Earth Resources: The Little Engine That Could Brake SustainabilityE-an Zen* (1), Paul B. Barton, Jr. (2), Paul H. Reitan (3), Susan W. Kieffer (4), and Allison R. Palmer (5)
* To whom correspondence should be sent. E-mail: ezen@geol.umd.edu Recent discussions on a sustainable future for human society have identified many scientific, social, organizational and philosophical issues (1). Planet Earth can be regarded as an engine that drives all the biological, physical, and chemical activities for ecosystems and human life by providing habitats and affordable materials. Successful pursuit of sustainability depends on the reliability of this engine. In this essay, we focus on the adequate and sustainable supply of four earth materials - water, soil, minerals, and sources of energy (2), how they affect one another, and why they need better stewardship. Water and soil form the basis of all terrestrial ecosystems and of food production; they are absolutely indispensable and have no substitutes. Like all earth resources, they are "consumed" by human use; to replenish them at rates demanded by the modern world requires time and dedicated human attention. Some earth resources can recycle at rates commensurate with the human time scale: years to centuries (e.g. water); we call these renewable. Others recycle on a geological time scale: millions of years or longer (e.g. mineral deposits; fossil fuel); we call these nonrenewable. However, if the rate of resource consumption is high, even "renewable" materials can become effectively nonrenewable. The relations among these rates are one way to gauge the sustainability of a given societal path. Another important metric is the abundance or scarcity of a material. Some resources (e.g. gravel and rocks) will always be available to society as a whole, albeit maybe at higher market and environmental prices. Some initially abundant materials may become scarce through increased demand or quality degradation (liquid petroleum and potable water, respectively). Demands for scarce and nonrenewable resources lead to production peaking, market scarcity, and even social stresses, unless unexpected new finds, and/or economically viable substitutions emerge. These factors are relevant because, except for solar energy input, the earth is essentially a closed system. Continued growth of human population and its growing resource demand have drastic consequences: a stock of "abundant" material that could last 1,000 years with constant demand would be gone in about 250 years with 1% growth, and in about 150 years with 2% growth. Yet, those who seek to manage our economy conventionally view even 2% growth as anemic; developing nations would not be able to escape from poverty at this growth rate if the population grows apace. As humans appropriate ever larger portions of the earth's resources, we modify both the physical environment and the health of the ecosystem (3). WATER. The total water endowment on Earth is large (about 1.4 billion cubic kilometers), but about 97.5% is saline (4) and most of the remainder is tied up in ice sheets and glaciers. Less than 1% of the total amount is accessible as fresh surface- and groundwater. Continued and adequate availability of potable fresh water is a looming problem because of increasing human use for food production, personal use, industry, and urbanization; desalination is not a viable option for much of the world that suffers water shortage (5). Industrial and agricultural enterprises often contaminate both surface water and groundwater (6); remediation of groundwater is a particularly slow and uncertain process. Groundwater distribution is determined by the subsurface distribution of aquifers, commonly independent of watershed configuration. Mining of groundwater has put arid and semi-arid land into food production (5) but groundwater is being pumped out, world wide, at nonrenewable rates. Once the water is pumped out, recharge can be slow and an aquifer may even lose its capacity to be fully recharged because of the collapse of the intergranular storage (pore) space, resulting in permanent aquifer loss and serious land subsidence (e.g. 7). We need to avoid unintended collateral ecological and economical harm, both local and
downstream, that result from water diversion for irrigation (4,5). We need to carry out water
conservation within a trans-national framework because national boundaries do not coincide
with watersheds and aquifers; unfortunately, the task is made difficult by both political realities SOIL. Unlike water, the renewal rate of soil is slow on the human time scale. Soil
regeneration is either by deposition of sediments or by the physical, chemical, and biological
breakdown of bedrock, plus its biologically driven restructuring into a highly organized, teeming, Plowing, overgrazing, acidification from acid rain, and use of fertilizers and biocides change the physical, chemical, and biological nature of soil. Though the additives may increase agricultural productivity, their excessive applications in the long run could result in leaching of mineral nutrients, harming of the indigenous biota, increased erosion, and desertification. Additive-laden runoffs produce effects such as down-stream eutrophication and deadzones (e.g., 8) Numerous studies reported that worldwide, soil erosion occurs many times faster than the renewal rates and seriously hampers prospects for adequate future food production (9), though the basis for the estimates has been challenged (10). MINERALS. Humans use minerals both directly and to transform or transport other materials. Some mineral resources are abundant, some are scarce; all are nonrenewable (11). Most mineral deposits are geochemically concentrated relative to the average rock; some scarce mineral resources are recovered as byproducts. Ironically, the inventory of scarce minerals (e.g. rare-earth elements-bearing minerals) may increase abruptly by a large new discovery, but the inventory of abundant ores (e.g., copper) is unlikely to increase significantly because a single or even a few new deposits would not increase the total by much. Increasing use and diminishing supply of a nonrenewable mineral will cause its market price to increase. Even though production can continue for a while, market economics will increasingly limit the use of the resource. Recycling and substitution then will become imperative to reduce the impact of depletion, but both recycling and substitution require energy, water, and other resources, and the process may be costly or environmentally harmful (12). ENERGY. All human activities use energy. At present, our main source of energy is fossil fuels - solar energy concentrated biologically and stored over geological eons. Two major sources of energy, liquid petroleum and natural gas, are being depleted by heavy use; global production peaking for both is expected to come before 2050 (13), ironically near the date predicted by NAS (1) for approaching sustainability. Coal is plentiful, but even a "stable" global population of 9 billion, coupled with increased per capita energy demand, will exhaust that resource in a couple of centuries (12). Environmentally benign use of coal urgently awaits a technological breakthrough. Even benign uses of coal and of "unconventional" resources, such as oil shale and tar sand, consume large amounts of water, produce unacceptable quantities of carbon dioxide, and can lead to major land destruction and environmental pollution (14). Other than solar energy, renewable energy resources, including wind and geothermal, even taken together cannot satisfy the world's needs (12), and each resource has its own environmental and ecological consequences, as well as economic and technological hurdles. Fuel cells that use fossil fuel can improve fuel efficiency but do not add to the total inventory. Fuel cells also can convert power-plant electricity into portable energy, but do not form a primary energy source. Nuclear energy can add to electricity production, but the world's conventional uranium resources may not last more than a few decades (15) so reprocessing and use of breeder reactors would be necessary and require overcoming political barriers. A PRUDENT STRATEGY. To reduce the societal shock of shortfalls of earth materials, a global monitor system comparable to the ongoing inventory for selected minerals is highly desirable (16; 10). The system must be able to identify problem areas in advance so as to allow timely development of substitutes, and must include reliable estimates of uncertainty in the data and the inferences. It also should include constantly updated, realistically accurate and credible (though not necessarily precise) global assessment of current and future material demand, flow, and availability. We need to make sure that in allocating earth resources the non-human ecosystems get fair shares, so that they too may sustain a healthy existence instead of the current situation where the ecosystems receive mostly human rejects (3). The ongoing efforts to rehabilitate the Pacific salmon, and the vigorous debates on assigning priority to irrigation, timber harvesting, or ecosystem preservation, constitute forward-looking dialogues (17). If only from self-interest, humans must learn that we are not outside of the global ecosystem (18). If we are to be responsible stewards of the Earth for the benefit of future generations as well as our own, then we must use all earth resources efficiently, and frugality must be our guiding principle (19). To reverse our profligate trend is a stupendous task. Rich and poor societies must work together to understand in a holistic way how they affect the earth. We who live in wealthy societies must reexamine our value systems, and recognize that we ignore the misery of other humans at our own peril. We need to examine our pricing and subsidy policies so as to better track the real cost of commodities. We must reexamine our premise that "growth" is intrinsically good or desirable; we need to recognize and enforce trans-cultural, trans-national, trans-generational, and even trans-human equity. The little engine that drives our economic and ecologic train is powered by the ingenuity of humans in the use of Earth resources. Properly maintained and used, this big little engine will pull a train to its destination; otherwise, it could put a serious brake on our journey toward sustainability. A successful journey requires all of us to understand and use our human and Earth resources wisely Notes and References: (1) National Research Council, Our Common Journey: A Transition Toward Sustainability, National Acad Press, Washington, DC (1999); R.W. Kates, W.C. Clark, et al., Science 292, 641 (2001); J.E. Tilton, Resources Policy 22, 91 (1996); World's Scientific Academies, Transition to Sustainability in the 21st Century (2000), http://interacademies.net/intracad/tokyo2000.nsf/all/home. (2) P.J. Cook, Brit. Geol. Survey Tech Rpt WQ/97/1 (1997). We do not discuss air in this review. (3) P.M. Vitousek et al., Science 277, 494 (1997). (4) M. de Villiers, Water: the Fate of Our Most Precious Resource (Houghton Mifflin, 2000); P.H. Gleick, ed., Water in Crisis (Oxford Univ. Press, 1993). (5) S.L. Postel, G.C. Daily, P.R. Ehrlich, Science 271, 785 (1996); S. Postel, Last Oasis: Facing Water Scarcity (Norton, 1997); S. Postel, Pillar of Sand: Can the Irrigation Miracle Last? (Norton, 1999); P.H. Gleick, (1993); P.H. Gleick, The world's water, 2000-2001 (Island Press, 2000). (6) S. Steingraber, Living Downstream (Vintage, 1998). (7) National Research Council, Mexico City's Water Supply: Improving the Outlook for Sustainability National Acad Press, Washington, DC (1995) (8) D. Malakoff, Science 281, 190 (1998). (9) D. Pimentel, et al., Science 267, 1117 (1995); H.W. Kendall, D. Pimentel, Ambio 23, 198 (1994); C.J. Barrow, Land Degradation (Cambridge Univ Press, 1991); World Resources Institute, World Resources 1998-99 (Oxford Univ Press, 1998). Channelization and dam construction on large rivers deprive the lower, generally most productive delta regions of replenishment (e.g., the Mississippi and the Nile rivers), leading to waterlogging, land subsidence, loss of nutrients, and damage to the ecosystem. See, for example, D.J. Stanley, A.G. Warne, J. Coastal Research 14, 794 (1998). (10) S.W. Trimble, P. Crosson, Science 289, 248 (2000). (11) Examples of essential and major mineral resources are aluminum, copper, gold, iron, phosphate, sand and gravel, and silver. Many other mineral resources are essential to our economy; these include boron, chromium, cobalt, gallium (a "hitchhiker" from aluminum ore), fluorine, helium, manganese, nickel, platinum group, rare earths, sulfur, titanium, and tungsten. (12) W. Youngquist, GeoDestinies (National Book Co., 1997); P. Hawken, A. Lovins, L.H. Lovins, Natural Capitalism (Little, Brown, 1999). (13) C.J. Campbell, The Coming Oil Crisis (Multi-science Publ. Co., 1997); R.C. Duncan, W. Youngquist, Natural Resources Research 8, 219 (1999); H. Gluskoter, Div Fuel Chem, Am Chem Soc, Preprints 44, no. 1, 36 (1999). Even a rare, 10 billion barrel supergiant field, if all could be extracted, would delay peaking by only a few months. (14) S. Fetter, Bull. Atomic Sci., 28 (2000). One large potential energy resource, methane clathrate, occurs in buried strata of shallow continental shelves and in permafrost regions, commonly in low concentrations. Even if the concentration is favourable, its mining in such fragile ecosystems may be environmentally extremely harmful. See R.L. Kleinberg, P.G. Brewer, Amer. Scientist 89, 244 (2001). (15) World Resources Institute, World Resources 1996-97 (Oxford Univ. Press, 1996); W.C. Sailor et al., Science 288, 1177 (2000). (16) U.S. Geol. Survey, Circular 1178 (1998); Worldwatch Institute, State of the World series; International Energy Agency, World Energy Outlook series; National Research Council, Nature's Numbers, National Acad. Press, Washington DC (2000); National Research Council, Assigning Economic Value to Natural Resources, National Acad. Press, Washington DC (1994). In an economic system where market price reflects the true cost, including the resource and environmental costs, price might provide the early warning, but that is not the reality. Price is not likely to give warning far enough ahead for planning purposes, and the adequacy of this throttle is not assured. (17) National Research Council, Upstream: Salmon and Society in the Pacific Northwest National Acad Press, Washington DC (1996); N. Johnson et al., Science 292, 1071 (2001). (18) A.R. Palmer et al., GSA Today (2000), also http://bcn.boulder.co.us/basin/local/sustainintro.html (19) For instance, labour-saving devices require material and energy and produce wastes: with our large human workforce, these become double loads to the Earth and barriers to sustainability. We need to prioritize our use of resources and emphasize regional coordination, bearing in mind that the current open global commerce could end abruptly. See J.P. Holdren, Issues in Sci Tech 17, no. 3, 43 (2001). (20) We thank Bill Clark, Julio Friedmann, Bob Hatcher, Walter Hearn, George Hornberger, Bob Kates, and Alta Walker for their helpful comments. |
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