agricultural, industrial, and municipal uses. Cloud seeding technology 

 for these purposes, however, is still at an experimental stage. Before it 

 can be employed on a practical basis, much more must be learned about 

 the specific conditions under which a particular seeding treatment 

 produces the desired cloud response. In addition, the impact of 

 successful seeding in one region on the precipitation in adjacent and 

 distant regions must be better understood. Furthermore, the seeding 

 technology needs to be improved in order to provide for closer and 

 more reliable control over the extent of the modification. 



But the most perplexing problems involved in modifying the 

 amount of rain and snow may not be scientific or technological. They 

 center, instead, around the economic, political, and social implications 

 of such weather modification. Unlike the mitigation of storms and 

 severe weather, almost any change in precipitation is likely to be 

 advantageous to some but harmful to others. Under these conditions, 

 how are the disadvantaged groups to be compensated? Modification in 

 one region may affect the precipitation in adjoining or even distant 

 regions. How is it to be decided when and where weather is to be 

 modified? These are only a few of the baffling issues that stand 

 between the present limited capability for modifying weather and the 

 realization of a system for managing precipitation. 



While public attention has focused largely on intentional 

 modification of weather, there is growing concern over the possibility 

 of the inadvertent modification of climate. Specific examples of these 

 concerns include the recent debate over the possible effects of the SST 

 on the global atmosphere, impacts of the heat output from large power 

 plants, and the effects of the higher temperatures and particulate 

 emissions of cities on downwind rainfall. 



Human activity may be involved on an even broader scale in 

 changing the global climate. The growth and pattern of agricultural 

 and industrial development over the last century may have influenced 

 the mean temperature of the world. Warming temperatures prevailed 

 for about 100 years, from the mid-19th to the mid-20th centuries, 

 following the "little ice age" which lasted some 200 years. During the 

 last 20-30 years, world temperature has fallen, irregularly at first but 

 more sharply over the last decade. 



The cause of the cooling trend is not known with certainty. But 

 there is increasing concern that man himself may be implicated, not 

 only in the recent cooling trend but also in the warming temperatures 

 over the last century. According to this view, activities of the 

 expanding human population — especially those involved with the 

 burning of fossil fuels — raised the carbon dioxide content of the 

 atmosphere, which acts as a "greenhouse" for retaining the heat 

 radiated from the earth's surface. This, it is believed, may have 

 produced the warming temperatures after the mid-19th century. But 

 simultaneously, according to this view, growing industrialization and 



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