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Troubled Waters of Greenhouse Earth: Summary and Synthesis
Abstract
I began to prepare for the symposium on which this book is based with the same predisposition as many of the audience and (now) you readers, that global climate change is imminent . . . even an accomplished fact. Many of you will recognize, as I have come to, that this may not be the case; that it is not all that certain. While the likelihood of global change due to human activities may be quite high, there are still many uncertainties, particularly with regard to the timing, magnitude, and regional patterns (IPCC, 1990).
... Riparian habitats are especially important as refugia during periods of environmental stress, such as annual drought or rapid shifts in long-term climate patterns, because of the improved climatic conditions they provide to many species along river valleys (Gregory et al. 1991, Minshall 1992. As a result of the favorable conditions and heterogeneous nature of riparian habitats, riparian plant communities exhibit a high degree of structural and compositional diversity (Gregory et al. 1991). ...
According to current consensus, the world will become warmer over the next century as greenhouse gases continue to accumulate in the atmosphere (see Levine, Chapter 1, this volume; Slade, 1990). Changes in atmospheric circulation patterns will lead to geographic adjustments in climate and thereby affect regional and local hydrologic cycles, but in ways that are currently difficult to predict. For example, precipitation in climatically distinct regions may change by ± 20% and runoff may change by ± 50% (Schneider et al., 1990). Substantial regional shifts in climate may alter not only the quantity of runoff but its variability and timing as well. Because many ecological processes are regulated by the quantity and the temporal distribution of streamflow, major alterations in hydrologic regimes are likely to result in modifications of freshwater ecosystem structure and function.
Increasing atmospheric concentrations of carbon dioxide and other infrared-absorbing gases appear to be raising air temperatures and changing precipitation to a varying extent worldwide (Schlesinger and Mitchell, 1987; Mitchell, 1989), although there are many uncertainties involved in the interpretation of climatic records (Bradley et al., 1987; Kuo et al., 1990; Wigley and Raper, 1990) and in the predictive models currently in use (Abelson, 1990). Despite these uncertainties, however, the evidence for potential large-scale climatic change is now sufficiently strong to warrant further investigations of the causes and consequences of climatic change in a variety of environments. Such investigations must consider multiple spatial and temporal scales, and they must address the complex interactions among terrestrial, aquatic, and atmospheric systems (Mooney et al., 1987; Avissar and Verstraete, 1990; Tans et al., 1990; Levine 1990).
Experts (see other chapters in this book) expect the concentration of atmospheric carbon dioxide (CO2) to double over the next four decades and expect even larger increases in other radiation-trapping gases or “greenhouse gases” during the same period. As a result, global temperatures may increase significantly and regions may undergo significant changes in moisture regimes. In response to these climate changes, freshwater ecosystems may undergo rapid transformations. In addition, human activity has been significantly affecting freshwater systems. The Industrial Revolution and human population growth have brought increases in the particulate content of the atmosphere by activities such as farming and the increased use of fossil fuels. Humankind’s increasing needs for fuel, food, and fiber have resulted in severe impacts on watersheds, including riparian zones, in many freshwater systems in the world. The press and the public are focusing on the question of the validity of forecasted global warming and its effects on the ecosystems while downplaying the fact that significant global changes in the environment are already occurring due to human activities. It is as if we, as a global society, should relax if the much anticipated global warming fails to happen. The on-going impacts to the environment by other means are, in fact, affecting severely freshwater ecosystems.
While both models and scientific opinions about future climates vary, many agree that a global temperature rise of 1–2°C by 2050 is a near certainty (Levine, Chapter 1, this volume). Large scale general circulation models (GCMs) that predict climatic effects based on increases in atmospheric CO2 project a significant temperature rise in the northern hemisphere (Schlesinger and Mitchell, 1985) accompanied by less rainfall in midlatitudes and more rainfall northward (e.g., Wigley et al., 1980; Schlesinger and Mitchell, 1985; Levine, Chapter 1, this volume). Several investigators have used GCM output, hypothetical rainfall and temperature scenarios, and empirical historical data on climate extremes to generate more specific predictions at regional scales. Global models fit regional scales rather poorly, however (Coleman, 1988; Cushman and Spring, 1989; Dahm and Molles, Chapter 12, this volume), largely due to uncertainties attributable to positive (Ravel and Ramanathan, 1989) and negative (Mitchell et al., 1989) feedback effects of clouds and influences of orogeny (Manabe and Broccoli, 1990; Dickinson, 1989). It may therefore be necessary to generate regional climate predictions from combinations of empirical studies, local models, and comparative ecosystem studies. Difficulties in predicting future hydrologic budgets are even greater, because numerous interactions among temperature, vegetation type, plant physiological response, precipitation, and runoff confound predictions of hydrology even if temperature change is accurately known.
In this chapter, we explore the potential of Alaskan rivers and streams as exemplary systems for the study of effects of global climate change on high latitude freshwaters in northern regions. A wide range of climates and resulting ecosystem types are found in high latitudes. A major factor in the distribution of these ecosystem types is the latitudinal decrease in yearly input of solar energy and the latitudinal increase in its seasonal amplitude. In addition, the ameliorating effects of maritime influences (especially from warm ocean currents) produce regional differences in climate. Warming of northern Europe and much of Alaska by ocean currents (compared to frigid Greenland at a similar latitude) are classic examples (Young, 1989; Stonehouse, 1989). Alaska’s climate includes maritime in the southeast panhandle, continental in the central interior, and arctic in the northwest and north. Likewise, distribution of permafrost and vegetation range from coastal Western Hemlock-Sitka Spruce forest with no permafrost to arctic tundra underlain by continuous permafrost. Any attempt to assess potential impacts of climate change in polar and subpolar regions must take into account both regional physiographic differences (e.g., distribution of permafrost) and changes in heat transfers from lower latitudes (e.g., Roots, 1989).
Stream ecosystems are an integral part of the landscape. Their structure and function are modified by events occurring in the surrounding catchment (Hynes, 1975) and by the forms of organic matter and nutrients entering the ecosystem from systems upslope or upstream (Vannote et al., 1980, Minshall et al., 1985). Hence, when considering the impact of climate change on freshwaters, it is particularly important that we consider terrestrial-aquatic interactions.
Human activities are changing the chemical composition of the Earth’s atmosphere. Emissions of pollutant gases from the burning of fossil fuels, production and use of synthetic chemicals, and the conversion of natural environments to agricultural systems have increased the atmospheric concentrations of carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons to the highest levels known for at least 160,000 years of Earth history. Trapped ancient gases in ice cores, and direct monitoring of more recent changes in air chemistry, have convincingly documented the links between the growth of the human population, the evolution of industrial societies, and increasing concentrations of these gases (e.g., Rowland and Isaksen, 1988; Chappellaz et al., 1990; Lorius et al., 1990). One likely consequence of the increasing concentrations of atmospheric gases like carbon dioxide and methane is a change in global climate. These gases have long lifetimes in the atmosphere, and as they accumulate they trap, in the lower atmosphere, increasing amounts of energy emitted from the earth’s surface (Ramanathan et al., 1987). The current consensus among climate experts is that the increasing burden of atmospheric gases projected for the next century will result in a global climate warming of some 2–6°C (Dickinson, 1986; Levine, Chapter 1, this volume). A warming of this magnitude would be unprecedentedly rapid and extreme in the history of industrial society.
The scientific community has proposed a major long-term interdisciplinary research program [Global Change or the International Geosphere-Biosphere Program (IGBP)] to address environmental change on a global scale (National Research Council, 1986, 1988) with much recent attention directed toward the impacts of global warming from greenhouse gases (e.g., Houghton and Woodwell, 1989; Abrahamson, 1989). A crucial component of this program will be a worldwide network of interacting research sites dedicated to both experimental studies and long-term observations; these sites have been called “geo-biosphere observatories” by the IGBP (National Research Council, 1988) but are simply referred to as biosphere observatories in this chapter (see also SCOPE/MAB, 1987; University Corporation for Atmospheric Research, 1985). It is the observational or long-term environmental monitoring feature of these proposed biosphere observatories that we address.
There has been a growing concern over the past two decades that global warming is underway and that it will occur more rapidly than has ever been recorded in geologic history (Levine, this volume). While some of the consequences of this warming such as sea level rise, desertification, and shifts in precipitation are recognized, the full implications of global climate change are poorly understood. Numerous studies have investigated potential effects of climate change on surface water runoff (Aston, 1984; Gleick, 1987; Idso and Brazel, 1984; Revelle and Waggoner, 1983) but only recently have the potential effects on water resources and water management been investigated (Gleick, 1989; Kates et al., 1985; Klemes, 1985; WMO, 1987; Waggoner, 1990). One of the major concerns of shifting precipitation patterns are the resulting changes in water quantity and water quality, which can have profound effects on water resources management at the local and regional level. Water resources management practices, in general, have focused on single project management for extreme events (Linsley and Franzini, 1979). Techniques for multiproject management have been applied for water quantity but these techniques typically do not consider cumulative impacts on water quality. Moreover, the effects of climate change on regional studies of water quality and water resources are limited.
One of the most important factors affecting the life history characteristics and biogeography of aquatic insects is temperature (Sweeney, 1984). Insects are poikilothermic (cold-blooded) animals whose metabolism, rate and magnitude of growth, development, and overall behavioral activities respond significantly to thermal change on a diel, seasonal, and annual basis (Ward and Stanford, 1982). Despite this sensitivity to temperature, most aquatic insect species can be found in aquatic habitats over a broad geographic area that includes a wide range of thermal regimes. Obviously, these aquatic insect species possess bioenergetic, developmental, and/or behavioral mechanisms that enable conspecific populations to survive and reproduce in very different environmental conditions.
It is pointed out that the release of chemicals into the atmosphere has grown greatly over the last 50 years. Contributed to the observed perturbations of trace chemicals in the atmosphere have an increased reliance on synthetic chemicals, deforestation, biomass burning, and fossil fuel combustion. As trace chemicals modify the radiation energy of the earth-atmosphere system, the considered developments can produce an alteration of the earth's climate. One of the major objectives of the present study is related to the characterization of the trace gases, taking into account the observed abundances, known sources, and sinks in the present-day atmosphere. Other objectives include an estimate of the future concentration of trace gases, an inference of the preindustrial concentrations of trace gases, and an estimate of the radiative effects of the trace gases and their potentials for climate changes.
It is concluded that the idea of longitudinal succession on a geological time scale is wrong but that the concept when considered at the level of the flow-through time of a river is not. Climate operates at several scales of space and time; larger-scale aspects beyond the stream-specific level are just beginning to be addressed but their consideration is necessary if broad-scale patterns in stream ecosystems are to be discerned. Southwood's habitat templet lends itself to the development of hypotheses and the ordering of knowledge along spatiotemporal axes. Application of this model to streams is illustrated for flow-related disturbance. Several misconceptions concerning disturbance in streams seem to have arisen from failure to consider the full range of spatial-temporal dimensions. The explicit recognition and utilization of appropriate spatial and temporal scales is essential to the development of an accurate stream theory having a truly world-wide perspective. (
The 1989 Forest and Rangeland Renewable Resources Planning Act (RPA) Assessment is the third prepared in response to the original 1974 legislation. It is composed of 13 overview documents, including supporting documents of analyses for each of the resources and on interactions among the resources, etc. This analysis considers the "greenhouse effect'; quantifying the atmospheric and ecological responses of climate warming through modelling; forest changes under climate change, by region; sensitivity of forest species predictions to uncertainties in the general circulation models; and forest management in the future; concluding with a relevant reference list. -J.W.Cooper
At the 1985 conference on carbon dioxide in Villach, Austria, an international group of scientists called for changes in world policy to meet the impact of global warming. The compelling evidence for their concern - and the uncertainties associated with the science - are presented in this report on the work of the conference. The article discusses future carbon dioxide emissions and atmospheric concentrations, the role of other greenhouse gases, effects on climate (projections and observations thus far), changes in sea level, and effects on terrestrial ecosystems (agriculture and forests).
New and published climate-model results are discussed which indicate that global warming favors increased rates of forest disturbance as a result of weather more likely to cause forest fires, convective wind storms, coastal flooding, and hurricanes. New sensitivity tests carried out with a vegetation model indicate that climate-induced increases in disturbance could, in turn, significantly alter the total biomass and compositional response of forests to future warming. An increase in disturbance frequency is also likely to increase the rate at which natural vegetation responses to future climate change. The results reinforce the hypothesis that forests could be significantly altered by the first part of the next century. The modeling also confirms the potential utility of selected time series of fossil pollen data for investigating the poorly understood natural patterns of century-scale climate variability.
Some 4.5 billion years ago, soon after the Earth and its atmosphere formed, atmospheric gases energized by solar ultraviolet radiation and atmospheric lightning formed the key molecules needed for the synthesis of amino acids, the building blocks of all living systems. The process of forming complex organic molecules from simple atmospheric gases is termed “chemical evolution.” In the early oceans of our planet, which offered protection from the biologically lethal ultraviolet radiation emitted by the Sun, the amino acids and other complex organic molecules combined chemically to form the first living systems. Protected by the early oceans, the first living systems developed, evolved, and increased in numbers. One group of early organisms developed the ability to synthesize carbohydrates used for food through the biochemical process of photosynthesis. During this process, a gaseous byproduct was given off—oxygen. Prior to this important evolutionary development, the early atmosphere contained little or no oxygen. Beginning about 3.5 billion years ago, photosynthetic oxygen began to accumulate in the atmosphere. About 600 million years ago, atmospheric oxygen evolved to about one-tenth of its present atmospheric level, which is about 21% by volume. This was a very significant milestone in the history of life. At this level of oxygen, natural atmospheric chemical reactions produced enough ozone (O3) from the oxygen (O2) to shield the surface of our planet from biologically lethal solar ultraviolet radiation.
Detecting climate change. I. Taking the world’s shifting temperature. II. The impact of the water budget
- La Brecque
- M Brecque La
Wildfires and Yellowstone’s stream ecosystems: A temporal perspective shows that aquatic recovery parallels forest succession
- G W Minshall
- J T Brock
- J D Varley
- GW Minshall
Stream management: Emerging global similarities
- R C Petersen
- B L Madsen
- M A Wilzbach
- Chd Magadza
- A Paarlberg
- A Kullberg
- K W Cummins
- RC Petersen