[Music] Hello everyone and welcome to this course devoted to tracks for a sustainable world so this course will present the state of the world and the different options to find sustainable solutions it is composed in two main parts the first part is devoted to the space of the problems ie what is the nature and the complexity of the stakes which one faces and then the presentation of the key concepts The orders of magnitude, the main principles. Secondly, once we have assimilated all this, we can focus on the solutions, that is to say what are the tracks and characteristics of the possible solutions and what are the skills necessary for their construction. So in this first course devoted to the problem space, we will start with a notion that you have probably already heard about: the Anthropocene, and to introduce it I would like to quickly present to you some images that illustrate this general theme that the mankind has domesticated the earth. So in this first image we see a forest that has been razed to make room for crops. It can be in Africa, it can be in Asia, it can be Latin America, it's a scene that can be found quite often. In this second image, we see Mexico City there too. I took this city there but we could have taken others; we can see the urban sprawl, the amount of land that has been artificialized to build buildings. This one is perhaps a little less well-known, this checkerboard, this Gruyere, each of these little white squares, it's a hole. These are shale gas or shale oil extraction sites in the United States. Each of these locations represents a drilling site from which the oil has been extracted. and then this one, which is still quite impressive. If you look closely in front of the gaping hole at the very small things , the little squares, the little rectangles, these are buildings. In fact, this open pit mine is a kilometer in diameter. it is a very big mine as you can see that comes to us from Siberia. So there are not only images where man transforms nature in order to artificialize it. This image which comes to us from Holland, in Oostvaardersplassen, comes from Flevoland. Flevoland is a Dutch province that was built on the sea, and is totally artificial. It is the largest artificial island in the world which was therefore reclaimed from the sea and which is now devoted to different uses. Villages, towns, agriculture and in its western part, a nature reserve from which this photo was taken. So all of these images show us that man on a whole bunch of different scales has become a geological power, is able to transform the earth and this is in a way called the Anthropocene. . So in this figure we represent the trajectory of man and his impact on the planet. And what we observe is that for a very long period this impact has been gradual, gradual and then there was a kind of acceleration which roughly originated around the industrial revolution. We measure these impacts, we will detail it later and these impacts increase so that we find ourselves as humanity in an area, which is a zone of danger, of uncertainty that we call the limits of the planet, the limits of the earth. Beyond that, we do not know what can happen, it is what is called the rupture of the Anthropocene, that is to say the period in which we are: the era of Man. We must in a certain way find ourselves inside this space so that one can live in conditions sufficiently stable and sufficiently known so that there is no problem. One of the features of its limits that takes us into an uncertain future is obviously climate change that everyone has heard about. There are others and it is the object of this course to look at them and to look at the different components. So this figure presents in detail the characteristics of the socio-economic trends which have led to a founding concept called the great acceleration. It is a work which for about fifteen years consists in looking at what are the different effects of man and how can they be measured over a relatively short period of time: namely, the last two centuries. What we observe is that the population is increasing, the GDP is increasing exponentially, the investments are increasing, the consumption of fertilizers is increasing etc. etc. The set of socio-cultural or socio-economic characteristics of the earth system increases exponentially from the 19th century and in two generations from 1950, is found to be multiplied by an absolutely considerable factor which we will now detail. So this first figure shows us the demographic evolution of humanity. What we observe is that a relatively stable growth around 1 billion individuals suddenly sees its slope increase, an acceleration from 1950 and then we are projected today at 7.8 billion and this extremely rapid growth takes place on all continents but mainly in Asia for the last thirty years. This increase in population is accompanied by an increase in the quality of life. The number of people in poverty in red here finally remains stable, increases a little then decreases massively mainly due to the rise of China and we observe in green, that the number of people who are no longer in extreme poverty increases dramatically. The populations are therefore more numerous, they have better living conditions, they are also better educated. In this graph, the amount of people with access to education, being able to write and count increases in blue, while the amount of illiterate in red decreases. And then that also translates into better health for all since there on this graph all the countries listed all follow this type of trajectory with a more or less important timeframe. The overall health of the population will increase considerably in the twentieth century to have, here it is the life expectancy passed from 40 years to 80 years. So the overall life expectancy of the earth will have doubled in less than a century. This increase in the standard of living, in health and education will also come along an increase in rights and we can see on this slide that the countries on average which have the largest GDP per capita of inhabitants are also those who have access to the greatest number of human rights. So now, if we no longer take the socio-economic indicators but take the indicators of the planet, we observe the same thing: namely a considerable increase in a whole bunch of different parameters such as, for example, the increase in carbon dioxide, a greenhouse gas of nitrous oxide, methane, ocean acidification, number of fish caught at sea, etc, etc. What we see in this great acceleration, is both an exponential increase of the population and the quality of life and also at the same time the impact on the environment in a number of dimensions. In summary, the great acceleration is the fact that in two generations humanity has exceeded the earth's capacity to support its activities in a stable manner, this is essentially due to scientific and technical progress, to the increase in communications. This involves taking non-renewable natural resources and this has considerable impacts on geology, the environment, the climate and on terrestrial ecosystems. The almost Gordian knot of the problem is that human prosperity today depends on economic development. That this requires a lot of energy, we will see, and that is what transforms the metabolism of the biosphere. This set reduces the earth's capacity to welcome us. So to go into a little more detail in particular in this notion of metabolism, we will recall some principles of physics and biology and the first is the law of the conservation of matter. So it's very simple, it's Lavoisier's law: nothing is lost, nothing is created, everything is transformed. That is to say that all the matter which is today on the planet will be there tomorrow and was there yesterday almost. Most of the material that was on the earth 4 billion years ago is still there today; I put almost because you never know, an asteroid can fall, a satellite can leave, but all that is really “epsilonesque” it is very very very small and it is negligible compared to the quantity of the Earth system. So from the point of view of the conservation of matter, we can say that the earth is isolated. The second law that interests us here is the law of conservation of energy which is also called the first principle of thermodynamics. It's very simple, we don't create energy, we transform it. There is no creation, there is no destruction of energy. Energy cannot be reproduced ex nihilo, it can only be transmitted from one system to another. So in a way, energy is the measure of the capacity of a system to modify a state, to produce work. Energy can be transformed and for example if you are in a dam when the water is going down you have potential energy which is transformed into kinetic energy. Itself driving the turbine will produce electrical energy. You have a transformation from one energy to another but in no case do you have a disappearance of the energy. This notion is key because when we are going to talk about energy in an abusive way, the consumption of energy or the production of energy is not quite correct. We should say to have access to energy because it transforms but it will always remain constant. On the other hand, the quality of the energy, it changes and that is due to the second principle linked to the energy which is called the second principle of thermodynamics. So the second law of thermodynamics introduces a very interesting concept called entropy and entropy roughly characterizes the state of disorder of a system. It is linked to energy, the quality of energy in a closed system tends to decrease, to deteriorate. If we take our analogy from earlier, we have the dam, we have the water which passes from potential energy to kinetic energy When it is on the turbine there is probably friction, it heats up a little, this heat which is dispersed in the medium, it is an energy which is lost for the electrical conduction The electrical energy which will then pass in the network it will also produce heat and it is as much of energy which, between quotes, degrades and which is lost so there is indeed a link between entropy, disorder and the property of energy to lose its quality again in a closed system it is important. In this diagram we see an illustration of this if we let things happen spontaneously, the word here, the ink, will tend to diffuse, dissolve and become illegible because it will tend to occupy all the space. So we have a link between time, the irreversibility of time and the form which will tend to disappear, the energy which will tend to decrease in quality, to degrade. So the first principle tells us that there is conservation of energy. The second principle tells us that energy with time tends to degrade. How do living things ensure the continuity of form? At first glance whatever species is represented in this diagram, or if you think of any species, what is it doing? It makes offspring who have the same shape as the parents, roughly over the generations that can change, it can evolve but this maintenance of the form it seems to violate the second principle of thermodynamics since the form during life, he a priori, time has no hold over him and that is something really fundamental. So, this is the key to the living and this is what distinguishes the living from the non-living, if you compare a tomato and a rock: over time the rock will disappear, the tomato will remain a tomato and will make small tomatoes that go themselves make small tomatoes. The duplication, the reproduction, the evolution of the form requires matter and energy to be able to be maintained. In fact the thing of the living, all living beings have a metabolism, i.e. a large amount of chemical reactions that will take energy from the environment, take material from the environment to maintain itself or even duplicate itself and increase in size or make descendants. This direct link that there is between taking energy and matter is what ensures, if you will, to bypass or do with the second principle of thermodynamics. Because the living being is not a closed system, it uses external energy to be able to ensure that its form is maintained and it is the whole that will follow the second principle, therefore the metabolism of all living beings, will excrete waste, will produce heat which will tend to heat the environment and in quotes “pollute it” but it is something fundamental which is intrinsic to life. Metabolism is the fact that to compensate for the growth of entropy, living beings draw energy from the environment and structure matter using information. This is what makes the difference between the living and the non-living. And therefore living beings having the habit of eating each other, we have what we call trophic cascades , that is to say large networks with primary predators, secondary etc. I could have presented a forest to you, there I took a marine ecosystem, in this case lake, but it's exactly the same, you have the first chain which is the chain of the entry of energy into the system namely through photosynthesis that allows plants to grow and themselves become the source of nutrients and energy for the first trophic level, ie for the first organisms that eat them then there are the bigger ones that will eat the smaller ones, etc., this succession of trophic levels constitutes the trophic network, it constitutes an ecosystem. So in summary, photosynthesis provides most of the primary access to energy, ie the energy from the sun enters ecosystems via plants. Until the end of the 1970s, it was thought that photosynthesis was the only way for energy to enter an ecosystem and it was discovered in the late 1970s that hydrothermal vents were themselves a source of totally ecosystems. organized with multiple food webs but independent of the sun since they are much too deep to be able to have access to light. And the source which has now been well identified, the source of the energy which ensures this ecosystem, is chemosynthesis. That is to say the transformation of molecules: in this case in this specific case, sulfur oxide which is degraded and this degradation produces energy which is used by bacteria to be able to grow and that's it which allows, in symbiosis, to produce worms, crabs, fish and an entire ecosystem that lives at a depth of 3000 meters in total disconnection with the light. So it is not photosynthesis as such that is the fundamental point to be able to create life on earth, it is the access to energy and the fact that it can be metabolizable in forms, in the occurrence of sugars, which will allow other organisms to develop. So if now, we imagine all the ecosystems on the surface of the earth, we come to a key concept, the concept of the biosphere, the sphere of life that Vladimir Vernadsky presented in 1926 in his book Biosfera. What is it? I am giving you the definition here, the biosphere is the region of the earth's crust occupied by transformers which change cosmic rays into active terrestrial energy, electrical, chemical, mechanical, thermal energy ... It is a little the synthesis of everything we have just seen, the transformers are living beings: in this case cosmic radiation because chemosynthesis was not yet found but today we could quite extend this notion . All living beings will transform by the use of this energy, the different compartments of what is called the biosphere: that is to say, three large compartments if we think of life on the surface of the planet, life interacts with air, land and water. And these three compartments and the living are therefore interacting with its three compartments, if we imagine that on the surface of the earth, it is something extremely small. Imagine the earth, now imagine the greatest of depths: it is around 10,000 meters underwater . The highest altitude where life can be found, birds that circulate over the Himalayas, around again, roughly 10,000 meters above. So finally, on the whole of the earth the biosphere, it is a very small layer which is at most 20 km thick. and much less for the most part, and covering all of the earth. The biosphere performs a number of considerable functions for man and these are traditionally divided into four main functions. Of the support functions, the most important for us is food: everything we eat comes from the biosphere, whether animal or plant. Supply functions : for example, we can extract water or wood, other materials that come directly from the production of the biosphere. Control functions: it is for example the fact to be able to purify the water or air or ensure carbon storage. And then finally, cultural or social functions: because man has a propensity to appreciate being in a natural environment and it is an economic service, for example to be able to go for a walk in nature or to go hiking. kayaking on the banks of a river. There is another dimension which is not marked here and which is very important, it is the relationship with health. It is now known that people who have a better relationship with nature are traditionally in better health and in particular are less prone to depression. So what is this biosphere made of? If we look a little under the hood, what does it look like? So here in this figure, there are only eukaryotic species, that is to say cells that have a large nucleus. It doesn't include viruses and bacteria whether prokaryotes or archeobacteria for those who know. So on the eukaryotes here, we have different groups and in green it is the number of known species, described, and in yellow, the species that are not described. The quantity of species in the biosphere is very important. Estimates vary from job to job and the most conservative estimates are in the order of 3 million species. On average the consensus is rather around 8 million and then there is some work which indicates that they might have the possibility that there is up to 100 million. So we don't even know how many species there are on earth. These are pharaonic quantities anyway , and most of these species are still not described And I'm only talking about eukaryotes, prokaryotes and viruses and archaeobacteria are completely fallow fields since every time we look, there are different organisms that are not described and since they have been much less well studied than eukaryotes. So we saw the diversity, tens of millions, maybe more species, many of which are not described. What does this represent from a weight point of view? in biomass? So that's a very nice job, from an Israeli researcher called Ron Milo, who published the great masses, an estimate of what we know about the great masses of different organizations. So if we take all living things: the estimate is that we are roughly around 570. The unit is gigatons of carbon. What does it mean? This is 570 billion tonnes of carbon That is to say that each organism is reduced to what it would weigh in carbon equivalent . Well, that's for the measure. What is important here are the different orders of magnitude. So the living, here, is of the order of 570 billion tons of carbon. Of these 570 billion, 450 are represented by plants and mainly land plants. So the biggest, and by far, of the world's biodiversity in mass: it is plants. The second part is bacteria, which is not necessarily completely trivial. Then you have fungi and viruses. All the organisms that we traditionally think of: that is to say animals, it represents a very small 2 gigatons here, which is very low since it is of the order of 4% of the global biomass. Now, if we zoom in on this very small part and see what it represents. Here, it is understood mainly of arthropods: then insects, crustaceans, spiders, etc. which represent half: a giga tonne so we are more of the order of 2% of the total mass and if we are looking for the man we realize that it's a tiny 0.06 gigatons of carbon. That is to say really not much and what is even more interesting is to see that the whole of the cattle, the whole of the breeding corresponds to 0.1 gigatons, that is to say roughly twice the amount, by weight, of humans. And wild animals are a very small part. We can see it better on the following diagram so in summary, for a given quantity that would represent the whole of humanity, there are about three times as many viruses, about three times as many worms, 12 times more fish, etc, etc and 7,500 times more plants. Here you have a representation, to scale, between the quantity of men on earth, the quantity of cattle on earth and the quantity of wild animals, wild mammals on earth: a very small 4%. These figures, these diagrams from the Guardian come directly from the work of Ron Milo that I cited previously. They are the same figures and it is the same work but it is a better way perhaps to learn where we are today, between the distribution which is given to the man, to the cattle and to the world. wild. So a very big characteristic of the biosphere is interdependence. It is the number of relationships that there are between organisms. This figure, it comes from the northwest Atlantic, which we will talk about later, and which brings together all of what we call the trophic network : that is to say the relationships of who eats which among the organisms that have been identified and characterized in this part of the ocean. So I'm obviously not going to have fun describing everything to you , you just have to look at the top; it's birds and below it's fish, who are in the center: and this is the one that will interest interest us, this one is the cod, we will talk about it later, it is a fish which, as you can see, is at the center of a large network, with both predators and then prey. Just note the density of this network, the complexity of this network, the whole, all the organisms being linked to all the other organisms. So it's a way of representing the interdependence of biodiversity, but it's also a way of representing it that is quite simplistic because we are only dealing here with who eats whom. However, there is much more than that. Some twenty years ago Suzanne Simard, who studied trees in Canada, realized that trees communicated with each other and that nutrients could pass from one tree to another. In this case, between two different species, in this case between birch and pine, communication between the different trees is ensured by mycorrhizae. That is to say, mushrooms. In fact the quantity of fungi in the soil is absolutely huge, the networks that are woven are reminiscent of the Internet network and that is why this phenomenon is called the wood wide web, obviously referring to the world wide web. And the underlying idea, the concept that has been brought out in this way, is that you have different species communicating with each other and going so far as to help each other. In this case, it is the case between the pine and the birch: they are very nice experiences when you have one of the species which has no more leaves, for example because it is autumn and the birch loses its leaves, and well the pine will transmit nutrients. On the other hand, if the pine has a problem because it is sick, then the birch will itself transmit nutrients to them. So we have something that is of the order of symbiosis which puts in relation different species mediated by fungi. It is still extremely complex. So we are very far from a simple food web; we have links or relationships between different organisms. And so if we want to go even further, we can try to disregard organisms as such. So there is a rabbit and then a few plants and then a fungus, but now what I would like is that we are not interested in the organisms as such but in the nutrients which pass from one to the other: in this case in this diagram there is nitrogen. There is a lot of nitrogen in the atmosphere, but it is fundamental. It is one of the fundamental elements of life. It is fundamental for all living beings and we have a problem: living beings have a basic problem which is to be able to capture nitrogen. So there are several mechanisms, I don't want to go into detail at all, what I want to insist is that nitrogen can be treated by bacteria to be reduced or oxidized, depending on the type of reaction. There again, I wouldn't go into detail, but you have different types of bacteria that will produce different types of nitrogen form and its different types of form will be, or not assimilated, by different plants. So, we have for a given nutrient, in this case nitrogen, what is called a cycle which will bring into play different types of bacteria and all the organisms of the biosphere which, when they die, return to the ground, are degraded, will re-enter a cycle etc. Beyond the interdependence between organisms, what we see here is a kind of nutrient cycle and that is a fundamental notion . In fact all the key elements of life: carbon, nitrogen, phosphorus and sulfur, oxygen and water, with the possible exception of hydrogen, but that's all a detail. These key elements have the property of being in cycles within the biosphere Cycles in time and cycles in space define what are called biogeochemical cycles. We have this notion of the biosphere: it links both living things and compartments: air, water, earth with transformation properties. So a biogeochemical cycle: it is the process of transport and cyclic transformation of an element or a molecule between the large reservoirs: that is to say again, water, air and soil. So if, for example, we take the case of carbon here, you have different forms released into the atmosphere. Carbon dioxide and methane but you have, via photosynthesis, the possibility of capturing this CO2 to make plant growth and then enter a food web. It can also be dissolved in water and then it will have a whole bunch of adventures. Among these adventures, if the CO2 is dissolved in water, it can get trapped in the sediment and reenter the rock for a few thousand or hundreds of thousands or even millions or hundreds of millions of years. So, we have cycles which are over extremely short time steps, like respiration and photosynthesis, and others which are extremely long since these are cycles which are geological. So, the key notion of these biogeochemical cycles is that the essential elements of living things: carbon, nitrogen, phosphorus and sulfur, oxygen are in cycle within an ecosystem between organisms but also via a number of reactions circulating between the large reservoirs of the atmosphere, the lithosphere and the hydrosphere. So to take an example of this type of cycle and in this case this type of oscillation, I took an illustration that comes from Yadvinder Malhi who put over a year, what is the primary productivity of ecosystems; it is ie the amount of carbon that is absorbed by ecosystems. Here is the image of January; so as we can see it is winter in the northern hemisphere, it is summer in the southern hemisphere, the absorption capacity is maximum in the southern ecosystems tropical in particular, which is quite normal and so what happens now if we do not take the picture in January, but in February, March, April, May, etc. surprising no? one has the impression that the earth breathes and that it is the annual cycle of respiration of the earth. The concept I would like to introduce now is that of engineering species , it is a concept that comes from Clive Jones who is an American ecologist who developed this idea of ""ecological engineering"". So, in the first image, we see a sheet of water with a kind of dam: it is the construction of a beaver. This is the typical example of the engineer species. That is to say of the species which will transform its environment to be able to adapt it to its needs. So typically, here we have a beaver dam that creates a body of water that will allow him to meet his needs, build his lodge, etc. Here, we have a mangrove where the mangroves generate a totally different ecosystem which allows the creation of a fish nursery and to facilitate the sedimentation which itself will create an ecosystem, etc. When we look at the one from below, we have this time here, the great barrier reef. The coral is the type of species that make the ecological engineering Ecological engineering because it builds a habitat that will be used by a multitude of other organisms. Closer to home, the earthworm performs essential functions by transforming the first part of the lithosphere, this is also very important work and then in the same vein, we have the now well-known examples of African savannas where nitrogen and phosphorus in particular are extremely rare and it is found concentrated in termite mounds by termites. And in fact, if we look in a savannah where the trees are distributed and the trees are born in the termite mounds because that is where the nutrients are, and where you have some sort of nutrient concentration provided by termites to trees. So if we go even further and take what's on the screen, these little pads come to us from Australia, they are stromatolites. What does that mean? it's a funny name for bacteria called cyanobacteria. Cyanobacteria, they produce a lot of oxygen, it's algae if you want, and this oxygen and well a long time ago it made a lot of noise because we call the great oxidation. It is the fact that there is for a very long time, around 3.5 billion years ago, when cyanobacteria appeared, cyanobacteria began via photosynthesis to release oxygen into the air and then this oxygen must have reduced a whole bunch of atoms and in particular iron and happened at a time around two billion years ago, say, where there is an extraordinary amount of oxygen that has accumulated in the atmosphere. This is called the great oxidation and this great oxidation it eradicated all other life forms on the surface because it is oxygen, it is an extremely strong oxidant that destroys the life forms that are not able to resist it. These are forms of life that have plunged into the depths of the earth and are now found instead at great depths. And then life, as we know it today, which is an aerobic life, a life that consumes oxygen has been able to develop. So you have a species whose metabolism rejected a waste of oxygen, an extremely violent poison for all the other forms of life of the time but which gave, after the fact very long after the whole of the life as we see it today. So in summary on the main principles of the biosphere, we have seen that the diversity and interdependence of living things ensures the functioning of the biosphere that matter is in permanent movement in a multitude of cycles, which go from the smallest to the largest , that certain species are capable of very strongly transforming their environment and that the wastes of some are food for others and that those which are not metabolizable accumulate, and even are toxic. So we have here, in summary, the story of our species: homo sapiens who began to move matter in a multitude of cycles specific to its economy, which profoundly transformed its environment and which today release a whole quantity of waste which is absolutely not metabolizable and which becomes a real pollution for others. So we have now reviewed the different physical and biological principles that give us a little bit the nature of our relationship to our environment. This session is coming to an end and we will look in the next one, how human activities transform the metabolism of the biosphere.