The Science of Global Change

Scientists working to improve the understanding of human impacts on global environmental systems are today challenged to synthesize fragmented studies into a global perspective (1,2). The challenge arises because these scientists must work with partial information. Scientists by nature are reductionist and tend to isolate a few variables for study and ignore the rest (3). The goal of this paper is to provide a guide for synthesis of the information presented in the papers that follow. It is critical that researchers explicitly define the boundaries of the domains they study, their selected temporal and spatial resolution, their specific variables, and the units they employ. A discussion of the papers in this volume is used to demonstrate how these characteristics are critical to synthesizing fragmented studies of the global environment.

The ozone layer is a very important component of the atmosphere which shields the earth's surface from damaging ultraviolet radiation from the sun. Ozone is continuously being generated by the action of solar radiation on atmospheric oxygen, and it is destroyed by catalytic processes involving trace amounts of free radical species such as nitrogen oxides. More than a decade ago the release of chlorofluorocarbons (CFCs) of industrial origin was predicted to lead to stratospheric ozone depletion. Photodecomposition of the CFCs in the stratosphere produces significant amounts of chlorine free radicals, which are very efficient catalysts for the destruction of ozone. Recent observations have established clearly that the rapid decline in ozone over Antarctica in the spring months is indeed caused by man-made chlorine species.

Acid deposition has been known to exist since early in the industrial age. The principle pollutants responsible for the elevated levels of acidity are the oxidized forms of sulphur and nitrogen that have been emitted as by-products from non-ferrous smelters, fossil-fueled power generating stations, and motor vehicles. The pollutants are transported substantial distances from the source areas by the atmosphere. They are deposited on receptor regions remote from the sources as acidic rain, snow, and fog or as gasses and dry particulates.

Sensitive ecosystems that cannot neutralize the unnatural levels of acidity are adversely affected. Soil nutrient systems may be altered with a resulting direct or indirect damage to forest. Aquatic habitats have been chemically altered and many lakes and streams no longer support the traditional life forms. Fish have been lost from many lakes with a resulting affect on other food-web elements.

Human respiratory functions may be impaired. Elevated levels of metals have been observed in some foods and drinking water in some locations. Masonry works, stone structures and heritage sculptures are subject to accelerated rates of erosion.

Control and reduction of emissions of acidifying pollutants have been legislated in United States, Canada and in some European nations. When these reductions are affected, a reduction of about 60,000 in the number of acidified lakes is expected to be achieved in Canada. However, many highly sensitive lakes will be expected to remain acidified.

The trace free radicals HO and HO₂ (collectively HO_x) play central roles in chemical processes in the lower atmosphere. On the one hand, they are active in controlling buildup of atmospheric trace-gas concentrations that could have marked effects on earth's climate or habitability. On the other hand, they are responsible for the symptoms of anthropogenic gaseous emissions known as acid precipitation or photochemical smog. We review the characteristic chemical processes of the lower atmosphere from the perspective of HO_x free-radical chemistry. The discussion incorporates chemical processes both in the natural atmosphere and in polluted air. Uncertainties in our chemical understanding of tropospheric HO_x processes are enumerated, along with the role that HO_x measurements may play in exploring these uncertainties. Finally, we examine the role of HO and HO₂ in controlling trace-gas concentrations and the reciprocal control that hydrocarbons and oxides of nitrogen exert on these radicals.

The name "dust", is used in a variety of ways, and with different meanings. These range from the material that accumulates on the earth's surface, such as on streets and in living and working environments, to the particulate material suspended in the atmosphere. In this paper I wish to consider these two materials in terms of their chemical composition, sources and relationship between them. The names used for the two materials will be "surface dust" and "atmospheric dust". The word "aerosol" may also be used for atmospheric dust but it more properly applies to the finer particles of atmospheric dust and includes liquid aerosol (1). Both surface and atmospheric dusts are increasingly seen to be a hazard to human beings as they are a source of intake of toxic materials such as heavy metals. For this reason study is important of the composition and sources of the dusts.

Both dusts

Through the processes of atmospheric transport and deposition, many anthropogenic contaminants such as industrial organics, pesticides, and trace metals have become widely distributed around the globe. Due to the phenomenon of long-range atmospheric transport, even the most remote areas of the planet are not out of range of contaminants emitted from distant anthropogenic sources. Many of these airborne contaminants are toxic and persistent, can bioaccumulate, and may remain biologically harmful for long periods of time. Although airborne contaminants are considered primarily a human health problem, there is increasing concern that they may have deleterious ecological consequences. When sensitive terrestrial plants and other biota experience chronic exposure to low concentrations of airborne toxic chemicals, sublethal effects may occur, with subsequent impacts on ecosystem structure and function.

In Mexico City, several air quality parameters are measured continuously by an Automated Monitoring Network operated by the Under Secretariat of Ecology. Carbon monoxide, particulate matter, sulfur dioxide, nitrogen oxide, and ozone are the contaminants exceeding Air Quality Standards. Emissions produced by 2.7 million vehicles and 35,000 commercial and industrial outfits are not easily dispersed in a Valley located at 2240 m and surrounded by two mountain chains which hinder air circulation. An Integral Program, recently established to alleviate pollution, is briefly described.

The World Health Organization (WHO) and the United Nations Environmental Programme (UNEP) have been collaborating since 1974 on an urban ambient air monitoring project. Monitoring results indicate that about 50% of the cities do not exceed the annual WHO SO₂ guideline of 40-60 μg/m3 and only about 20% of the cities do not exceed the annual suspended particulate matter guideline of 60-90 μg/m3. Fortunately, progress in controlling sources is indicated by the downward trends in levels of SO₂ and particulates measured in many of the cities. Fewer data are available for nitrogen dioxide, carbon monoxide and lead. It appears that emissions are increasing for all five pollutants in developing countries which will likely result in an increased risk to the public health of the world's 1.8 billion city dwellers.

A month-long study of the effects of ultraviolet radiation (UV) on phytoplankton and ice-algae collected from Arthur Harbor, Anvers Island, Antarctica, was carried out during November-December 1987. The parameters studied included: primary production rates, photosynthetic pigments and the photosynthesis-irradiance (P vs I) relation-ship. The results showed an enhancement of the photosynthetic rates when UV was excluded; conversely, production rates were lower under enhanced UV conditions. Significant changes in phytoplankton pigmentation also occurred as a result of changes in the UV levels. The implications of these findings to our understanding of the trophodynamics of the Southern Ocean and the bearing these have on global marine productivity are discussed.

Pollution of the Laurentian Great Lakes exemplifies the serious problems associated with the impact of human activities on a major aquatic ecosystem. Problems have included serious bacteriological contamination, cultural eutrophication and contamination by hundreds of anthropogenic, potentially toxic substances. Management of the Great Lakes is divided between Canada and the United States and involves eleven governments at federal, state and provincial levels. Despite this environmental and institutional complexity, the Great Lakes have responded dramatically to remediation initiatives. Human impacts on the lakes associated with development of the Great Lakes Basin are discussed in the context of the unique binational arrangements agreed to by the two countries to restore and protect this shared, unique global ecosystem.

The distribution of persistent marine debris, adrift on world oceans and stranded on beaches globally, is reviewed and related to the known inputs and transport by the major surface currents. Since naturally occurring processes eventually degrade petroleum in the environment, international measures to reduce the inputs have been largely successful in alleviating oil pollution on a global, if not on a local, scale. Many plastics, however, are so resistant to natural degradation that merely controlling inputs will be insufficient, and more drastic and costly measures will be needed to cope with the emerging global problem posed by these materials.

Human activities that are transforming the global environment are reflected in the chemical, physical and biological constituents and dynamics of the world's rivers. However, because of the spatial and temporal variability of rivers and the complexity of river dynamics, relatively little is known with much certainty about the water quality of the world's rivers, especially as quality relates to human activities and global change. Shortcomings of current river water quality assessment approaches include inadequate emphasis on river hydrology and how it relates to biogeochemical transformations, uncertainties arising from inter-laboratory variation in methodologies, and the common grab sample "shotgun" or parametric approach often utilized by water quality monitoring agencies.

An alternative to the traditional fixed-station parametric river sampling network is the mechanistic or intensive survey approach in which interrelationships among topography, geology, climatology, ecology, hydrology, biogeochemistry and human activities are utilized in the assessment process. Mechanistic approaches may be classified as quantitative, semi-quantitative and qualitative. These are illustrated with examples from three major problem areas which have developed as a result of human activity: dissolved oxygen depletion, erosion/deposition of soil and potentially toxic trace elements.

Rivers, like the atmosphere and oceans, are integrative and reflect conditions within their boundaries. Critical to an understanding of the role of human activity in environmental change is an understanding of the impact of human activity on river quality and how river quality may be used as an indicator of environmental change. Current data collection practices, based largely on the traditional parametric or ambient fixed-station network approach, do not generally provide the information necessary to relate human activity to quality of river water or to utilize water quality data as an indicator of global environmental change.

What is needed is an alternative approach which permits development of valid cause and effect relationships. This strategy, one involving intensive surveys, is referred to here as mechanistic. The Willamette River, Oregon, USA, is used as a case study to illustrate quantitative, semi-quantitative and qualitative approaches to mechanistic assessment of river water quality using, respectively, dissolved oxygen depletion, erosion/deposition and potentially toxic trace elements as examples.

Metal and hydrocarbon pollution and eutrophication that have occurred in the Lagoon of Venice in this century are discussed. The evolution of pollutant concentrations and fluxes has been determined by analyzing sections of radioisotopically-dated sediment cores. Metal loads in the superficial sediments and concentrations of metals and hydrocarbons in various organisms are reported. The eutrophication increase has been monitored both by analyzing changes occurring in algal and animal associations, and by comparing nutrient concentrations obtained during different periods using the same methodologies. An evaluation of present Lagoon conditions is presented in conjunction with some possible interventions that would improve future Lagoon quality.

Despite the use of 2.5 million tons of pesticide worldwide, approximately 35% of potential crop production is lost to pests. An additional 20% is lost to pests that attack the food post-harvest. Thus, nearly one-half of all potential world food supply is lost to pests despite human efforts to prevent this loss. Pesticides, in addition to saving about 10% of world food supply, cause serious environmental and public health problems. These problems include: human pesticide poisonings; fish and bird kills; destruction of beneficial natural enemies; pesticide resistance; contamination of food and water with pesticide residues; and inadvertent destruction of some crops.

About 16% of the U. S. commercial energy use is in agriculture for food production and processing. The processing of food requires nearly twice as much energy as for production. As commercial energy has replaced animal power and human effort in farming and has helped provide fertilizer and chemicals for plant production, production has increased by two orders of magnitude over the past 100 years. There has been a rapid shift of processing off-the-farm to commercial enterprises. The possibilities of using the products of agriculture to meet energy needs particularly by substituting biomass products for commercial energy are discussed.

Biological formation of methane is the process by which bacteria decompose organic matter using carbon dioxide as an electron acceptor in absence of dioxygen or other electron acceptors. This microbial activity is responsible for carbon recycling in anaerobic environments, including wetlands, rice paddies, intestines of animals, aquatic sediments, and manures. The mixed consortium of microorganisms involved includes a unique group of bacteria, the methanogens, which may be considered to be in a separate kingdom based on genetic and phylogenetic variance from all other life forms. Because methane is a greenhouse gas that is increasing in concentration, its fluxes from various sources are of concern. Biomethanogenesis may be harnessed for conversion of renewable resources to significant quantities of substitute natural gas and to reduce levels of atmospheric carbon dioxide.

Processes that reduce the productivity of arid and semi-arid lands, collectively known as desertification, affect more than 3 billion hectares or more than 80% of such lands. The degradation process results in redistribution of water and nutrients, loss of find soil fractions and replacement of palatable plants with undesirable plants. These changes frequently uncouple rainfall and productivity on a temporal scale. This uncoupling is probably due to modification of the nitrogen cycle as a result of the desertification processes. Changes in vegetation can produce changes in fluxes of radiatively active gasses and a variety of organic volatiles to the atmosphere. Redistribution of soil and water may produce "hot" spots for denitrification and for ammonia volatilization that differ in extent both spatially and temporally from undesertified ecosystems. Dust from desertified areas can modify the chemistry of rainfall in areas distant from the dust source.

Contemporary forest declines were initiated about 1950-1960, virtually simultaneously throughout the industrial world at the same time as damage to aquatic systems and structures became apparent. A broad array of natural and anthropogenic stresses have been identified as components of a complex web of primary causal factors that vary in time and space, interact among each other, affect various plant growth and development systems and may result in the death of trees in mountainous ecosystems. As these ecosystems decline, the alterations in forest ecology, independent of the initial causal complex, become themselves additional stress factor complexes leading to further alterations.

This paper reviews some lessons of the climatic past that are useful in evaluating forecasts of the climatic future. Researchers have employed numerical models of the earth-atmosphere system in experiments designed to predict temperature and moisture anomaly patterns that might accompany continued increases in concentrations of greenhouse gases. It is instructive to consider the well-publicized results of those experiments in view of what is understood about climatic behavior based on instrument-derived and reconstructed climatic records. Such analyses indicate that climate is inherently variable over a broad range of time scales, climatic change is geographically non-uniform in both direction and magnitude, climatic fluctuations may involve changes in frequency of extreme episodes as well as trends in mean values, and climate is shaped by a host of interacting factors. Thus, the lessons of the climatic past enable us to set boundary conditions and make realistic demands on climate predictions based on numerical models.

Increasing atmospheric CO₂ is likely to produce chronic changes in global climate, as it may have done in the geologic past. Future CO₂-induced changes in temperature and precipitation distribution changes could equal or exceed the changes which have occurred over the past 160,000 years and have affected the global carbon cycle. We consider ocean and terrestrial processes that could involve large changes in carbon fluxes (>2 Pg C·yr^-1) or changes in storage in large carbon pools (>200 Pg C) resulting from CO₂-induced climate changes. These include (1) air-sea exchange of CO₂ in response to changes in temperature and salinity; (2) climate-induced changes in ocean circulation; (3) changes in oceanic new production and regeneration of organic debris caused directly by climate change; (4) altered oceanic nutrient supply needed to support new production due to climate-induced alteration of ocean circulation and river discharge; (5) CaCO₃ compensation in sea water; (6) altered river nutrient flux and effects on coastal organic matter production and sediment accumulation; (7) seasonal balance between GPP and decomposition-respiration in terrestrial ecosystems in response to changes in temperature and precipitation; (8) successional processes in terrestrial ecosystems and formation of new plant associations in response to climatic change; (9) effects on soil nutrient availability, which amplifies ecosystem responses to climate change; (10) and responses of northern forests, tundra, and peatlands which have, until recently, been a sink for CO₂. The potential effect of these processes on the rate of atmospheric CO₂ concentration changes are estimated where possible, but not much quantitative information at a global scale is known, so uncertainty in these estimates is high. Each of these secondary feedbacks, however, has the potential of changing atmospheric CO₂ concentration in magnitude similar to the effects of the direct human processes (fossil fuel burning and land clearing) responsible for the concern about global warming in the first place. It is therefore urgent that these uncertainties be resolved. Lines of research to accomplish this are suggested.

Qualitatively, terrestrial vegetation is known to be an important part of the global carbon cycle. It affects the carbon cycle directly through photosynthesis, respiration, and decay of organic matter; and indirectly by affecting climate. Quantitatively, however, little is known about how vegetation fits into the global carbon budget.

Computer models are the primary tools used to assess the functioning of vegetation in the global carbon cycle, but models use poor data and are too simple to give reliable results. The most commonly used estimates of global vegetation reservoir size range between 420 and 830 gigatons of carbon. However, using the most current estimates of carbon density we have calculated a new estimate of 328 gigatons of carbon. This result demonstrates that a concerted effort must be made to systematically measure the biomass of vegetation on a global scale. Until this is done, basic questions such as whether vegetation is a net source or sink of carbon in the global carbon budget will be left unresolved.

Cutting and burning of the world's forests is occurring at unprecedented levels and is dramatically influencing biogeochemical cycles at local, as well as global scales. Biogeochemical cycles are altered through losses associated with wood export, volatilization, convective transport, and accelerated rates of erosion and leaching losses. These anthropogenic activities are resulting in nutrient losses that far exceed natural rates of reaccumulation. As deforestation alters microclimates and hydrological cycles, internal nutrient cycles can be influenced for decades to centuries. The ultimate results of excessive levels of deforestation and biomass burning include losses in site productivity, desertification and/or species extinctions. Biomass burning is also a significant source of CO₂, CH₄, NO_x, and other products of combustion that influence climate and atmospheric geochemistry.

Global change instruction for undergraduate college students should emphasize relationships among the natural sciences, social sciences, and humanities over specialized study of each. Potentially any of these areas of knowledge could be the starting point for multidisciplinary understanding of a changing global environment. A groundwork has been laid at Florida State University, based on experience in teaching honors students from a natural science and especially chemistry perspective, for a broader teaching program for general freshman and sophomore students who intend to major in any area.

High school students should have a greater understanding of global environmental issues. This can be accomplished by using environmentally-relevant examples to teach high school chemistry. Appropriate demonstrations and laboratory experiments that illustrate these topics are suggested. To incorporate additional environmental chemistry in the secondary curriculum, help from environmental scientists will be needed.

Universities must take responsibility for the general environmental education of all graduates and the preparation of greater numbers of appropriately educated environmental specialists. All university students must be environmentally educated because the health of the environment depends upon knowledge and attitudes about the environment among leaders in all walks of life. The issue here is how to fit the environment into the long list of things all students need to know. The eclectic nature of environmental problems requires that environmental specialists also need to be broadly educated. Here the issue seems to be how broad is broad enough, since breadth comes at the expense of depth. Perhaps we need a number of different ways of preparing environmental workers.