 Okay, can you hear? All right. Well, thanks very much. First of all to Bouchia and Matthias for inviting me. Of course Matthias is not here, but okay, this is the way things go. I took him a long time to invite me and then we chose the wrong week for him, but anyways so they asked me to give a very basic presentation on climate change. I thought I would touch on three issues which are sort of fundamental issues in this whole debate about climate change. The first one is the so-called detection issue. We're trying to address the question whether we are indeed actually seeing a warming of the global climate system. The second is called attribution issue, addressing the question of, of course, if the answer to the first question is yes, what is causing this warming? And if we get there and it's not too late, I would like to talk a little bit about how we actually simulate or predict there's not the right word. We prefer to use the word projection. You will see why. How climate will evolve in the next decades or up to the end of the century. Okay, okay, so we start with the basic notion that climate has always changed in the past. In fact, millions of years ago during the dinosaur times, it was about 50 million to 150 million years ago, climate was much warmer than today. It was maybe five or six, something changed. Okay, I think they raised the volume. Okay. During the dinosaur times, climate was five, six degrees warmer. CO2 was much, much higher than today. Eventually, CO2 was buried in the soil and we're sort of putting it back into the atmosphere. About three million years ago, there was sort of a shift in the climate system where climate became relatively cooler and close to the temperatures that we have today. Now what you see here, these are some reconstructions of two variables for the last 400,000 years. These are reconstructions that are made through the analysis of these ice cores. We've seen the movie the day after tomorrow. I'm sure that many of you have seen it. The first scene where Dennis Quaid falls into the cracks and whatever, what they were doing, they were sort of digging these ice cores. They can go actually a few kilometers in depth in areas like Greenland and Antarctica. Through the analysis, you can go back in time. The ice has in it some small bubbles of air. Through the analysis of this of this air, you can actually go back to the composition of the atmosphere. Again, back millions of years and from the composition of the atmosphere, you can learn something about temperature. What you see here in the top panel, this is the reconstruction of CO2 concentrations in the last 400,000 years. We are here more or less. This is a reconstruction of temperature based on water isotopes. What you see here, you see these ups and downs. Of course, these are the glacial and interglacial periods. This has nothing to do with, of course, human interference. Talking about hundreds of thousands year ago. These are called the Milankovitch cycles and they're related to some small variations of the Earth's orbit. The inclination of the orbital of the axis of rotation or the ellipsicity. They have some small variations. Regular variations and this can cause these variations in time. For example, you see a periodicity at 100,000 or 120,000 years, but there are other periods inside. One is about 20,000 years. We are here, so we are towards the end of a interglacial time, a relatively world period. If nothing happens, or the next tens of thousands of years, we should go towards the next ice age. The last very cold period happened about 18,000 to 21,000 years ago. See why I mentioned this because back then the temperature of the Earth was about four to five degrees colder than today. So what happened, let's say 200 years ago. We started this industrial revolution and then we started injecting into the atmosphere a lot of pollutants, different types of pollutants, different types of gases. This is the beginning of what we call today the Anthropocene, where we can actually see the human imprint on the Earth's climate in many different aspects, not just the sort of global warming. In one of the gases, or some of the gases that are being injected and are being injected into the atmosphere are the so-called greenhouse gases. These are gases that produce so-called greenhouse effect. Anybody does not know what is the greenhouse effect. Everybody knows what is the greenhouse effect. Okay, so I don't need to explain it again, right? It's nothing to do with the solar radiation. I've heard several theories about this. One is that since there is the ozone hole, there is more solar radiation going through and this warms the atmosphere. Another says that these gases absorb the solar radiation. It's not like this. Greenhouse gases are gases like in fact the water vapor, carbon dioxide, ozone, methane that actually are pretty transparent to solar radiation. But they can absorb the infrared radiation emitted by the surface of the Earth. So this radiation instead of escaping into space and thus cooling the atmosphere, cooling the surface, it's absorbed and re-emitted in all directions. So also towards the surface. In this way, it warms the surface, then it warms the lower troposphere and eventually the full troposphere. So this is the greenhouse effect. This is nothing new. Already in 1896, it was already a well-known phenomenon and in fact, the Rhenius had estimated that the doubling of the concentration of carbon dioxide in the atmosphere would lead to a global warming of five to six degrees. And this is actually not so far from what the latest models are actually telling us. Actually, this greenhouse effect is in general good for the atmosphere because it keeps the temperature at relatively pleasant values for the development of life. Otherwise, the temperature of the surface would be 30 to 35 degrees colder than it is today. So what is the problem with this greenhouse effect? The problem is this. This is a curve of CO2 carbon dioxide concentrations taken at a site in Mauna Loa, top of this mountain in Hawaii by a very famous scientist called Chalsky. He started taking these measurements in the late 50s and the early 60s and by the 70s he had seen that the concentration of CO2 was actually increasing. These oscillations are due to the vegetation in the northern hemisphere, the seasonal cycle of vegetation because of course photosynthesis removes CO2. But in the 70s, the CO2 concentration was actually increasing. So he launched an alarm. He said if the CO2 actually increases, we expect that this may have an effect on the global climate. When he started taking measurements, the CO2 concentration was about 315 parts per million. Very small concentration, but still sufficient because an important greenhouse effect, important warming of the atmosphere. The concentration has grown over the last 50 years pretty much not really exponentially, but between exponentially and linearly. You might have heard that this year we passed the 400 parts per million threshold for the first time. It's not like this threshold is anything really specific as far as the threshold is concerned. It's just sort of a psychological threshold where for the first time we are stably above the 400 parts per million. Now if you go back in time, these are concentrations of CO2 and methane in the last 10,000 years. You see that more or less the natural values are about 280 parts per million. So if we now are 400, this is an increase of about 40%. In 100 years, more or less. So this is a huge increase in a very very short time if you actually compare this with a long-term trend. The same for methane and for nitrous oxide. We know that this increase in is due to the use, at least for CO2, is due to the use of fossil fuels for a number of reasons. Besides the fact that there's no natural phenomenon that can explain this. Also, the isotopic composition of CO2 is consistent with the burning of fossil fuels and the oxygen to nitrogen ratio. It's very interesting that the person who actually advised the method to measure very accurately this oxygen to nitrogen ratio is the son of Charles Keeling. He wrote a science paper. Actually, I met him because we were working in the same place back then. He said this is the only big paper I wrote, but it received like 10,000 citations, so he became famous just for this paper. Of course, this is a big evidence for the anthropogenic source of CO2. So the theory tells us that if the concentration of CO2, CH4, N2O of these greenhouse gases increases, we should see a warming of the climate system. Right? Now one thing to remember is that the climate warms for a number of reasons if you increase greenhouse gases. The first one that we just described before is the sort of direct radiative forcing of these gases. But there are other processes that can amplify using a positive feedback or what we call a positive feedback or can inhibit the warming, a negative feedback. Very important feedback process is the water vapor feedback mechanism. So if you have a warmer atmosphere and warmer oceans, you are more of an operation. From the Clausius-Clapeyron equation, the atmosphere can hold more water. The water is itself a greenhouse gas. This increases the warming and so on with a positive feedback. Another one, very important, is the so-called ice-albedo feedback mechanism. If you have a warmer surface, you melt the ice. The ice is a very large reflectivity. So a large albedo, you decrease the albedo, you absorb more solar radiation this time. Right? So you increase the warming, melt more ice, make more warming, positive feedback. Another one is the carbon feedback mechanism. A warmer atmosphere, warmer soil, you have more bacterial activity, more release of CO2, more warming and so on. Clouds is a big feedback, well, not big, but important feedback because it can be positive or negative. High clouds are thin clouds, so they're relatively transparent to solar radiation. If you have high-serus clouds, you can still see the sun. They're very cold and they don't, they're like perfect greenhouse bodies, but they don't emit a lot of infrared radiation towards space. So if you increase high clouds, you have a warming mechanism, right? Because you trap the radiation from the surface, you know, you don't emit much and you don't shield the sun very much. If you have low clouds, it's the opposite. They're perfect reflectance. You cannot see the sun if you have a big, you know, cumulus cloud on your head. And they're warm clouds, so they emit a lot of infrared radiation. So depending on whether you have more high clouds or more low clouds, you can have a positive or a negative feedback. This is very important because these feedback processes are very important because the actual directory, the edi-forcing, is only a part of the warming. In fact, most of the warming is due to these feedback processes. And also the representation of these feedback processes in the models is what make the models very different from each other. All the models know how to do the direct absorption by CO2. That's an easy thing. I'm not a radiative transfer expert, but they tell me that's not an issue. But clouds, for example, is a big issue in the models. And water vapor and the ice, the response of the ice. So this is what makes a model very different from another in terms of how this is what is the response to the increase in greenhouse gases. And we'll see why this is important. Is this clear to everyone? Any questions on any of this? Please stop me if you have any questions. Okay, especially the diploma students. If you have never kind of seen this before. Now the first question is global warming happening. This is the there are many different lines of evidence for this. The first one is the surface temperature surface temperature observations or measurements. These are taken with tens of thousands of stations worldwide or buoys in the oceans, ships, whatever. These are all compounded together. They're homogenized. The urban effect is taken out. It's filtered out in different ways. So after you clean up all this data, you homogenize it. This is what you more or less end up with. These are different datasets from different groups. I'm showing this figure because it has the most recent data up to 2016. This temperature here is in Fahrenheit. I think this was produced by NOAA or some American institution. But more or less the global temperatures have increased since the beginning of the century by a little bit less than one degree. Yeah, I didn't understand. Oh, how is the average taken? There are different ways to do this. Now you have of course station observations and then you have you interpolate there are many different ways of doing it. Doing this interpolation. It's average of the whole globe. And it's an anomaly. Okay, so you try to look at how things have changed over time. So which makes it easier rather than having an absolute number. Okay? There's an error. Here the error is not shown, but this 0.9 is plus or minus 0.2. Clouds, the cloud, the high clouds. Sorry, the low clouds is a negative feedback mechanism. Yeah, the only one I know of. Okay, so this is the temperature record, surface temperature, surface air temperature, okay? Now this record, there are a few things that I wanted to highlight. First of all, you see that you don't have a straight curve here. Okay, you have these oscillations. Oscillations happen at year-to-year variability because climate is never the same from one year to the next. Or at decadal timescales. For example, you have this plateau here. This is 1940 to 1960. This was actually also due to increase in aerosols. But in particular, you had, you might have heard that the climate hasn't wormed for the last 10 years. A lot of people were saying this up to two years ago. That's why I'm showing this that has the last two years. This is what we call the hiatus, the temperature hiatus. Essentially what you have, and you should always remember this, you have, if you have temperature here, this is time. This is temperature or temperature anomaly. If you have no increasing greenhouse gases, you would have something that goes like this. Okay, it has some sort of internal variability. If you only had greenhouse gases and you had a linear response, you would have something like this. Okay, if the greenhouse gases increase, you put these two together and you have a curve like this. You can very well have a year that is cooler than the previous one. To you, this may seem obvious, but every time there is a cool year, you will see on the press global warming has stopped. And there are different ways of looking at this. For example, this is the famous hiatus. Big headlines was, or if you talk to any skeptic, you would tell you in 2012. Since 1998, warming has stopped. 1998 is this year here. This year, there happened to be a big El Nino. El Nino is a warm anomaly in the equatorial Pacific. Every time you have an El Nino, you have relatively warm conditions. If you actually start from 1998 to 2010, you think, okay, global warming has stopped. But, if you start from 1997 or from 1999, you will see that global warming has not stopped. So when you actually look at these curves, you have to be very careful. You have to look, of course, at the long-term trend. In the long-term trend, the warming is actually, at least in this record, in these records, is quite obvious. Incidentally, the last two years, 2015 and 2016, have been incredibly warm, actually. And there were El Nino conditions. So you might think, oh, this is all El Nino. But you can actually filter El Nino years, La Nina years, and neutral years. And if you only take the trends in these three types of years, you actually see that you still get the warming. Okay, so this warming is not due to El Nino, that for some years is warm or La Nina is cold or whatever. But it's a long-term, ongoing warming. This is geographically, also, this is a important curve. It gives you the trend. It's a function of space. So you see, this is from 1901 to 2012. So you see that it's red almost everywhere. In some areas, warming is larger than others. For example, in these areas, it's a snow-albedo feedback. Other areas could be something else, but some areas are actually blue. Okay, this one is because of the melting of the ice. So you have cool waters in the Northern Atlantic. But here you have some blue areas. Okay, so for whatever reason, these two boxes have not seen a warming. Of course, if you live there, you may think that there is no global warming. I don't know if you know that Michael Crichton wrote a book on this. I don't know if some of you have actually read the book like Conspiracy of Something. Did somebody read it? And he was showing a curve in the US. Temperature record, and he was taken exactly here. So of course, you know, you can manipulate the data, not sure whatever you want, but if you actually look at the global average, the warming is quite clear. But there are other evidence, other lines of evidence. One is the polar ice cap. This is the long-term trend. Also in this case, you have oscillations. Not every year you have less ice than the year before. Every time there is a bit more ice, you will see headlines saying, oh, but there's a lot of ice. Maybe here we can start this. Can we start the animation? I want to show you this animation, which I think is very, very nice. This is a NASA animation. There's our satellite data. We're going very slow, actually. I think we need to hurry up. Okay, so the light, the white, is the deep ice, is the supposedly non-seasonal ice, and the gray is the seasonal ice. You're starting from its success. Try again. You should see from 1986 to 2016. Otherwise, you can just Google 85, 86, 87. Okay, this is only at the end of September. But anyways, you can see the reduction, actually one with higher temporal resolution. But this is, you can see, okay, you can see anything. I think we, okay, just Google NASA Arctic sea ice, and you will see this. Now what you will see is the reduction of sea ice, especially the reduction of the, which right another one, and then it's a bit different, but let's see if it works. So you can see slowly the reduction of the polar sea ice. It is variations from year to year. Thousand. Thousand eight was a big hit. It was a nice curve on top. Thousand ten last year was pretty bad as well. Anyways, this was not as spectacular as others that I've seen, but the reduction of the polar ice is another very solid piece of evidence. You see it here. This is the long-term trend. Essentially in 2008 and 2015, at the end of September, the ice cover was about half of the pre global warming values. Third piece of evidence is melting of glaciers. Those of you who like mountains, you can see it with your eyes, but essentially all of the glaciers, the major glaciers in the continents, in all continents, are in the face of a recession. Ocean warming. The ocean is warming at a rate a bit slower than the continents because of the higher thermal capacity of the oceans, but it's actually uptaking a lot of heat and that sooner or later we'll go back to the atmosphere. Sea level rise. This is another very important piece of evidence. In the last 20, in the last 100 years, the global sea level has increased by about 20 centimeters. The sea level actually increases for two reasons. One is the melting of glaciers on land, right? If an iceberg melts, this does not increase the sea level, and the other one is the expansion of water getting warmer. It's a very small expansion, but there's a lot of water, so even a small expansion actually is detectable. More or less the glaciers are about 60 to 70 percent of this global trend, and the expansion is about 30 to 40 percent. Also in this case, you have a large spatial variability because the sea level actually different locations may depend on changes in ocean currents, subduction or many different factors, but again at the global scale, this is a very important trend. The contribution by Greenland is a very interesting contribution. Right now it's not the largest contribution, the melting of the Greenland ice, but it's the one that is growing faster. If all the ice of Greenland was to melt, we would see something like six or seven meters of sea level rise, which of course would be a very large number. If you're sort of curious to see in Trieste, this is the Trieste data that are more or less in line with the global average. Warming of the troposphere, this has been a contentious measurement for a long time because the first analysis of satellite, because the tropospheric temperatures are calculated using satellite data, and up until 2000, they were not showing any warming, and this was sort of a big weapon in the hands of the so-called skeptics, but then after they found actually an error in the first analysis of this data, there was a science paper that said there is no warming, and after they found this calibration error, they retracted this paper, and now the warming in the troposphere is more or less in line with the surface warming. So you have at least several pieces of evidence that have led the scientific community to actually state that global warming is unequivocal, and I think this is a statement that is very very difficult not to agree with, although you will still find some people that will say strange things about it. The warming has an interesting effect on the hydrologic cycle. I don't have time now to go through the details, but one of the things is that because you have more water vapor in the atmosphere, of course when it rains, you have bigger reservoir of water to draw from, so you expect to have more intense events. This is something that is seen very very frequently. Actually, there's a paper we wrote in 2014 where we actually looked at this, and we found that something that is happening is both in the observations and in the models is that the intensity of rain events is increasing and the frequency is actually decreasing. So when it rains, it tends to rain much more intensely because you have more water vapor, but it takes more time to actually reach the level where you get condensation and actually rain. This is leading to an increase in extreme events. This is a sort of graphics of natural catastrophes from 1980 to 2014 from Munich Insurance Company. You have geophysical events in red, and these are different types of sort of meteorological and climatological events. You see that the crust of the earth is not doing anything particularly strange. Maybe not in central Italy, but at least globally things look pretty stable. But in terms of extreme events related to climate and meteorology, there is a clear increase. There have been many credible events in the last ten years, but again, I think we have to hurry up a little bit. But one of the very strong signals of global warming is this increase in extreme meteorological events. Now, the second question is what is causing this? I will skip all this about climate models. I will just say that climate models are not perfect, but they're not that bad either. If you actually look at the climate model, it will give you a decent representation of the observed climate. So how do we try to identify a human fingerprint in this global warming? Now, as we have seen, the earth's climate can change because of three factors, essentially. Okay, let's say in the last 100 years. Human factors related especially to the increase in greenhouse gases, land use change can also affect climate and aerosols can affect climate, but this is tropospheric aerosols only very locally. You have natural force things, variations in the solar irradiance, not only the 11-year cycle, but also on decade-old timescales. Volcanic activity, they inject a lot of aerosols in the stratosphere when they can stay there for a few years, and you can actually see the signature of major volcanoes like El Chichón, Pina Tubo, and so on. Of course, natural variability. We could be seeing just warming due to the natural variability of the climate system. So we will look at these three effects. How do we actually do the fingerprinting of the anthropogenic effects? We take the climate models, we force climate models, we do three sets of experiments. In one set, we put all the known anthropogenic and natural force things. So we put greenhouse gases, aerosols, and variations in solar radiation. Okay, these are the three essential external force things. We do another simulation where we put only anthropogenic force things, so only the increase in greenhouse gases. Then we do another simulation where we put only natural force things. Okay, but the comparison of these three sets of simulations, you can see which one brings you close to the observed trends. So these are the results from this analysis. So what you see here, you have three plots. Let's see. Let's look at this case first. This is the natural forcing case. In this case, you take a number of models, all the different lines here. These are the observations. The black line is the observation. Okay? We have already seen this. All these yellow lines are different models doing these runs. There are some 25 models in the world that actually do these runs. In this first set of runs, all that has been included are the natural force things. So variation in solar radiation that can be reconstructed through the analysis of ice cores, again from the composition of the atmosphere. These are major volcanoes. And essentially what you see here is that up until about the mid of the 20th century, the observation curve is pretty much in the inside the sort of range of uncertainty of the model simulations. Even the natural force things can actually explain the global temperature trend up until the mid of the 20th century. But from the mid of the 20th century to the present day, actually this is probably up to 2010, I think, you see that none of the simulations that alone the model ensemble, the intermodal ensemble actually can capture the actual warming. Okay? So based on this analysis, we can say that as far as our science knows and as far as good as our models are, okay, the models are not perfect, but all the models actually are saying the same thing. External force things cannot explain the warming since the middle of the 20th century. Okay? This is clear to everyone? This one? This one? These are two different observation data sets. Okay? Now if you put only greenhouse gas force things, now this is only the increase in greenhouse gases. This is what you find. Actually the line in the middle is the ensemble averages, the ensemble average of all the models. So you see a pretty stable increase, well in the ensemble average of course, you see that also in this case you can more or less explain what happens in the first half of the century, well up until the first half of the century, but greenhouse gas force things only actually overshoots even the warming. The main reason for this is that these simulations here do not include aerosols. Do not include aerosols of anthropogenic and natural origin. If you put everything together you actually can reproduce the observed curve quite well. The important thing is not so much that the ensemble average is on top of the observations or whatever, but that the actual curve is outside of the range of the models. So it's even outside one or two standard deviations of the range of the models. So based essentially on studies like this, we can say that the only way, well not the only way, we can rule out external force things as the cause of the warming in the since the mid of the 20th century. Okay? Is clear to everyone? In fact the external force things maybe even because the sun has actually decreased its radiance just a little bit in the last 30, 40 years. They even cost a little bit of cooling. So it's not external force things. And definitely it can be explained with greenhouse gases when you put the two of them together, but there's still the chance of the third option that we might be seeing a natural swing of climate due to internal variability. Of course this cannot be ruled out in any ways, but what we can do is to see how how probable is this? How likely is that we get a swing like this? To do this you have to look at the past. Okay? This is a reconstruction paper in Science 2013 by Mark Oedal that reconstructed the climate reconstruction from I think 73 sites with a pretty good global coverage of global temperature in the Holocene. The Holocene started about 11,500 years ago. We said before that the last ice age was 21,000 years ago, so this curve goes all the way down here. You get to 21,000 years. But the climate is done in the Holocene, it went up. This is again climate anomalies. There was a maximum starting about 9,000 years ago until about 6,000 years ago, and then it started decreasing. Okay? This is what happened in the last 100 years. You can see that the temperature in the last, say the last decades is not higher in absolute terms than some of the temperatures that you find in the middle of the Holocene. But the rate of increase in temperature is very much higher. Essentially, you see the same anomaly about one degree that you have seen in the last century. In the past, it takes about 5,000 years to produce sort of the same anomaly. This already tells you that we are seeing something to say the least highly improbable just because of natural variability. You might have heard the point that the climate was as warmer now, but they are even warmer in the medieval times, the times of the Vikings. More or less the same 9,000, yeah, during this peak time here. Well, this I don't know actually what was this issue in the sea level 6,000 years ago, but we'll go back to the 21,000 years ago. Probably was similar to today, but at least I cannot give you any precise number. So this issue of the medieval times, this is something we hear a lot in the news. Time of the Vikings, the climate was much warmer, it was warmer than today, a lot of Greenland was ice free or whatever. There have been several reconstructions of temperature in the last 1,000 years or 1,300 years. You see here and you can see that actually the temperature in the last 50 years are actually warmer than during the medieval, the so-called medieval warm period, which is this period here around 1,000 years ago. Also in this case, especially you see that the rate of the warming is very unusual compared to the trend in the last 1,000 years. Very interesting is also the Arctic temperature, because this issue of Greenland, there have been reconstructions of Arctic temperature and also in this case, this is the medieval warm period. Actually it was not that unusual, especially over the Arctic and this is the situation now. So I think we're actually seeing in the last 100 years, at least in terms of temperature, something that is very, very unlikely within the context at least of the last 20,000 years. It's still possible that we are seeing some incredible natural event, but usually these very sharp events are related to something like the collapse of the ocean circulation or something that is not happening. In reality, I think we are, I think everybody thinks we are seeing something that is extremely anomalous compared to the natural behavior of the global temperatures. So this is the conclusion on this attribution statement. In this case, there's not a word like unequivocal. There is a word like extremely likely. Now the important thing is that this is the warming only from the mid of the 20th century. This attribution statement does not apply to anything that happened before the mid of the 20th century. If you actually look at the temperature record, the mid of the, up to the mid of the 20th century is not so strange. Just to put it, when Paul Krutzen once came here to visit, he won the Nobel Prize for chemistry for the research on the ozone hole, and he put it very simply. He said, you know, after this maximum in the 40th, 60th, the temperature should have gone down. And he said it went up. This is the real, I mean, it went up very fast in the last 50 years, and this is really where it became very, very anomalous. So there is still, it's not a certainty. There is a likelihood, 95%. Over the years, they started with 66% in the 90s, went to 90% in 2000. Now it's 95%. There are also other sort of fingerprints on different aspects of the atmosphere, of the climate system. But this is sort of the state of the art. Now at this point, just towards, I don't think I will have time to talk about the projections a lot, but I just wanted to mention another issue, very important issue, is the attribution to individual events. This is a very hot topic of research now. Let's say that you have a Katrina. Okay, Katrina has been a very destructive event. It cost billions of dollars of damage or whatever. Can we say that Katrina was due to climate change? Of course, if we can say this, then we can say climate change is called by CO2. Oil companies are emitting a lot of CO2. Oil companies have to pay the damage. Actually, this is happening a lot and I think will happen more and more. I think it's essentially impossible to say that a specific event is due to climate change. It's a bit like smoke. You know the smoke increases the frequency of cancer, but if somebody gets cancer, even if he smokes, you cannot say that that particular cancer was due to smoke. What you can say is that smoking has increased the probability that that guy got an event. Climate change is the same thing with these extreme events. You can say that climate change will increase the probability that you get extreme events. In some ways, it's increased the probability of Katrina to happen. In fact, what I'm showing here is the summer of 2015, I think, 2013-14 in Australia, where there was the biggest heat wave ever and it was the first case in which a probability higher than 50% was attributed to global warming. Of course, there's a lot of big implications in terms of insurance companies and so on. Now, I want to talk a little bit about the future, but we don't have much time. I just want to show you this figure here. These are the projections for the future. These are the two sort of most extreme scenarios. The blue here is the famous two-degree global warming target that the EU has proposed that has been taken by the UN. This is two degrees compared to pre-industrial temperatures, so it's one degree compared to current temperatures. What you see here, this number is the number of models that have sort of made these future projections. How do we do this projection? We have some scenarios of how emissions and concentrations may change in the future. For example, these are the current scenarios that have names like RCP 8.5, 4.5, and 3. These are numbers that would be a bit too long to explain, but this is the highest scenario. This RCP 8.5 is what we call the business-as-usual scenario, so if there's no sort of policies to decrease emissions. In this case, the models are actually telling us that this is the uncertainty, this is sort of the range to spread among these 39 models. The warming will be about four degrees, plus or minus maybe one. These are the sea level rise projections, 80 centimeters, plus or minus whatever, 20 centimeters, but since the time is running out, four degrees, you might wonder how much is four degrees. I will get to this later. This is four degrees. This is the last glacial maximum, the last ice age, 18,000 years ago, the temperatures were four to six degrees lower. The sea level, just to address your question, was 125 meters lower than today because much of the water was actually stored as ice, especially in the Arctic camps. 120 meters sea level difference. I don't know if you... Now, what we could do, based on what the models are saying, is to give a kick similar to this. Four degrees in 100 years is what nature does in ice age, the difference between a glacial and an interglacial time. Four degrees for several hundred years means that all ice of Greenland may melt. It's about, as I said, seven meters sea level rise. Parts of the West Antarctica ice sheet may melt. If you put the two together, it's 12 meters of sea level height. I don't know if this room would be underwater or not, but it certainly would not be very pleasant. There was a very recent paper in Science of Nature that said that if we actually go into business as usual scenario, and reach this four degree warming, we will actually avoid the next ice age. I don't know, it's like humans making a black hole or something. Humans changing the history of the climate of the Earth. So, fortunately, I had many other things to say, but there was not much time. My main message is that global warming is happening. It will continue to happen. I think it's virtually certain that it's due to this increase in greenhouse gases. In our talk, we can discuss what we can do to sort of face this problem, and the consequences of this in the business as usual scenarios can be really very, very important. We can really change the climate of the Earth in a very fundamental way. We could have a totally different climate than we have today. We are really, I think, risking a lot by avoiding to face this problem one way or another. I think with these words of wisdom, I thank you very much. There are many other things that I wanted to say, but okay, I always talk too much. Are there any questions? Thank you, sir, for the nice talk. My question is, if mankind stops using fossil fuels tomorrow, nobody's using fossil fuels, do you expect that the temperature will go down in presence of other feedbacks like water vapor and ice albedo feedback? Yeah, if the emissions decrease, okay, the issue now is not to stop the emissions, but to stabilize the concentrations. If the concentrations stabilize, you can stabilize the temperatures. Essentially, there is a pretty good relationship between the amount of greenhouse gases and the temperature, the warming, let's say. So all the models actually show that if you actually can stabilize the concentrations, not the emissions, the concentrations, then you also stabilize the temperatures, at higher values, of course, stabilize these temperatures after maybe some transient of a few decades. But to stabilize the concentrations, you have to actually reduce the emissions, because the system is not in equilibrium, cannot absorb already the current emissions of CO2. This is why there's this discussion of decreasing by 20% by 2020 or 80% by 2050 or whatever. So what do you think will be the consequences of the nomination of Scott Pruitt at the EPA? Let's put it this way. After the Paris Agreement, the message we all got from different communities, look at the low-end scenarios. I think this will change. Low-end scenarios means look at the two-degree global warming or whatever. And I think this may change. If you want my prediction by 2100, you will see a two-and-a-half-degree warming. This is... I mean, it's not based on any... Based on... When I was in the U.S., there were three independent surveys among climate people at three different times. What do you think the temperatures will go? It was always 2.5. I was going to bet the most reasonable change would be 2.5 degrees. Will this be... They are stating we don't know. Well, no. Some things, yes, for some things, no. We another talk about impacts, but I have not lived to 2100, so I don't know. I can live maybe in my memories. Actually, a couple of questions. Are insurance companies starting to adjust according to these scenarios? And second, do you think they will use your models or maybe they're using... Or maybe they will use? Using them right now. The answer is yes to both, actually. We are actually working with the insurance company now to produce some... sort of risk hazard maps also with an outlook to the future. But actually, the insurance company are the most interested in this. Because one thing... Okay, the three things that are virtually certain, 99% probability that will increase in the future with global warming are glacier melting. It's obvious. Sea level rise, in my opinion, that will happen. Because a lot of people live in coastal areas. And increase in extreme events. Every model, all the observations are showing this increase in the intensity of events. And the insurance companies know this. And they are actually... I don't know if adjusting is the right word, but they are actually asking the scientific community to give them some estimates of how the risk of increased events may change. Do you think the volumes have already changed? Yes, I don't know. Maybe, yes. No comment on this one. What's that? So one argument that I've heard from the skeptics is like this dependence on the CO2 is logarithmic. The increase in temperature is related to the volume of CO2 by logarithm. If you have to double the... you need to double the CO2 to increase the temperature linearly. So... Double of CO2 will lead to... A linear increase, right? So it's a logarithmic scale rather than linear... Yeah, but the doubling CO2 will lead to two and a half degrees warming or three degrees warming. And so basically you are expecting... In this, I can show you the actual numbers. But these are the models, you know, then you can say whatever you want. But based on the models, okay, so you have four degrees, four, okay? Now, how much is the CO2 increasing? It's the RCP 4.8.5 So 2100 is radiative forcing. I think it's a bit more than doubling. Two and a half. So it's not logarithmic. No, it is logarithmic, right? You have to double to increase... But we are saying that but that much CO2 will increase. Of course, yeah. But the increase in CO2 that is foreseen is enough, is sufficient to cause this linear warming. But it's not an exponential increase. It's a... Sorry. It's a linear increase. Because you have to remember that you have these feedbacks that if you had only the radiative effects, maybe it would be right, but you have these feedbacks by the warming. This is really the feedbacks are key. This is really what causes most of the magnitude. Not just the pure radiative effect. I have a question about your models. Can they also be applied to local situations? So being somehow predictive to how much the temperature increases locally? Because what I think of is that this is drastic already, but the first thing I think of in terms of global warming is the geopolitical effects. Imagine some regions in the planet do not have water supply anymore. Because glaciers do melt. Yeah, of course these models this is actually what we do our group. We actually look at the... I'm glad you asked this question because I didn't have time to actually go through this. These are three-dimensional models. So they have the geographical distributions, the continent and everything. The issue is the resolution. The resolution of today's global models is maybe one degree or something like this 100 kilometers. So down to that sort of resolution you can get information it's not local, of course it's sort of a regional type of resolution and you get maps like this. For example this is the change in temperature and precipitation in boreal winter, boreal summer. End of century compared to today. For example if you look at precipitation the blue is an increase the yellow and brown is a decrease so what you're seeing here is that one of the things that global warming does is to expand the Hadley cell. You know we have this Hadley cell the air rising sorry I have a cold Dutch. You have air rising in the equator and it goes towards the pole and then there's a tropical area where you have the deserts essentially. Now with global warming you have more warming in the tropics actually in the tropical troposphere then at high latitudes because of convection of different things so you have an expansion of this Hadley cell. So what happens you get the storms are deflected towards the poles. So the mid to high latitudes will receive more precipitation for example northern Europe they're actually in the last 50 years have seen an increase in precipitation especially big extreme events but subtropical areas like the Mediterranean will see a decrease so these models can give you information at the regional level and then you can get even finer scale resolution finer scale information something that we do here for example to use the regional models so there's a way that you can actually take a limited area model and sort of nest it we call we say in a global model and you can get you can get information down to maybe 10 kilometers scale. Of course when you go to these high fine scales the variability is more the noise is more the errors get larger so you have to interpret the data much I mean the global is easy compared to the regional and local scale but that's where a lot of research is actually going. Okay let's thank Professor Georgie again. Thank you.