Noun. The heating of the Earth's temperature as a result of abundant greenhouse gases from mankind. Although global warming is the consensus of the world's scientists, just like plate tectonics, evolution, or gravity, there are skeptics who tend to think other wise. Even if you don't think it exists, it is still no reason not to live a sustainable (or "green", whatever) lifestyle. That's what we call a win-win situation. However, the people that don't think it exists are basically looking for a reason to justify their fear of getting rid of their material possessions they hold so dearly; be it a car, hamburger (large carbon footprint), air conditioner, etc.
The people against the conservation of our earth are the reasons global warming exists. Don't be another coward unwilling to make a change. Do yourself, others, and the planet a favor by researching sustainable alternatives to lower your carbon emissions and contribute in the preservation of the world. Caring about something other than yourself doesn't make you a hippie, it makes you a human being.