 Greetings and welcome to the Introduction to Astronomy. In this lecture, we are going to talk about climate change and look at how Earth has changed over the billions of years it has been around. So, let's go ahead. We talked previously about the atmosphere. Let's look a little bit about some of those changes. So, what kind of changes do we get to the Earth's atmosphere? Well, there are two types. We can have natural changes and we can have man-made changes. And both of these do occur. We have volcanic activity does spew material into the atmosphere, changing it and, in fact, how our atmosphere changed from that original composition to what it has currently. Life, just by existing, has created oxygen in the atmosphere. And, of course, we have man-made things like pollution and greenhouse gases, which also affect our atmosphere. Now, one of the important things to talk about here is the greenhouse effect. So, the greenhouse effect, in the greenhouse effect, sunlight passes through Earth's atmosphere and heats the ground. So, the surface will heat, the atmosphere will heat, and the Earth will radiate that temperature away. Now, sunlight comes in in the visible part of the spectrum, which penetrates the atmosphere. The Earth radiates infrared light because it is a lower temperature. Remember from previous lectures how a black body works. It absorbs all of the radiation coming in, and it emits radiation depending only on its temperature. Since the Earth is cool, it emits infrared. And some of this infrared is then trapped by gases in the atmosphere. We know of carbon dioxide, water, methane, and others. So, depending on exactly what is here, the sunlight comes in. Even some sunlight will get through the clouds, and then the surface radiates that, which traps the heat in there. Some sunlight is reflected away, depending on the amount of cloud cover. And we can notice this through the greenhouse effect on the morning. Sorry, in the morning. So, if you get up in the morning early and it's really cold outside and you look up, you'll probably see that it's nice and clear. And that's because there were no clouds which have water vapor, which is an extremely efficient greenhouse gas to trap in the heat. When you wake up on that hot, stuffy morning where it's very warm, then you can look up and it's usually cloudy. And that's because the clouds are there keeping that extra heat in and keeping Earth warmer. So, what about the greenhouse effect? Well, is it a bad thing? Actually, not really. It warms the Earth by about 30 degrees Celsius or 86 degrees Fahrenheit. So, think of what our temperatures would be like without that. It would rarely get above freezing and life would not be possible. Everything would be frozen, except maybe the equatorial regions would be completely frozen. And we do see the greenhouse effect occurring on other planets as well when we talk about Venus we will see where the greenhouse effect can run away. So, what is the problem when we talk about climate change? Well, measurements show that the Earth has warmed about one degree Celsius over 150 years. Now, while that may not sound like a lot, it is a pretty big increase for just 150 years. Now, the question is, what is causing this increase? Is it something natural? As we've talked about previously, the Earth does change. So, the temperatures and properties of the Earth are not always the same. Is it man-made? Is it through things that we have done? Or is it some combination of the two? And here we see the graph showing from 1880 temperatures and how they have increased really pretty drastically, especially over the last few decades. So, temperatures have increased quite a bit there. So, what do we believe is happening here? Well, what is the consensus? First of all, what does a consensus mean? Well, it's the general agreement that this is the current best explanation for something. That does change. A consensus can change. So, just to be fair, a scientific consensus was once that Earth was the center of the universe. There was a point where you could have figured out that, you know, 99% of the scientists would have said the Earth was the center of the universe, and everything moves around it. So, with new evidence, things do change. But the consensus is that this, the best explanation is that the man-made causes are dominant here. So, we have carbon dioxide emission from fossil fuels. We have methane emission from livestock. So, what do we mean when we look at a model of this? What do the models show? Well, most models predict a couple of degrees rise over the next hundred years. The question is how accurate are these models? Remember that a model is a simplification of the real world. We can't model the Earth precisely. It's just not possible to model such a complex system. So, any models do have to make simplifications and assumptions. And we can't tell you how accurate they are because they're based on future predictions. If we could wait a couple hundred years and see what happens, then we could judge how accurate the models were. But the Earth's atmosphere is very complex. So, this is not something like predicting an eclipse. We can tell you when the next eclipse will occur, and we can tell you hundreds of years from now when eclipses will occur down to the second as to when they will start and end. We cannot tell you with the same accuracy, even close to that, what the average temperature of Earth will be a hundred years from now. So, is this a hoax? Sometimes you hear that there is a hoax, and that's really doubtful. Certainly scientists do have biases, like everyone else, where we see what we want to see. If something agrees with our beliefs, then we tend to agree with that, we tend to assume that, and if it doesn't, then we tend to look for other explanations. And the scientists can only go by the data that they have. So, how accurate are these measurements? Well, that's a good question, and observations have changed over those 150 years. Certainly, technology has improved, and we have better ways of measuring the temperatures now than we did 150 years ago. So, how do these measurements compare to those made in the 1800s? What adjustments have been made to the data? Now, there's nothing wrong with making adjustments to the data. You tend to do this, you'll make calibrations, and you may have to adjust the data, and that is a perfectly legitimate part of science. However, that does have to be clear as to what adjustments are being made, and the original data should always be available, because maybe those adjustments were off, and maybe you have to readjust, and it may find that things were not as bad as we thought, or it may find that things are worse than we thought. So, the original data, it is always important to have that original data there. Now, how does this tie into politics? So, we do get a lot of politics in climate change, and in many cases, the politics has really began to overwhelm the scientific aspects. We get things where people are called deniers of climate change. Well, there's a difference between being called a denier or a skeptic. So, what we're looking at, these two things can be in the same person, and they can have very different connotations. A denier is something we talk about denying science. And could you be a skeptic that just says that you are making questions about something, but not actually denying it? So, to be fair, it's not a bad thing to be skeptical in science. We should question everything and challenge all of these models, and push them to be the best that they can be. Obviously, we don't also want to deny obvious facts. So, we've talked previously about, you know, whether the earth is round or not. Well, that has now been proven very well. So, there are some things that are very, very well established, and there are other things that are still in process, and we are still trying to better understand them. But to be fair again, someone who expressed reservations about the climate studies is not necessarily denying science. Now, don't get me wrong, there are people who are denying science who are deniers of climate change. But there are also those who are skeptical and could be considered trying to push this to better understand. And those would be people who are open to changing on either side, based on new data. So, the whole idea is to push things to their limit. What about petroleum? Well, a lot of the climate change is based on carbon emissions, and that is because of petroleum. How much is left? Well, depending on when you look at it, if you go back to books from 30, 40 years ago, it said we would run out by now, and of course we found more. But there is a limited resource. So, we will likely uncover new petroleum resources, but can we go for another 50, 100, or 200-year supply? Eventually, no matter what it is, even if it's 500 years, eventually those supplies will run out and new energy sources are needed. There is simply no way that petroleum can replenish itself, and we will eventually run out of ways to be able to get this. So, we also use petroleum in other ways than just energy. The other thing is that we will not find any resources of this in the solar system other than on Earth. You can imagine, perhaps, finding other sources of energy. Solar energy would be one, nuclear energy would be another. It's quite possible that you could find deposits of things like uranium elsewhere in the solar system. However, petroleum is confined to Earth being a fossil fuel, and Earth being the only planet that has had life. So, what do we do when we think about climate change? Well, be skeptical. Always skeptical, but not just in general, but skeptical towards both sides. Make sure that they can convince you as to what they are saying. So, you always want to look at the scientific side. When you start talking emotional, that gets out of the topic of science. So, when it starts to get overly emotional or appealing to your emotional side, again, regardless of what side is doing this, it is not a... You're getting out of the science. The science really needs to take the emotions out of it. That's when you're putting it into politics. And it's not necessarily that it's bad, it's just not science. So, when you're getting to the emotional, that may appeal to how you want to handle things in a political debate. But when we're looking at the scientific side, we want to look at the basic facts and understand how the studies are done and what modifications have been made and what the models are showing and what the variations are in the models. Again, we also want to look at the background of the person. You might want to give more credit to a scientist than a politician or an actor. What are their interests? If they're working in the oil industry? Again, they may have a bias toward not thinking that climate change is man-made. What if they're working in alternative fuels? Well, they may have the opposite bias. So, it is a good idea to look at the background. Even if it is a scientist, we have to look at their interests. And it's not necessary that they are purposefully doing this. But again, there are always things that bias us internally. Sometimes we don't even notice these. Overall, again, think and reason for yourself. Don't just accept things blindly, but don't just reject things blindly or emotionally either. So, let's go ahead and finish up with our summary. And what we've looked at is, yes, the Earth's atmosphere and climate have changed in the past and will change in the future regardless of what we do. The greenhouse effect has warmed Earth, making life possible here. Now, we've seen that over the past 150 years, temperatures have risen. And again, the question is, how much of it is man-made? And there's a big difference as to what we can do depending on how much. So, I specified before, is there a man-made climate change? Well, there's probably some combination. Maybe we're responsible some and maybe some is natural. And the question as to how much we can do depends on where that percentage lies. If we are 90% responsible, which is the current consensus, then we could probably do a lot to affect this. If we are 10% responsible, there's probably a lot less that we can do that will actually be able to change anything here. So that concludes this 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.