But enviromental expert Dr. Carl Sagan has arrived at the scene and I think we’re going to go to him now. In the air there is a kind of invisible blanket of gases that keeps the heat in, makes the temperature of the earth higher than it would otherwise be. That’s called the greenhouse effect, and one of the most important gases that make the greenhouse effect go is carbon dioxide, CO2. They come from burning fossil fuels, you know coal, oil, gas every time you drive your car or turn on the furnace in your house or anything like that, CO2 gets put into the atmosphere. There’s a dispute among scientists on this issue, especially on how quickly it happened. Most think there will be significant warming by sometime the next century. Suppose we thought it was only a, say 10% chance of that happening. What would a reasonable person do faced with a 10% chance of such a serious consequence? Well, the military always says: “Plan for the worst case”. Insurance policies say: “Plan for the worst case”.
Clearly here too. Part of the atmosphere, tiny part of it, is the protective ozone layer, it absorbs dangerous ultraviolet light from the sun. Well, that ozone layer is in trouble. There’s a big hole over Antarctica in the ozone layer it’s thinning elsewhere and we understand the reason for this, it’s a molecule called CFC, it’s in air conditioners and refrigeretors. Nobody figured it was a danger. But those molecules attack ozone..