Planet Earth is changing and the consequences of change could have serious implications for human health, the world's food and energy supplies, and the global economy. There is need for greater understanding of the complex mechanisms that control Earth's behavior. That need is being met by a coordinated international research program designed to reduce the uncertainties of global change.

NASA's part of the program is the Mission To Planet Earth (MTPE), a space science effort of such importance that it has been elevated to status as a separate program office. MTPE, which involves extensive cooperation and contributions from other U.S. federal agencies and other nations, employs satellites and other tools to generate data about Earth; it is intended to expand understanding of how natural processes affect humankind, and how humans may be effecting those processes. MTPE studies are expected to yield improved weather forecasts, tools for managing forests and agriculture, information for fishing fleets and coastal planners, and - eventually - an ability to predict how the climate will change in the future.

Phase I of the MTPE program has been under way since September 1991. Among the major contributors is the U.S./France satellite TOPEX/Poseidon which addresses how ocean circulation influences global climate by mapping the circulation patterns of the world's oceans over several years.

TOPEX/Poseidon is an altimeter-type satellite; the illustration shows how such satellites, working with tide-gauge networks and land-based and orbital geodetic location systems, can enable accurate, long-term, continuous monitoring of climate and sea level.

TOPEX/Poseidon's radar altimeter has demonstrated a capability for very precise measurement of sea surface heights and satellite data indicates that sea levels increased during 1994-95. Although the data is not sufficient to establish a trend, sustained increases in sea levels could worsen the effects of hurricanes and other storms, threaten coastal regions, and possibly indicate global warming.In a related discovery, TOPEX/Poseidon provided data that enabled scientists to track disturbances caused by the lingering effect of the El Nino climate event of 1991 - 93. Although scientists don't know why El Nino occurs, records show that it has been happening for hundreds of years, profoundly affecting weather patterns and causing floods and droughts in various parts of the world. Over the past decade, the pattern of El Nino occurrences has increased dramatically; some researchers believe the 1993 Mississippi and 1995 California floods were caused by El Nino.

Another MTPE tool is the Shuttle-based Space Radar Laboratory (SRL), which flew two 1994 missions that enabled an international team of scientists to observe shifting boundaries between tem- perate and boreal (northern) forests. The results of these observations permit study of how such changes might affect climatic change; they are also being used for map-making, study and interpretation. NASA and Canadian scientists also used SRL data, along with aircraft and ground data, for the Boreal Ecosystem/Atmosphere Study of northern forests, a large scale investigation into how the forests and the atmosphere interchange energy, heat, water, carbon dioxide and other trace gases.

Data from the Upper Atmosphere Research Satellite, which is investigating the role of the upper atmosphere in climate and climatic change, provided conclusive evidence that human-produced chemicals, including chlorofluorocarbons, are breaking down in the stratosphere and causing depletion of ozone over the Antarctic.

Another satellite-based instrument, the Total Ozone Mapping Spectrometer (TOMS) aboard the Russian Meteor-3 satellite, reported that the 1994 Antarctic "ozone hole" was the largest on record. However, measurements by NASA and other agencies indicated that control measures to protect the ozone layer were beginning to work and that the atmospheric concentration of damaging chemicals was stabilizing.


Phase II of MTPE will begin in 1998 with the launch of the first Earth Observing System (EOS) spacecraft, EOS AM-1 (above). EOS is the first integrated satellite/surface research system for observing how the Earth's parts (air, water, land and life) interact with each other. Studying these interactions is the critical next step in understanding the complexities of the global climate. EOS will contribute to such understanding by observing Earth in 24 measurement areas over 15 years, employing instruments on satellites of varying size and configuration. Each spacecraft will focus on a different aspect of global climate change and the interrelation among Earth's environmental components. EOS data, along with data from airborne and ground-based systems, will enable scientists to model Earth as a global system, thus fostering fundamental advances in weather and climate planning, disaster relief and, ultimately, providing the answers to scientists' many important questions about long-term climate changes.