Not long ago wintertime actually meant cold and snow for some people. These days many Eskimos are taking surfing lessons. Every time we start an engine, chop down a tree, or start our own herd of cattle greenhouse gases are emitted. These gases, which include carbon dioxide, methane, ozone, halocarbons and nitrous oxide, let in sunlight but tend to insulate the planet against the loss of heat, not unlike the glass of a greenhouse. While all the greenhouse gases present problems, the biggest villain is carbon dioxide.
Carbon dioxide has a nasty habit of remaining trapped in our atmosphere, sometimes for centuries.
Over time these gases start to build and slowly warm our atmosphere. During the 1980's human beings released 7.2 billion tons of carbon dioxide into the atmosphere each year. Since then things have gone up, up and away. While many of the changes would be negative a few could be beneficial. GOOD - A warming planet might expand the length and geographical reach of human cultivation.