Ep. 653: Climate Change: Looking at the Variables (1)
Fraser Cain: Astronomy Cast, Episode 653. Climate Change: Looking into the Variables. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. I'm Fraser Cain. I'm the publisher of Universe Today. I've been a space and astronomy journalist for 20 years. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how you doin'?
Dr. Pamela Gay: I am doing well. This is one of those topics that I never look forward to, but I feel has to be discussed. So, dear, audience, please don't send us hate letters. Listen –
Fraser Cain: Yeah, wait –
Dr. Pamela Gay: – and then send us comments.
Fraser Cain: Well, you know, I don't care. This isn't the show for you. If you think the climate change isn't real, then just go away.
Dr. Pamela Gay: Yeah.
Fraser Cain: Just go talk to your friends who also disbelieve in climate change. It's not – I'm not gonna get bullied and harassed at talking about the scientific consensus. And it is a little unusual to me that people will just get so boisterous about it. And I think about the political misinformation campaign that has just done such a brilliant job, like the people who helped make people confused about whether or not cigarettes cause cancer and then –
Dr. Pamela Gay: Clean coal.
Fraser Cain: – moved on to clean coal, and then moved on to climate change, and the effect is long-lasting. You know what's funny? I love my electric car. Like if I had to choose between a gas car – If my electric car destroyed the planet, I would choose it over my gas car, because it's so much cooler and better and quieter and faster and I just plug it in, and it works better. And I'm genuinely excited at the electrification, the modernization, the self-reliance that we're moving towards. And, again, it's so cool. It's exciting. It's a technology. It turns everything into a technology that I find real exciting.
Anyway, let's get into the show. Climate change is on our minds these days with increasing wildfires, droughts, and floods. What are the variables that play into a planet's changing climate, and what can this teach us about the search for habitable planets in the solar system and across the Milky Way? All right, Pamela, where do you wanna start on this one? How do you wanna crack into this episode?
Dr. Pamela Gay: So, the starting premise is there are variables that determine in part how our atmosphere is able to hold onto heat and release heat, and there are variables that determine how the planet itself is able to retain and reflect heat. Pick a variable.
Fraser Cain: I guess let's start with the main one, which is the main input: the sun.
Dr. Pamela Gay: Yes.
Fraser Cain: So, let's start with that one. Energy in.
Dr. Pamela Gay: Yes. So, in general, our sun is a mid-life star. It has changed in brightness very slightly over time and it will continue to get ever-so-slightly brighter over time. These variations are things that are occurring over literally millions and billions of years. And while we can see differences in what was going on in the earliest days of our planet, billions of years ago, over the course of human history's small fraction of our time on this earth, the sun's output hasn't had an overall effect outside of the 11-year solar cycle.
And there was one minor dark patch in the Dark Ages, where the sun was like, “I'm not gonna have sunspots. You do you, I'm gonna do me.” And during that period, we did see some cooling that occurred.
Fraser Cain: But the point being, without the input from the sun, we wouldn't have a global warming problem. Right? If there was no sun, there would be no global warming.
Dr. Pamela Gay: I can't contradict that. I also feel though that life as we know it would not exist, so that is really not a concern to me. We have a sun. It's there.
Fraser Cain: Right, right, right. But the point being that the sun is the input.
Dr. Pamela Gay: Yes.
Fraser Cain: And then how that input gets reflected, changed, absorbed, released, et cetera, all depends on the variables that are happening here on Planet Earth.
Dr. Pamela Gay: Yes.
Fraser Cain: And there are minor variations on the sun. We saw, as you said, we had a time, you know, there's increased sun activity can change things. Increased solar activity can change things but are not changing things today currently.
Dr. Pamela Gay: No.
Fraser Cain: And in 500 million years from now, the sun will heat up to the point that the earth's oceans will boil. But that is not tomorrow. And that is not within the next hundred years. That is measured in the amount of time animals have existed on Planet Earth. That's how long it's gonna take. All right, so the sun is the input.
Dr. Pamela Gay: Right.
Fraser Cain: So, then what are the variables that define the temperature that we experience here on the planet? I guess, the distance from the sun matters? The shape of our orbit?
Dr. Pamela Gay: The distance from the sun. The shape of our orbit. These things both matter. They aren't, again, changing over periods of time that matter for humans. We find that the winter in the Southern Hemisphere is slightly worse – ever-so-slightly worse than winter in the Northern Hemisphere simply because the earth is ever so slightly closer to the sun in January, which is northern winter and southern summer, so southern summer doesn't get quite as much sun. In the grand scheme of things, this is just a constant over the course of human scales.
Fraser Cain: Now what about the tilt – the axial tilt of the planet? Because that changes, not in a human lifetime, but in, I guess, civilization's lifetime.
Dr. Pamela Gay: What we're seeing with that though –
Fraser Cain: The wobble.
Dr. Pamela Gay: Yeah, so our planet is a top, and I'm gonna use a coffee stirrer to indicate it. And I am going to use a hairbrush to be the sun. We are high-tech around here, humans. So, as our – disappearing entirely into my background and getting ready to be replaced by a red pen that is easier to see – Okay, so we have our planet, Earth, and it's going around, and as it's going around it is constantly pointed towards the same star. But, over time, it's slowly going to change what star it's pointed to. But its tilt relative to the sun isn't really changing.
So, well yes, over the grandest scales of time there is some wobble to that tilt, the big thing that we're able to see over the course of history is the change of where the North Pole and the South Pole are pointed. But the difference between the location of the sun and the tilt of the earth, that angular distance is fairly constant even though what star the planet is pointed to is varying. So, with the tilt not really changing, it's not changing how the seasons occur, other than what stars are there.
Fraser Cain: I mean, I guess it's not changing the total amount of energy that's falling on the surface of Planet Earth.
Dr. Pamela Gay: Right.
Fraser Cain: It is changing – Like, right now, the cool thing that you discover is that the earth is at the closest point of its orbit during winter in the Northern Hemisphere.
Dr. Pamela Gay: Yes.
Fraser Cain: And it's at the farthest point of its orbit during summer in the Northern Hemisphere, and that slightly moderates both the winter and the summer. You mentioned earlier that the winter in the Southern Hemisphere is more extreme, partly because there's more ocean and less land, but also because the earth is at the closest point during its summer and the farthest point during its winter. So, you just get both the tilt and the distance adding up, as opposed to them mildly canceling out as we get in the Northern Hemisphere.
Dr. Pamela Gay: Yeah.
Fraser Cain: All right, so tilt, we can sort of remove that from the system because the total amount of energy is going to hit the earth no matter how the earth is tilted. So, let's talk about the big, I guess, the variables in terms of how the planet appears to the radiation that's coming at it.
Dr. Pamela Gay: Right.
Fraser Cain: So, the amount of land versus sea versus ice, et cetera. How does that have an effect?
Dr. Pamela Gay: So, as the sunlight comes down, it hits our planet. And what happens when it hits our planet depends on exactly what it's hitting. If the sunlight hits ice, it's going to get reflected upwards. If it hits dirt, it's going to get absorbed, and over time reradiate that energy but slowly and in the infrared. So, what the sun hits, determines how well we keep or reflect that heat. And over time, what we're finding is, as we remove forests, that changes how, well, the forests absorb light versus the ground absorbing light.
It changes the colors that the light is reradiated at. As we see the ice melt, that's causing less reflection to occur. As we see less snowfall occurring, that's causing less reflection to occur.
Fraser Cain: When you think about the Snowball Earth – back a billion years ago, the earth was completely covered in ice which is highly reflective. And that's kind of self-reinforcing, it locks in because the sunlight is falling on the earth and then the sunlight is being reflected back out, it doesn't get a chance to warm, and it stays icy. And, you know, it was thought that you needed to have some amount of volcanism to seriously impact the environment on Earth to kick it out of that Snowball Earth cycle that it was trapped in. Which is kind of interesting. You do wonder, could we get back into a Snowball Earth in the future? What could that take?
All right, so we've talked about the surface composition of the planet. We've talked about the actual orbital mechanics of it. The sun. Let's talk about the composition of the atmosphere. This is where the big factors start to come into play.
Dr. Pamela Gay: Yeah, so –
Fraser Cain: Or, I guess, the big factors for variation. I mean, again, back to it, sorry – The sun is the key, but as we change the atmosphere, that's what will have an impact.
Dr. Pamela Gay: So, as the sunlight comes down through our atmosphere, a whole wide variety of colors of light are able to make it down to the surface of the planet. There are colors that are luckily reflected, like x-rays, they don't hit us. We're very grateful because that would cause cancer. Now, all these colors of light coming down through the atmosphere, they get reradiated or reflected depending on if they hit ice or if they're absorbed by land or water and then released. The reflected light goes back up through the atmosphere. Some of it escapes. Some of it bounces off of molecules and comes back down.
With that infrared radiation, a lot of it hits stuff in the atmosphere and then becomes trapped in our atmosphere. And this is exactly how a greenhouse out in your yard might work. Sunlight comes down through the glass, it warms up the flower beds, it warms up the air. That infrared radiation then hits the glass, and the glass isn't as transparent, so the heat stays in the greenhouse.
