MODELING

is an investigative technique which uses a mathematical or physical representation of a system or theory to test for effects that changes in system components may have on the overall functioning of the system. Mathematical modeling using computers plays a major role in climate research, by simulating how Earth's climate will respond to changes in atmospheric concentrations of greenhouse gases. Molecule means two or more atoms of one or more elements chemically combined in fixed proportions. For example, atoms of the elements carbon and oxygen, chemically bonded in a 1:2 proportion, create molecules of the compound carbon dioxide (CO2). Molecules can also be formed of a single element, as in ozone (O3). Monsoon refers to a particular seasonal weather pattern in sub-tropical regions, especially when characterized by periods of heavy winds and rainfall. Monsoons are caused by a pronounced seasonal change in wind direction. Winds usually blow from land to sea in winter, while in the summer, th:is reverses, bringing precipitation. Monsoons are most typical in India and southern Asia. Montreal Protocol on Substances that Deplete the Ozone Layer :is an international agreement that prescribes a timetable for ending the production of chlorofluorocarbons (CFCs) and related compounds. Begun in 1987, th:is unprecedented international treaty :is a unique example of scient:ists and industry working with governments to seek a global solution to the human-caused environmental challenge of ozone depletion. After the original agreement was signed, new evidence arose proving that deeper cuts in CFC production were necessary to protect the ozone layer. The 1990 London amendments and the 1992 Copenhagen amendments sped up the halocarbon phase out and controlled several other chemicals that were not in the original agreement: methyl chloroform, carbon tetrachloride, methyl bromide, and HCFCs. The rev:ised agreement now calls for the phaseout of CFCs to be complete by 1996. The treaty also attempts to make the phaseouts fair to developing countries by setting up a fund, paid for by developed nations, to ass:ist developing countries in making the switch to ozone-safe chemicals.