 Greetings and welcome to the Introduction to Astronomy. In this video we are going to talk about the subject of climate change and what kind of changes have gone on here in the Earth and what some of those causes might be. As something you've probably heard of it can be a relatively controversial topic so let's see a little bit about the basic information that we know that goes into this. We'll start off looking at some of the basic changes that can occur to the Earth's atmosphere. These changes can be divided into two parts. They can be natural changes or they can be man-made changes. So there are natural changes to the Earth's atmosphere that occur all the time. Volcanic activity would be one example that spews material into the Earth's atmosphere and what can actually change the composition of the Earth's atmosphere. This may be where a lot of the original Earth's atmosphere came from. Things like life can also impact the Earth's atmosphere by putting oxygen in it. The Earth is the only planet, only object that we know of that has oxygen in its atmosphere and that is all caused by life that puts the oxygen in the atmosphere. Everything else, every other object we look at has no free oxygen in the atmosphere. So both of these can cause some changes to the climate. Volcanic activity can put dust into the atmosphere so massive eruptions, if you hear about things like a super volcano, very massive eruption can actually increase the dust content of the atmosphere blocking out sunlight and cooling off the Earth. Now there are also man-made changes, things like pollution, and greenhouse gases that can have an effect on the Earth. Greenhouse gases, carbon dioxide is the one that you hear of all the time, but that is just one example. We also have things like methane and water vapor. These are all very good at absorbing ultraviolet, I'm sorry, at absorbing infrared radiation. And if you recall, we put telescopes on high mountains to get them above the water vapor to allow them to be able to see the infrared portion of the spectrum. So the greenhouse effect is what this all comes down to, so let's look a little bit at how that works. When the greenhouse effect occurs, the sunlight passes through the Earth's atmosphere and heats up the surface of the Earth. So you have incoming radiation from the Sun and a certain percentage of that is then absorbed by the Earth's surface and that is then re-radiated back out. Now the Earth does not re-radiate it in the visible part of the spectrum, it re-radiates it in the infrared. Remember, it has a lower temperature than the Sun, Sun being nearly 6,000 degrees and the Earth being just a couple hundred degrees in terms of Kelvin's. So it is radiating off in the infrared, so some of that material heads off into space and that infrared radiation can be trapped by gases in the atmosphere. Things that we looked at before, carbon dioxide, water and methane are three very good examples of things that can absorb that infrared radiation and keep it from escaping. Now you can notice a little bit about how the greenhouse effect works and especially the impact of water vapor by just looking at what you're used to from looking at very cold nights or very warm nights. If you get a cold winter night, you'll look out and you can see the stars, it's very clear. That means that a lot of this infrared radiation is able to escape back out into space and cools off the Earth. When you get a very cloudy night, there's a lot more clouds up here and a lot more of that radiation is trapped in keeping the atmosphere significantly warmer. So that's kind of a part of the greenhouse effect that you're used to. You may also be used to it in terms of a car on a hot day. When the visible light comes in, heats up the, heats up the atmosphere, heats up the Earth, heats up the car and then is re-radiated and trapped in there as infrared radiation making the car very, very hot. Now is the greenhouse effect bad? And we want to look at that and really, no it's not. It's very important for the Earth. In fact, it warms the Earth by about 30 degrees Celsius or about 54 degrees Fahrenheit. Now, why is that important? Well, the average temperature is about 59 degrees Fahrenheit. So you can imagine if the greenhouse effect did not exist at all, if there was no such thing, then the average temperature on the Earth would be well below freezing. It would be five degrees Fahrenheit way below freezing, meaning that large chunks of the Earth and most of it, the average temperature would be well below freezing and it would be not be possible for life. So life would probably never have formed on Earth if the greenhouse effect did not exist. So we do need some greenhouse effect. Obviously, we don't want to turn into a Venus that has too much of a greenhouse effect and has had what we call the runaway greenhouse effect where temperatures are very, very hot, hot enough to melt lead. So let's look at what the problem is here that we want to discuss. And what it is, is that measurements have shown that the Earth has warmed by about one degree Celsius over the past 150 years. So that's what's showing here, setting out a mean temperature here, average at zero. And here, back in the late 1800s, early 1900s, we were a little bit below that average, but you can see how the temperature has definitely climbed over that time period. So there can be a couple things that could be causing this rise. It could be, as we've said, there are natural effects and there are manmade processes that occur. There are natural things that will change the temperature on the Earth. Certainly the Earth's temperature has varied in the past, long before we were putting greenhouse gases into the atmosphere. But it is very suggestive because we do see this temperature rise occurring around the same time period that we have been really expanding use of fossil fuels and therefore greenhouse gases. Now, if you look at the models, right now they show that deforestation would be a responsible for 25% of this and greenhouse gases would be responsible for about 75%. And it could also be some kind of combination of the two. So could it be 50% and 50% or could it be 10% and 90%? So really, the question is not that the Earth is warming that is definitely seen in the data, so not really something that you can significantly argue, but it's what the reasoning for it is and that is the difficulty is trying to determine what the reasoning for the rise in temperatures is. Is it due to fossil fuels or is it a natural rising from a cooler temperature a hundred and so hundred hundred and fifty years ago? So is it just a natural rise or is it associated with man-made procedures? And that is usually where the disagreement is. Our natural processes 1% and man-made processes 99% then there's a lot we can do to change this by eliminating it. If it happens to be the other way around in natural processes or 99% and man-made processes are 1% then even eliminating our fossil fuel use is not going to make any significant change in the overall temperature changes. So let's look a little bit about what do we mean? You often hear the scientific consensus and I want to go over a little bit about what that means. It is certainly what we call a general agreement among scientists as to what the current explanation is. So this is currently what we assume. So what we see the scientific consensus is that general relativity is the best explanation of gravity we have right now. That can change with time. So just because something is the scientific consensus today does not mean it will be tomorrow. And if we recall there was once a scientific consensus that nearly all scientists would have agreed just a matter of several hundred years ago, five, six hundred years ago, that the Earth was the center of the universe. So that was once the scientific consensus with some new evidence and observations by Galileo and some theories by Copernicus, we were able to change that and now we know that the Earth is not the center of the universe. The current scientific consensus is that the man-made causes dominate the climate, the changes to the climate. And that includes things like carbon dioxide from the burning of fossil fuels and methane emission from livestock. So both of those are very important in terms of putting the excess concentrations of those greenhouse gases into the atmosphere. So what do our models show at this point? Well, a model predicts that a couple of degrees rise over the next hundred years. The question is of course how accurate are they? And various models, different models will show different amounts of rise from smaller amounts to larger amounts. So they're based on future predictions. They are very definitely scientific. They are making predictions that we can test. But in some cases, if we're going to see what the temperature is like a hundred years from now, then we have to wait 100 years to see if they were correct. If we want to see what the temperature is like 20 years from now, we have to wait 20 years to find out if they are correct. So we do find, however, that when we talk about comparing climate models and the weather, well, we can't even predict the weather. How can we predict what will happen 100 years from now? It is actually a lot easier to model the long-term climate variations than it is short-term weather changes. We can smooth out a lot of the variables and it's easier to get a better model of the long-term variations. And they seem to match at least going backwards with observations that we can try to estimate as to what the climate on the Earth was like. So it is easier to make those models, but still we need to know what they are going to predict in the future. And there are a lot of different models that predict a lot of different things. So the Earth's atmosphere is a complex system and there are a lot of variables that go into the model. So we have to put in all these different variables and we can adjust those to try to fit the observations that we see. So as we get more data, we're able to better refine those variables. But what I want to emphasize is that this is not like predicting an eclipse. We can predict an eclipse and I can tell you that an eclipse will occur on a certain date 100 years from now and we are absolutely certain that that will occur. So that will definitely occur. We can model that very precisely. Whereas predicting what the climate will be like 100 years from now, there are a lot more variables involved. So we can make some estimates, we can make some guesses and some educated guesses and try to determine that. But it is nowhere near like trying to, like predicting an eclipse. I can tell you that there will be an eclipse across the eastern part of the United States on April the 8th of 2024. And there is no doubt about that. We predicted, we knew in the eclipse of 2017, was going to occur. So we can, those are very much, the determining orbits in that is much more settled than something like the climate. So one of the other things that you hear sometimes, you know, is this all a big hoax? I really will say that's very doubtful and probably absolutely not. You would not be able to get that in the scientific community. So if there were that many, if there were people, it would have to be a complete hoax with everybody involved, some great big conspiracy, trying to convince everyone that yes, the climate change is real and that it is caused by humans. Now, we do have to acknowledge that scientists do have biases like everyone else. We see things that we want to see and you can only go on the data that you actually have. So we have to look at how accurate are the measurements? How do the measurements made today compare with those made 150 years ago? And so those in the late 1800s, you know, instruments and technology have changed. So how do we compare them and how do we make adjustments to that data to be able to compare those measurements? And could there be any adjustments that were needed? Certainly making adjustments to the data are not a bad thing. Although of course, you want to hold on to your original data to make sure that anyone else who wants to study it can see what changes have been made. And maybe something new will come up later and you find out that the adjustments you made, you made too big of an adjustment or you didn't make a big enough adjustment and you want to go back to that original raw data because that is what was observed. But as I mentioned up here, you know, scientists do have biases. We are going to throw out observations that don't seem to fit with our current models. That doesn't mean if they're all over the if they're if everything is pointing a different direction. But when you start to see a few random points that just don't seem to fit in, they do have a tendency to get removed. And that again, is not a bad thing. There are glitches and observations and scientists will always edit their data to try to get the best best fit for their models. So what has really happened now is that this has become the politics become a political issue more than a scientific issue. The scientific issue is determining, you know, what has changed, what the temperature is doing and how we can model that over time. The politics are now completely completely different and really overwhelm in many cases the scientific aspect of the issue. Now, one of the things that you hear, you know, you can have a denier or a skeptic. Sometimes they're used interchangeably. Sometimes it is used by one side in the political argument against another. So those who favor or believe in a man made climate change will call those who do not agree with them a denier. Those who disagree with climate change may call themselves skeptics. And there are very different connotations with either of those. You know, if you are denying something, it has a very negative connotation, whereas a skeptic is very important for science. So in science, it's not a thing, good thing to be, it's not a bad thing to be skeptical. However, it is also not a good thing to deny obvious facts. The earth is round. We have watched the temperatures rise. We know that that is occurring. We just, what we don't know as well is why that has occurred. But I want to emphasize here one big thing is that just because someone expresses reservations about climate studies, it does not mean that they are denying science. Certainly, there are some people who will just deny everything to do with climate change. And that is not correct. However, just having reservations or expressing that is all part of the scientific method. And that is something we want to encourage. We want to constantly push our models of the climate to be able to make them better and better. Now, one of the things that is part of that is the petroleum resources. Now, we see all sorts of various numbers. You know, what is the limited resource? Do we have a 50 year supply, 100, 200 years? Classes back in the 1980s said that we'd be out of petroleum by 2020, which doesn't seem like it is going to happen. But one thing that is important is that it is a limited resource. We will probably uncover new resources. We will probably also be able to access sources that were previously inaccessible. So things that were not considered part of the petroleum resources 30 or 30 years ago are now part of those and things that we can actually use. However, eventually supplies will run out. There is only a limited source there. We do need new energy sources and petroleum is not just used for energy. It's used in a lot of other things as well. And it's good to point out that there is no petroleum. It is based on, we call it fossil fuel because it is based on living organisms. So it is dead organisms from millions of years ago. We are not going to find that any place else other than here on earth. So we may find a supply of uranium elsewhere in the solar system. We are not going to find petroleum supplies elsewhere. So coming towards the end here, what we want you to think, what I'd like you to think about climate change is do be skeptical, but towards both sides. Look at the scientific side. Don't look at the emotion as to, oh, it's all a big hoax or it's all we're destroying the planet. You don't want to look at the, when you look at the emotional side, you're losing the science side. Look at the science. And when you're looking at what somebody is saying about it, you know, who are they? So who is the person discussing the topic? If it is, is it a scientist? Is it a politician? Is it an actor? Is it someone else? So what is their background that would be important? Hopefully you give a scientist more credit than you would give an actor or a politician because they should have the scientific background to be able to reason what is going on. What are their interests? Are they working in the oil industry? So certainly a scientist working in the oil industry might have a bias that to discourage man made climate change to say that it is not real. What if they're working in the alternative fuel industry in solar power or other green technologies, then they might have a reason to be able to push the other direction and say that, well, yes, man made climate change is important. So we have to look at who they are and what kind of interest they might have because that makes a big difference as to what you're as to how you're what kind of weight you're going to put on their arguments. And you want to look at it through that filter. How are what are their interests? Overall, what I tell you to do is to think and reason for yourself. Look at what they're saying. Look at who they're saying and go look at the numbers for themselves. Look at what has been done in terms of calculations and make your own decisions. So let's finish up here with the last section here just to summarize. First of all, yes, the earth's atmosphere has changed in the past and will change again in the future. The greenhouse effect has warmed the earth, making life possible. No life without the greenhouse effect. We do note that the over the last hundred and fifty years the earth's temperature has risen. And we can say that man-made climate change is certainly something controversial and requires careful consideration. So that concludes our lecture on climate change. We'll be back again next time for another topic in astronomy. So until then, have a great day everyone and I will see you in class.