`EARTH,'' says, NASA Administrator James C. Fletcher, ``is a spacecraft in a deadly vacuum, with a life-support system as precious as is an astronaut's backpack.'' And because people have begun to fiddle ignorantly with that precious system, he extends Buckminster Fuller's Spaceship Earth metaphor to say that it's time we found out what we're doing to our craft. It's time to ``track ... and understand this global change.'' People erode soil, destroy forests, and create deserts. They pollute the air with carbon dioxide and other heat-trapping gases to a degree that may change the climate. They make and release chemicals never before known in nature, such as spray-can propellants and refrigerator coolants that threaten the ozone layer. They've joined wind, rain, volcanoes, and the ponderous drift of continents as a major force for global change. They don't know what they're doing to Earth. But the scale of their activity is immense.
As a report by the National Academy of Sciences notes:
``More than 10 percent of the land area of the earth is now under cultivation. More than 30 percent is under active management for purposes of mankind.
``Chemical compounds for which there are no natural analogues are being produced and released into the air and water in ever-growing proportions; and rates of natural chemical and hydrologic cycles have been altered with currently unpredictable consequences for climate and for the local and global environment.''
Forest destruction illustrates how subtle and far-reaching this impact may be. Peter Raven, director of the Missouri Botanical Garden, warned the annual meeting of the American Association for the Advancement of Science in February that, at the present rate of destruction, we could lose Earth's tropical forests in 30 years. He explained that a forest area the size of Kansas vanishes every year out of a total tropical forest which now covers an area two-thirds the size of the contiguous United States.
Not only are we losing hundreds of thousands of species of plants and animals, most of which have not even been identified, but the loss of forest cover can directly affect the climate system. In the Amazon Basin, for example, evaporation and transpiration from the leafy forest return about half the rainfall to the atmosphere.
Robert E. Dickerson of the National Center for Atmospheric Research (NCAR) and Ann Henderson-Sellers of the University of Liverpool in Britain have studied this water cycle with a computer-based climate model.
They find that, without the broadleaf tropical forests, there would be extensive drought. Instead of lasting about a month, the periods of driest soil conditions would run several times as long.
Average temperatures would rise 3 to 5 degrees C. Furthermore, Dr. Dickinson says, ``Such changes would likely have a detrimental impact on survival of remaining forests and attempts at cultivation in deforested areas.'' In other words, clearing tropical forests for such uses as cattle ranches is a ``no win'' strategy that can permanently alter the region's climate.
INDEED, loss of the Amazon forests could have global impact. A joint US-Brazilian program - the Global Tropospheric Experiment/Amazon Boundary Layer Experiment - has found carbon monoxide, organic chemicals, and other gases diffusing copiously from the forest's rich biological activity. Thunderstorms carry these chemicals several miles high. They move out with atmospheric circulations that take them all over the planet.
No one yet knows what role these chemicals play in our planet's system. But scientists studying this warn it is important to understand that role before deforestation irrevocably cuts off this natural ``pollution'' at its source.
With that kind of potential impact, it's no overstatement to rank human activity with the major natural forces. However, NCAR climate modeler Stephen H. Schneider cautions that it's also ``almost a trivial statement.'' He explains: ``We're clearly a major force. The question is, though, is that for better or for worse and, on the whole, so what? The fact that we're a force, by itself, doesn't mean anything.... And that's where you need earth system science [to explain global change] because you have to start answering those questions.''
The idea of tracking and understanding global change has fired the imagination of scientists around the world and caught the attention of their governments. For Earth scientists, it represents a renaissance in their subject and the biggest professional challenge they've faced. For environmentalists, it's the ultimate issue. For government agencies, it's an important new mission.
IN the United States, three major agencies are cooperating to tackle it. The National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the National Science Foundation (NSF) are planning a comprehensive study of Earth and its living envelope that will continue into the next century.
Globally, the International Council of Scientific Unions (ICSU) - the umbrella organization that manages global research - has begun a major program to look at Earth in an integrated way. Called the International Geosphere/Biosphere Program (IGBP), it too will run through the rest of the century and probably into the next. It will focus efforts of most of the nations. Indeed, the programs being planned by NASA, NOAA, and NSF will be a large part of the United States's IGBP contribution.
``For the first time in history, we have the capability to observe the entire Earth, from the outer reaches of its atmosphere to its molten inner core,'' observes NSF director Erich Bloch.
BUCKMINISTER FULLER'S metaphor provides an apt image as these global researchers seek to understand what man is doing to his planet. A spacecraft is not an assemblage of vaguely related parts. It's an integrated system. Earth is not a dead hunk of rock that happens to support life. It, too, is an integrated system in which all the parts - including the living part - interact and contribute to the harmonious working of the whole.
That presents a two-fold challenge, says Francis P. Bretherton, chairman of NASA's Earth System Sciences Committee. It will be a herculean effort just to understand how the planetary system works. But because humans now are an important - and disruptive - influence in that system, Dr. Bretherton says, scientists also have ``to develop the capability to predict those changes that will occur in the next decade to century, both naturally and in response to human activity.''
Seeing the `big, blue marble' as a life-support system
WHAT does it mean to call Earth a ``system?'' One way to come at this question is to start from the inside out with the core of the planet.
In ways scientists still don't fully understand, movements in the partly molten nickel-iron material there generate the planet's magnetic field.
This magnetic influence reaches out into space. It surrounds Earth with a magnetic shield that deflects many cosmic-ray particles - a damaging radiation that, otherwise, might seriously impair Earth's ability to support life.
Surrounding the core is a thick layer called the mantle, and outside that the thin layer of crust that makes up the continents and the bed of the sea. Slow circulations within the mantle constantly renew much of the planet's crust.
New material wells up along great cracks, mainly beneath the major oceans. This material slowly spreads out as old crust dives back into the mantle to be reabsorbed along the great ocean trenches that flank some continental margins. This ceaseless motion slowly moves the great plates into which the crust is broken. Over hundreds of millions of years, these motions displace continents and open and close various seas. Shaping the atmosphere
This action renews the planet's surface and has helped build its atmosphere. Hot material from the upper mantle emerging through volcanoes sometimes builds new land. Volcanic gases add water, carbon dioxide (CO2), and other substances to the air. But the atmosphere we have today has also been shaped by organic life.
Venus, a planet nearly as large as Earth, has an atmosphere 90 times as massive as ours. It's mainly CO2. And that heat-trapping blanket keeps the Venusian surface hot enough to melt lead. Earth has just as much CO2. But most of it is locked up in limestone rocks made of the carbonate shells of marine organisms.
There is some evidence that life forms have ``regulated'' atmospheric CO2 concentrations over many hundreds of millions of years of Earth's evolution. If the planet tended to cool, reduced CO2 removal by life forms allowed the gas to accumulate. At other times, warmer conditions stimulated organisms to remove more CO2.
In general, the biosphere's interaction with the atmosphere is complex and little understood. Many other chemicals are exchanged, including additional heat-trapping gases such as methane.
Scientists now realize they cannot fully understand atmospheric processes and climate change without knowing the influence of life, nor can they fully understand the biosphere without taking account of the effect of weather, climate, and ocean conditions.
Even microscopic marine organisms such as coccoliths affect weather by emitting dimethyl sulfide which in turn forms cloud-seeding particles in the air. As Ralph J. Cicerone of the National Center for Amospheric Research (NCAR) has observed, the cell biology of the ocean ``could represent a hitherto unconsidered ... leverage on the Earth's atmosphere'' by influencing marine cloudiness. Thus, in addition to considering the interaction of ocean, air, and ice sheets, scientists studying climate change have to take account of Earth's life. An ambitious goal
Francis P. Bretherton, chairman of NASA's Earth System Sciences Committee, has described an ambitious goal.
Scientists, he says, need ``to obtain a scientific understanding of the entire Earth system on a global scale by describing how its component parts and their interactions have evolved, how they function, and how they may be expected to continue to evolve on all time scales.''
For NCAR climatologist Stephen H. Schneider, studying Earth as a dynamic, interactive system is long overdue. Taking the issue of CO2 heating due to the burning of fossil fuels as a case in point, he explains:
``In order to have reasonably credible predictive capacity, one has to know how physical and biological and social systems interact. And that means taking a larger-scale view than is traditionally done by [scientific] disciplines....
``That, in turn, means coupling ecology with planet modeling [on computers] with glaciology with economic and social projections of what future chemical output [and fuel use] will be and so forth.''
He goes on, ``I think there are a lot of good reasons to do that. It's just simply that the field is catching up with the need that's been there for a decade or two.''
First of a three-part series. Tomorrow: mission to planet Earth.