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0:01
Welcome to a tutorial on the science of global warming. I have made this video with the hope that in understanding the mechanism of global warming people will better understand that reducing greenhouse gases in the atmosphere is essential for the health of our planet and its inhabitants. This video aims to explain the major points of the chemistry and physics involved in global warming. There is a large body of work that explains the mechanism of global warming,
0:29
primarily concerning one the interplay of energy and matter within the earth-sun system, and 2. The mechanism of the greenhouse effect. How does the presence of greenhouse gases increase the temperature of the earth and its atmosphere? These two points cover many concepts, all of which are interrelated. And so the approach of this video is to explain those many concepts and emphasize their connections.
0:52
Regarding greenhouse gases, the video will focus on carbon dioxide and water vapor, which are not the only greenhouse gases, but carbon dioxide and water vapor account for the majority of current warming, and the mechanism for warming the earth is the same for all greenhouse gases. We will explore the connection of carbon dioxide and water vapor to global warming, and briefly connect that to the result of global warming which is climate change.
1:20
You probably have heard of both the terms global warming and climate change and may have wondered how or even if they are related. Global warming refers to the rising temperature of the land oceans and atmosphere since the late 1800s due to increasing presence of greenhouse gases in the atmosphere. Historians mark 1750 as the start of the industrial revolution. However industrialization was not significant enough to affect global temperature until the latter half
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of the 1800s when the more significant rise of industry began to more significantly increase atmospheric carbon dioxide as a result of burning fossil fuels. The chemical reaction of burning any fossil fuel follows the same process: All fossil fuels, coal, natural gas, and petroleum-based fuels are hydrocarbons. They are all composed of some amount of carbon and hydrogen atoms. When burning or combining with oxygen, the result is the production of carbon dioxide
2:19
and water vapor. However the amount of water vapor produced is negligibly small compared to the amount of water vapor already present in the atmosphere. But fossil fuel burning results in a large increase in carbon dioxide compared to the carbon dioxide already present in the atmosphere, which produces a global rise in temperature. The result of that rising temperature is a change in
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the earth's climate. Climate change encompasses all of the physical and meteorological consequences of global warming such as changes in precipitation patterns, changes in storm patterns, changes in cloud formation, changes in wind patterns, and increasing natural disasters. All of which result from increasing global temperature of the land, oceans, and atmosphere.
3:09
So the two processes, global warming and climate change, are intimately connected.
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OK now for the next two minutes I'm going to summarize the entire technical story.
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Second, the earth seeks to reach an energy equilibrium, meaning the earth emits an amount of energy that is equal to the amount of absorbed sunlight. That emitted energy is infrared energy.
3:48
Third, the key here is that it is the temperature that dictates the amount of infrared energy emitted, and the earth's surface temperature at which the earth energy equilibrium can be reached is negative 18 degrees Celsius or zero Fahrenheit. Fourth, greenhouse gases absorb and emit infrared energy which prevents the infrared energy emitted at the earth's surface from being directly lost to space, which disrupts that equilibrium. Fifth, due to those greenhouse gases interfering,
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infrared is lost to space where the air is colder than negative 18 Celsius, and so the earth heats the atmosphere until that altitude, where infrared is lost to space, warms to negative 18 Celsius.
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That warming allows the earth to reach that earth energy equilibrium. But we live at the earth's surface! Far below that cold negative 18 Celsius altitude. At the earth's surface, that warming results in an average temperature of about 14 degrees Celsius 57 degrees Fahrenheit, allowing water to exist as a liquid. Finally adding more greenhouse gases results in infrared lost at even colder temperatures due to it being at a higher altitude, resulting in
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the earth heating the atmosphere even more until that altitude, where infrared is now lost, warms to negative 18 Celsius, which means our average temperature at the earth's surface, even further below that cold altitude, has risen and will continue to rise as we add more greenhouse gases.
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So how does all that happen? A crucial point in understanding global warming is the connection between the temperature of an object and the emission of electromagnetic energy. All objects in the universe emit electromagnetic radiation, and the energy of the emitted radiation is proportional to the temperature of the object's surface to the fourth power. This is described by the Stefan-Boltzmann Law which we will go into a bit later and is known as black body radiation.
6:01
In this illustration of the electromagnetic spectrum, the energy of radiation increases when going from left to right, corresponding to increasing frequency. And since it is the energy of electromagnetic radiation in which we are interested, we will refer to it as radiant energy.
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The entire earth and everything on the earth are in a temperature range that constantly emits infrared energy. The earth constantly glows infrared light. We can set up a graph corresponding to the frequency spectrum representing the range of infrared frequencies emitted by the earth, while the sun, due to its higher surface temperature, emits higher energy radiation in the infrared to visible to ultraviolet range seen here in the graph. We can see here the range of
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incoming solar energy, as well as outgoing infrared energy. These emissions are both important to understanding how the incoming versus outgoing energies relate to global warming, which will be addressed throughout the video. We can express the outgoing radiant energy from the earth as a proportion to its absolute temperature to the fourth power. This relationship is the Stefan- Boltzmann Law. Thermodynamics tells us that the amount
7:25
of incoming energy, and outgoing energy, should reach an equilibrium. In other words incoming and outgoing energy are in balance, and this is often called the earth energy balance model. And this will be looked at in more detail throughout this video since it ultimately explains global warming.
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We can apply the Stefan-Boltzmann Law to the earth energy balance model because we can determine the amount of incoming energy from the sun, which the earth energy balance model tells us will be equal to the amount of energy emitted by the earth. The reason for this balance will be explored later in the video, but let's see how we can use this relationship to determine the earth's temperature. In particular because that will help us understand changes in the earth's temperature.
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The Stefan-Boltzmann Law is here modified to accommodate the earth energy balance model, and this equation is a key step toward understanding global warming, the increase in the earth's temperature. In order to understand what the equation tells us, let's look at each term in the equation: S represents what is called solar flux: the amount of solar energy available at the earth's distance from the sun. Solar energy is measured to be about
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1366 watts per square meter of space at the earth's distance from the sun.
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You can think of a watt in terms of light bulbs: the average LED bulb you might use in your home would have about an 8 watt output, making 1366 watts equivalent to about 170 light bulbs for every square meter of space. A watt refers to energy per second, so 1366 watts per square meter is the same as saying 1366 joules per second per square meter. One watt is one joule per second. To give you an idea of the amount of energy in one joule, the average person's body uses
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about 90 joules per second, or 90 watts, to stay alive over a 24-hour period.
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But S is modified because not all of that solar energy coming from the earth is absorbed by the earth. About 30 percent of solar energy is reflected back into space, which is termed albedo, having the symbol alpha. And so 70% of incoming solar energy is absorbed by the earth.
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So S, the amount of incoming solar energy, is modified by multiplying it by 1 minus the albedo, the fraction of S, the fraction of incoming solar energy, that is warming the earth.
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This term, 1 minus albedo, accounts for the reflectivity of the earth, and so a higher albedo means this term will decrease, and so will the temperature of the earth, and vice versa, so the amount of solar energy reflected is a very important consideration. For example, as the polar ice caps melt there is less albedo, less reflected energy, and therefore a higher temperature on the earth due to greater solar energy absorbed.
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S is expressed in energy per square meter of space, a square meter of direct sunlight, so we multiply by the area of the earth that is equivalent to receiving direct sunlight. You may notice that this is the formula for the area of a circle: pi r squared. Because the incidence of solar energy hitting the earth gets less direct toward the outer earth, the total area of direct sunlight is equal to the area of the cross section of the earth, the area of a circle.
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So this term in the equation tells us the total solar energy per second being absorbed by the earth's surface. Let's determine that value by plugging in the values we just learned: 0.3 for alpha, 1366 for S, and the earth's radius is about 6.4 million meters, and so this gives us an energy input of 1.23 x 10^17 watts, or about 50 000 times humanity's total electrical energy consumption per second! The amount of earth's energy lost to
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space seeks to be in balance with this amount, in other words the incoming solar energy is equal to the energy emitted by the earth. So we can use this term to find what temperature the earth's surface needs to be at in order to emit this amount of energy, which maintains the earth energy balance.
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The equation gives temperature in kelvin to the fourth power, and it equates temperature to the energy emitted through sigma, which is the Stefan- Boltzmann proportionality constant: 5.67 x 10^-8 watts per square meter per kelvin^4. Note that the constant is given per square meter, and so we multiply by the amount of square meters on the earth's surface, which if you remember your geometry, is 4 pi r^2, the surface area of a sphere.
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It is the entire surface of the earth that is emitting this energy back into space, originally absorbed as solar energy. This is our earth energy balance model, representing the equilibrium between incoming and outgoing energy. What is nice about this last step, adding the 4 pi r^2, is that it allows us to drop the pi r^2 on each side, simplifying the calculation for temperature. Before going further let's plug in the first term, 1 minus albedo, 1 minus
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0.3, which is 0.7. We can now rearrange the equation, first to isolate temperature to the fourth power, and then if we take the fourth root of the expression on the left we can get temperature. Let's review what we have and then plug it in and see what we get. 0.7 is the fraction of solar energy absorbed by the earth, S is the amount of solar energy hitting the earth, 1366 watts per square meter, sigma is the proportionality constant relating earth's emitted energy to the
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fourth power of the temperature, and T is the temperature at the earth's surface in kelvin.
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Plugging in S, and sigma, gives us a temperature of 255 kelvin, or negative 18 degrees Celsius, zero degrees Fahrenheit. What this is telling us is that 255 kelvin is the average surface temperature at which the earth's outgoing infrared energy is equal to the absorbed solar energy. So here is the earth's balance between incoming and outgoing energy. However there is a problem. 255 kelvin is very cold: negative 18 Celsius, zero degrees Fahrenheit. If the earth's surface was that
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temperature it would be a frozen ball of ice. 255 kelvin is 33 kelvin less than the current average temperature of 288 kelvin. I hope you have noticed what we are missing here, which is the earth's atmosphere. However an atmosphere of 100% oxygen and nitrogen would not be able to hold in any of that emitted infrared and so the surface would be that calculated amount of 255 kelvin. If the earth was that cold we would not be here trying to understand why the earth is warming.
15:20
But there are molecules in the atmosphere, called greenhouse gases, that capture that infrared energy, and give us an average surface temperature, 15 degrees Celsius 59 Fahrenheit, that keeps water in the liquid state, and that allows life to emerge and evolve. So is 255 kelvin relevant? And in particular is it related to our current 288 kelvin surface temperature? Here's a hint: it is very relevant, and ultimately explains global warming.
15:53
Let's take a look at the mechanism for greenhouse gases warming the earth using carbon dioxide as our example since it is the most significant contributor to warming the earth during the past 150 years there are other greenhouse gases such as water methane nitrous oxide ozone and other pollutants and they all have the same warming mechanism as carbon dioxide although water does have other considerations which we will take into account later in the video water
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and carbon dioxide are the most potent greenhouse gases in terms of their ability to increase global temperature per volume of increased gas in the air a common misconception is that methane and some other gases are more potent than carbon dioxide or water which they are not but the rate of methanes and other greenhouse gases increase in atmospheric concentration has been very steep in the last few
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decades which is of great concern but we focus on carbon dioxide because it is the most powerful of all the greenhouse gases that humans have altered water vapor is a much more potent greenhouse gas than carbon dioxide but its presence is not directly altered by human activity carbon dioxide has generated by far the largest increase in global temperature carbon dioxide's current level of 0.041 percent of atmospheric molecules 410 parts per million has risen considerably from
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0.028 percent of atmospheric molecules 280 parts per million before about 1870 when an increase in industrialization meant burning more significant amounts of fossil fuels
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you can see here in the past 800 000 years the highest amount of atmospheric carbon dioxide was 300 parts per million until that recent dramatic increase in carbon dioxide
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if we just look at carbon dioxide levels since 1750 which is when most historians place the beginning of the industrial revolution you can see that it is about 1870 when emissions of carbon dioxide the blue line starts to become more significant
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we can calculate the change in the amount of carbon dioxide molecules per unit volume of air using the ideal gas law which gives us 2.55 times 10 to the 22 air molecules in a single liter of air at 15 degrees celsius the current average earth temperature and 2.56 times 10 to the 22 air molecules per liter at 14 degrees celsius the pre-1870 average temperature 0.028 percent of that is 0.768 times 10 to the 19 molecules of carbon dioxide per liter of air increasing to 1.05
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times 10 to the 19 molecules of carbon dioxide per liter a 1.5 fold increase over the past 150 years
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these are tremendously large numbers but they are still a very small percentage of the total air molecules why does such a small percent of carbon dioxide have such a large effect on temperature the answer to that must include looking into the importance of water vapor as a greenhouse gas which we will do a little bit later in the video first it will be very helpful to get an idea of what heat is and how it is related to temperature there are three categories of heat
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all of which are important to global warming the first type of heat is conduction when two particles collide energy is transferred from the fast-moving particle to the slow-moving particle since we measure temperature as the average kinetic energy the transfer of kinetic energy is a change in temperature this gives us the basis for heat of flow of kinetic energy from hot to cold how does this happen let's look at the result of two blocks in contact that
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are initially at different temperatures heat is transferred from the warmer to the cooler block
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let's look at what is occurring between the two blocks
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through conduction there is a constant kinetic energy transfer through colliding particles bringing the two blocks to thermal equilibrium in other words they both reach the same temperature
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very importantly there is also radiant heat energy transfer through electromagnetic radiation when light is absorbed its energy is transferred to the absorbing body increasing the kinetic energy of its atoms remember that temperature is defined as the average kinetic energy of whatever is being measured and so an increase in kinetic energy is an increase in temperature
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and equally important the third type of heat is convection which is heat transfer through the movement of large aggregates of molecules through a fluid for example a large aggregate of air molecules heated through conduction by a warmer earth will expand and transfer that increase in kinetic energy due to buoyancy while air with a lower kinetic energy in other words a lower temperature will move to take its place
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now we have more tools to understand the role of carbon dioxide in the earth's warming when specific frequencies of infrared hit carbon dioxide that energy is absorbed increasing carbon dioxide's kinetic energy however carbon dioxide also generates infrared radiation while these two events are independent of each other together they form the basis for the greenhouse effect so let's see how carbon dioxide is able to absorb infrared
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and that will also allow us to understand how carbon dioxide generates infrared both absorption and emission of infrared by greenhouse gases is what creates the greenhouse effect understanding carbon dioxide's interaction with infrared begins with looking at the structure of carbon dioxide shown here with bonds between the oxygens and carbon portrayed as springs the springs illustrate that atoms in a molecule vibrate constantly which is a manifestation of its kinetic energy
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the various ways that carbon dioxide atoms vibrate are called vibrational modes and this forms the basis for carbon dioxide's ability to absorb as well as generate infrared light let's take a closer look at that the electronegativity values assigned to oxygen and carbon tell us that the oxygens more strongly attract electrons than carbon however due to the molecule being linear the two opposing bond polarities effectively cancel each other and linear carbon dioxide is
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nonpolar in other words it has no concentration of charge which is what polarity refers to however any asymmetric vibration of the molecule such as shown here will create a temporary dipole so now there is a concentration of negative charge at the oxygens and positive charge at the carbon
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this vibrational mode results in a moving charge allowing it to interact with infrared and any asymmetric vibrations in carbon dioxide will generate a dipole this allows for a range of frequencies of atomic vibration that can match frequencies of infrared energy being emitted by the earth so we are looking at two types of frequency that of infrared and that of the vibrations occurring in carbon dioxide let's look more closely at infrared light
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and then we can see more clearly why there is an interaction between carbon dioxide and infrared
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the frequencies of infrared and any electromagnetic wave is the measure of how fast their electric and magnetic fields oscillate
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if those two frequencies match that of infrared end of carbon dioxide then the carbon dioxide molecule will absorb infrared energy and this is the essential point carbon dioxide vibrational frequencies are in phase with a range of infrared frequencies emitted by the earth and so carbon dioxide can absorb that energy and just as important it is those vibrational frequencies of carbon dioxide that enable co2 to generate infrared let's go back to carbon dioxide
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absorbing infrared here we can see the earth's emitted infrared energy which would all be lost to space without greenhouse gases absorbing infrared and these are the specific infrared frequencies that are absorbed by carbon dioxide preventing those energies from being directly lost to space
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carbon dioxide absorbing infrared energy is a way that emitted infrared energy from the earth's surface gets redistributed throughout the lower atmosphere
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and here i would like to address a common misconception which is that carbon dioxide absorbing infrared energy directly increases atmospheric temperature that is not the case any change in kinetic energy is momentary it is the redistribution of infrared energy toward a higher altitude that we need to investigate this illustration shows that energy getting bounced around and that emission of infrared can occur in any direction meaning there are two net results of
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the infrared bouncing around among greenhouse gases and that results relative to the earth
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one is that infrared is emitted back toward the earth and absorbed by the earth starting the cycle anew or infrared energy is emitted toward space and ultimately lost to space if the emitting greenhouse gas is high enough in the atmosphere let's take a much closer look at this key point
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to understand the consequences of infrared energy being lost to space we need to shift from our current micro perspective to a macro perspective first by looking at relevant features of the atmosphere and then by exploring more in depth the larger earth sun energy interaction the lower part of the atmosphere is called the troposphere and this is where everything we are discussing takes place to get you oriented mount everest at nine kilometers is here
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and most commercial jets fly at about 10 to 11 kilometers let's add greenhouse gases to the atmosphere the bent line represents the minimum of three atoms that any greenhouse gas has
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the distribution of greenhouse gases is the same as oxygen and nitrogen and any other atmospheric gas which is that it is denser at the earth's surface and gradually expands as height increases there is much more variability with water vapor and we will get to that a bit later what we will see here is a macro view of what was seen previously in the particle illustration so the infrared here represented by a red line released at the earth's surface
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bounces around the various greenhouse gases until it gets to an atmospheric height where the density of greenhouse gases is low enough such that any upward release of infrared is largely lost to space this atmospheric height where the earth loses on infrared energy is called the emission height which we will come back to through much of the video this emission height of 5.4 kilometers is approximately the pre-1870 emission height
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a baseline that we will use to understand the mechanism resulting in the increase in global temperature of approximately one degree celsius we are now experiencing about 150 years later
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so we are starting with the atmosphere before the point at which the burning of fossil fuels by increasing industrialization started to release enough carbon dioxide to begin affecting global temperature let's add a horizontal axis for temperature the height we are interested in occurs in the troposphere which is where all our weather occurs in looking at the troposphere's temperature gradient from the earth's surface we see that temperature decreases as atmospheric height
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increases think of climbing up a mountain the air gets colder the higher you get
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this decrease in temperature corresponding to atmospheric height is very significant to global warming as we will see in the remainder of the video it occurs due to expanding atmospheric gases losing kinetic energy the amount of cooling called the lapse rate is about 6 degrees celsius for every kilometer of altitude
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note the temperature at the emission height it is 255 kelvin negative 18 degrees celsius if you remember earlier in the video we calculated 255 kelvin as the surface temperature that would emit an amount of outgoing energy that would equal the sun's incoming absorbed energy however that is the surface of an earth without an atmosphere but we not only have an atmosphere we have one with gases that absorb and release that outgoing infrared energy
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the presence of greenhouse gases pushed the surface of where infrared energy is lost to space to about five and a half kilometers above the earth's surface and this is where the temperature averages 255 kelvin or negative 18 celsius so when we talk about the earth's surface in the earth energy balance equation we are referring to where the infrared energy is lost where outgoing infrared energy is equal to absorbed solar energy we are now getting closer to global warming
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the significance of the rise of industry is that the burning of fossil fuels is the driver of industrialization burning fossil fuels produces carbon dioxide and so the amount of carbon dioxide in the atmosphere began to increase so how does adding more carbon dioxide warm the earth even more let's first see the temperature we are starting at in the late 1800s at that time the average global temperature was about 287 kelvin or 14 degrees celsius and that
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matches the known average change in temperature of 6 degrees celsius per kilometer of altitude the lapse rate referred to earlier as we come back to the earth from the 5.4 kilometer emission height
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let's see how added carbon dioxide changes the conditions that give us the emission height this represents anything that is burning fossil fuels putting more carbon dioxide into the atmosphere added carbon dioxide disperses throughout the atmosphere and if we look at just the vertical distribution of added carbon dioxide we see that the spreading of more carbon dioxide includes more carbon dioxide at high altitudes the result is an increase in emission height
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the infrared has to get to a higher altitude before it is lost to space
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let's head back the temperature axis showing the 255 kelvin at the initial emission height the point here is to understand that as emission height increases due to added carbon dioxide which happens gradually over time that makes the temperature at which infrared energy is lost to space lower than it was before less than 255 kelvin due to that lapse rate
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so increasing emission height due to added carbon dioxide means less infrared energy will be lost to space why is that the case why would a lower temperature emission height decrease the amount of lost radiant energy going back to the earth energy balance equation tells us that emitted radiant energy is proportional to temperature at 255 kelvin the amount of outgoing infrared energy is equal to the amount of incoming solar energy absorbed
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however if the emission temperature is lowered less energy is lost from the earth and the amount of outgoing energy is now less than the amount of incoming energy this is why global warming occurs
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there is no longer a balance between incoming and outgoing energy we are changing outgoing energy added carbon dioxide raises the emission height which decreases the temperature at which emission occurs there is a decrease in outgoing energy with more energy coming in than going out more solar energy stays within the earth atmosphere system and the earth warms up through that excess energy shown by the double arrow and this is called radiative forcing an important term to remember
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radiative forcing is the imbalance between outgoing and incoming energy here representing the solar energy the earth needs to retain in order to re-establish the earth energy balance
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but the earth warms only to the point where that emission height gets warmed back to 255 kelvin restoring that energy equilibrium the earth energy balance if you think about it the earth would have to stop warming at that point because if it kept warming past that equilibrium then the earth's energy output would be greater than its input meaning it would immediately cool down from excess lost energy so the equilibrium is maintained the earth seeks a temperature where its
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energy output balances solar input the amount of radiative forcing that has occurred from increased carbon dioxide levels since the late 1800s greater than 1.8 watts per square meter results in an increased emission height of close to 100 meters so the earth retains that energy difference the radiative forcing and warms the earth until that lower temperature of the higher emission height is back to 255 kelvin and that means an increase in temperature at the earth's surface
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using the six kelvin per kilometer lapse rate a 0.6 kelvin warming at the surface would occur bringing the surface temperature to 287.6 kelvin however we know that the earth's surface has warmed more than that about one kelvin one degrees celsius the current global average is 288 kelvin not 287.6 kelvin how can we account for this gap remember we have only accounted for warming due to increased carbon dioxide to account for that temperature gap we need to address the effect of
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water vapor as a greenhouse gas our story would be woefully incomplete without discussing water vapor as a molecule water's mechanism for warming the earth is the same as carbon dioxide but there are important differences unlike carbon dioxide water has a permanently bent shape which means it has a permanent dipole rather than those momentary dipoles produced through carbon dioxide's vibrational motion it is also a strong dipole having a large distribution of charge
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the presence of concentrated charge within a molecule allows it to absorb and emit infrared so having a large permanent dipole a permanent concentration of charge makes water much more efficient than carbon dioxide at absorbing infrared energy a comparison of the infrared absorption spectrum of carbon dioxide and water vapor shows that water vapor absorbs a much wider range of infrared than carbon dioxide however while there is no limit to how much carbon
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dioxide can mix with atmospheric gases water vapor concentration is between zero percent and four percent of atmospheric gases depending on air temperature and other conditions water vapor above its maximum will condense and no longer be a gas a warmer atmosphere can hold more water vapor which in turn warms the atmosphere even more and so a positive feedback exists between water vapor and atmospheric temperature as well as between water vapor and carbon dioxide
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let's see how that works starting from a baseline of pre-1870 temperature and water vapor nothing would happen here those two arrows would remain constant without an initial increase in temperature where did that initial temperature increase come from yes you were right it came from the carbon dioxide added by the rise of industrialization the burning of fossil fuels which raised atmospheric temperature which allowed more water vapor to exist in the atmosphere
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which raised atmospheric temperature which allowed more water vapor to exist in the atmosphere and the feedback continues until atmospheric temperature is high enough so that the earth energy balance is maintained however the constant temperature increase due to the constant increase in atmospheric carbon dioxide makes that water vapor temperature feedback loop occur with larger increases than would otherwise happen
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without that constant adding of carbon dioxide into the atmosphere of the last 150 years
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we can now account for most of the missing temperature increase which is the result of more water vapor raising the emission height even more
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you may have noticed i said that water accounts for most of the missing temperature increase of the last 150 years we have to also include all the other greenhouse gases here which in the last few decades have rapidly become a bigger part of the rising global temperature picture the oil and gas industry emits a substantial amount of methane via leaks from shoddy processing and transporting infrastructure as well as from fracking more cattle produces more methane
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and our high-tech way of life produces more of the many other greenhouse gases we are increasing methane and those other greenhouse gases even more dramatically than we are increasing carbon dioxide but luckily for us they are less potent than carbon dioxide so overall they matter somewhat less than carbon dioxide but are still very much of a problem so far we have created a picture in which increased presence of greenhouse gases continually reduce outgoing energy producing
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constant increments of radiative forcing that is then compensated by rising global temperature
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up to this point we have talked about the loss of absorbed solar energy through the emission of infrared energy so what specifically explains the increase in global temperature which is an increase in global kinetic energy well as you may have guessed it all comes from the sun not all of the absorbed solar energy is lost as infrared a significant amount of that energy is either kept by land and c as higher temperature however if any colder air molecules collide with that
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warmer surface then kinetic energy is transferred and air molecules close to the surface increase in temperature and this is heat transfer via conduction and now convection comes into play here as conduction warms air molecules at the surface that warmer air expands and becomes less dense which then makes it buoyant and so it rises and warms the upper troposphere while cooler air moves to take its place this is heat convection though constant movement of large aggregates of
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air molecules moving energy around the atmosphere far beyond what could occur through air molecular collisions alone so a higher kinetic energy at the earth's surface from absorbed solar energy results in one higher earth's surface temperature both land and sea and two kinetic energy transferred to air molecules along with convection results in higher air temperature the higher global temperature needed to maintain this earth energy balance originates with the sun's
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radiant energy absorbed by the earth the amount of infrared lost by the earth dictates the amount of solar energy retained by the earth to maintain that balance the earth energy equilibrium we are now in a position to answer this very important question how can such a proportionately small amount of carbon dioxide have such a large impact one a single carbon dioxide molecule absorbs infrared releases infrared or transfers kinetic energy about one million times per second
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so carbon dioxide molecules are always available to absorb outgoing infrared from the earth's surface as well as release infrared at the emission height in extremely small time frames making small amounts of carbon dioxide have a very large impact and therefore small changes in the amount of carbon dioxide as well as other greenhouse gases have a large impact however the change in the last 150 years has been quite large as can be seen here in the blue emissions line
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and also carbon dioxide makes water vapor already a potent greenhouse gas and even more potent greenhouse gas by increasing water vapor's feedback mechanism of increasing atmospheric water vapor and increasing global temperature so small increases in carbon dioxide have large consequences for global warming as do all other greenhouse gases
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a couple more important items and then we will look at a summary slide why is the increase up to now one degree celsius considered such a significant temperature change there are many answers to this question all of which involve changing the climate among those are that as previously stated a higher temperature atmosphere can hold more water vapor a single gram of liquid water requires 2 267 joules of energy to evaporate that means
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a single gram of water vapor contains 2267 more joules than a gram of liquid water
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so an extra 2267 joules is added to the atmosphere for every one gram of added water vapor when one gram of water vapor condenses it releases 2267 joules of energy with more water vapor in the air storms will condense more water which leads to heavier rain as well as that greater energy release translating to greater hardship loss and destruction from atmospheric events a second consideration is that higher temperature means increasing rates of melting polar ice
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and therefore higher ocean levels resulting in large-scale environmental and economic disruption along the world's coasts shrinking ice and snow also decreases the earth's albedo in other words it decreases the amount of reflected solar energy which results in increasing global temperature through greater absorbed solar energy
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levels of greenhouse gases have increased dramatically in the last few decades which makes addressing the problem of global warming all the more urgent if greenhouse gases are not reduced a temperature rise of three or four degrees celsius will lead to devastation with massive habitat destruction and massive economic destabilization last question why don't oxygen and nitrogen which
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make up 99 of dry air interact with infrared it is because they each only have two atoms and a single vibrational mode that is not in phase with any emitted infrared and there is no concentration of charge no polarity and so there is no interaction with infrared in summary the earth's outgoing energy and sun's incoming energy seek to be in balance the presence of greenhouse gases decrease the earth's outgoing energy by decreasing the temperature at which infrared is released
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atmospheric temperature will then increase so that earth's outgoing energy can match incoming solar energy greenhouse gases absorb and release infrared because they match infrared frequencies
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increasing global temperatures results from retaining absorbed solar energy in the form of higher kinetic energy in the land oceans and the atmosphere and small changes in the amount of greenhouse gases have a large impact on global temperature and so the intention of this video is to help you understand that urgency and the hope that people will find ways to reduce their reliance on anything that produces carbon dioxide methane and other greenhouse gases thanks for
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listening don't hesitate to put any questions or comments in the comments section below
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