Independent variables

National population Total, urban-rural split, agricultural-nonagricultural, birth rates, age distribution

Economic activity Gross national product (GNP); production of manufacturing, mining, agricultural, service sectors; income distribution

Energy demand Consumption of coal, oil, gas, nuclear electricity, hydroelectricity, biomass; demand for transportation, space heating, manufacturing process heat, and other major end uses

Technology Transportation subdivided by technology used (e.g., number of passenger miles by automobile, number of ton-miles by train); capacity and fuel efficiency of industrial boilers, steel furnace, etc.

Prices Major energy sources, labor, agricultural land; interest rate for capital investment

Land use Hectares in wetland crops, dryland crops, pasture, forest; number of cattle; dispersion of population around urban centers

Institutions Distribution of land across agricultural users and by land-tenure system; degree of market vs. nonmarket control over markets for energy, land; environmental regulatory style

These data, even when they are desired only on an annual basis and at the national level, are unevenly available. Some, such as national population, are fairly accurate and available, but too infrequent; some, such as GNP, are available and sufficiently frequent, but of highly variable and sometimes unknown accuracy; some, such as energy use subdivided by economic sector, are sufficiently accurate and frequent for some countries (typically, OECD countries), but not available at all for many other countries; and some, such as the degree of market control of the economy, are unavailable because a reliable index does not yet exist. For most of the international data sets that are available, information on data quality is scanty and of uncertain reliability.

HUMAN CONSEQUENCES OF DEPLETION OF STRATOSPHERIC OZONE

Global change researchers want to be able to monitor the possible effects on things humans value of ongoing changes in the level of stratospheric ozone and to attribute the effects to ozone depletion rather than other possible causes. One way to shed light on the issue would be continuing analysis of a time series of data on values that might be affected by increased UV-B radiation at the earth's surface. These include the productivity of crop and forest flora,



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