NASA's Description of Earth System Science
Earth is the only planet we know of that sustains life. Life on Earth is critically dependent on the abundance of water in all three phases-liquid, vapor and ice. Carbon, existing in a variety of forms, is the very basis of life, and its greatest reservoir. In the atmosphere, carbon fully oxidized as carbon dioxide, fully reduced as methane, and in particulate form as black carbon soot produces the greenhouse effect making Earth habitable. Earth's atmosphere and electromagnetic field protect the planet from harmful radiation while allowing useful radiation to reach the surface and sustain life. Earth exists within the Sun's zone of habitation, and with the moon, maintains the precise orbital inclination needed to produce our seasons.
These remarkable factors have contributed to Earth maintaining a temperature range conducive to the evolution of life for billions of years. The great circulation systems of Earth-water, carbon and the nutrients-replenish what life needs and help regulate the climate system. Earth is a dynamic planet; the continents, atmosphere, oceans, ice, and life ever changing, ever interacting in myriad ways. These complex and interconnected processes comprise the Earth system, which forms the basis of the scientific research and space observation that we refer to as Earth system science.
In Earth system science, researchers take a contextual approach to scientific inquiry-they explore extreme weather events in the context of changing climate, earthquakes and volcanic eruptions in the context of tectonic shifts, and losses in biodiversity in the context of changes in Earth's ecosystems. This leads to the exploration and discovery of causes and effects in the environment. For instance, Earth system scientists have linked ocean temperatures and circulation to the moderate climate of northern Europe relative to its latitude, the annual changes of ozone concentration over Antarctica with the production of industrial refrigerants in the Northern Hemisphere, and the physics and chemistry of the atmosphere to air quality and fresh water availability.
From space we can view the Earth as a whole system, observe the net results of complex interactions, and begin to understand how the planet is changing in response to natural and human influences. For example, Earth system science has begun to understand and quantify the effects of "forcings" on the climate system produced by the Sun's solar variability and the atmosphere's increasing concentrations of carbon dioxide and aerosols. The fact that researchers detect not just variability but trends in the key measures of Earth systems make it imperative for us to ask, "How is the Earth system changing, and what are the consequences for life on Earth?"
(From NASA's Earth Science Enterprise Strategy, 2003)