As pointed out at the beginning of the passage, people used to think that air pollution ________. A. caused widespread damage in the countryside B. affected the entire eastern half of the United States C. had damaged effect on health D. existed merely in urban and industries areas.
Another view, less widely held, is that increasing particular matter in the atmosphere is blocking sunlight and lowering the earth’s temperature -- a result that would be equally disastrous. A drop of just a few degrees could create something close to a new ice age, and would make agriculture difficult or impossible in many of our top farming areas. Today we do not know for sure that either of these conditions will happen (though one recent government report drafted by experts in the field concluded that the greenhouse effect is very possible). Perhaps, if we are lucky enough, the two tendencies will offset each other and the world’s temperature will stay about the same as it is now.