 Today, we're going to take a step back in time and look at history's first-ever global warming myth. It's a myth about the greenhouse effect. Now in this day and age, we measure the greenhouse effect getting stronger by using modern instruments, aircraft and satellites. But in 1900, when this myth was born, scientists didn't have these measurements. Now, we understand the greenhouse effect a bit better. Greenhouse gases let sunlight through to warm the surface. The surface then glows with infrared light. Our eyes aren't tuned to its frequency, so it's invisible to us. But greenhouse gases absorb some of this infrared. At the same time, they glow with their own infrared. They glow in all directions, and the part of the glow that goes up can be absorbed by greenhouse gases higher up in the atmosphere. It's useful to think of the atmosphere as layers. Each layer of the atmosphere has a greenhouse glow in every direction. Meanwhile, each layer absorbs some of the infrared glow that comes from the layer above and some from the layer below. Now, low down in the atmosphere, the air is thicker than higher up. Each layer has enough greenhouse gas to absorb much of the infrared going through it. Higher up in the atmosphere, the air gets thinner, and that's why it's harder to breathe at the top of a mountain. Each layer doesn't have enough greenhouse gas to fully trap passing infrared. Burning coal, oil and gas releases carbon dioxide, a greenhouse gas. Stirred by the winds, it mixes through the atmosphere. The biggest effect is high up, where the air is thinner. This is where infrared previously escaped to space. Adding more greenhouse gases captures this infrared. The upper layer now glows a little bit more brightly, and a little more heat is recycled back into the atmosphere. This is how adding more greenhouse gases makes us warmer. One myth distorts this by ignoring the last century of research. In 1900, Swedish physicist Knut Angstrom and his assistant did an experiment. They shone infrared light through a tube filled with carbon dioxide. They changed the amount of carbon dioxide, and they found that the amount of absorbed infrared stayed about the same. They thought that this showed that carbon dioxide's greenhouse effect is saturated, that adding more to the atmosphere won't cause warming. Now, this was a good experiment, but the atmosphere isn't the same thing as a tube full of gas in a lab. In the upper layers of the atmosphere, the greenhouse effect isn't saturated. The concentration of greenhouse gases is a lot less than in Angstrom's tube. Adding greenhouse gases blocks the infrared's escape path to space. Some of the infrared that used to escape has now been trapped. And the layer's greenhouse glow sends some of it back down to warm us up. To calculate this effect, scientists use computers. They apply the laws of physics in their calculations. In the early 2000s, aircraft measured the infrared of the eastern USA and near Ascension Island. Scientists took the aircraft measurements and the computer predictions. They compared them and found that the match was excellent. Physics does a good job, and it says that more greenhouse gases cause more warming. We've also measured the greenhouse effect with satellites and at observatories all around the world. We've measured that the greenhouse effect is getting stronger. We're adding greenhouse gases to the atmosphere, and we're boosting the greenhouse effect. The extra heat that they trap is staggering. It's more powerful than the entire world's electricity grid.