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THE CHANGING ATMOSPHERE-CHALLENGES AND OPPORTUNITIES

physical, chemical, and biological vital signs of the planet while at the same time pressing forward our understanding of the earth as a system. In this country an organizational structure is in place that will tie scientific guidance from the National Academy of Sciences to an interagency infrastructure through the Office of Science and Technology Policy to coordinate the efforts of the National Aeronautics and Space Administration (NASA), the National Science Foundation (NOAA), the Environmental Protection Agency (EPA), and six other United States government agencies in a national program to study global aspects of environmental and social changes driven by climate change-a program referred to as the Global Change Program. An unprecedented team of scientists and policy makers is being called into action. What is still needed is the announced commitment of this nation to assume a role of leadership.

The climate system is exceedingly complex, consisting of multiple atmospheric, oceanic, biospheric, and cryospheric processes and interactions. A balanced climate research program must therefore involve programs in solar physics, atmospheric chemistry and dynamics, oceanography, and the interactions of the biosphere, cryosphere, and land surface with the atmosphere and oceans.

The required research program is based on two major components-a comprehensive global observational program to document the extent and rate of global and regional change, and improvement and verification of computer models of climate to convert these observations into reliable predictions.

Because of the global nature of the climate system and the necessity to understand its multiple processes in interaction, many of the needed measurements must be made from space. An approach to understanding the global system has been developed by NASA through its Earth System Sciences Committee. Central to this plan is its Earth Observing Systems (Eos) program to study the earth system. Eos involves three new space platforms in polar orbit to measure temperature, winds, precipitation, moisture, chemical species, and sea-surface characteristics, including temperature and color (which is related to biological activity). This satellite system will be created in cooperation with Japan and several European countries, and will replace our present weather satellites.

Despite the unprecedented power of Eos, other complementary missions will be essential. For example, rainfall, with its associated release of heat, is one of the most important components in the hydrological cycle, and tropical rain variability is a crucial link associated with the far-reaching effects of El Niño events. Yet it is presently not possible to obtain adequate precipitation information over the oceans or from most of the Third World nations. It is feasible to obtain a tropical precipitation climatology from space, and NASA has planned a Tropical Rainfall Measuring Mission as early as 1994 to do that.