3 - Le changement climatique (1) - Cours des Mines 2019 - Jancovici - [EN subtitles available]

so today were going to talk about something really cool and i think youll enjoy it lets get started the rules say ignore this but hello world how are you today we are going to talk about climate. who knows this gentleman on the right, there? only this few people?

about ten, or about fifteen people know him? who knows what he was doing back then? ***audience answer*** very good.

and his name is? ***audience answer*** laurent fabius, absolutely, former prime minister of france. so, mr laurent fabius, in december 2015, like an auctioneer, strikes his hammer on the desk and declares to accept or approve the paris agreement, which says that the signatory countries will do their best to ensure that the temperature increase remains well below 2°c.

if this agreement had an effective, practical scope, i could replace this course with a big break and tell you that the problem is solved and that there is no need to bother you by explaining to you what the problem is, since the problem is solved. unfortunately, it will still take two and a half hours to explain to you that the problem is very, very far from being solved and that there is still quite a little way to go between the cup and the lips. here is a curve of the atmospheric concentration of co2 expressed in millionths.

usually the atmospheric concentration of co2 -- i will come back at length to what co2 is and where it comes from, etc. -- is expressed in parts per volume, that is, the molar fraction of the atmosphere -- expressed in volume -- which is composed of co2. this is expressed in millionths.

so, when you have 300 ppm on this graph -- that's 300 millionths -- it's in fact close to 0. 3%, this is also how you can look at it. and instead of graduating according to years and saying that this year corresponds to 1995 and this year corresponds to 2017, i graduated according to the number of the annual meeting of the conference of the parties of the climate convention.

the climate convention -- i will also come back to this during this course and the next one -- is the un agreement that all the countries on the planet signed and ratified, saying that we would take care of you, that is, future generations. indeed, it was signed in 1992 and i think that in 1992, there were not many people in this room that had already been born. what we called “future generations” is: you.

and in this paper, we said that we would take care of future generations. it was signed in 1992 and ratified in 1995. so, 1995 was a great success because the climate convention, which says that we will take care of you, came into effect and there was the first annual meeting of the conference of the parties.

what we call the conference of the parties is not butchers meeting to discuss on what pieces of beef taste best, no. the conference of the parties is the annual meeting of the parties at the convention, because in un jargon whatever country signing or ratifying a convention is called a party, that's how it is. so, the parties at the convention are the countries or entities -- the european union for example -- that have ratified the convention.

so, year 1 of the life of this convention, which enters into force in 1995: a great success, of course. 1997: this is the year of the kyoto protocol, which is -- i will not go into detail about it -- an annex to the climate convention in which it is stated that there are a number of countries in the world that will make quantitative reduction commitments, including france. so, france said: “the emissions that come from my country will drop by 5% between this year and this year”, and a number of other countries have made exactly the same kind of commitments.

so, you can see the effect it had on the atmospheric concentration afterwards. then arrives copenhagen, described as a huge failure. .

. ok. then comes paris, described as a huge success.

. . .

we'll see about that… this little introduction is here to show you that unfortunately -- and we will see it on a number of other curves that i will show you -- so far, the amount of noise made on climate change is a parameter that has no influence on what is really happening. there are two uncorrelated processes in the world, which are: what is really happening in terms of emissions and the resulting climate processes, and the number of people who say something should be done. these are two completely separate processes at the moment, unfortunately.

we are going to talk about climate, and, speaking of climate, i will insist -- even for the well-made brains that you are -- because we are going to talk about something that is inaccessible to your senses. you may be vERY bright student engineers selected to enter a vERY selective school, but you are still animals like me, and so you trust your senses because the human species is a species that trusts its senses. we date back to a time when our senses told us that we had to run in order to escape the sabre-toothed tiger that was only thinking of doing its afternoon tea with us.

so we know the things that our senses tell us in our immediate environment. as far as climate parameters are concerned, what our senses can tell us about our immediate environment is: the temperature right now and right where we stand, possibly also the amount of precipitation that there is right now and right where we are, the luminosity that there is immediately where we are, the cloudiness -- that is, the clouds -- that there is immediately where we are, etc. these parameters, appreciated locally and instantly, in science, lead to what is called weather.

weather is the instantaneous and local evolution, or in the very near future, of things that speak to our senses -- that is, the conditions that are going to exist here. this morning, to find out if i was wearing a coat or not, i looked at the weather forecast in paris and i didn't care whatsoever about what the weather today in buenos aires may be. i did not care at all.

all i care about to know whether i should wear a coat or not, is the weather today in paris. but the climate, on the contrary -- about which we are going to talk now -- is something that is inaccessible to your senses, at least in a direct way. it is accessible in an indirect way, but it is inaccessible directly because when we talk about climate, we are going to talk about averages, and an average -- you know it as well as i do -- is an intellectual construct.

it's a series or an integral, so it's not something you observe in nature. it is an intellectual construction, an average. however, it is this intellectual construction that will make it possible to understand whether or not we are drifting out of the norm regarding our usual environment.

you can still see indirect manifestations of climate in the world around us. indirect manifestations include, for instance, vegetation. obviously, the vegetation in greenland -- there is not much of it -- the vegetation in africa and the vegetation around the mediterranean basin are not the same because the climate is not the same.

so, one can see some indirect manifestations of climate. but direct manifestations, that is, approaching an average through one's senses, that is not possible. so there is a confusion ***audience question*** both, general!

the confusion comes from the fact that in either case, we manipulate the same criteria – or in other words it is the same variables that we manipulate, but in one case we will look at instantaneous and local values, and in the other case we will look at spatial, or temporal, or both, averages and at the regular variations of these averages. for example, seasonal variation is part of the climate. you have seasonal variations in temperature which may concern the fact that there is sunlight: at the mid-latitudes and at the poles.

or about the fact that there is a lot of rain or little rain: these are rather the equatorial regions. so, you can have seasonal variations that are not always the same wherever you go. i'm now going to go back to my favourite enemies -- namely journalists -- and i'm going to give you an example of something that happened a few years ago, that i found interesting.

there had been an article in the newspaper a while ago, as there is from time to time, with people who want to make themselves interesting by saying, “look, there can't be global warming because the planet is not warming up right now: it's cold. ” so here we are, one day, it just so happens that by chance there were negative anomalies, i. e.

cooler than average temperatures in a whole bunch of heavily populated areas: as you see, a piece of europe, a piece of the united states, a piece of japan, etc. however, wherever there are men, there also happens to be news agencies and there are people to send press releases. so, there are a lot of people who say, “look, where i am now, today, it's cold right now.

” except that at the same time, neither the penguins nor the dolphins in the middle of the atlantic, nor all these people could say: “oh but you know, it's much hotter than average here right now. ” so, if you really average with where it is colder, and where it is warmer, there is no problem, the average of the entire planetary surface is well above its reference value. and that continues from time to time.

it's rarer now, but you know, there are still a few people playing these kinds of little games. again, it's quite easy to confuse an instantaneous value with an average: that's all it takes. and it is very easy, once again, to abuse people who are not familiar with the subject because we use the same parameters for both and because our senses do not tell us what an average is.

there is another thing that's quite classic --- i have to change the year every year, but it's always the same principle -- when we're interested in this subject, its to misinterpret a series. so here, i could say that the effect of this process is to raise temperatures. i could also say that it is the decrease in the number of pirate ships because in fact, underwear has decreased at the same time as the number of pirate ships has decreased.

anyway, it's very easy to misinterpret what you're observing until you understand the processes. so it's very easy to have a bad conclusion. climate is therefore made of geographical, spatial and temporal average values.

but even these averages are changing. in fact, the earth's climate, since the earth existed, has never been stable over geological periods. the geological period doesn't really matter when you're a man or a woman because your life expectancy, if everything goes well, is on the order of the century – and even, if everything goes badly, for a few decades -- at least i hope so.

so what happens over a few million years: prrrrt. but the earth has been through very, very different times in terms of its climate. for example, there was a time when there was no oxygen in the earth's atmosphere, when the earth's atmosphere was composed mainly of co2, and then of methane and nitrogen.

there were times when the earth was probably almost completely frozen: the ice cap covered almost the entire earth. there was a time when there was no continent, in short: the earth went through extremely varied states and if we look at the last few million years, i. e.

the quaternary era, there were, even then, great climatic oscillations which are glaciations-deglaciations. so the climate has not remained stable at all. if we place ourselves on time scales that are one million years or less, we have a first forcing factor called astronomical forcing.

the astronomical forcing comes from the fact that the solar system is a household of 10 and not a household of 2, and therefore the earth is attracted by the large planets of the solar system. so we are not in a perfect ellipse, regular over time, which is the one you know how to calculate in geometry with just two bodies. we're in a ten-body system -- it's not working as well -- at least it's not regular.

so there are variations in the orbit -- i'll come to that just after -- and it can distort the climate system on time scales that are in the order of a hundred thousand years. the continents are not always where they are: there is a drift, as you know, of the continents, and depending on where a continent is, well the reflection of sunlight is more or less important. for example, when continents approach the poles, permanent ice caps can appear, typically greenland, and at that moment you create a very reflective surface, much more reflective than the ocean water that was there before.

the installation of the antarctic ice cap on the south pole a few tens of millions of years ago -- i read it’s 30 here, 15 there, but eventually the order of magnitude is the same -- cooled the global climate by a few degrees. that is because of the creation of this large mirror that evacuates some of the sun's rays without them having time to heat the ground. after that you have internal oscillations in the fluid compartment of the atmosphere.

and in particular processes that are linked to large-scale ocean circulation, that can change the climate over time periods ranging from the century to the millennium, and obviously you have the internal dynamics of the atmosphere but that changes the climate over very, very short periods of time. and then, now you have us, at the very bottom there, the anthropogenic cause. so: bravo !

, we have become a climatic agent. we have become an agent that forces the climate system. when you do meteorology – let me come back to this -- the only compartment that reacts on a daily basis is the atmosphere.

so, make a good model of atmosphere: not you because you don't know how to do it, but take your friends at supaero, they know how to do it. and you send them to météo france, you ask them to make a climate model, and they forecast the weather correctly. however, if you want to look at how the system is evolving over the century, which is what we are going to talk about now, it is no longer enough to make a good atmospheric model.

one needs to know how to model the evolution, at these time scales, of other compartments of the planet, and in particular of the ocean. and especially from the ocean. the ocean is the fluid compartment that drives the evolution of the climate system over the century, much more so than the atmosphere.

so if you want to make a good weather model you look up, if you want to make a good climate model, on the contrary, you bow your head. at even longer time scales, as i said, astronomical parameters dominate. so what are the variations of these astronomical parameters?

the first is that, because of the attraction of the large planets of the solar system, you have three parameters that will vary over time. the first is that the earth does not make an exact ellipse because it deforms. but finally it is a quasi-ellipse, whose eccentricity is more or less great, with a quasi-periodicity of a hundred thousand years.

this is a first variation that is introduced by the attraction of the big planets. the second variation that is introduced by the large planets is that you have the axis of rotation of the earth which is more or less inclined in the plane of the orbit. you understand that if the axis of rotation of the earth were totally perpendicular to the plane of the orbit, would there be seasons?

no, we wouldn't have seasons. do you agree with that? because the solar inclination would be the same all year round.

yes i will come back to this just after. the axis of the earth's rotation rotates around the perpendicular to the plane of the orbit. this means that since there is an apogee and a perigee, the earth will show its head or buttocks alternately, i.

e. the northern hemisphere or the southern hemisphere, as close or as far from the sun as possible. so with a quasi-frequency of twenty thousand years, it is the northern hemisphere that, when you are as close as possible to the sun, looks at the sun.

or rather the southern hemisphere. all right? either one or the other.

and that changes with an almost 20,000-year periodicity. when you put all this together, there is something that is going to vary greatly: the sunshine insolation at 65° north. you're going to tell me: “insolation at 65° north, why are we suddenly interested in that?

” so why? because it is the very sensitive area that determines glaciation entries or exits during the quaternary era. because it is a place where, with the variations of these astronomical parameters, there can be a very important variation of the insolation that is received, especially in summer.

the more the axis straightens up and the lesser contrast between the seasons, and so at this time, the summer is proportionally less hot. summer is proportionally less hot and, when you are close enough to the poles for snow to fall in winter, you end up with snow that no longer wants to melt much in summer. the snow begins to accumulate year after year and the earth enters glaciation.

so in fact, one of the conditions for glaciation is that the axis should straighten up in terms of orbit. and correlatively, when it tilts, the opposite happens: you have very hot summers, and the snow starts to melt. so these variations of insolation go along with the entries and exits of the last glaciation that are shown here.

in all these parameters, there is one that has now become the dominant parameter. so i'm going to have to interrupt myself for 30 seconds to find the little animation that is well suited here. here you have a little animation made by the only serious people who matter in this world, that is, champagne producers.

it is true, they gave me this little animation in 2002 for a conference, which tries to explain what the dynamics of the greenhouse effect consists in, which is one of the processes at work as far as climate formation is concerned. so here you see a simplified illustration of the earth's surface made up of land and water, oceans, and the energy supply that allows the climate machine to function, that is, solar energy. since the climate machine is like all machines in the world, it is subject to the first law of thermodynamics.

for it to do something, it needs energy, and that energy is essentially brought in by solar radiation. about a third of this solar radiation, when it reaches the surface of the atmosphere, is reflected into space by everything that is bright when seen from space. so if you look at a satellite photo of the earth, you have two types of surfaces that are particularly bright.

which are? snow, that's what you're going to find, and then what? deserts, absolutely.

snow and deserts are particularly reflective. this evacuates about a third of the incident solar energy. the remaining two thirds, since they are not reflected, are absorbed, and namely absorbed by the soil.

and the ground, as for any energy system, recovers energy through absorption of light radiation, or electromagnetic radiation to be more precise. because about 50% of solar radiation is near infrared, and there is only 40% visible and 10% ultraviolet. so, the soil absorbing solar energy will also seek to achieve an energy balance.

the ground has three ways of getting into energy balance, i. e. restoring the energy supplied to it by the sun in a stationary regime.

the first way it has is contact heat. for instance, if you are above a warm floor, you blow air on it, and the heat is transferred directly to air by contact. this is a first way through which the ground releases energy.

a second way the ground has to release energy -- it's not very well represented but you can see it there, with this kind of little blue flashy thing there -- it's the latent heat of the water: evaporation-condensation. so when you heat the ground, which happens to be made of two-thirds of water -- because two-thirds of the planet is covered with water -- well, water evaporates and the latent heat that is used for evaporation is released into the atmosphere. and you will have a third mode of energy restitution: the ground is going to radiate infrared.

because you remember that any body above 0 kelvin radiates something. so the sun, which on the surface is at 6,000 kelvins, has a spectrum in which there is a lot of visible, a lot of near infrared, a little ultraviolet. the earth, which is on average 300 kelvins in order of magnitude -- well, a little more, 310 -- has a spectrum that is much longer.

it's a lot, it's moved to wavelengths that are much longer. and in these longer wavelengths, there is essentially what is called far infrared.