Global warming exists and is happening but it is probably due to the natural changing of the Earth's temperature than any man-made factor. I believe this current warming trend is a normal warming period much like the Earth has had in the past. In the early 1400's, before the climatological event known as the Little Ice Age, ships were able to sail around Greenland, which is impossible today, and the maximum extent of pack ice in the Southern Ocean was much less than it is today. By the late 1400's though a period of global cooling occured which dropped world temperatures between .5-1 degree centigrade. This caused the pack ice around both poles to expand and for harsh winters in Europe, Asia and North America. Ever since the 1500's we have slowly been getting warmer as the temperatures tried to normalize with pre-Little Ice Age temperatures. Even before this event we can see small changes in the Earth's temperature before, this often explains the cycle of droughts and wet periods in the equitorial regions. My final thought on Global Warming is to say that it is definitely happening but it is more likely, in my mind, that it is caused by natural enviromental factors than my man-made/artificial factors.
Do you know about "The Year without a summer" in the early 1800s?
http://www.ncdc.noaa.gov/paleo/ei/ei_reconsb.html
