Climate Change: Science, Policy and Risks
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Molina, Mario J.
Climate change is the most serious environmental challenge facing society in the 21st century. The average temperature of the Earth's surface has increased about one degree Celsius since the Industrial Revolution, and the frequency of extreme weather events such as heat waves, droughts, and floods has also increased. The consensus among climate change experts is that it is very likely that human activities have caused these changes in the Earth’s climate. The basic science is very clear, although the climate is a complex system and hence there are scientific uncertainties connected with issues such as the feedback effects of clouds and aerosols. The risk of causing dangerous changes to the climate system increases rapidly if the average temperature rises more than two or three degrees Celsius; society faces an enormous challenge to effectively reduce greenhouse gas emissions by increasing energy efficiency and using renewable energy sources to avoid such dangerous interference with the climate system.
 Thank you very much. Let me just to get started, I will talk about climate change. We just heard some talks in physics and before that chemistry, well, this is climate change has some chemistry in it, but I will be talking more about the science, policy and risks perspective. We already heard the talk by Steve Chu, presented by William Murner. So my presentation will be complimentary. There will be just a few things that will be repeated, but in a very general sense it will be complimentary. I've known Steve Chu and I've worked with him for many years now, so we are good friends. So I just regret that he was not able to be here. So what I'm going to do to stress again the science, policy issues is let me talk about some of the myths that are connected with climate change. Climate change, we understand, we have heard it already several times, is one of the most pressing, if not the most pressing problem that society has at the moment, certainly the most pressing environmental problems. But there is a very common view that is expressed in the media and by many people leave it that climate change is natural, climate has always changed in the past, so it really has no connection with human activities. Well it turns out that there have been some very careful surveys of the literature, the scientific literature followed by personal surveys and so on, that really demonstrate that there is an unusual situation that doesn't always happen in science, but there is this consensus among scientists, more than 97% according to some of these reviews that are now several years old, certainly agree that climate change and that it is most likely caused by human activities. There are of course always some scientists that disagree, here we have 3%, it turns out we know these scientists very well and so we know their arguments, they have been tested, explored and certainly do not convince the rest of the 97%. But there is something else interesting happening, which is we are talking here about not your scientists but climate change scientists. In general, scientists are skeptical, so they question things, that's okay, that's the way science works. So one, I'm just going to show you an example of this attitude of scientists that are not necessarily climate scientists, namely there was an op-ed in the Wall Street Journal that as you know is fairly conservative, some years ago claiming that, well, that many of us were really exaggerating, that it is not really true that something dramatic needs to be done and so on and a large number of distinguished scientists do not agree with this. It turns out that subsequent to this there was also a massive sort of survey but that included, it was claimed to be scientists but it included many artists, many non-scientists but anyhow in this particular case it turns out that most of these 16 scientists were not connected to climate science. So fortunately the Wall Street Journal did agree to publish a response and as you can see the way this is labeled, well, if you have a heart attack or you have a problem with your heart, you don't go to see your dentist, you normally go to see the experts. So what is very clear, seems to be very clear now, is most people, certainly including scientists that talk about climate change in the fashion I showed here, really know practically nothing about the science of climate change. So what I want to do next is just review historically this climate change science. I want to deal very much with the science itself but we just want to review a few facts that remind you that probably all of you know. First of all just a view of our planet just to show the atmosphere but the atmosphere is very thin, you cannot really see it, it's like the skin of an apple but that's what determines the climate of our system. And just one point to indicate while I have this photograph is that to indicate here if you emit something to the atmosphere, say a gas that is relatively long lived, some gases survive just a few hours and some particles perhaps can survive a few weeks but there are some gases that remain there longer but if you emit something, say here in the Northern Hemisphere, the winds work in such a way that within a few months that substance is mixed throughout the Northern Hemisphere. It takes a little longer to mix in the Southern Hemisphere because there's a mixing barrier but it takes roughly a year and a half, less than two years for this mixing to take place and this is what gives rise to what we call global problems because when we're talking about emissions of the species, gases that last more than a few months, more than a few years, it doesn't matter where they are emitted on the planet. They are really giving rise to little global problems. One such problem is the stratospheric ozone issue which is not what is called here, what we work with Paul. If I have time I'll mention a few things about it at the end but the other is that important global issue is of course climate change. Now historically, the idea is the following. How did scientists first assess what should be the climate of our planet? This really started with Joseph Fourier, a very well-known mathematician, who first sort of figured out the Earth receives energy from the Sun. So that's really what should determine what should be our climate. And he was already talking about non-luminous heat, electromagnetic radiation that we cannot see and he connected that with the expected temperature of the Earth. The next sort of important finding there was from John Tinda which is that there are certain gases in the atmosphere that they are transparent to the energy from the Sun but they actually absorb a part of the electromagnetic radiation. He was able to identify very clearly water and carbon dioxide as the two main components of this sort of additional species that are transparent to visible but not transparent to infrared radiation. The third important scientist here, Suantia rhenius and of course for those of you that are chemists, we know that the rhenius made several important discoveries. They are for me as a gas kineticist, the rhenius equation that describes how fast chemical reactions proceed but also he received an oil price. It was actually for his discovery that something like sodium chloride in water gives ions, sodium ions, chloride ions and so on. But he also worried about climate change and what he did is with the knowledge I just described he was able to do calculations, very tedious calculations predicting that if humans were to continue to generate carbon dioxide, the temperature of the planet might rise by about by this century, perhaps even something like four or more degrees. And that's remarkable considering that he did that at the beginning of the 20th century it is remarkably accurate. Well, let me explain now a little bit in more detail how does this come about. This is some basic science, this is something with each two even high school students and so on. Here is the idea of course the earth receives electromagnetic radiation mostly in the form of visible energy but we know that this energy is also lost to space and that's what was discussed in the early days. I should have mentioned when I was talking about Fourier that at that time there was the idea that heat itself was some sort of fluid, phlogiston or caloric and that this heat was somehow or all this fluid was transmitted from one body to another and so on and so forth. So it took a while for thermodynamics to really become a science and it is really the first law of thermodynamics that is very important in establishing this idea what determines the climate of our planet. That's the idea is the following energy is conserved that means if the earth receives a certain amount of energy and if it reaches equilibrium which is something that it has done millions of years ago, equilibrium is a state of the situation in which things no longer the physical properties no longer change with time and of course oversimplifying here but for our planet many millions of years ago the amount of energy that it receives equals the amount of energy that it loses. This is in contrast to what people normally think that say when you put a mantle on your body it traps the heat so it doesn't allow energy to flow anymore. Of course we know that after a while the amount of heat generated by your body is lost to space and that happens with our planet as well. The amount of energy received equals the amount of energy lost but because the earth is at a much lower temperature it loses the energy in the form of infrared radiation and this came out of experiments so-called black body radiation experiments where you could measure in the laboratory this amount of energy lost by any particular body in the laboratory which depends only on its temperature but it was an empirical law but considering that particular law which was just experimentally determined and considering the fact that you could measure the amount of energy going from the sun you would determine that the average surface temperature of our planet should be about minus 18 degrees Celsius or degrees centigrade and if that were to be correct we wouldn't be here because the planet would be frozen. Well here is what happened this black body radiation law which is it was for some time not understood where it came from but it was of course the Max Planck that then interpreted this black body radiation law that's what gave rise to quantum mechanics by suggesting with something which at the beginning of the 20th century was sort of not quite reasonable that the energy comes in packets okay so anyhow that's the origin of quantum mechanics has to do with that description Einstein himself also provided a very important component not only that the energy comes in packets but also radiation photons okay they are quantized and that's why the temperature it's very sensitive to the temperature. Now if so we what this gives rise to what we call the natural greenhouse effect which is the following if our planet had just a transparent atmosphere it receives say a hundred in some units of energy from the sun about one third is reflected to space but the rest is submitted by the surface and that's what would keep the temperature at minus 18 but what really happens is that the atmosphere is not transparent it's like a blanket the atmosphere has a blanket and that's what means that the temperature has to rise at the surface it has to emit a lot more energy because a good fraction of that energy is not lost to space it comes back to the surface. And I won't go into the details but of course that's oversimplified there have been all sorts of measurements and the overall energy balance is a bit more complicated but it's very well understood this is fundamental science and one more piece of information is that basically it's only a small fraction of the atmosphere that gives rise to this natural greenhouse effect a lot less than one percent if water vapor was understood to be the most important so-called greenhouse gas because of this natural greenhouse effect absorbing about three-fourths of this infrared energy we're talking about and carbon dioxide the other fourth so from that perspective one would think water vapor is what controls temperature but as you know water vapor the amount in the atmosphere depends critically on temperature so what I have here is just to give you a sense particularly not to you people that work with science but to public in general that are not very familiar with gases the amount of water vapor if we were to condense it typically what is in the atmosphere would occupy just a few centimeters on the amount of carbon dioxide if it were to be solid say just four millimeters that's the blankets that our planet has a very small blanket if you want that raises a temperature these 33 degrees the earth or the natural greenhouse effect but if we were to remove carbon dioxide the water would condense and then we would have a frozen planet so that's why carbon dioxide is called the thermostat of of of the planet and what what's happened to carbon dioxide this you already heard from Steve choose presentation I could go back millions of years but in more recent years ten thousand years what you see is how suddenly in very recent times the concentration has increased quite dramatically and it's very clear that this comes from burning fossil fuels you can do isotope analysis things like that it's also quite clear that the temperature in on the same time scale has abnormally changed just in recent times so the question the obvious question is that where does this come from and the the best explanation this this has to do with the greenhouse effect but in any event the scientific community got gets together and every few years this intergovernmental panel on climate change makes statements about what is the status of the science and the last big report was a few years ago and the conclusion in the previous report that says that yes this temperature changes indeed connected to the carbon dioxide change but we're not absolutely sure of the connection so we talk about probabilities at that time it was 90 percent but in the last report they raise it to 95 percent so it's possible that is naturally just extremely unlikely but let's move on with with the meets and I want to get to several additional points one other meat is quite worried about this let our children and grandchildren take care of the problem because this will happen towards the end of the century when more carbon dioxide will pile up but that's not really the case what we know is that for example the Arctic sea in the summer is melting as you can see from these pictures this is something very dramatic has happened particularly recent times but more worrisome perhaps is what we call extreme weather events this is this doesn't represent the relatively small change in temperature that we have seen I should have quantified that it's of the order of just one degree centigrade but we have extreme weather events heat waves slots and so on that have increased in recent times storms landslides and so on and the scientific community was very sort of careful and until some years ago they thought they didn't have enough statistics to make any connection but in recent years it's very clear now that the connection is statistical climate change doesn't cause these extreme events but it certainly increases their intensity and that's why this is what I'm stating these that scientists were very skeptical but the conclusion is that yes these events are indeed affected by climate change for example the hurricane Sandy that was so expensive in the United States it is most likely influenced then by climate change but let's now move on to the to the last of the myths I have here and this is no longer science okay this is economics we shouldn't do anything about climate change because fossil fuels are so important for for the functioning of of society that we just shouldn't risk doing anything about this well that turns out to be also a myth and some years ago it was already indicated by our colleagues at Princeton that the way to solve the climate change problem if there's no silver bullet there's no simple big solution that you can do so if we have emissions here as a function of time what you need to do is many things simultaneously so-called wedges you have to improve the the fuel economy the efficiency with which you use particularly fossil fuel more efficient buildings and so on but you have to start using renewable energies okay even nuclear energy that's of course question or that gives rise to a different debate but wind and solar are particularly important as we see here but what is very dramatic about this particular energy forms now renewable energy forms as you already heard in Steve choose presentations is that the price has come down quite fast so it turns out that in in in recent years these types of energies are quite competitive now with fossil fuels they still have problems with storage and so on but but that's coming along now it's it's moving and so if we see reports from economists were capsule one of the most famous one is from from lord Nicholas turn from some years ago where he stated already that decade ago or something that it would only take about 1% of global GDP to make the necessary changes so that we wouldn't have to risk this huge temperature rise that might occur otherwise anyhow that was quite well substantiated but what is quite interesting is in much more recent reports in order for society to decide whether to do it or not it's not only how much does it cost but how much does it cost not to do it so that's how society should function science doesn't tell you what to do science doesn't tell you it's not it's neither good nor bad so science just provides the facts it can make predictions what would happen if you do this if you do that and that's why the intergovernmental panel on climate change is supposed to be non political it just states the facts what the scientific community thinks what you mix then the science with economics and with social and political aspects and that's how you take decisions and that's where ethical principles are very important to mention more in just a moment but the point is that the damage that would be caused by climate change in general have been grossly underestimated this is what is very worrisome so if in principle what would need to happen to control climate change I won't go to this into detail but ideally from an economist perspective you put a price on emissions but this has not been practical there was a meeting of this intergovernmental panel on climate change already in 2009 for about 150 heads of state were there and they agreed let's change things so that the temperature doesn't increase more than two degrees but the negotiators didn't agree the heads of state did so it took a bit longer it took some more time until 2015 December of 2015 finally an international agreement was reached the so-called Paris Agreement in which practically all the countries of the planet together agreed that indeed let's try and see whether we can keep the temperature rise below two degrees and the way we will do it is in contrast to the earlier attempts where for example the Kyoto protocol the first attempts they were assuming that only developed countries which were the ones that originally caused the problem would do something and then developing countries would wait until things would stabilize a bit more that didn't work that was not a practical way to do it so the big change in the Paris Agreement is practically all the countries including China developing countries India Mexico and so on would commit themselves to do something on a voluntary basis however something that could be measured that could be demonstrated and so it was a very big achievement and here is if I put emissions versus time we can see that the Paris Accord doesn't reach the two degrees okay it goes well above that because it's just a first step the ideas of all the nations will collaborate will work together and they will try to strengthen the Paris Agreement itself but as such it's not sufficient I should also mention here why was what's the nature of the Paris Accord mean advising the president of Mexico but I was also a member of PCAST which is the advisory group about 20 scientists the scientific advisory group to President Obama so we work closely with him on the Paris Accord and it was essentially designed by the limits that the United States have to place namely to do something that would not require the approval of Congress because the Congress in the United States as you know is lived by Republicans who question the nature of climate change and so this is let me just spend a few minutes very rapidly talking about this it turns out that it's well established already for some time now that it was industrial groups that put in question the science of climate change but it's those groups were the people that were managing those groups are exactly the same those are the same people that delayed governments to do something about smoking and about several other interventions they were just representing industry but what's happened more recently is not just that there are industrial perspectives economic perspectives but it became climate change became politicized and so it was a mantra of the Republican Party in the United States just to not to believe in climate change science and to mention that it was all just a hoax in some sense that it is not something real so I have just a couple of minutes I need to mention what has happened recently namely as you know the United States President Trump did not agree with with they decided not to accept the Paris agreement but let me go back in time just in times of the election this was just typical of anybody belonging to the Republican Party in the United States and why do I mention the United States because it's crucial for this international agreement but as you see the idea is that this is the climate change is just something that is not believable that's very worrisome for us as a scientific community because as I mentioned it's very well established it's basic science and so on so we're living in a world where very important politicians question that there are always people questioning many aspects of science as we know I could give lots of examples with vaccines and so on but the worry here at it's the president of the United States that is making such incredible statements well let me just move on there were I mentioned this because there were lots and lots of the pieces in the media criticizing of course Trump's decision a few of them as expected would agree with what the United States decided namely to not to accept the Paris agreement I won't go into the details except that most of the scientific organizations practically all of them made strong statements strongly disagreeing with with President Trump's situation well President Trump's perspective but there what I want to highlight that was not very much highlighted in the news is something that for example Jeffrey Sacks mentioned that global warming is an existential threat okay it's a big worry for the following so I want to spend probably one extra minute I was a professor at MIT for many years but so there it was acknowledged because the climate is a complex system you cannot predict with certainty what will be the temperature change in the future for any particular scenario so they had these two spinning wheels the one in the left with red is if you do business as usual which is what President Trump's and his team would argue but you can actually change that if you have reductions in in in the emissions the big problem is that there are some red portions there in these flags and and the same thing the same results were actually projected by the international panel climate change namely the red part here is what happens if you do the business as usual scenario if you don't worry about climate change if you think it that's indeed it's a hoax and so on and here is what is most worrisome here is how the scientific community we try to summarize this it's not necessarily what's the most likely change if we do nothing that might be three or four degrees but we look at what we call the economists are worried a lot about this which is just the tales of the distributions and the summary situation is the following there is a probability of roughly one in five that the temperature will increase more than five five or six degrees towards the end of the century if that were to be the case that that is a very highly irresponsible act namely to allow that probability to go on for future generations because it really is doesn't respect the the rights of future generations it's an ethical issue highly highly irresponsible because if the temperature goes up more than five degrees you could have all sorts of extreme events for example parts of the planet would be uninhabitable there would be all sorts of food production problem mass migrations wars and so on and so forth so that that that's my summary that it would it's extremely irresponsible and irrational it's extraordinary irrational the attitude that the US president he has taken so let me just finish with mentioning very briefly that we fortunately have one example of a global issue that has been solved Paul Crutzen here has been instrumental with that and that's it the depletion of the ozone layer and without this international agreement which is a montero protocol we would be in very big trouble today but fortunately all the countries in the planet practically accepted the agreement and so with the protocol we know that the ozone layer is finally recovered so we know it can be done we can all work together and avoid this extreme irresponsibilities thank you for your attention
 Thank you very much.  Let me just to get started, I will talk about climate change.  We just heard some talks in physics and before that chemistry, well, this is climate change  has some chemistry in it, but I will be talking more about the science, policy and risks perspective.  We already heard the talk by Steve Chu, presented by William Murner.  So my presentation will be complimentary.  There will be just a few things that will be repeated, but in a very general sense it  will be complimentary.  I've known Steve Chu and I've worked with him for many years now, so we are good friends.  So I just regret that he was not able to be here.  So what I'm going to do to stress again the science, policy issues is let me talk about  some of the myths that are connected with climate change.  Climate change, we understand, we have heard it already several times, is one of the most  pressing, if not the most pressing problem that society has at the moment, certainly  the most pressing environmental problems.  But there is a very common view that is expressed in the media and by many people leave it that  climate change is natural, climate has always changed in the past, so it really has no connection  with human activities.  Well it turns out that there have been some very careful surveys of the literature, the  scientific literature followed by personal surveys and so on, that really demonstrate  that there is an unusual situation that doesn't always happen in science, but there is this  consensus among scientists, more than 97% according to some of these reviews that are  now several years old, certainly agree that climate change and that it is most likely  caused by human activities.  There are of course always some scientists that disagree, here we have 3%, it turns out  we know these scientists very well and so we know their arguments, they have been tested,  explored and certainly do not convince the rest of the 97%.  But there is something else interesting happening, which is we are talking here about not your  scientists but climate change scientists.  In general, scientists are skeptical, so they question things, that's okay, that's the way  science works.  So one, I'm just going to show you an example of this attitude of scientists that are not  necessarily climate scientists, namely there was an op-ed in the Wall Street Journal that  as you know is fairly conservative, some years ago claiming that, well, that many of us were  really exaggerating, that it is not really true that something dramatic needs to be done  and so on and a large number of distinguished scientists do not agree with this.  It turns out that subsequent to this there was also a massive sort of survey but that  included, it was claimed to be scientists but it included many artists, many non-scientists  but anyhow in this particular case it turns out that most of these 16 scientists were  not connected to climate science.  So fortunately the Wall Street Journal did agree to publish a response and as you can  see the way this is labeled, well, if you have a heart attack or you have a problem with  your heart, you don't go to see your dentist, you normally go to see the experts.  So what is very clear, seems to be very clear now, is most people, certainly including scientists  that talk about climate change in the fashion I showed here, really know practically nothing  about the science of climate change.  So what I want to do next is just review historically this climate change science.  I want to deal very much with the science itself but we just want to review a few facts  that remind you that probably all of you know.  First of all just a view of our planet just to show the atmosphere but the atmosphere  is very thin, you cannot really see it, it's like the skin of an apple but that's what  determines the climate of our system.  And just one point to indicate while I have this photograph is that to indicate here if  you emit something to the atmosphere, say a gas that is relatively long lived, some  gases survive just a few hours and some particles perhaps can survive a few weeks but there  are some gases that remain there longer but if you emit something, say here in the Northern  Hemisphere, the winds work in such a way that within a few months that substance is mixed  throughout the Northern Hemisphere.  It takes a little longer to mix in the Southern Hemisphere because there's a mixing barrier  but it takes roughly a year and a half, less than two years for this mixing to take place  and this is what gives rise to what we call global problems because when we're talking  about emissions of the species, gases that last more than a few months, more than a few  years, it doesn't matter where they are emitted on the planet.  They are really giving rise to little global problems.  One such problem is the stratospheric ozone issue which is not what is called here, what  we work with Paul.  If I have time I'll mention a few things about it at the end but the other is that  important global issue is of course climate change.  Now historically, the idea is the following.  How did scientists first assess what should be the climate of our planet?  This really started with Joseph Fourier, a very well-known mathematician, who first  sort of figured out the Earth receives energy from the Sun.  So that's really what should determine what should be our climate.  And he was already talking about non-luminous heat, electromagnetic radiation that we cannot  see and he connected that with the expected temperature of the Earth.  The next sort of important finding there was from John Tinda which is that there are certain  gases in the atmosphere that they are transparent to the energy from the Sun but they actually  absorb a part of the electromagnetic radiation.  He was able to identify very clearly water and carbon dioxide as the two main components  of this sort of additional species that are transparent to visible but not transparent  to infrared radiation.  The third important scientist here, Suantia rhenius and of course for those of you that  are chemists, we know that the rhenius made several important discoveries.  They are for me as a gas kineticist, the rhenius equation that describes how fast chemical  reactions proceed but also he received an oil price.  It was actually for his discovery that something like sodium chloride in water gives ions,  sodium ions, chloride ions and so on.  But he also worried about climate change and what he did is with the knowledge I just described  he was able to do calculations, very tedious calculations predicting that if humans were  to continue to generate carbon dioxide, the temperature of the planet might rise by about  by this century, perhaps even something like four or more degrees.  And that's remarkable considering that he did that at the beginning of the 20th century  it is remarkably accurate.  Well, let me explain now a little bit in more detail how does this come about.  This is some basic science, this is something with each two even high school students and  so on.  Here is the idea of course the earth receives electromagnetic radiation mostly in the form  of visible energy but we know that this energy is also lost to space and that's what was  discussed in the early days.  I should have mentioned when I was talking about Fourier that at that time there was the idea  that heat itself was some sort of fluid, phlogiston or caloric and that this heat was somehow  or all this fluid was transmitted from one body to another and so on and so forth.  So it took a while for thermodynamics to really become a science and it is really the first  law of thermodynamics that is very important in establishing this idea what determines  the climate of our planet.  That's the idea is the following energy is conserved that means if the earth receives  a certain amount of energy and if it reaches equilibrium which is something that it has  done millions of years ago, equilibrium is a state of the situation in which things no  longer the physical properties no longer change with time and of course oversimplifying here  but for our planet many millions of years ago the amount of energy that it receives equals  the amount of energy that it loses.  This is in contrast to what people normally think that say when you put a mantle on your  body it traps the heat so it doesn't allow energy to flow anymore.  Of course we know that after a while the amount of heat generated by your body is lost to  space and that happens with our planet as well.  The amount of energy received equals the amount of energy lost but because the earth is at  a much lower temperature it loses the energy in the form of infrared radiation and this  came out of experiments so-called black body radiation experiments where you could measure  in the laboratory this amount of energy lost by any particular body in the laboratory which  depends only on its temperature but it was an empirical law but considering that particular  law which was just experimentally determined and considering the fact that you could measure  the amount of energy going from the sun you would determine that the average surface temperature  of our planet should be about minus 18 degrees Celsius or degrees centigrade and if that were  to be correct we wouldn't be here because the planet would be frozen.  Well here is what happened this black body radiation law which is it was for some time  not understood where it came from but it was of course the Max Planck that then interpreted  this black body radiation law that's what gave rise to quantum mechanics by suggesting  with something which at the beginning of the 20th century was sort of not quite reasonable  that the energy comes in packets okay so anyhow that's the origin of quantum mechanics has  to do with that description Einstein himself also provided a very important component not  only that the energy comes in packets but also radiation photons okay they are quantized  and that's why the temperature it's very sensitive to the temperature.  Now if so we what this gives rise to what we call the natural greenhouse effect which  is the following if our planet had just a transparent atmosphere it receives say a hundred  in some units of energy from the sun about one third is reflected to space but the rest  is submitted by the surface and that's what would keep the temperature at minus 18 but  what really happens is that the atmosphere is not transparent it's like a blanket the  atmosphere has a blanket and that's what means that the temperature has to rise at the surface  it has to emit a lot more energy because a good fraction of that energy is not lost to  space it comes back to the surface.  And I won't go into the details but of course that's oversimplified there have been all  sorts of measurements and the overall energy balance is a bit more complicated but it's  very well understood this is fundamental science and one more piece of information is that basically  it's only a small fraction of the atmosphere that gives rise to this natural greenhouse  effect a lot less than one percent if water vapor was understood to be the most important  so-called greenhouse gas because of this natural greenhouse effect absorbing about three-fourths  of this infrared energy we're talking about and carbon dioxide the other fourth so from  that perspective one would think water vapor is what controls temperature but as you know  water vapor the amount in the atmosphere depends critically on temperature so what I have here  is just to give you a sense particularly not to you people that work with science but to  public in general that are not very familiar with gases the amount of water vapor if we  were to condense it typically what is in the atmosphere would occupy just a few centimeters  on the amount of carbon dioxide if it were to be solid say just four millimeters that's  the blankets that our planet has a very small blanket if you want that raises a temperature  these 33 degrees the earth or the natural greenhouse effect but if we were to remove  carbon dioxide the water would condense and then we would have a frozen planet so that's  why carbon dioxide is called the thermostat of of of the planet and what what's happened  to carbon dioxide this you already heard from Steve choose presentation I could go back  millions of years but in more recent years ten thousand years what you see is how suddenly  in very recent times the concentration has increased quite dramatically and it's very  clear that this comes from burning fossil fuels you can do isotope analysis things like  that it's also quite clear that the temperature in on the same time scale has abnormally changed  just in recent times so the question the obvious question is that where does this come from  and the the best explanation this this has to do with the greenhouse effect but in any  event the scientific community got gets together and every few years this intergovernmental  panel on climate change makes statements about what is the status of the science and the  last big report was a few years ago and the conclusion in the previous report that says  that yes this temperature changes indeed connected to the carbon dioxide change but we're not  absolutely sure of the connection so we talk about probabilities at that time it was 90  percent but in the last report they raise it to 95 percent so it's possible that is  naturally just extremely unlikely but let's move on with with the meets and I want to  get to several additional points one other meat is quite worried about this let our children  and grandchildren take care of the problem because this will happen towards the end of  the century when more carbon dioxide will pile up but that's not really the case what  we know is that for example the Arctic sea in the summer is melting as you can see from  these pictures this is something very dramatic has happened particularly recent times but  more worrisome perhaps is what we call extreme weather events this is this doesn't represent  the relatively small change in temperature that we have seen I should have quantified  that it's of the order of just one degree centigrade but we have extreme weather events heat waves  slots and so on that have increased in recent times storms landslides and so on and the  scientific community was very sort of careful and until some years ago they thought they  didn't have enough statistics to make any connection but in recent years it's very clear  now that the connection is statistical climate change doesn't cause these extreme events  but it certainly increases their intensity and that's why this is what I'm stating these  that scientists were very skeptical but the conclusion is that yes these events are indeed  affected by climate change for example the hurricane Sandy that was so expensive in the  United States it is most likely influenced then by climate change but let's now move  on to the to the last of the myths I have here and this is no longer science okay this  is economics we shouldn't do anything about climate change because fossil fuels are so  important for for the functioning of of society that we just shouldn't risk doing anything  about this well that turns out to be also a myth and some years ago it was already indicated  by our colleagues at Princeton that the way to solve the climate change problem if there's  no silver bullet there's no simple big solution that you can do so if we have emissions here  as a function of time what you need to do is many things simultaneously so-called wedges  you have to improve the the fuel economy the efficiency with which you use particularly  fossil fuel more efficient buildings and so on but you have to start using renewable  energies okay even nuclear energy that's of course question or that gives rise to a different  debate but wind and solar are particularly important as we see here but what is very  dramatic about this particular energy forms now renewable energy forms as you already  heard in Steve choose presentations is that the price has come down quite fast so it turns  out that in in in recent years these types of energies are quite competitive now with  fossil fuels they still have problems with storage and so on but but that's coming along  now it's it's moving and so if we see reports from economists were capsule one of the most  famous one is from from lord Nicholas turn from some years ago where he stated already  that decade ago or something that it would only take about 1% of global GDP to make the  necessary changes so that we wouldn't have to risk this huge temperature rise that might  occur otherwise anyhow that was quite well substantiated but what is quite interesting  is in much more recent reports in order for society to decide whether to do it or not  it's not only how much does it cost but how much does it cost not to do it so that's how  society should function science doesn't tell you what to do science doesn't tell you it's  not it's neither good nor bad so science just provides the facts it can make predictions  what would happen if you do this if you do that and that's why the intergovernmental  panel on climate change is supposed to be non political it just states the facts what  the scientific community thinks what you mix then the science with economics and with social  and political aspects and that's how you take decisions and that's where ethical principles  are very important to mention more in just a moment but the point is that the damage  that would be caused by climate change in general have been grossly underestimated this  is what is very worrisome so if in principle what would need to happen to control climate  change I won't go to this into detail but ideally from an economist perspective you  put a price on emissions but this has not been practical there was a meeting of this  intergovernmental panel on climate change already in 2009 for about 150 heads of state were  there and they agreed let's change things so that the temperature doesn't increase  more than two degrees but the negotiators didn't agree the heads of state did so it  took a bit longer it took some more time until 2015 December of 2015 finally an international  agreement was reached the so-called Paris Agreement in which practically all the countries  of the planet together agreed that indeed let's try and see whether we can keep the  temperature rise below two degrees and the way we will do it is in contrast to the earlier  attempts where for example the Kyoto protocol the first attempts they were assuming that  only developed countries which were the ones that originally caused the problem would do  something and then developing countries would wait until things would stabilize a bit more  that didn't work that was not a practical way to do it so the big change in the Paris  Agreement is practically all the countries including China developing countries India  Mexico and so on would commit themselves to do something on a voluntary basis however  something that could be measured that could be demonstrated and so it was a very big  achievement and here is if I put emissions versus time we can see that the Paris Accord  doesn't reach the two degrees okay it goes well above that because it's just a first  step the ideas of all the nations will collaborate will work together and they will try to strengthen  the Paris Agreement itself but as such it's not sufficient I should also mention here  why was what's the nature of the Paris Accord mean advising the president of Mexico but  I was also a member of PCAST which is the advisory group about 20 scientists the scientific  advisory group to President Obama so we work closely with him on the Paris Accord and it  was essentially designed by the limits that the United States have to place namely to  do something that would not require the approval of Congress because the Congress in the United  States as you know is lived by Republicans who question the nature of climate change  and so this is let me just spend a few minutes very rapidly talking about this it turns out  that it's well established already for some time now that it was industrial groups that  put in question the science of climate change but it's those groups were the people that  were managing those groups are exactly the same those are the same people that delayed  governments to do something about smoking and about several other interventions they  were just representing industry but what's happened more recently is not just that there  are industrial perspectives economic perspectives but it became climate change became politicized  and so it was a mantra of the Republican Party in the United States just to not to believe  in climate change science and to mention that it was all just a hoax in some sense that  it is not something real so I have just a couple of minutes I need to mention what has  happened recently namely as you know the United States President Trump did not agree with  with they decided not to accept the Paris agreement but let me go back in time just in times of  the election this was just typical of anybody belonging to the Republican Party in the United  States and why do I mention the United States because it's crucial for this international  agreement but as you see the idea is that this is the climate change is just something  that is not believable that's very worrisome for us as a scientific community because as  I mentioned it's very well established it's basic science and so on so we're living in  a world where very important politicians question that there are always people questioning many  aspects of science as we know I could give lots of examples with vaccines and so on  but the worry here at it's the president of the United States that is making such incredible  statements well let me just move on there were I mentioned this because there were lots  and lots of the pieces in the media criticizing of course Trump's decision a few of them as  expected would agree with what the United States decided namely to not to accept the  Paris agreement I won't go into the details except that most of the scientific organizations  practically all of them made strong statements strongly disagreeing with with President Trump's  situation well President Trump's perspective but there what I want to highlight that was  not very much highlighted in the news is something that for example Jeffrey Sacks mentioned that  global warming is an existential threat okay it's a big worry for the following so I want to  spend probably one extra minute I was a professor at MIT for many years but so there it was  acknowledged because the climate is a complex system you cannot predict with certainty what  will be the temperature change in the future for any particular scenario so they had these two  spinning wheels the one in the left with red is if you do business as usual which is what President  Trump's and his team would argue but you can actually change that if you have reductions in  in in the emissions the big problem is that there are some red portions there in these flags and  and the same thing the same results were actually projected by the international panel climate  change namely the red part here is what happens if you do the business as usual scenario if you  don't worry about climate change if you think it that's indeed it's a hoax and so on and here is  what is most worrisome here is how the scientific community we try to summarize this it's not  necessarily what's the most likely change if we do nothing that might be three or four degrees but  we look at what we call the economists are worried a lot about this which is just the tales of the  distributions and the summary situation is the following there is a probability of roughly one  in five that the temperature will increase more than five five or six degrees towards the end of  the century if that were to be the case that that is a very highly irresponsible act namely to allow  that probability to go on for future generations because it really is doesn't respect the the  rights of future generations it's an ethical issue highly highly irresponsible because if the  temperature goes up more than five degrees you could have all sorts of extreme events for example  parts of the planet would be uninhabitable there would be all sorts of food production  problem mass migrations wars and so on and so forth so that that that's my summary that it  would it's extremely irresponsible and irrational it's extraordinary irrational the attitude that  the US president he has taken so let me just finish with mentioning very briefly that we fortunately  have one example of a global issue that has been solved Paul Crutzen here has been instrumental  with that and that's it the depletion of the ozone layer and without this international agreement  which is a montero protocol we would be in very big trouble today but fortunately all the countries  in the planet practically accepted the agreement and so with the protocol we know that the ozone  layer is finally recovered so we know it can be done we can all work together and avoid this  extreme irresponsibilities thank you for your attention
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