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Science Background

[Global Warming]

Humanity has been adding gases to the atmosphere that tend to warm the earth, known as "greenhouse gases." We are also adding small particles and droplets called aerosols that reflect light back into space and tend to cause some areas to cool. In the coming decades, we are likely to continue to change our atmosphere. Because the greenhouse gases that warm the earth stay in the atmosphere longer than the aerosols that cool the earth, the earth's average temperature is likely to continue to warm.

The continued addition of greenhouse gases to the atmosphere is likely to raise the earth¹s average temperature by several degrees in the next century, which will in turn raise the level of the sea. In the future, most of the United States is expected to warm, although sulfates may limit that warming in some areas. Scientists are currently unable to determine which parts of the United States will become wetter or drier, but there is likely to be an overall trend toward increased precipitation and evaporation, more intense rainstorms, and drier soils. (EPA)

Links to Sites on Global Warming

Environmental Protection Agency Global Warming

World Climate Report

Global Warming International Center

Conference on Climate Change - Kyoto, Japan. December 1-10, 1997

Leaves are the primary photosynthetic organs of most plants. Leaf surfaces are equipped with small openings or pores called stomata which allows carbon dioxide to enter the leaf and oxygen to escape to facilitate photosynthesis. In addition, water is lost through stomata during a process called transpiration. It is estimated that approximately 99% of the water absorbed by the roots of the plant is lost by the leaves in transpiration. The number of stomata on leaf surfaces varies widely among different species of plants. Generally, the lower epidermis of the leaf tends to have a higher total than the upper surface. Botanists have made stomatal counts for many species. Their data indicates that the number of stomata may vary from zero on the upper epidermis of an apple leaf to as high as 58,140 per square centimeter on the lower epidermis of black oak leaves.

Information on

Atmospheric Carbon Dioxide

Additional References and Interesting Articles

The original technique for stomata counting came from "The American Biology Teacher", January 1990. "Is there a Correlation Between Rainfall Amounts and the Number of Stomata in Cottonwood Leaves". Neill, Robert L., David M. Neill, Bernard F. Frye.

Stomatal Index - The Botanical Review Vol. 40, January - March 1974

Stomatal numbers are sensitive to increases in CO2 from pre-industrial levels, F. I. Woodard, Nature June 1987 : 617-619.

Van Der Burgh, Johan , Jenk Visscher, David Dilcher, Wolfram M. Kurschner. "Paleoatmospheric Signatures in Neogene Fossil Leaves." Science, Vol. 260, June 18 1993, 1788-1790.

Garbutt, K., W. E. Williams, and F. A. Bazzaz (1990) "Analysis of differential response of five annuals to elevated CO2 during growth. " Ecology 71(3).1185-1194.

Bazzaz, F. A. "The Response of Natural Ecosystems to the Rising Global CO2 Levels." Annual Review of Ecology Systematic, 1990, 21: 167-196.

Penuelas, Josep, Riser Matamala. (1990) "Changes in N and S Leaf Content, Stomatal Density and Specific leaf Area of 14 Plant Species during the Last Three Centuries of CO2 Increase." Journal of Experimental Botany 41.1119-1124.

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