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The dynamic biosphere


Earth's atmosphere and biosphere exchange energy, water, carbon dioxide, and other trace substances on all space and time scales. These linked exchanges depend on, and in turn alter, the states of the atmosphere and biosphere themselves. Because the atmosphere-biosphere is thus a coupled and dynamic system, no global scientific or socioeconomic question can be usefully examined in isolation; our knowledge of the processes that maintain planetary equilibrium--and of the events that could disturb that balance--is necessarily interdisciplinary. For this reason, 21stC has assembled a wide range of topics, ideas, and perspectives in this special issue, "Biospheres," to illuminate what contemporary research tells us about these interlocking global issues.

From leaf level to climate level, and vice versa

IT'S ESSENTIAL to appreciate how small-scale events can influence larger-scale events in a complex system. The most frequently cited example of this principle is a butterfly's flapping wings provoking a hurricane thousands of miles away, but a better-understood case might be the relations between plant physiology and global climate. Temperature at the land surface results directly from competition between the energies gained and energies lost by the biosphere. The solar energy absorbed is the difference between incident and reflected energy, and the reflectivity of the biosphere is governed by leaf phenology and soil conditions. Another source of energy is downwelling longwave (infrared) radiation emitted by the atmosphere; the magnitude of this radiation depends on temperature and amounts of CO2, water vapor, and other greenhouse gases. The biosphere cools itself by emitting longwave radiation, sensible heat associated with turbulence, and latent heat associated with evaporation and transpiration. The thermal and water status of the biosphere regulate these heat losses.

In most plants, the exit points for water, stomates on the undersurfaces of leaves, are also the entry points for CO2 for photosynthesis. The flow rates are determined by the stomatal closure, which plants adjust according to the ambient climate and CO2 concentrations so as to use water most efficiently, or gain the maximum carbon for the water loss. In this way, the atmosphere-biosphere exchanges of energy, water, and carbon are intricately linked, and perturbation of one cycle invariably perturbs the others. Changes in one aspect of climate, e.g., atmospheric CO2 levels, may affect water use efficiency of plants and the allocation of plant material to leaves and roots, altering the reflective ability, transpiration, and photosynthesis of the entire plant. These in turn would foster further feedback effects on the climate. Science has begun to understand these processes in detail, but there is much information to accumulate and synthesize on a systemic level. Columbia's Biosphere 2 facility for ecological research and education, as discussed in several articles in this issue, now makes it possible to connect leaf-level events with observations at a full ecosystemic scale, offering the hope that research can explicitly address questions whose answers we have only been able to infer piecemeal.

Change, the only constant

EVIDENCE FOR THE co-variation of the atmosphere and biosphere abounds in the historical and paleo-records. In the past 40 years of continuous CO2 measurements, the atmospheric CO2 increase is only about half that from fossil fuel combustion, because the terrestrial biosphere and the oceans have shared in ameliorating the CO2 growth rate by absorbing some of the anthropogenic CO2. The year-to-year fluctuations in atmospheric CO2 are also partially related to varying photosynthesis and/or respiration in response to climate changes related to El Niño/Southern Oscillation events and volcanic eruptions. Furthermore, seasonal amplitudes of atmospheric CO2, a measure of biospheric breathing, have increased since the 1980s together with surface air temperature, suggesting that the biosphere has been churning at a faster rate related to the longer growing season at middle to higher latitudes in the Northern hemisphere. Since transpiration and CO2 absorption are under the same stomatal controls, the CO2 amplitude changes imply feedbacks on the atmospheric water and energy cycles as well.

On longer time scales, the paleo-data show that vegetation distributions have varied with climate. About 6,000 years ago, when the Earth's orbit around the sun produced enhanced seasonality in the Northern hemisphere, and summer temperatures over the Northern continents were 2 to 4 °C warmer than the present, boreal forests extended 300 to 500 km further north, and the Sahara desert was smaller. About 20,000 years ago, during the Last Glacial Maximum, low-density vegetation, typical of those in cold, dry climates, covered the ice-free portions of the Earth's surface.

These planetary-scale changes in vegetation distribution translate immediately to, and result from, changes in the energy, water, and carbon transfers between the atmosphere and the biosphere on the leaf scale. Equally important, as the amount of carbon stored in the biosphere is altered, mass balance requires alteration of the atmospheric and oceanic carbon reservoirs as well: CO2 was about 25 percent lower during the Last Glacial Maximum than in the pre-industrial era. Cooling was maintained not only by the highly reflective ice cover, but also by the reduced levels of CO2 and water vapor in the atmosphere and the more reflective vegetation, which absorbed less sunlight.

The coupled climate-biosphere changes in the past show clearly that neither system has remained untouched while the other was disturbed. The terrestrial biosphere has been important in determining the levels of CO2 and water vapor in the atmosphere, which in turn have contributed to defining the climate for the biosphere. The biosphere acted to magnify in some cases, and temper in others, the climate changes.

Humanity's impact

OUR SPECIES IS the agent of the most extensive and most rapid change in the biosphere--the productivity of which sustains our existence. The annual net primary productivity (NPP) of the biosphere, i.e., the amount of matter fixed by photosynthesis after accounting for autotrophic respiration, is about 130 gigatons per year. We directly use 3 percent of the annual NPP as food, materials, or fuel, but we destroy or turn over nearly 40 percent of the terrestrial and aquatic NPP in acquiring that 3 percent. Meeting the needs of an expanded human population thus presents a risk to the biosphere's self-regulating processes as well as a strain on consumable resources, as Drs. Joel Cohen, John Bongaarts, and Allan Rosenfield discuss in their conversation about the processes and implications of population growth.

Agricultural issues are far from peripheral concerns for an urban research university, as Scott Veggeberg points out in describing Columbia's research into the relations of agriculture, plant biology, and climatology. While increasing CO2 in the atmosphere and the anticipated climate change may benefit some agricultural practices in some regions, they are not likely to meet the needs of the expanded population. Agriculture has taken over most areas suitable for cultivation, and there is little potential for expansion. Already, about 50 percent of the Earth's land surface--or 75 percent of the surface excluding rock, ice, and uninhabitable barren lands--has undergone some degree of human disturbance; what we do with the rest remains an open question.

The remaining undisturbed habitats are found in the rain forests of South America, the arid and semi-arid regions of Australia, and the taiga and tundra areas of the Arctic. In Brazil in 1991 alone, about 11,100 km²--half the size of Massachusetts--was destroyed. However, only about 30 percent of the deforestation in Amazonia is by small farmers in their quest for arable lands; the remainder occurs on larger properties for cattle ranching and land speculation. Natural erosion and erosion of the cultivated and abandoned areas also diminish arable land. To date, global economic processes have fared poorly in protecting such regions, but efforts are under way to marshal market forces to value, rather than undervalue, public goods such as land and air quality. Whether human economic institutions are well suited to this task is the subject of Doug Henwood's examination of the theories of Columbia economist Graciela Chichilnisky.

A related question, the reduction of biodiversity, poses different threats to our well-being: In defending our species against its microbial enemies, we rely on nature's chemical laboratory more than most of us are aware. A genetically impoverished biosphere, as Dickson Despommier illustrates, would rob us of potential armor that we may deeply regret losing; preserving diversity benefits all species, including humans.

The outlook: stewardship, like it or not

LIFE IS CONTINGENT upon the availability within a tolerable range of resources, from climate to nutrients to DNA. Alteration of these resources leads to alteration in the structure and functioning of life. The atmosphere-biosphere system has danced and lurched through its own rhythm of natural oscillations, through which each adjusts to changes in the other in an attempt to achieve a temporary equilibrium. Humans, through their increasing demands for energy, food, and other resources, have set into motion biogeophysical and biogeochemical feedbacks that can disturb the energy, water, and carbon cycling of the entire system. The human perturbations are happening at a magnitude and pace faster than any known natural oscillation. In this way, our pressures on the environment are also taxing resources we need to survive. Predicting how the Earth system may respond to this deliberate and unprecedented perturbation, and how humans can sustain themselves, presents an inescapable challenge.

Knowledge of how our biosphere has behaved in the past, as reconstructed by Wallace Broecker in his discussion of Earth's oxygen reserves, provides an indispensable context for our understanding of that challenge. Turning toward the future, some researchers speculate that massive new geoengineering endeavors might be a way to better handle our responsibilities as stewards of the Earth; as evinced by the various projects discussed by Patrick Huyghe, geoengineering offers both great promise and great risk. Regardless of whether humans ever decide to send huge mirrors aloft or fertilize the oceans with iron, the traces of Homo sapiens's activities are an ineradicable component of the modern biosphere, and the philosophy of planetary management--the argument that we should consciously, rather than unconsciously, shape our planet--is likely to occupy a prominent place in coming debates.

An essential task for researchers in a democracy is educating the public about earth science. In an age when the public consciousness floats on unprecedented tides of information and pseudo-information, the "Publisher's Corner" editorial by Maxine Singer argues forcefully that scientists bear a responsibility to be more informative, not just impressive, in addressing laypeople. 21stC's Metanews department also presents three cases in which the press has handled stories involving global research--including one that continues to rattle the foundations of international politics--with varying degrees of responsibility. Educators and scholars at Biosphere 2, the newest and perhaps most adventurous of Columbia's research enterprises, take seriously the idea that the scientific community and the community as a whole should comprehend each other, expressing this commitment by combining the missions of research, academics, and public education. The research university cannot stand alone among social institutions in preparing citizens for biospheric leadership, but universities have the distinct privilege and responsibility of translating the biosphere's complex languages into messages that can motivate everyone who is willing to listen.

Related links...

  • Greenpeace International, Amsterdam

  • Sierra Club

  • Environmental Defense Fund

  • Union of Concerned Scientists Global Resources Program

  • U.S. Global Change Research Program

  • Strategic Environmental Research and Development Program (SERDP), U.S. Department of Defense multi-agency program

  • Earth Sciences Directorate, NASA-Goddard Space Flight Center

  • Earth & Sky radio series, sponsored by National Science Foundation and National Oceanic and Atmospheric Administration

  • Global and Planetary Change, Elsevier Publishing

  • Center for Environmental Information, Rochester

  • United Nations Environment Programme, Geneva

  • National Center for Atmospheric Research

  • U.S. Long Term Ecological Research (LTER) program

  • Institute for Global Environmental Strategies

  • International Institute for Sustainable Development

  • EnviroWeb

  • CoVis (Learning Through Collaborative Visualization) Geosciences Web Server

  • Green Parties of North America (political as well as environmental material)

  • EcoNet, Institute for Global Communications

  • David Brower's Earth Island Institute

  • Program for the Human Environment , Rockefeller University

  • Consortium for International Earth Science Information Network (CIESIN)

  • BioNet (Biodiversity Action Network)

  • Rainforest Action Network

  • Elisabet Sahtouris, Earthdance: Living Systems in Evolution, online book of Gaian philosophy; foreword by James E. Lovelock

  • Michael Wysession, "The Inner Workings of the Earth," American Scientist, March-April 1995

  • Eric J. Barron, "Climate Models: How Reliable Are Their Predictions?"

  • Global Change

    INEZ FUNG, ScD.,NASA/Goddard Institute for Space Studies and is at the School of Earth and Ocean Sciences, University of Victoria, Canada. She is an adjunct senior scientist at Columbia's Lamont-Doherty Earth Observatory.

    PHOTOS: O.C. Rejlander, adapted by Howard Roberts

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