I think that cars and trucks emit gases that destroy the ozone layer and the ozone layer protects us from harmful uv rays, so when the o zone layer is destroyed more and more, become exposed to these harmful uv rays. Hence, global warming
I can't say that I believe that driving cars or trucks cause global warming. In fact, I seriously doubt it! AT this time 27 yrs. Ago, in this very town, it was 110 degrees. Today it is about 75 degrees. Perhaps it's cooling down..here anyway.