Ground Truth Studies Teacher Handbook - Aspen Global Change ...

Global Change Primer
These are unique times. Our use of energy and other resources has increased to the point where we are having a measurable
effect of a global scale on Earth systems such as the atmosphere. Humans have moved from mere spectators of
Earth processes to center stage in the twentieth century, where we have become major players. It is no accident that we
are hearing about many different global change issues all at once: climate change, the ozone hole and worldwide loss of
biodiversity, just to name a few. It is, in fact, because we humans have become so numerous and consumptive, that our
combined individual effects are precipitating changes on a global scale. A number of key concepts are central to the
scientific study of global change and help put the issue of natural and human induced global change into perspective.
Change is the norm for Earth’s natural systems
The Earth is constantly changing. Some of this change occurs slowly over many millennia, and some occurs relatively
rapidly over decades. Major natural forces cause such changes as volcanoes, continental shifts, building and erosion of
mountains, reorganization of oceans, appearance and disappearance of deserts and marshlands, advances and retreats of
great ice sheets, rise and fall of sea and lake levels, and the evolution and extinction of vast numbers of species.
Recently, human beings have become a key agent of change
In addition to the changes brought about by natural forces, it has recently become apparent that a relative newcomer to
planet Earth — the human being — has become a powerful agent of environmental change. The chemistry of the
atmosphere has been significantly altered by the agricultural and industrial revolutions. The erosion of continents and the
sedimentation of rivers and shorelines has been accelerated by construction, agriculture, and other human activities. The
production and release of toxic chemicals has affected the health and distribution of plant and animal populations. The
development of water resources for human use has affected patterns of natural water exchange in the hydrologic cycle
(e.g., enhanced evaporation from reservoirs and irrigation as compared to that from unregulated rivers). As human
population grows and technology develops, the role of human beings as agents of global change will undoubtedly
expand.
Earth’s systems are linked through interactive processes
Evidence accumulated in the last two decades indicates that environmental changes are the result of complex interactions
between natural and human-related systems. For example, the Earth’s climate changes are due not only to wind and
clouds in the atmosphere, but also the effects of ocean currents, human influences on atmospheric chemistry, the Earth’s
orbit and albedo, the Sun’s energy output, and the distribution of water between the atmosphere, hydrosphere (oceans,
lakes, rivers), and cryosphere (icecaps, glaciers, sea ice). The aggregate of these interactive linkages among the major
systems that affect the environment is known as Global Change.
© ASPEN GLOBAL CHANGE INSTITUTE 1995 GROUND TRUTH STUDIES
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