Since its creation in 1958, NASA has been studying the Earth and its changing environment by observing the atmosphere, oceans, land, ice, and snow, and their influence on climate and weather. We now realize that the key to gaining a better understanding of the global environment is exploring how the Earth's systems of air, land, water, and life interact with each other. This approach -- called Earth System Science -- blends together fields like meteorology, oceanography, biology, and atmospheric science.

In 1991, NASA launched a more comprehensive program to study the Earth as an environmental system, now called the Earth Science Enterprise. By using satellites and other tools to intensively study the Earth, we hope to expand our understanding of how natural processes affect us, and how we might be affecting them. Such studies will yield improved weather forecasts, tools for managing agriculture and forests, information for fishermen and local planners, and, eventually, the ability to predict how the climate will change in the future.

The Earth Science Enterprise has three main components: a series of Earth-observing satellites, an advanced data system, and teams of scientists who will study the data. Key areas of study include clouds; water and energy cycles; oceans; chemistry of the atmosphere; land surface; water and ecosystem processes; glaciers and polar ice sheets; and the solid Earth.

Phase I of the Earth Science Enterprise was comprised of focused, free-flying satellites, Space Shuttle missions, and various airborne and ground-based studies. Phase II began in December of 1999 with the launch of the first Earth Observing System (EOS) satellite Terra (formerly AM-1). EOS is the first observing system to offer integrated measurements of the Earth's processes. It consists of a science component and a data system supporting a coordinated series of polar-orbiting and low-inclination satellites for long-term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans. We have initiated an era of unprecedented observational capability for understanding the planet.

Just as the first weather and communications satellites fundamentally changed our way of thinking about those fields, so the elements of the Earth Science Enterprise will expand our perspective of the global environment and climate. Working together with our partners around the world, we are well on our way to improving our knowledge of the Earth and using that knowledge to the benefit of all humanity.