Since the United Nations Environment Program (UNEP) was created, more than a dozen years ago, public understanding of the environmental issues confronting our planet has increased enormously. The Global Environment Monitoring System (GEMS) has provided several environmental assessments including urban air pollution, climate modification, threatened species on our planet, and the degradation of our tropical forests. The aim of the UNEP/GEMS Environment Library is to provide authoritative statements, written in plain language, about the major environmental issues the world is now facing. This issue concerns greenhouse gases and the possible effects these gases will have on the Earth's climate. An overview of the problem is presented followed by a summation of scientific facts and theories to provide a background to the problem. Major topics include: (1) the greenhouse effect; (2) heat balance on Earth; (3) carbon dioxide; (4) nitrous oxide; (5) methane; (6) fluorocarbons; and (7) climatic change. The future effects on society and the world are investigated with in-depth discussions of the major resulting problems. Lastly, possible ways of dealing with the problem are identified and summarized. (MVL)