Global climate is probably influenced by man's activity, which disrupts the atmospheric heat balance through carbon dioxide, smog (dust), and heat pollution. Ways must be found to compensate for these undesired effects. Properly understood, global climate can be influenced to either maximize climatic resources or to avoid unwanted changes. Two major factors have severely limited progress. (1) Limited observation: Only about 20 percent of the global atmosphere could be observed at one time. Satellite systems now enable some quantities to be observed over the entire planet every day. (2) Lack of understanding: No adequate theoretical basis exists to explain interactions of the global heat engine and to account for observed changes in climate. Increased computer power and the development of mathematical models of atmospheric and oceanic circulation will provide tools for testing hypotheses and causal relationships. Cooperative study has been mainly limited to the United States and the Soviet Union, but the United Nations has fostered some recent efforts in international research. The United States should (1) coordinate its various research groups under a systematic program, (2) initiate small programs to evaluate large-scale weather-modification techniques, and (3) define historical climatic patterns.