You really need to watch Al Gore's movie to understand "Global Warming". I put it in quotes because perhaps "global warming" should be called "global climate change".
What is explained in the movie is that basically "global warming" does not mean it gets warmer worldwide. It means there will be drastic changes in the earth's
climate patterns. "Patterns" is the key word.
One example that is explained is the "prevailing winds". These wind patterns cause warm air from the equator in the Atlantic Ocean to move weather systems northeast up towards Europe. As a result, much of Europe actually experiences much warmer weather than the what would be normal for a location at that latitude. For example, Madrid is the same distance north of the equator as New York City. But we all know New York has much colder weather than Madrid. London is much further north of the Equator than any place in the United States. But as well all know, there are plenty of places in the Northern United States that are much colder than London.
Back to what I was saying, one of the climate changes that will occur with "Global Warming" is that these prevailing winds in the Atlantic will change. As a result, weather in Europe is more likely to get much much colder and much of Europe will fall into an ice age.
What will cause all this is not "global warming", but a sharp increase in CO2 levels that is occuring worldwide:
The example of Europe is not the only one. Basically, climate as we know it on earth will drastically change. Places that are colder could get much warmer, places that are wet could become dry, places that are dry could become flooded, etc.
One change they expect is that Greenland will become significantly warmer causing all the glaciers in Greenland to melt. This alone will cause water levels worldwide to rise 20 feet. So many areas that are at sea level will be under water.
The scarey thing about this is that such changes will not happen gradually over a long period of time as has happened in the past with climate change. Many of the experts are predicting such drastic change over the next 30-50 years.