Funded Grants

Regime shifts in the Sahel: Exploring interactions among ecological, hydrological and climate systems of semiarid Africa

HUMAN ACTIVITY AND A CHANGING PLANET

Growing population... Diminishing energy and water resources... Tropical deforestation... Changing patterns of climate... Loss of biological diversity... Growing potential for conflicts over resources and pollution...

The effects of human activity can now be seen throughout the biosphere.

Lester Brown, in his essay "The Acceleration of History" (Brown et al., 1996), illustrates how the last few decades have seen an explosion of human activity. For example, Brown notes that between 1950 and 1995:

o human population increased from 2.5 billion to 5. 7 billion (a 2.3x increase)

o global economic output increased five-fold

o worldwide consumption of grain and water tripled

o the use of fossil fuels increased four-fold

These changes in human population and activity, which occurred in only forty-five years, completely outpaced the actions of all previous human generations put together.

We can recognize the impact of Homo sapiens throughout the global environment, ranging from fundamental changes in the chemistry of the atmosphere to the wholesale modification of Earth's land cover. For example, approximately 18 million km2 (an area roughly the size of South America) is currently in some form of cultivation. Furthermore, anthropogenic nitrogen sources into the environment (from fertilizers and atmospheric pollutants) now exceed all natural sources, and atmospheric C02 concentrations have risen (as a result of energy- and land-use) by roughly one-third since the Industrial Revolution.

Ironically, just as our collective activities are changing climatic and environmental processes across the globe, humanity has become increasingly dependent on the goods and services provided by the environment. Increases in our population and standard of living have driven rapidly accelerating rates of food and freshwater consumption, timber harvesting, and energy use. For example, Vitousek et al. (1997) reported that nearly one-third to one-half of global ecosystem production is now co-opted by human activity. Furthermore, Postel et al. (1996) estimated that roughly half of the world's available freshwater supply is now being used by humanity. Finally, Costanza et al. (1997) estimated that the goods and services provided by the natural environment have the equivalent economic value of between US$16-54 trillion per year, compared to the global gross domestic product of roughly US$18 trillion per year.

The natural question arises: Are human activities changing the Earth's environment in ways that may jeopardize the sustainable use of our planet's natural resources and, ultimately, our future health and welfare?

UNDERSTANDING GLOBAL ENVIRONMENTAL PROCESSES

My research team aims to answer this question, by improving our understanding the changing nature of the world's ecosystems and watersheds, and how they interact with the atmosphere and oceans.

In particular, much of my research focuses on building and testing computer models of the Earth's ecosystems, watersheds and climate. Using computer models, we can explore how ecological, climatic, and hydrological processes interact to support the rich diversity of life found on this planet.

My work has three major foci:

o Understanding Terrestrial Ecosystems - From the Field to the Globe. The Earth's terrestrial ecosystems are critically important to the welfare of humankind. Food, fiber, fresh water, medicines, and forest products are all derived from our terrestrial ecosystems. In addition, terrestrial ecosystems play a central role in regulating the biogeochemical and climate systems of this planet.

To better understand ecological processes, and to evaluate their response to human activity, my research team is developing IBIS (Integrated Biosphere Simulator) - a new comprehensive computer model of the Earth's terrestrial ecosystems. We are currently using the model to study how ecosystems respond to changes in land use and climate. We continue to test the IBIS model against field measurements collected from ecosystems around the world.

o Understanding Freshwater Systems - Rivers, Lakes and Wetlands. The Earth's freshwater systems, as sources of potable water, hydroelectric power and food, are of great importance to human society.

Our research team is focused on the behavior of whole watersheds - including lakes, wetlands, rivers and groundwater systems. In particular, we are interested in how land use and variations in climate can affect the availability and quality of fresh water resources. In order to help answer these questions, we are developing new computer modeling tools to examine the impact of human activities on freshwater supplies across the globe.

Recent efforts have been focused on the HYDRA (HYDrological Routing Algorithm) model, which simulates the flow of water through groundwater systems, rivers, lakes and wetlands. We are currently working to understand the effects of management practices, artificial structures, and land use changes on the water cycle. We continue to improve the modeling tools, and test them against field data and satellite measurements.

o Linkages Between Climate and Ecosystems. Looking across the globe, we see that patterns of temperature and rainfall limit the range of many plant and animal species. In fact, we see strong geographic associations between climate and ecosystems, ranging from the tropical rainforests, through the subtropical deserts and temperate forests, all the way to the northern boreal forests and Arctic tundra.

But changes in vegetation cover can also affect the physical properties of the land surface and how it interacts with the atmosphere. Removing the forest cover over a large area, for example, reduces the amount of water evaporated back into the atmosphere, leaving less water and energy available to fuel weather systems.

Our research team is building new computer models that fully link the two-way relationships between climate and ecosystems. In particular, we have incorporated our IBIS terrestrial ecosystem model directly within global climate models of the atmosphere and ocean. We have used these "coupled" models to examine how changes in ecosystems could affect the future climate of our planet. For example, shifting patterns of global vegetation cover, caused by future greenhouse warming, might induce large feedbacks on the climate system. Our initial results suggest that changes in vegetation could magnify the effects of global warming, especially in high northern latitudes.

USING MODELS TO EXPLORE THE FUTURE

Computer modeling tools allow us to explore the complex behavior of global environmental systems, and examine how they may respond to human activity. But these models are not perfect "crystal balls", capable of foretelling the future in a perfectly accurate way. Rather they are "virtual laboratories", where we can test hypotheses about nature, and explore the consequences of different decisions.

Using these "virtual laboratories", we can peer beyond our own time and our own limited experience. They can help chart a path toward the future, and tell us something about the landscape ahead. But we may still be surprised when we arrive at our destination.

Perhaps the best use of the models is to help us understand the variety of possible futures we may face - rather than betting everything on any one particular forecast. Are there uncertainties ahead? Are there are abrupt cliffs lurking out there, just waiting to surprise us with a sudden drop? Are there "points of no return", where we cannot undo environmental damages once they occur? Where are these critical decision-making points?

In our research, we use global environmental models in this exploratory mode. We aim to learn more about the behavior of environmental systems, so that we may better understand the consequences of the many possible future paths we may take. For example:

o Global modeling tools can be used to examine how "non-linear" environmental systems are. That is, how do they respond to change? In a predictable "linear" fashion, by following existing trends? Or a highly "non-linear" way, which can show sudden and sometimes unpredictable changes?

o Computer models also help us see potential "threshold responses" or "regime shifts" in our natural resources. For example, some environmental systems appear to be stable, until they reach a critical threshold where they will show a sudden, large response to human activity. Without understanding where the thresholds are in our natural resource systems, we may be in for unpleasant surprises.

o Finally, global environmental models can show us "hot spots", where future environmental changes could be highly disruptive. As an example, we can consider the response of crops to global warming: are there "hot spots", where crops are much more sensitive to changes in rainfall and temperature? Using computer models to detect the "hot spots" of potential change in our ecosystems and freshwater resources helps us focus our attention to critical geographic regions, where scientific monitoring and discussions of policy options must be undertaken in earnest.

A FINAL COMMENT

We are now facing critical environmental problems that will affect the quality of human life for decades and centuries to come. Solving these problems, in many cases, will require interdisciplinary research to help us understand how the Earth's complex environmental systems function and respond to human activity. Understanding the complex behavior of environmental systems, seen through the lens of a computer model, may help us chart a path towards a more environmentally secure future.

But we also must integrate these research results more completely into decision-making and public policy, with the ultimate goat of managing our planet's natural resources - the air, freshwater, land and biological diversity upon which all life depends - sustainably into the future.

ESSAY REFERENCES

Brown, L.R., et al., 1996: Chapter 1 - The acceleration of history. State of the World - 1996, Norton, New York, 249 pp.

Costanza, R., et al., 1997: The value of the world's ecosystem services and natural capital. Nature, 387, 253-260.

Postel, S.L., G.C. Daily, and P.R. Ehrlich, 1996: Human appropriation of renewable fresh water. Science, 271, 785-788.

Vitousek, P.M., H.A. Mooney, J. Lubchenco, and J.M. Melillo, 1997: Human domination of Earth's ecosystems. Science, 277, 494-499.