Answer to Question 1
ANSWER: Answers may vary, but should address the following:
Studies show that about half the rainfall in the Amazon River Basin is returned to the atmosphere through evaporation and through transpiration from the leaves of trees. Consequently, clearing large areas of tropical rain forests in South America to create open areas for farms and cattle ranges will most likely cause a decrease in evaporative cooling. This decrease, in turn, could lead to a warming in that area of at least several degrees Celsius. In turn, the reflectivity of the deforested area will change. Similar changes in albedo result from the overgrazing and excessive cultivation of grasslands in semi-arid regions, causing an increase in desert conditions (a process known as desertification).
Answer to Question 2
ANSWER: Particles can enter the atmosphere in a variety of natural ways. For example, wildfires can produce copious amounts of tiny smoke particles, and dust storms sweep tons of fine particles into the atmosphere. Smoldering volcanoes can release significant quantities of sulfur-rich aerosols into the lower atmosphere. And even the oceans are a major source of natural sulfur aerosols, as tiny drifting aquatic plantsphytoplankton produce a form of sulfur (dimethylsulphide, DMS) that slowly diffuses into the atmosphere, where it combines with oxygen to form sulfur dioxide, which in turn converts to sulfate aerosols. Although the effect these particles have on the climate system is complex, the overall effect they have is to cool the surface by preventing sunlight from reaching the surface.
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