time we dig coal out of the ground and burn it. The carbon in the coal combines with the oxygen in the atmosphere to produce carbon dioxide and thereby raises the co2 level and when we burn natural gas or petroleum the same phenomenon. So Arrhenius said raise the co2 level will raise the temperature and humanity is on a path of raising the co2 level. And here we have it. We’re shooting straight up and so fast that we’re creating a massive danger. Well for decades after Arrhenius’ findings, there were big debates. Would the water vapor in the atmosphere really be a feedback? What would happen to clouds? Wouldn’t the carbon dioxide just be dissolved into the oceans and thereby not create this blanket of greenhouse gases in the atmosphere.
Another great scientist in the nineteen fifties, Roger Revelle, dispelled some of the calm by saying the ocean would not absorb the atmospheric carbon dioxide and Revelle, who is shown here, produced the first integrated assessment of oceans, atmosphere, and climate, and gave the alarm that Arrhenius was right. We can’t rely on the oceans to take away the carbon dioxide. We have a problem. Another great scientist, who was a young man, said we better measure the carbon dioxide and we’re going to be seeing his measurements which we rely on still, that started in 1958.
This is Charles Keeling. He created the best measurements we have of the human-induced changes of carbon dioxide and those measures taken at the top of a mountain in Hawaii, Mauna Loa, give us a record vividly showing that humanity is causing a rise of carbon dioxide. So start in 1958 and you see the carbon dioxide levels rising year by year. Within the year there’s a zig-zag because that is the seasonal change of carbon dioxide concentrations when we have spring and summer in the Northern Hemisphere of Earth and the forests fill with the plant life and the leaves and trees are growing and photosynthesis, the carbon dioxide in the atmosphere is absorbed backed into the biosphere and we get a little bit of a downturn in the atmospheric concentration of CO2
Then comes the fall and winter. The leaves fall; they decompose; the carbon dioxide in the leaves enters the atmosphere once again and the cycle turns up. And so there’s an annual up and down, up and down, depending on summer, winter in the northern hemisphere, but there is a upward slope that is really the main part of our story. We are burning so much coal, oil, and gas that the carbon dioxide levels are rising, and Arrhenius’ warnings need to be taken to heart. Now who told Congress of the United States, ‘You better listen and watch nature.
That was my wonderful and brilliant colleague, Dr. James Hansen, who for thirty years was the US government’s lead climate scientist. He’s recently stepped down from being Director of NASA’s Goddard Institute of Space Studies. Professor Hansen is one of the most brilliant scientists I’ve ever met and one of the bravest also because he tells it as he sees it and he sees it as clearly as anybody can because he knows every aspect of this science. And in 1988 he went to the US Congress and for the first time said this is real, this is serious, you better listen. And think about it, 1988 – we are now 26 years later and still don’t have an adequate response. But fair warning was given. Professor Hansen, who has lead teams of scientists, putting up satellite measurements, looking at the most sophisticated measures of how the atmospheric chemistry is changing, how the ocean chemistry is changing, how the energy balance of the Earth is changing, has given the warning and he’s sounded the alarm for all of the years since then. We’re here in part to listen carefully to what he’s been telling us. What he’s been telling us is what Arrhenius warned about and what Joseph Fourier hypothesized already almost two centuries ago.
The Earth is warming. Not only was May 2014 the hottest May in recorded history, but on average temperatures have continued to rise. They have increased now compared to the mean or average temperature on the planet before the start of the Industrial Revolution by almost one degree centigrade. And we’re on a path, as we’re going to note, not to stop there, not even to stop a two degrees centigrade, but on our current trajectory to reach 3, 4, 5, 6 even more degrees Celsius in the future, if we don’t start to heed these warnings. Well another great scientist said we’re changing the atmosphere chemistry in so many dangerous ways and we’re changing the planet in so many dangerous ways that the entire geology of Earth is creating a new phase of Earth’s history. this is Paul Crutzen, one of the great scientists who discovered the ozone depletion effect from the so-called CFC’s or chlorofluorocarbons. And Professor Crutzen, another Nobel laureate said all this human impact has brought us to a new geologic epoc, which he is called the anthropocene. The Anthropocene is from the Greek meaning the human induced phase of the planet. Some time scientists say that human change is driving the planet but I call it drunk driving. We don’t know the way we’re driving the planet. We are changing the planet but we’re changing it in a reckless way.
That is a pantheon of great scientific leaders, but I do also want you to be introduced to some of the anti- scientists on the planet because as hard as it is for the scientists to uncover the principles of nature we have people of great irresponsibility trying to hide the scientific evidence and they are delaying an appropriate response. One of them, one of the world’s leading media magnates, Rupert Murdoch, has used his vast media empire to propagandize against the science. Another, these two brothers, two of the richest people in the world, the Koch brothers – Charles and David Koch – worth a combined 100 billion dollars, are using their vast fortunes to help spread anti-science, anti-climate change science, to call the climate scientists agents of a hoax.
They spend a lot of money financing campaigns of politicians who oppose Climate Action. Why do they do this? Well, one reason no doubt is that they own the world’s largest private oil company, Koch Industries, and they are contributing massively through their own industrial activities to climate change. And they’re funding the anti climate effort. And some of the biggest companies in the world, the oil giants, have not taken a responsible stand. Here’s the CEO of Exxon Mobil, a part of our job is to ask them the question, as leader of one of the most powerful companies in the world, a company responsible for the exploration, development, production, and shipping of one of the fossil fuels, petroleum, that is leading to this climate change, what is your company doing to keep us safe? The climate scientists have given us the warning. It’s our responsibility to understand the science, and to take heed and to take action before disaster ensues.