Issue Guide: Global Change

by Kenneth B. Pierce Jr.

Purpose:

This issue guide is designed to give a brief introduction to the study of Global Change and provide links to the most up to date research available.

Atmospheric Change

Global Warming

Ozone Depletion

Biogeochemical Cycles

Links to Other Sites

Introduction:

Global Change is a new mutli-disciplinary science which seeks to understand the various ways the environment is being altered by man's activities. The mechanisms of change are referred to as anthropogenic forcings and are usually involved with atmospheric alteration or land-use changes. The atmosphere is being altered by the addition of many chemicals including carbon dioxide, oxides of nitrogen, sulfur compounds, halogen compounds and various aerosols. Land-use changes include habitat fragmentation, conversion to agricultural uses and biome conversion from introduced exotic species. As the human population continues to expand it puts increasing pressure on ecosystem services (Cairns, 1996). Ecosystem services are those benefits man derives from the natural world including air and water of a composition which promotes health, soil and nutrients in which to grow food, plants to convert sunlight into energy and an atmosphere which provides livable climate conditions. Global Change research attempts to quantify and understand these processes and how human activities may alter them. Current research programs are being conducted by the National Science Foundation, the United Nations, the International Geosphere-Biosphere Project (Walker, 1994), the World Wildlife Fund for Nature and many other nations and international organizations.

Atmospheric Change

Global Warming

One of the most heated debates on global change is the possibility of global warming. The first hints of global warming came from David Keeling's Mauna Loa Observatory carbon dioxide data which showed repeated yearly fluctuations and a definite upward trend in atmospheric carbon dioxide concentrations (Graedel, 1993). Since then an enourmous amount of research has been conducted trying to ascertain the implications of changes is various gases. The atmosphere is heated by sunlight. That heat is captured by individual gas molecules. Increasing the number of molecules able to store heat is believed to increase the total amount of heat stored. Different molecules have different heat storage capacities. Curiously the most important gas for heat retention in the atmosphere is water vapor. Water vapor is however not a direct concern for global warming researchers as man does not directly influence the concentration of water vapor in the atmosphere and water vapor returns to the Earth very quickly after evaporation. The gases of concern are anthropogenically introduced and remain in the atmosphere for long periods of time allowing their concentrations to build up. The most important of these are carbon dioxide, methane and nitrous oxide which can remain in the atmosphere for 50-200, 10 and 150 years respectively (Berner, 1994). Current information is maintained by the U.S. Department of Energy at the Carbon Dioxide Information Analysis Center, where David Keeling's original data can be viewed.

Ozone Depletion

In 1986, three british scientists published a landmark article in the journal Nature showing wide yearly fluctuations in stratospheric ozone over the Antarctic. Statospheric ozone is responsible for most of the atmosphere's absorption of UV-B radiation. UV-B radiation degrades DNA which can induce many forms of cancer. The ozone hole over the Antarctic is derived from a complex mixture of the polar vortex during the Antartic winter (June-September) and heterogeneous chlorine chemistry in polar stratospheric clouds.

Biogeochemical Cycles

The major constituents of living organisms are made up of carbon, oxygen, hydrogen, nitrogen, phosphorous and sulfur. Oxygen is readily usable in its elemental form but carbon, nitrogen, phosphorous and sulfur must be fixed for biological utilisation. These substances cycle between living and non-living reservoirs and these cycles are referred to as biogeochemical cycles. Part of global change research is to identify the major reservoirs of each of these elements and determine the rates at which they are transported or converted between these reservoirs. Man alters the carbon cycle through fossil fuel emissions and forest clearing. The nitrogen cycle has historically involved the uptake of nitrogen by bacteria which makes it available to plants. Thus it is kept in the organic reservoir until death and decomposition return nitrogen to the atmosphere. Through chemical processes man now fixes nitrogen in order to create fertilizer. Fifteen percent of fixed nitrogen is by industrial processes (Hopkins, 1995). Additional nitrogen is added as a combustion product and is a major ingredient in photochemical smog.

Land-Use Change

Habitat Fragmentation

Fragmentation of native habitat is one of the biggest causes of extinctions. A single road bisecting a habitat patch cuts the habitat in half effectively reducing the individual population sizes in half. Different creatures are variably sensitive to fragmentation. Birds can access different patches separated by small divisions but small mammals, being less mobile, can be seriously affected. Conversion of habitat to farm land or commercial uses not only divided habitat it increases the relative amount of habitat edge. The edge of an area provides a buffer between two different habitat types. As habitat is fragmented not only is the land divided but by the act of division part of the habitat is converted to buffer or edge which may support a different flora and fauna from the original habitat. Additionally microclimate conditions can be altered by a change in tree structure, creation or erosion channels or road cuts and altered solar flux (Saunders, 1991).

Invasions by Exotic Species

Exotic invasions are the second largest cause of extinctions. Exotics out compete both animals and plants. In southern California former grasslands and coastal sage scrub are often completely replaced by mustard and artichoke. These monocrops are sometimes short lived annuals which replace more stable perrenial communities and reduce habitat heterogeneity for small mammals and birds. The Nature Conservancy publishes a list of the top unwanted species which invade and outcompete the natural inhabitants. Exotic invasions by animals have been documented in many areas of the world and have been especially destructive in lakes and streams.

References

1. Cairns, John. 1996. Determining the Balance Between Technological and Ecosystem Services. Pages 13-29 in P. C. Schulze, editor. Engineering Within Ecological Constraints. National Academy Press, New York.

2. Walker, Brian H. 1994. Landscape to Regional-Scale Responses of Terrestrial Ecosystems to Global Change. Ambio 23:67-73.

3. Graedel, T.E. and P. J. Crutzen. 1993. Atmospheric Change: An Earth System Perspective. W. H. Freeman & Co., New York.

4. Berner, E. K. and R. A. Berner. 1994. Global Environment: Water, Air, and Geochemical Cycles. Prentice Hall, Upper Saddle River, New Jersey.

5. Cox, George W. 1997. Conservation Biology 2nd ed. Wm. C. Brown Publishers, Dubuque, IA.

6. Hopkins, William G. 1995. Introduction to Plant Physiology. John Wiley & Sons, Inc. New York.

7. Saunders, Denis A., Richard J. Hobbs & Chris R. Margules. 1991. Biological Consequences of Ecosystem Fragmentation: A Review. Conservation Biology 5:18-32.

Links

1. World Wildlife Federation Climate Change Program http://www.panda.org/climate/

2. USGS Global Change http://www.geochange.er.usgs.gov/

3. US Global Change Research Program Global Change Data & Info System http://www.gcdis.usgcrp.gov/

4. Global Change Electronic Edition http://www.globalchange.org/

5. Electronic Development & Environmental Info Systems http://www.ids.ac.uk/eldis/eldbr.html

6. Map Collection http://www.lib.utexas.edu:80:/Libs/PCL/Map_collection/ Map_collection.html

7. Sustainable Development http://www.ulb.ac.be/ceese/sustvl.html

8. Environment Today http://enviro.mond.org/

9. National Biological Survey http://www.im.nbs.gov/

10. University Corporation for Atmospheric Research http://www.unidata.ucar.edu/

11. National Climatic Data Center http://www.ncdc.noaa.gov/ncdc.html

12. United Nations International Panel on Climate Change http://www.unep.ch/ipcc/ipcc-O.html

13. Global Change Master Directory http://www.gcmd.gsfc.nasa.gov/

14. U.S. D.O.E. Carbon Dioxide Information Analysis Center http://cdiac.esd.ornl.gov/

15. The Nature Conservancy http://www.tnc.org/

16. EPA Global Warming Page http://www.epa.gov/globalwarming/home.htm

17. United Nations Global Environment Outlook 1997 http://www.grid.unep.ch/geol/

Last update March 4, 1997

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