The sea is unevenly heated. The surface of the tropic ocean is warmed, expands, and spreads outward north and south. To balance this, cooler water from north and south moves toward the tropics at deeper levels. This variable heating of the ocean, the changing density of water with temperature, and the rotation of Earth all combine to produce large ocean currents that WEND their way in enormous circles in some places, sink in others, and rise in still others. The net effect is to keep the ocean stirred up and the substances dissolved in it evenly spread out.

#13 Dissipated means:
a. Scattered
b. Solidified
c. Controlled
d. Converted

#12 Which of the following could not be said to be wending its way?
a. Astream of air flowing through an open window
b. A tourist sightseeing on foot
c. A butterfly flitting from flower to flower
d. A computer printing out the response to a question

Scientists differ about how much extra heat the Earth can absorb. Many claim that pollution accumulating in the atmosphere will have a greenhouse effect, trapping solar radiation that might otherwise be dissipated into space. With over 80 percent of the world’s ice locked up in Antarctica, even a slight increase in world temperatures would speed melting and flood Boston, New York, and every other major seaport.