Electricity, which, I don't know about you, but, is under the same category as turning on lights, hence you're using electricty. It causes global warming because in order to get electricity running in your home/office where ever, they use massive factories that burn coal, to produce energy. All the chemicals and what not go out into the enviroment and eat away the o-zone layer causing global warming. The o-zone layer protects us from alot of the harmful rays that the sun puts off. Driving hummers guzzle gas, which is not a plentiful resource on our planet, if you've been aware. I'm not sure how it directly causes global warming, but the way the world is going you're an idiot if your driving a hummer, there is not an infinate number or source of resources on our planet