[SOUND] Do you have insurance on your house? Almost every person I know does, why? Well, gee, if your house burns down, that's really bad. It's typically a given person's biggest single investment. And insurance doesn't really cost that much, because the house burning down is rare, right? So do you take some of your money to buy that insurance policy, just in case, to protect against a large risk, yes. I think that's also what makes a lot of sense in the global warming debate. We know that CO2 and temperature correlate. If we can do things that are sensible, that use a portion of our income, let's reduce our CO2 emissions. Let's do things through tax incentives to promote renewables, to promote nuclear power, to promote non-carbon based fuels. We do the same thing with insurance, we should do the same thing with the insurance for our planet. Not sound the alarm bells and say, my God, we've gotta all stop using carbon. China, you can't get more energy, India, forget it. Keep everyone at the same standard of living. There's a real human need in those types of places and in the third world for more energy use, and fossil fuels are their easiest way to do it. In the developed world, like the United States and Europe, we're using energy more efficiently and we are transferring slowly to non-fossil fuel sources. This makes sense. Let's start talking about what happens if indeed the planet gets warmer. One worry that people talk about is sea level rising, and flooding out all the coastal communities. That is indeed a potential worry. But, let's be really careful to explain what exactly are we worried about melting. So, let's take a little thought experiment. Let's say, I take some ball of water, okay? So I have a ball of water. Now, if I freeze this water, if I freeze this water, the density of ice is a little less, so it'll actually make a little bit more ice. So, this was my volume of water, but this entire volume is the volume of ice, because ice is less dense. Now I've got an iceberg and here is my water level. And indeed, although I've exaggerated a bit here, part of an iceberg is above the water and most of it is below. What happens when the ice melts? If it's floating ice, nothing, look at this example, right? How much water is this ice going to turn into? Well, exactly this amount of water, the amount that's below the surface. If the ice melts, we are left with the same level of sea level. That's floating ice, that's the North Pole. There's no land under the North Pole. If all the North Pole melts, sea level doesn't change a bit. But remember, all the ice on our planet is not at the North Pole. A lot of it is on top of landmasses, like the South Pole. South Pole is a landmass, Antarctica, and the ice on top of it, if it melts, that does indeed raise the sea level. If the ice on Greenland melts, that indeed does rise the sea level. That indeed does raise the level of the sea. Sea level, though, is a complicated factor. There are tectonic plates that hold the continents, that are constantly and slowly moving. Some of them are subducting, going down, some are being pushed up. Certainly tectonic plate movement changes sea level effects as well. And in terms of human effect of sea level changing, it really depends on how fast it occurs. If I tell you that, hey, sea level's going to change a couple of inches, a few centimeters, over the next 50 years, you probably could get by with building a sea wall. If you have enough time, enough energy, enough money to say, okay, that's not good, but we can probably prevent that. If it happens very quickly though, then your investment to be able to do that is probably for nought. Growing areas, we need to feed the population of the world and that means you need to grow crops. In North America, a slight increase in temperature actually makes us more productive. Why, because of Canada, there's a lot of land in the middle of the continent, plenty of water for that land, it's just too cold. If you raise the temperature just a bit, the growing areas move north. The growing areas become longer in a still fertile area, and it would be okay. Certainly not true in Europe, it's actually not true in most of the world. Food production could go down, if temperature goes up. Some of the scarier things about temperature increase, though, has to do with ocean currents. Let's draw the coast here, of America. And somewhere here is the Great Lakes and Canada, right, okay. This level is about even with the south of Europe. Spain, maybe the same level as Chicago with Italy sticking down, and then you got France and Germany, and this is all way far north. How can anyone live there? No one lives over here in Canada, that far north. Well, the answer is, that it's warmer than it should be. There's a current that comes up the coast of the US, comes across the Atlantic, goes up the coast of Europe, this is the Gulf Stream. And the Gulf Stream is very important, bringing warmer water and therefore warmer air and warmer temperatures to Western Europe. You might say, well if the water is going this way How does it ever get back? You have to do a kind of three-dimensional picture here. We do a three-dimensional picture. After the water has lost enough of its heat ,okay, it becomes denser, and colder water sinks. And so this colder water sinks down, this is down along the bottom, and it comes back. And of course, this eventually again warms up in the tropics and continues on it's journey, a conveyor belt, bringing heat from the equator up to northern latitudes. Well, a change in temperature has the worry of being able to turn this off. It actually happened in prehistoric times, when the same giant melting glacial lake that filled up the Great Lakes in the first place, broke, and suddenly dumped a lot of fresh water into the Atlantic Ocean. When you add that fresh water, this warmer water that has accumulated and now lost its heat, can't sink anymore. It's salt water after all, fresh water floats on top of salt water. You ruin this buoyancy effect and you interrupt this conveyor belt. Temperatures change very dramatically according to the fossil and other types of records. So, what you want to do is keep this going to keep the temperatures constant across the planet. And if, somehow, too much fresh water, because of melting ice, whether it's the North Pole or Greenland, or elsewhere melts, this conveyor belt could be in question. The debate about what to do about global warming is not an easy one to settle. There is real no debate that men-made CO2 does indeed warm up the planet. The effects of that warming it up, how quickly it warms up, and what the human response should be to stop that warming in the face of so many other human needs. The needs for energy, the needs for higher standards of living, the needs to take the impoverished billions of people across the planet and bring them into a higher standard of living. Those competing needs will play out over the next 100 years. What we can do here and what you need to know is what you need to know to understand it. You need to understand the science behind it and what some of the implications are. [MUSIC]
