There are a few reasons a lot conservatives do not believe in global warming.
1) The guys who are the loudest voices for changing lifestyle to prevent "Global warming" are not themselves setting the example. Obama has not cut back on his travel, driven more than flying, or moved into a smaller more austere residence. Al Gore lives in a large home, flies on private aircraft, and rides around in SUVs, the very things he says he opposes. What Gore does do is making millions selling bogus carbon credits to people who have bought into this fiction.
2) There were a number of ice ages before man lived on the earth. In order for this to happen, the climate would have to cool and then warm. The earth was also a giant ball of fire at one time and was hit by an object that created the moon. These things have happened throughout the planet's history and continue to happen to this day. It was not SUVs or factories that caused the earth to warm in those days.
3) We are basing these conclusions on a little over 100 years of data about a planet that is 4,000,000,000 years old. This is like viewing an 80 year old man walking by your front door for one second and thinking you can determine everything about his life.
4) There are numerous instances of problems collecting the data we do have, including improperly placed and covered thermometers (there are certain standards these specialized thermometers must meet to avoid incorrect readings such as being in the shade rather than direct sun, being a certain distance from cities which generate heat, etc). Pictures of these improperly positioned thermometers are available online. Just recently, several e-mails were uncovered in which certain researchers admitted to burying data that did not support the theory of global warming.
5) There are plenty of meteorologists and scientists who do not agree with the hypothesis, it is not a consensus.
6) Plants absorb CO2 for photosynthesis and expel oxygen. If you increase the CO2 in the air, it is good for plant life, more plant life means more oxygen. This is one of the reasons we do not run out of air with 6 billion people breathing, the same rules apply to man-made exhaust.
7) The solution for global warming is inevitably more government in your life. It is always more money for US taxpayers and we never demand other countries like China clean up their act as a condition of doing business with us. A legitimate case can be made that the Green Movement is an anti-capitalism, anti-US movement.
Conservatives are suspicious of anything that gives the State more power over the individual and many of us see Global warming as a scare tactic/lever into our private lives and freedom. Adolf Hitler used environmentalism as a cover for some of his intrusions into the lives of Germans.