New disease outbreaks have occurred throughout the world. In 1988, an estimated 18,000 harbor seals were killed in the Baltic Sea near Denmark. The epidemic was caused by a virus related to canine distemper and measles, which had not previously attacked harbor seals. The same virus killed hundreds of dolphins in the Gulf of Mexico in 1990 and 1995 and on the Mediterranean coast in 1990. Though the underlying causes of these new diseases have not been established, scientists suspect that pollution is responsible.
Pollution makes marine species vulnerable to disease by weakening their immune systems.
By increasing demands for food, fuel, shelter, and other amenities, population growth and urbanization contribute to the loss of forests around the world. Nearly one-half of the forests that covered the Earth 8,000 years ago are gone, primarily because of human activities, according to a recent study by the World Resources Institute and the World Conservation Monitoring Centre. 53 Logging threatens 70 percent, and agriculture threatens 20 percent, of the world's remaining frontier forests. The world's forests are essential for a number of reasons. Forests provide wood pulp and timber and offer areas of natural beauty and recreation for people.