text: The foremost issue is of course, the environmental effects of cars.  According to the New York times, cars are on average responsible for "12 percent of greenhouse gas emissions in Europe . . . and up to 50 percent in some car-intensive areas".  These emissions can often make cities uninhabitable.  In places such as Shanghai, Hong Kong, and other urban centers; heavy pollution requires citizens to wear gas masks, and acid rain devstates plant life.  This heavy pollution has such an effect that it causes black snow in Russia, thousands of miles away.  But the scale of the problem is much larger than acid rains and black snow; our planet is heating up, and greenhouse gases are to blame.  If you want evidence just look at our neighbor, Venus.  Roughly the size of Earth, scientists believe that Venus once has water, but look at it today, and you will see our solar system's hottest planet.  Several million years ago Venus was overcome by volcanic activity; of much greater extent than anything ever seen on Earth since it's formation in pre-cambrian time.  These volcanos spewed thousands of tons of carbon monoxide into the atmosphere, and thus began the greenhouse effect.  The sun's rays would pierce through the smog and reflect off of the surface of the planet, but when they went back up the smog stopped them and turned them away, back down towards the planet's surface.  This caused the planet to practically absorb all of the energy and heat of the sun.  Before long the surface temperature became hot enough to melt lead, making Venus utterly uninhabitable.  If nothing is done to stop atmospheric pollution, this is our future.