 So now we can talk about why this is called the greenhouse effect. And a lot of this has to do with the fact that a greenhouse, which is a building which has glass walls and ceilings, behaves in a similar way to these greenhouse gases. Glass will let visible light photons through, but some of the infrared photons are absorbed and redirected back in other directions. So we move to the second part of the simulation. Now right now they've got some grass and representing the ground, and of course the blue representing the sky, and then I've got a thermometer over here. Now I have the option of putting in a glass pane, and I think that will show up when I actually start running things. So when I start running this, I have visible light photons coming down. Now the ground will absorb those and let out infrared photons. With no other atmosphere or glass panes there, all of the visible ones come down and all of the infrared ones go up. But if I add in a plane of glass, what I start to see is that the visible photons are still going down, but now the infrared photons, some of them are coming up and getting directed back down to the ground. And over time that causes the temperature of the ground to warm up, because it's being heated by the visible light, but it's also being reheated by the infrared light that's being redirected downwards. Not all of the heat energy is able to escape, and so the ground warms up. And the more layers of glass I have, the more of the infrared light ends up being directed downwards, and the temperature inside that greenhouse will increase. Now this can be good if you live in a cold climate and want to grow plants and the plants need it warmer, as you can put them inside the greenhouse where they get plenty of visible light and they'll have a warmer environment because of this greenhouse effect.