It is often said that man has become the enemy of our planet. This is no exaggeration , for reports show that man's greed has done much to destroy the earth. Man, in his greedy desire for financial growth, has polluted the air, land and water, and has robbed our valuable natural resources. Man's industrial plants pour out poisonous waste that pollutes the sea and puts life in the sea under the threat of dying out; at the same time, they release alarming amounts of carbon dioxide, chlorofluorocarbons (CFCs) and other pollutants. Small wonder that the air now is much warmer and more impure than ever before. Of course, this is not just because of man's greed--it is man's pressing need as well. For instance, in developing countries, huge financial foreign debts have forced governments to approve the cutting of forests for agriculture or ranching. As a result, forests are cut down just to meet man's immediate needs. Perhaps unknowingly,man has changed the make-up of the earth's atmosphere. Scientific studies have shown that CFCs used in refrigerators and industrial cleaners are fast destroying the ozone layer--a protective layer in the atmosphere that protects us against the harmful effects of the sun's ultraviolet  rays. In fact, documented reports have shown a terrible fact that there are "holes" in the ozone layer over the Antarctic. And they appear to be expanding. Faced with these environmental problems, world leaders have shown deep concern. The UN Environmental Programme (UNEP) has arranged international agreements like the Vienna convention of 1985 and the Montreal Protocol of 1989 to preserve the ozone layer by controlling the production, use and trade of destructive chemicals. There may be some doubt as to how effectual these agreements may be, given that some countries still maintain an "I-don't-care" attitude. Their attitude is probably due to their failure to grasp the importance of the problem. Then, there is no doubt that environmental education on an international scale is greatly needed, so that all countries, great and small--the "haves" and the "have nots"--may realize their responsibilities for our planet. In the meantime, the UNEP seems to have taken steps in the right direction, and it is hoped that in the not so distant future, all nations of the world will join hands in saving mother earth. The holes in the ozone layer are largely due to  _  .
man's research activities the greenhouse effect the ultraviolent harmful chemicals