So we saw in the second module, why there is a link between the quantities of greenhouse gases in the atmosphere and certain levels of temperature in the atmosphere. What we're going to see now is how climate might actually evolve in coming decades. So, in order to look at the future evolution of climate, based on different forms of human activity, whether it's industrial or agricultural activities, we need to have available to us what we call climate models. These are based on the physics of the Earth system, computer-based models that try to reproduce as faithfully as possible the different elements of the climate system that I mentioned right at the start of this particular part of the Mooc. That is to say, the interactions between the oceans and the atmosphere, ice and the oceans, ice and the atmosphere, and so on. Not only do we need physically-based climate models, we also need to know something about the way societies will be evolving in the future. Because the quantities of greenhouse gases that humans will be injecting into the atmosphere over coming years and coming decades, will depend upon a number of factors. Amongst these, we would have demographics, what will be the size of the world's population in the next 50 or 100 years, what will be the typical economic growth in different regions, and what will be some of the technological choices we might make in terms of the energy sector, for example. Will we continue to rely upon fossil fuels as much as we have in the past or will we try to invest more heavily in renewable energy technologies? For example. So, when we try to estimate what will be the future course of greenhouse gases in the atmosphere, we need to try and guess what will be the subtle links between demographics, economic growth, technological drive, basically, what will be our societal choices in coming years and coming decades. So, rather than try and guess just one future trajectory, scientists have come up with about 40 different scenarios that can be summarized in this table in the form of four major families of scenarios. One which is in the upper left part of the of the graph, shows a world in which we would not change very much our collective behavior, we would still continue to rely heavily on fossil fuels. So, we wouldn't be changing very much in that sense. So, this would translate into a very strong response of the climate system. Because by putting in more and more greenhouse gases into the atmosphere related essentially to fossil fuels, then of course the climate system will warm more rapidly than if we control the amounts of greenhouse gases that we put into the atmosphere. And then, on the bottom right corner, you have the so-called 1.5 degree policy, that was negotiated in Paris during the COP 21 negotiations in December 2015. Now, if we implement fully the terms of the Paris agreement, then we could theoretically limit future warming to 1.5°C, which of course would have a number of advantages in the sense that the impacts related to climate change would be much less severe than in a sort of business as usual world, which would be represented in the upper left corner of this diagram. Now, using different scenarios and using climate models, what we can do is try and simulate what the response of climate would be to one or more of these particular greenhouse gas emission scenarios. So, now you see in this animation, one of the climate models that was used in the evaluations of the Intergovernmental Panel on Climate Change, the IPCC, that has fed the scientific information to the negotiators of the Climate Convention and in particular the COP 21 accord in Paris, in December 2015. And on this animation, you see that as we move into the future over the coming decades. You see again, as we saw a few minutes ago with the animation of the real world from the 19th Century to today, you see that the warming is by no means uniform. It's going to be modulated by the distribution of continents and oceans. It's going to be modulated by the presence or absence of vegetation, the presence or absence of ice, and snow on the continents and so on. But by the end of the 21st Century, what you see is a general warming taking place. It will be fairly strong in certain regions, maybe anything up to 10 degrees more than today. Now, if 10 degrees more than today sounds a rather exaggerated figure, I just like to remind you that if you think about the 2003 heatwave in Europe, for example, we had temperatures that exceeded in certain parts of France and Western Europe up to 12 degrees more than the average August temperatures. So, this is the kind of world that we're going to move into. In other words, what can be considered to be an extreme climate today, might actually become the average climate of tomorrow. Now, when we think about climate change, we think above all of temperature change, but many other elements of the climate system will also be modified because of the changes in atmospheric temperatures, and in particular precipitation regimes will be modified in response to the enhanced greenhouse effect. On this animation, which is a very similar model to the one we saw previously for temperature change, you see a very noisy picture in terms of the response of precipitation patterns to the enhanced greenhouse effect. You see some parts of the world which will dry out compared to today, and you'll see other parts of the globe where precipitation is likely to increase with respect to today. On average, we can say that the equatorial region might experience more rainfall than today. The dry zones may experience less rainfall than today, which is very unfortunate for the populations living in these arid and semi-arid regions. And the mid to high latitudes are likely to experience more rainfall or more precipitation than currently.