REMOTE CHEMICAL SENSING 143 4. CONCLUSION One of the most important ecological issues for our planet is climate change. It is generally agreed that the Earth's climate will modify in response to radiative forcing induced by changes in atmospheric trace gases, cloud cover, cloud type, solar radiation, and tropospheric aerosols (liquid or solid particles suspended in the air). In order to develop conceptual and predictive global climate models, it is vital to monitor these properties. Unfortunately, our knowledge of most climatic parameters is limited, so good climate models exist only for very limited areas of the Earth. For example, atmospheric temperature data, a good index for measuring global warming, are very limited over the ocean. The distribution and sources of greenhouse gases are other major unknowns (http://modis.gsfc.nasa.gov). Satellite-derived data are essential to obtain global knowledge about these parameters. This require- ment led to the development of chemical sensors for monitoring atmosphere quality from space. Remote sensing satellites have many advantages for monitoring air quality. Satellite observations can provide a complete survey of a region, show the major sources of pollution, and the distribution pattern. Since the early 1970s, remote sensing instrumentation had been developed for remotely measuring several atmospheric parameters. Space-based monitoring is the only effective way to assess atmosphere contents distribution on a global basis, and many new chemical remote sensing sensors have been developed in recent years. Trace gas and aerosol instrumentation have been developed and operated to measure ambi- ent concentrations of trace gases and aerosols and the exchange of trace gases with the Earth's surface.