(1) Millions of people depend upon coral reefs for their livelihoods. (2) Small island countries with coral reefs rely on them to attract sightseers, scuba divers, snorkelers, and other tourists. (3) They are an important source of food for the people who live nearby. (4) Reefs in shore areas are shields from pounding waves, storm surges, and tsunamis. (5) Several important medical drugs for cancer research have been developed from chemicals found there. (6) However, coral reefs are threatened by water pollution, oil spills, and pesticides. (7) Another threat to coral reefs is a steady increase in average temperatures around the Earth, called climate change or global warming. (8) Most scientists think that the warming is caused by the greenhouse effect, an increase of carbon dioxide and other heat-trapping gases in our atmosphere. (9) This causes ocean temperature to rise, and as a result, some coral reefs are dying. (10) Coral reefs are also injured or destroyed when people mine the coral for building materials or break it to sell as souvenirs and jewelry. (11) Dangerous fishing practices, such as fishing by using explosives, also harm reefs.