F. Sherwood Rowland

Green House Gases and Climate Change

Category: Lectures

Date: 29 June 2009

Duration: 34 min

Quality: HD MD SD

Subtitles: EN

F. Sherwood  Rowland (2009) - Green House Gases and Climate Change

The “greenhouse gases (GHG)” intercept a fraction of outgoing terrestrial infrared radiation, creating the natural greenhouse effect which warmed the atmosphere by approximately 32° Celsius at the beginning of the 20th Century

The question of whether carbon dioxide could be considered a pollutant was considered by the Supreme Court in the United States in 2007 and I thought that the first paragraph of that statement from the Supreme Court was worth producing and showing the science as seen by a person from the Supreme Court, that is an intelligent layman essentially writing for intelligent laymen. And what he said was, ‘a well documented rise in global temperatures has coincided with a significant increase in the concentration of carbon dioxide in the atmosphere. Respected scientists believe the two trends are related’. So basically there are three thoughts there. One of them is that carbon dioxide is going up in the atmosphere. The second is that global temperatures are going up and the third is that scientists think the two things are connected to each other. And so I thought I would start out by showing you the evidence that one gets from the question of the greenhouse gases and the warming that they produce. In this description here of the composition of the atmosphere, what I’ll point, just want to point out is from being a hundred percent the only thing which is close is nitrogen and then this is one part in a thousand, one part in a million, one part in a billion, one part in a trillion. And so the question of what’s actually present is dominated by molecules up here but has also of course important aspects of the molecules that are present in a part per billion or less. The measurements that one has seen for carbon dioxide, that started back in 1958 and were taken by a man named David Keeling, and this is the last of Keeling’s diagrams because he died after this. If you look now, at the present time, his son Ralph Keeling is a distinguished scientist in his own right and Ralph Keeling has continued this. But what we see here is the growth and the measurements at Mauna Loa in Hawaii, measurements of carbon dioxide where one sees a seasonal effect in which the maximum happens every May and the minimum happens every November. And the reason we’re going from May to November is that this is the greening of the northern hemisphere is taking carbon dioxide out of the atmosphere. But what one sees overall is, of course there is a change that has gone from 315 parts per million to 390 parts per million over a period of about 50 years. And this is the evidence that carbon dioxide is going up in the atmosphere. A point, one more thing about it, that here, is that if you were back here in the sixties, the increase in the concentration of carbon dioxide was about one part per million per year. Up here this was around 380 parts per million, at the last measurement in 2004 and last month it was 390, so it’s going up two parts per million per year. That is, one part per million here and two parts per million now so it’s, not only is it carbon dioxide increasing, that is increasing at a more rapid rate as we go along. Measurements of the temperature of the earth have also shown that there is a steady change in here. There was a hiatus in this time period there, but the last thirty years or so have been a fairly steady rise. It is, especially if you look at it, look at the red line of the five year meaning that there is, there has been a steady rise in, all through here. So this is the evidence that, the temperature is, each of these points has millions of points involved in, in drawing the conclusion about what the temperature of the earth is at a particular year. The third aspect of the Supreme Court statement has to do with the question of that, and that takes more explanation. It has to do with why scientists think the two are covered, that these two are covered well in the same way. And this has to do with the escape of infrared radiation from the earth, and if the radiation in the infrared from the earth were to escape completely, then that would mean that the global warming effect was not present at all. But what you can see here is when an infrared telescope on a satellite, looking down on the Sahara Desert, that there is a region in which carbon dioxide is not absorbing, where ozone is not absorbing and the radiation gets out and goes up through the entire atmosphere and it corresponds to the amount that you expect if the temperature were 320 degrees Kelvin. But over here, where carbon dioxide is absorbing, most of the infrared radiation has been taken out here. And the consequence is equilibrating the atmosphere, in order to equilibrate when all of this is blocked, requires that the temperature would be higher. And this is the connection that the more interception of infrared radiation that goes here, the more the temperature has to go up in order to make up for this deficit from there. And it depends on where you are in the satellite, looking down at it. Here’s a satellite half an hour earlier, looking down from the... This was in a polar orbit and the infrared radiation escaping from the south Atlantic ocean, which is very cold coming up from Antarctica, there is the infrared radiation being given off is much lower at that point, simply because all of the ocean is very close to the freezing point and so you’re getting radiation out here, but you still see the carbon dioxide absorption. And if you do the physics of the capture of what one calls, how you calculate for the natural greenhouse effect, what you’re doing is calculating the difference between what the temperature of the earth would be if all that infrared radiation were escaping and what it is in real life. The difference is 32 degrees centigrade or 57 degrees Fahrenheit, is the natural greenhouse effect. And that’s the effect that was there for carbon dioxide in the year 1800 and from the other molecules that are greenhouse gases as well. When one talks about the greenhouse effect now, what you’re talking about is the enhanced greenhouse effect from the substitution of molecules like carbon dioxide into the atmosphere in larger quantities. And keep in mind that the major use of carbon dioxide in the world today is in burning fossil fuels, coal, gas and oil. About 85% of the industrial energy of the earth is combined in those three carbonatious fuels and that’s what’s putting the major effect of carbon dioxide in the most recent time. If you want to look at what the behaviour of the other greenhouse gases is, the question that you have is what does have to happen in order for something to be a greenhouse gas? And it’s really very simple. It needs to last a fairly long time and it needs to have at least three atoms in the molecule and the three atoms are needed in order to produce any substantial infrared absorption and so you’ve got not only carbon dioxide but also nitrous oxide. Nitrous oxide is given off in various ways but one of the major ones is in fertiliser and the nitrous oxide has been going up steadily in the measurements since 1980. There are variations in here but basically about every three years there is a one percent increase in the amount of nitrous oxide and it doesn’t look as though there is any change in the slope here, so that this is becoming a steady increase in the absorption from nitrous oxide to go along with the carbon dioxide. There is another of the greenhouse gases, methane. And methane is an interesting gas that has a substantial number of origins from it. Methane is natural gas but methane is also given off by rice paddies, it’s given off by animals, so that when you look at the amount of methane that’s in the atmosphere, it’s a complicated mix of various sources, so that if you see a methane increase it becomes a little bit hard sometimes to decide what it was that caused that increase. The lifetime of methane in the atmosphere also is only about eight years and that is different from N2O, which is a 120 years or thereabouts and carbon dioxide which takes more than a century to be eliminated from the atmosphere. This is a calculation from the data measured in our laboratory on air canisters that had been brought back from around the world or mostly in the Pacific. Every three months somebody from the research lab goes, everywhere from southern New Zealand to Northern Alaska and many places, forty or fifty places in between. And from that we get, we do that every March, June, September and December. And if you add March, June, September, December together, you can get a calculated average for that year. But then if you take the March values away, and add the March for a year, that year plus one, again you get another average. And this is what we call a rolling one year average, taken four times a year, and progressively having a lead month being March, June, September and December. And so what you see is that here in the 1980s, the amount of methane in the atmosphere was going up about one percent a year and then when it got into the 1990s it got somewhat more erratic and in the 2000s, it’s been, not constant, varying, but not increasing over the eight or nine year period by any significant amount there. So the question of the chemistry of methane is a complicated one and very interesting one, because it’s one that you could make progress in trying to control methane as to doing something about the global warming problem. This is an illustration of the relative importance of the various greenhouse gases, starting with carbon dioxide, which you can see is more than half of all of the absorption has been in 1979 into 2005 and will certainly be that way because it’s, for fossil fuels, goal gas and oil continue to be in great demand and increasing demand. Methane is as indicated, it’s been in the most recent years a total, the increase has been very minimal but jumping around some. And then that should say N2O, the O dropped down here and then you have chlorofluorocarbon 12 and chlorofluorocarbon 11, and then about eight or ten others. So there are lots of greenhouse gases but they are of the order of four or five that are the most important. In addition to the greenhouse gases themselves there are measurements that have other contributions to the radiation balance in the atmosphere and these include aerosols and the difference between aerosols and over here with the greenhouse gases is that the greenhouse gases spread around the world fairly uniformly and so with the amount of carbon dioxide that you see in the atmosphere will vary only a couple of percent, wherever you are, unless you’re sitting on top of a big source. But so you get a lot of good averaging out here. Over here, in a place where there’s still a lot of work to be done, has to do with the various kinds of aerosols that are emitted, but because they are emitted quickly and briefly and then stop and then appear again, it becomes much, much harder to get quantitative evaluation on them, simply because they aren’t uniform around the world. So this is an area where the contribution of these molecules is very much under investigation at the present time. Then the considering of the greenhouse effect, there are some situations in which you change the amount of radiation that’s being removed from the atmosphere allowed to get out and this for instance, the Albedo feedback, the positive feedback, coming when the ground that’s covered with snow, when the snow melts you replace something that’s very reflective by something which is not reflective. And that means that when you start raising the temperature in the Arctic regions, what you measure is, the remove some snow and get additional amounts of radiation that stay out because they’ve been absorbed in the ground rather than reflected away with the snow. It’s also true that the same thing happens with ice and water, again an Albedo feedback coming from the melting of ice and replacing it with the absorbing of water. And what that does, when you put these into a model calculation, it is to in, this is a 25 year old model and which is illustrative of the changing, the change that’s calculated and has been calculated for the models, have been showing it all along. That because of the Albedo change from the melting of ice and snow, one calculates that there will be a faster temperature change in the polar north than there will be in other areas here. And it’s different from the Southern because most of the ice and snow in the south, in Antarctica are not in contact with water, they’re not at the freezing point. They’re much colder and as a result you don’t have the same Albedo feedback in the Antarctic instead of the Arctic. Well, then there is also the greenhouse gas and most of the most effective greenhouse gas of all, which is not measured by the direct concentration of water, that’s here, but rather it has also positive feedback and that positive feedback comes just from the amount of gases, vapour water that is in equilibrium with the just water itself. And that just depends on the concentrations of that. As the temperature goes up, for water it goes up one degree centigrade, you get six percent more water molecules, so there is this Albedo effect that will hit for water just simply six percent for every once degree centigrade that you could increase the temperature there. I’ve a special mark in here that what one finds is that if you trace hurricanes back to their place of origin, what you find is that the temperature has to be 27 degrees centigrade or warmer. It isn’t enough to have it 27 degrees centigrade or warmer but it’s a requirement in order you do. It doesn’t automatically give you a hurricane with that high temperature. But it doesn’t give you the hurricane unless you have that for the starting point. So that’s a different kind of change that is temperature dependent. And then there are the chlorofluorocarbons. Chlorofluorocarbons, dichloro, difluoro, methane, trichlorofluoromethane and the dicarbon version as well here. These, in addition to being the origin of stratospheric ozone depletion are molecules, while they are existing in the atmosphere, are greenhouse gases. And this is the one place where greenhouse gases are being under control to some extent. They are under control, not for their greenhouse effect but for their stratospheric ozone depletion effect. And this is characteristic, going back to 1990’s, the Montreal protocol called for the abolition of the use of the CFCs in the various technological uses they had. And as a consequence, with fluorocarbon 12 which has a 100 year life time, the atmosphere, down at the surface level, has been about constant for a decade or so. Though if we look at fluorocarbon 11, which has a lifetime of about 45 years, then you can see when looking at it from down here, that this has gone through a maximum and is actually reducing its amount – but slowly because they have very long life times and are accumulating. They aren’t, they have accumulated and will slowly get rid of them, but on a time scale of a century or so. So here are the greenhouse gases that are important in the present understanding of the atmosphere and the question, but the really big one is carbon dioxide. You certainly would like to control methane, nitrous oxide, but unless you’re controlling carbon dioxide it won’t be really effective though in the future. Switching to asking some questions about the atmosphere, here is an ice core that was taken out of a digging through ice in Antarctica and with that ice core what you can do is date the time of when the ice froze over. And when it did you have, as the ice is getting crushed more and more down, it eventually cuts off and what you have is atmosphere that was trapped 10,000 years ago or 100,000 years ago, so that you could see, then you can measure the carbon dioxide and you can measure the methane in those samples. And this is the first really big report of it from Laureas in the 1990s, this is going back 150,000 years and the ice core shows in the green, it shows the changes in temperature. Changes in temperature are indicated, are actually measured by changes in the isotopic ratios of oxygen 16, oxygen 18 and deuterium, that is hydrogen 2 to hydrogen 1. So if you go back 140,000 years, there was another time period when the temperature of the earth was about what it is now, and over here we have the last 10,000 years, a very compressed and – but what one sees is that the methane and the carbon dioxide go with the temperature for the last 500,000 years and what you see is that the amount of methane effect was going between 350 and about 650 parts per million. So when it’s at a high peak then what you see, the temperature, the carbon dioxide, the methane was around 700, but it was, at a low it was around 350. Carbon dioxide varied between a 190 and 280, and now of course the 280, this is the, you know, the last 10,000 years and then just the last 200 years. Where carbon dioxide is now at this point and over here on the methane it’s 1,780 instead of around 700, so that this is indication that the atmosphere, as we have been experiencing it, as the earth, the atmosphere has been through a series of four sets of ice ages over substantial, so over hundreds of thousands of years. With it, just staying between 190 and 280, on carbon dioxide and now we’re at 380, so we’re really in uncharted waters there. And if I go back and show the methane measurements that we’ve made in our research group. Here we are, a little bit more methane in the northern hemisphere, in 1980. By 1987 it’s gone up about one percent a year during that time period. What you can see is all the way to the South Pole they, here from Guadalcanal to the South Pole, to the amount of methane did not vary very much. And then when you got into the 90s, it slows down and it slows down more and is now all, it actually alternates back and forth but around a zero line here. And these rolling one year averages show that there are some places, some times when something is in a large sense, has been injected and when we have measured ethane, we find that the ethane matches methane pretty closely and that suggests that since most sources of methane do not have ethane in large quantities, it suggests that this is bio mass burning, that is a burning of agricultural waste. And this was a period when Indonesia was on fire and so there was a lot of methane, there was a lot of carbon dioxide and there was a lot of ethane as well. I would just have a couple of quick comments and then I will conclude. Something that we Californians were almost unaware of is that going back in the 1970s, the State instituted a programme of doing something independently of controlling the waste energy. And what one found was that if you took the per capita use of electricity from about mid 1970s to the 2000, it was almost the same at the same time that the rest of the United States went up by 50%. And this was just saying that fiscal policies and regulations can make a difference and did make a difference over the last 25 years in California and saying that it could be done in other places as well. And I’m going to close with one other, one last figure here. This is the ozone hole over Antarctica. This is the Antarctic Peninsula here. And this is South America over there and on this particular day, the hole was very elongated. And this is an example of man’s effect on the atmosphere in a way that was producing something that was totally unknown before and played an important role as far as controlling the CFCs which are the ingredients that cause producing the ozone hole. So one finds that what takes a little bit of thinking first about it and then because to say that you do think that something that man is doing can make a major effect on the earth, in the atmosphere, well, that’s what this is certainly a signal of and what we need to be concerned about on the warming that comes from the carbon dioxide and the other greenhouse gases and with that I will conclude.


The “greenhouse gases (GHG)” intercept a fraction of outgoing terrestrial infrared radiation, creating the natural greenhouse effect which warmed the atmosphere by approximately 32° Celsius at the beginning of the 20th Century. The activities of mankind have caused several of these gases to increase in atmospheric concentration during the past century, raising the atmospheric temperature by another 0.7° Celsius. Carbon dioxide, the most prominent GHG is released primarily by the burning of the “fossil” fuels coal, oil and natural gas, and has increased from 315 ppmv (parts per million by volume) in 1958 to 388 ppmv in 2008. Methane increased about 1% per year in the 1980s from 1.52 ppmv, but has slowed down to a nearly constant 1.78 ppmv from 2000 to 2008. Nitrous oxide (N2O) and ground level ozone (O3) are also steadily increasing in concentrations. The increase in GHGs will warm the Earth much more during the 21st, Century unless controls on these gases are rapidly put in place.

The chlorofluorocarbons (CCl2F2, CCl3F, etc.) are not only GHG contributors but also the suppliers of atomic chlorine to the upper atmosphere, causing the loss of stratospheric ozone. Every September since the mid-1980s a rapid loss of ozone occurs in a few weeks over the south polar area, resulting in the formation of the well-known Antarctic Ozone Hole, which fades away in mid-spring (November). These losses in stratospheric ozone led in 1987 to the international adoption of the Montreal Protocol which banned the further manufacture and release of the chorofluorocarbon gases. This Protocol has now been in effect for 22 years, and has been very successful. Nevertheless, the Antarctic ozone loss will occur throughout the 21st century because of the long survival lifetimes of the CFCs which have already been released.

Feedback processes involving reductions in reflectance (albedo) from ice to water, or from to snow to rock cause enhanced warming in the polar north, and the climate is changing rapidly in the Arctic with substantial biological effects.