we've seen the potential importance of abrupt climate change, especially from the point of view of our ability to adapt to abrupt changes in temperature. So it's quite natural to look at whether abrupt climate changes happened in the past and what exactly happened when these changes occurred. So we're going to answer some questions, we want to try to find answers to questions such as how fast is abrupt. What are the mechanisms that could give rise to abrupt climate change and how likely is it that in the present conditions as we are pumping C02 in the atmosphere. This will give rise to abrupt climate change, what is to begin with abrupt climate change? And this is the definition that comes from the US Climate Change Science Program that defines abrupt climate change as a large change in the climate system. System that takes place over a decade or less, that persists for decades or more and that causes substantial disruption in human and natural systems. Clearly adaptation too abrupt climate change is particularly difficult, abrupt climate change would pose a clear risk for society. And to our ability to adapt via phenomena such that such as rapid changes in glaciers, ice sheets and therefore sea levels. By the way, what really matters is the melting of glaciers on land from the point of view of the sea level. If all of the North Pole were to melt, it wouldn't make any difference because the eyes of the North Pole is just ice floating. Therefore, the only thing that really matters, antarctic is a different matter because it's it's eyes on earth and Greenland glaciers do matter. Widespread and sustained changes to hydrological cycles would make a big difference. And we're going to look in particular at the North World northward flow of warm, salty water in the upper layers of the atlantic ocean, She's called the gulf stream. And then, we're going to look at permafrost, what might happen if there is a massive melting of permafrost. So scientific scientific evidence shows that occasionally major and widespread instances of climate change occur with startling speed, for instance, in the exit of the last ice age, about half over. Temperature change occurred in approximately one decade and this warming was happened in we have measurements in direct measures in North atlantic. And we have related measures of similar abrupt change progress of the globe. And similar events with local local warming's as large as 16 centigrade occurred repeatedly during the slide into an exit from the ice age. And it is important as we shall see in the graphs that abrupt climate changes happen in both directions. And it's also important to keep in mind that human civilizations arose after this extreme global ice age climate jumps abrupt. Climate changes seem to be particularly common when there is a change in forcing, remember again, forcing is the difference in balance, energy. And energy out and therefore the fear as that the forcing imposed by the emission of CO2 in the atmosphere make it rise to abrupt climate change just to be totally clear. The mechanics, the physics of abrupt climate changes is not fully understand and current climate models do not normally incorporate abrupt climate change and tend to underestimate the size. The speed and the extent of temperature changes, future abrupt changes cannot be predicted with accuracy, but climate surprises cannot be ruled out. And here I have a picture of what I call the younger dryas, dryas octopetala, octopetala with eight petals. If you count carefully, there are eight petals and I love these flowers because I loved mountaineering and when I meet these flowers during my clients on my hikes. I know that I am below above the tree level and true mountains are beginning and the fact that we find these flowers here is because the temperature is low. And these flowers thrive in cold temperature, these flowers suddenly disappears. And when I say suddenly, I mean suddenly 1, 11,500 years ago when the temperature in Greenland abruptly rose by 10 centigrades in a decade. And this graph here is showing this is so important that this period has become the younger driest period, so we have approximately 14,000 years ago. We see the abrupt fall in temperature and that is the younger dryer schooling and then we have the sudden exit, the warming at the end of the younger dryers. So this is the exit from the last ice age and then we see the remaining part on the right of the craft. This graph here is very interesting and it is a half quantitative half qualitative description of what might happen if we do not have good stewardship of the climate on earth in the years to come. So let's see what's on the on the two axis, on the horizontal X axis, I have a sea level and on the Y axis I have a temperature and I have two quadrants in the bottom quadrant. I have the glacial period and I have a change in temperature, low temperature at the bottom, low sea levels going towards the left in the glacial interglacial cycle. So this is a trajectory of the earth and we are no longer in a glacial period, so, as we have discussed, were in a greenhouse period. And currently the earth is in a position on the upper quadrant, which is where there is a little ball between point A and Point B and these are the two paths ahead of us. We would like to stabilize the earth into a, into the tight cycle that we see in this graph without anything run away, avoiding the hothouse earth. As I said, hothouse earth to the best of our hothouse, meaning really run away. Alla venus is at the moment considered extremely unlikely. But it is not an easy task to steward, to coax the trajectory of the earth into this tight circle that we have there. And we have a similar more quality, far more qualitative description here. The rolling ball which rolls down this stability landscape. Stability which is on the y axis is taken as the one over inverse of a potential energy. But it is really not. There is a pictorial representation and you have the earth exiting the last ice age, the last glacial interglacial period. We are at the bifurcation and we are trying to steer the earth, stabilize the earth towards coming down towards the right on the left as we look at the graph. And to avoid the earth falling into the hot house trough. If a abrupt climate change event happened, there will be many consequences in several aspects. We could expect severe changes in the sea levels, in the amount of rain, in the gulf stream's flow, in the release of methane. Why do we worry about the release of methane? It's obvious why we worry about sea levels. It's obvious why we worry about the gulf stream and the climate implications. Methane is important because methane is a very powerful greenhouse gas. So if the temperature rises and by permafrost thawing, we'll lose more methane, they will make the temperature rise even more, and give rise to a feedback mechanism. So let's look at these things in turn. First of all changes in sea levels. As I have seen what matters for changes in sea levels is the melting of glaciers that are on land, not the melting of icebergs or melting of ice which is floating such as the North Pole. So every measurement that we have made of glaciers all over in the Northern hemisphere, we have the thinning of glaciers to a very, very pronounced extent. The graph here shows oscillations up and down, but we have a progressive thinning of the glaciers on Greenland. And this is adding to the water, is adding to the level of the water which is important in itself. And as we shall see it changes the salinity because this is fresh water coming into the sea which may affect as we shall see in a moment the gulf stream. And here we have a picture of synchronized CO2 variations, global over temperature and sea level. And we are already familiar with the top of the green and the red lines. But it is the blue line to which I would like to draw your attention. Which is how closely synchronized changes in sea levels up, with the changes in CO2 concentration and global average temperature. Another effect that we should keep in mind potentially connected with abrupt climate change, is the amount of rain. And climate model suggests that a rigidity dryness in areas above and below the tropics, which are called subtropical. But it doesn't mean just below it is above and below the tropics, is likely to intensify and persist due to the increase in temperature. And this could result in severe and persistent droughts in these areas. The drying may have already begun, but the variability is too much to be able to say anything with certainty. And now we come to something really important, especially for countries such as Norway, such as the UK, and to some extent France. The gulf stream moves warm water from the tropic towards the North Pole. In the Norwegian sea, warm water from the gulf stream heats up the atmosphere. The heat which has been acquired by the atmosphere, is lost by the water then becomes cooler and therefore denser. Because it is now denser, the water sinks to the bottom of the ocean. Now more warm water is pushed north by the gulf stream and it pushes down the heavier water that now begins to flow south to make room for the incoming warm water. The cold water in the bottom, flow south all the way down to Antarctica. And eventually these cold bottom waters return to the surface through mixing and wind driven upwelling. As more water is transported north, the cooler water sinks and move south to make room for the incoming water. This sets up what is called the conveyor belt, which as this picture shows, starts what we can start anywhere, but it is easy to start from a place like Norway. We have the cooling of the water, the water becomes heavier, it goes to the bottom, it is pushed forward by incoming warm water and goes all the way around the earth. Now remember the engine for the conveyor belt was the warm water close to the North Pole, relatively warm that arise because of the gulf stream. If there is a significant melting of ice sheets, there's a lot of fresh water coming and mixing and the water will become less saline, less salty. Saline water is denser and heavier than freshwater. And that is why you swim better in the sea than in the swimming pool. Therefore less salty water, sinks less and therefore this can reduce the conveyor belt. This could disrupt the strength of the oceanic conveyor belt. Now it is very unlikely that the gulf stream will decrease in the 21st century because of temperature increases. But there it is decreased significantly, but it is likely that in may decrease by 25-30%. It is very unlikely all these terms are taken from Intergovernmental Panel of climate change terminology, that the gulf stream flow will collapse during the course of the 21st Century. It is unlikely not very unlikely, that in may collapse after the end of the 21st century, but we can't be sure. If there is a mistake, if the temperature outcomes are worse, if it is phenomenal are worse and the gulf stream were to reduce significantly. The climate consequences for countries such as the UK would be dramatic. You'd be surprised to hear that New York has the same latitude as Rome. I have never lived in Rome, but I've lived in new york and I can assure that in winter it can be bitterly cold. And I don't really think that in Rome they experienced anything as called as the winters experience in new york. And the difference is completely do to the gulf stream. Let's move to permafrost. What is permafrost? Permafrost is ground that has been frozen for at least two years. In much of the arctic, the ground has been frozen for tens of thousands of years. Permafrost in the northern hemisphere is big. It covers about 25% of the surface of the land area in the northern hemisphere. And the top 50-to-100 cm are what is called the active there, of the permafrost. This top layer thaws in the summer and freezes in winter. Underneath, in normal stable temperature conditions there is a permanently frozen layer of permafrost. Well, why does it matter? The arctic permafrost acts like a gigantic freezer. If you put organic matter in your freezer, it stays in a good condition as long as the freezer works. But if the freezer breaks down, the meat begins to go rotten. Bacteria begins to decompose the meat, and gases carbon dioxide, methane, and other gases are released. Now for tens of thousands of years, the permafrost is acted like a giant freezer, keeping about 1, 500 gigatons of organic carbon trapped in the soil. This is huge. That is more than double than the amount of carbon currently in the atmosphere. Now, as the temperature rises, more methane is released. Methane, which as we shall see, is a very powerful greenhouse gas contributes to further temperature increase. As the temperature increases, more methane is released and it is a positive feedback cycle. How serious is it, right? A dramatic abrupt release of methane into the atmosphere appears to be very unlikely. However, it is very likely that the climate change will accelerate the pace of release of methane. Further adding to the global warming, much larger or smaller increases cannot be excluded. So, overall conclusions, we know from paleoclimate studies that abrupt climate changes have happened in the past. And we believe that positive feedback mechanisms such as methane mechanisms are very likely to be involved. These are currently very difficult to know, but this means that the current models, climate models are likely to underestimate the tail events. And when we look at the economics of climate change, the existence and severity of the state events will pay will play a very big role. The possibility of an abrupt climate change is not currently a central scenario or it cannot be excluded. And this is important because adapting to an abrupt changing climate would be extremely difficult. And from the economics analysis point of view, it is also very important because the existence of fat tail events can change our decision making. If our utility function is not linear, is it obviously is not, and it is concave, we'll see what this means and what this implies in later sessions, right. [MUSIC]
